Essentials of Biology and Biotechnology

tomorrow.

1 Plant Science

1.0 Introduction to Biology

The study of living organisms is called Biology or Natural Science. Biology is derived from two Greek words (Bios = life, logos = discourse or science). The word Biology was first used by Lamarck (France) and Treviranus (Germany) in 19th century. Ethymologically, Biology is the study of life. But life is difficult to define. According to Hungarian Nobel Laureate Szent Gyorgyi, life as such does not exist, no body has ever seen. The noun life has no sense, there being no such thing. Life, therefore, may be considered as a property or as a manifestation or as a state of organism. This leads to further inquiry; what is an organism ? and what is the property of living organism ?

Organisms can be protists (prokaryote) composed of single cell or multicell (eukaryote) i.e. differentiated into tissues and organs as in plants or animals. According to Whittakar (1978) there are five kingdoms, namely, Monera (Prokaryotae), Protista, Fungi, Animalia and Plantae. Recently Woese et al (1990) on the basis of ribosomal RNA sequences distinguished, the kingdom Procaryotae comprise of two groups; Archaebacteria and Eubacteria and kingdom Eucaryotae to comprise the higher organisms. The living organisms tradionally comprise plants and animals : so biology include the study of plants (Botany) and animals (Zoology). Aristotle (384-322 BC) is considered as the father of Biology. Theophrastus, a Greek philosopher, disciple of Aristotle is credited with founding botany: Of the 200 botanical treatises written by him; only two are known to science; originally written in Greek about 300 BC their Latin translations are available. De Causis Plantarum and De Historia Plantarum contains the concepts of morphology, classification and their natural history of plants and these remained unchallenged for many centuries. He classified plants as trees, shrubs and herbs.

1.1 Origin of Life

According to the Hindu Mythology Brahma created life. Indians no less than the Greeks have shared in the work of constructing scientific concepts and methods of physical phenomena have deeply influenced the course of natural philosophy in Asia. They had their own concept of origin of life comparable to the modern theory of biochemical origin of life. Parasara (250 - 120 B.C) in his Vrikshayuveda (the Science of Plant life) suggests : Water transforms into a jelly-like substances (‘Kalalam’) in which a nucleus ('Pindaslhamikam') is formed later and regulated by terrestrial energies it transforms into a ‘germ’ (bija). The Indians also agrees with the modern concept of origin of Eukaryotes from Prokaryotes. They also knew that plants preceded animals and man on this earth. Such rudiments of evolutionary thought can be seen in the writings of ancient Indian writers like Uddalaka and Yajnavolkya. It is interesting to note that Indians more than 2000 years before Darwin had thought about problems of evolution and heredity (Chaudhury, 1932). They also held that protoplasm is a colloidal system ('Kalalibhutam’), formed quite possibly from inorganic matter (Hora, 1953). Bible states that God created life on 5th day. The Egyptians believed that life is produced from the mud, warmed up by sun rays. Plants came first then animals and finally man. Cosmic, biological and cultural evolutions are integral parts of the story of creation. All these beliefs have no experimental basis. Then came the theory of Abiogenesis or Spontaneous generation. It states that life arose from non-living matter. This was supported by Francesco Redi Lazzaro Spallazani and Louis Pasteur. Cell lineage theory conceived by Turpin (1862), enlarged by Schleiden & Schwann (1838) and extended by Naegeli (1854) and Rudolf Virchow (1858) from Germany. These gave a brake to all the views, then existing, about life and proposed that cell arise from its pre-existing cell (Omnis cellula e cellula). This theory was proposed only after the term protoplasm was proposed. The cells are atoms of life; unit of biological structure and function.

The following are the characteristics of the living matter :

1. Chemical composition including proteins and nucleic acids

2. Definite organisation.

3. Maintenance and growth through assimilation

4. Irritability and adaptations.

5. Reproduction and heredity

Plants, animals and human as well as prokaryotes exhibit all the above characteristics.

The living world (with the exception of viruses) is characterised by two types of cells based on internal structures they contain. The prokaryte and eukaryote contain the same basic kinds of macromolecules. The prokaryote (pro = before, karyote = nucleus) comprise the bacteria, cyanophyta and the archaebacteria. Their cells are simple, devoid of plastids, mitochondria; the cell wall is made of peptiodoglycan with a nucleid; devoid of nuclear envelope; cells divide every 20 minutes. No wonder the prokaryotic cells are the most abundant cell types on the earth. The eukaryote (Eu = true, karyote = nucleus) the nucleus is membrane bound, with a distinct cell wall, which may be cellulose molecule as in plants, animal and fungi. Surrounding the cell is a plasma membrane of phospholipid bilayer whose dual function of protection barrier between the extracellular and intercellular matrices and to regulate the flow of molecules into and out of the cell. A wide variety of cell organelles are found in the cytoplasm, mitochondria, chloroplast, etc. All the eukaryotic plant and animals cells are essentially similar in most respects yet they differ in the following characters.

Plant cell wall is cellulosic hence elastic with chloroplasts, chromoplast, dictyosomes, vacuoles (constitute 90% cell volume and performs various functions of storage and excretion), the animal cell wall is not cellulosic, devoid of chloroplast and vacoules but has Golgi bodies, centrosome with 2 centrioles and furrowing as against cell plate formation in plants during cell division. Thus, there are so many kinds of organisms but at the cellular level, the living world shows unity. This unity and diversity of life is because of (i) unity of plan; each cell possesses a nucleus emmbeded in protoplasms (ii) unity of function; each cell show the same metabolism and (iii) unity of composition Biochemically, the main molecules of all living organism are made of same molecules. with specific structures and specific functions. For the life to be perpetuated, these macromolecules have to work in coordination and cooperation. Thus the smallest unit of integration, cooperation and reproduction is cell. The macromolecules are nucleic acids (deoxyribonucleic acid and ribonucleic acid) and proteins. The central dogma of life is : DNA maks DNA, (replication) DNA makes RNA (transcription) and RNA makes (translation) protein. The proteins are made of 20 different amino acids. Since the nucleic acids and proteins are universally present in all the organisms, therefore are called as the fundamental constituents or essential metabolites. Nature indeed has made use of few selected and limited number of building blocks to build the immense diversity of the living systems.

In 1857 Leydig first described and defined the cell as a mass of protoplasm containing a nucleus. If a comparison of various cells is made, the microbial cell has a dark central body surrounded by dull ‘cytoplasm’ in contrast to the cells of multicellular organisms which are specialised : therefore differentiated into the liver cells, kidney cells, brain cells etc as in most animal or human. The differentiated cells are organised into tissues and the tissues into organs and organs collectively contribute the organism. The functioning of each cell is controlled by the organism as a whole. The cells of the multicellular organisms differ from the microbial cells, which function as organism itself, an independent system of reproduction. No wonder Leeuwenhoek (1676) after discovering the bacterial cell stated, dear god, what marvels there are in so small a creature!

Thus, the presence of protoplasm is the most important characteristic of living organisms. It is the physical basis of life.

1.2 Plant Kingdom

Botany (Plant Kingdom) is the study of plants. Plants were of pivotal importance not only to the early man but to the present mankind, as they depended upon them as prime source of food, fuel, fodder, shelter, clothing, tools, ornaments and also as medicines. In addition to their practical and economic value, green plants are indispensable to all life on earth, through the process of photosynthesis (plants transform solar energy into chemical energy of food) which makes all life possible on the planet earth.

The behaviour of pre-Stone Age man can be inferred by studying the botany of abriginal peoples in various parts of the world. The earliest man have developed systems of plant classification. The urge to recognise different kinds of plants and to give them names is as old as the human race. They not only collected the plants but were also responsible for their domestication, development of agriculture and earlier civilization.

The invention of the optical lens during the 16th century and development of the compound microscope by Jensen (1590) and later Anthony Van Leeuwenhoek (1650) opened an era of rich discoveries about plants. Led by Robert Hooke’s (1665) microscopic observations on cells of several plant tissues in his Micrographia, the wide spread use of the microscope during the 18th century onwards made botany an interesting and laboratory science. Carolus Linnaeus (1753) published his Species Plantarum which contains careful description of 6000 plant species. This was followed by his binomial nomenclature system which established the scientific naming of plants by two words, the genus name and the species name in Latin. This system is universally used even today. To date many systems of classification have been proposed and some classification systems even employ the application of computers.

Around the same time, Koelreuter (1760) conducted experiments in plant hybridization and obtained hybrids. During the next century, Gregor Mendel (1865) conducted experiments of hybridization using pea plants and proposed the laws of inheritance called as Mendelism.

With the rebirth of scientific botany during the begining of the 19th century and especially as a result of the emphasis placed by Schleiden, Nageli, Von Mohl and others on the importance of the study of developmental biology, attention was given to the sexuality in plants and in particular flowering plants. Amici (1847) demonstrated in Orchis that a germinal vesicle was present in the ovule before the entry of pollen tube and the vesicle in due course developed into embryo. William Hofmeister (1862) demonstrated the formation of embryo in flowering plants followed by similar observations on embryo development by Hanstein (1870) and Treub (1879).

Indian and French botanists have excelled in both classical and experimental embryology. With the advent of techniques of tissue and organ culture there has been a movement towards experimental investigations in various aspects of botany and Indians have excelled in this field also.

Plants and the immovable, amazing and highly diversified green property of the mother earth exhibit an enormous variety of form. They range from microscopic unicellular form Chlamydomonas to giant trees like Sequoia. Plants live in variety of habitats like water, marshes, plains, hills, valley, and where not ! every where, where the sun rays could penetrate. Habit of the plants changes according to habitat. Thus there are different forms of plants which include hydrophytes, mesophytes, halophytes, xerophytes etc.

Scope of Botany

Fundamentally botany is a pure science with several branches in it but over the years the frontiers of knowledge have broken and new disciplines have emerged, thus applied botany, biotechnology and bioinformatics are the craze of this century.

The various branches of botany :

1.3 Plant Classification and Biodiversity

Without classification - only chaos, remarked Linneaus to the science of biology. Therefore all organism must be classified. The term taxonomy was proposed by de Candolle (1813) and is the oldest discipline of botany and deals with three aspects of the organisms. Linnaeus adopted species the unit of classification in 1758 in his Systema Naturae and it has been used ever since.

1. Identification,

2. Nomenclature, and

3. Classification.

Taxonomy (Greek = rendering of order) and systematics (to put together) are currently used interchangely. The modern systems of classitication is the labour of several botanists especially during the last century.

Three main types of classification system of angiosperms are known based upon the morphology of the flowers, fruits and seeds.

1. Artificial system based on 1 or 2 characters of plants

2. Natural system based on as many characters as possible to group taxa seemingly related. Bentham and Hooker's (1862-1883) in their Genera Plantarum recognised 202 families.

3. Phylogenetic system is based on several characters to consider the inter relationship. Engler and Prantl, Hutchinson, Takhtajan and Cronquist have proposed phylogenetic systems.

In Hutchinson’s system the Angiosperms are divided into predominantly herbaceous and woody groups (the Herbaceae and Lignosae, respectively). All the "natural" classifications recognise two series; Dicotyledonae and Monocotyedonae. Although the names are based on a difference in the number of embryonic leaves (cotyledons) as monocotyledons and dicotyledons, the ending of the names of the taxonomic ranks are consistent and follow rules of international code of Botanical nomenclature. Thus, the classification of maize, Zea mays be summarised as follow.

It is customary to indicate the name of the author who described a genus and species. The name Zea mays would therefore be Zea mays Linnaeus or Zea mays L. The common name corn has no scientific value. The genus and species names together comprise the binomial system of nomenclature proposed by Swedish botanist C. Linnaeus in his Species Plantarum. The origin of this binomial name are basically latin, although words from many other languages including sanskrit are used and latinised. The scientific name of a plant is always written in italics and the genus name is always capitalized as per the International Botanical Code

A brief summary of Oswald Tippo’s (1942) phylogenetic classification is given in Table 1.1. The Magnoliales is considered primitive and Asteraceae as advanced and Orchidaceae more recent.

Table 1.1

The functions of taxonomy are :

1. To provide a means for the communication and retrieval of information concerning all plants, animals and other organisms.

2. To facilitate the gathering of new information by permitting the prediction of characters in unfamiliar organisms, and

3. To demonstrate at once the unity and diversity of organic life by expressing the evolutionary origins of the various taxa.

Ernst Haeckel (1894-1896) published his work Systematic Phylogeny; a sketch of a natural system of organism based on their descent, in which he presented what he believed to have been a genealogic tree of living world. A somewhat modified version of the phylogeny of plant kingdom is shown in Fig. 1.1. The primitive plant groups are kept at base and the advanced ones on top.

Fig. 1.1 Phylogeny of Plant Kingdom

Ancient Indians have also contributed to classification of plants based on three major considerations, namely :

1. Udhvida (botanical)

2. Virechanadi (medicinal), and

3. Annapanadi (dietic)

The systems was superficial and are similar to those of ancient Greeks and Romans, Charaka (1 century, A. D.) divided plants into the following groups and recognized two groups among Virudhs namely, Latas (creeper) and Gulmas (succulent herbs and shrubs).

Prasastapada, another medical practiontioner of this period classified plants and recognised six classes, namely :

There is an increasing emphasis in taxonomic research of new disciplines in utilizing information other than external morphology, the structure and development of pollen grains and embryo sacs anatomy, analysis of chemical constituents, genetics, serology, etc. Studies of the numbers and morphology of chromosomes and their behaviour at meiosis have been made and have generally shown a good correlation with existing classifications. The range of basic chromosome numbers is from n = 2 (Haplopapus gracilis) and (Brochycome Iineariloba of Asteracae) to n = 154 Morus nigra of Moraceae.

The kinds of plants are inestimable. It is estimated that there are 4 lakh different kinds of plants. These are differentiated into various groups as shown in Table 1.2.

Table 1.2

Biodiversity is variety and variability of plant and animal species on the earth. There are three broad levels of biodiversity : genetic variation within species : the variety of species within a habitat or ecosystem; and the variety of habitats on the earth. The biodiversity has two basic functions, first; it depends on the stability of the biosphere and second, it is the source of species on which mankind depends for food, fodder, fibre, shelter, medicine etc. Biodiversity is not only an important resource but also a country’s strength.

Species do not occur evenly around the world and therefore there is a need to know about the distribution and in density of species in difterent habitats/localities. India has a very rich, variety of plants and is recognised as one of the 12 megadiversity countries (Mc Neely et al 1990). It is established that about 17,000 species of flowering plants belonging to 315 families are represented in India.

The green aquatic, filamentous or thalloid plants are called algae. This is the first distinct group of plants and hence primitive.

The non-green filamentous mycelial to fleshy mushroom are Fungi. It is the heterotrophic groups of plants capable of living any where, either as parasitic or saprophytic.

The thalloid group of green land plants are called Bryophytes. These are the first embryo bearing plants and are also called as amphibians of the plant kingdom. Algae, Fungi and Bryophytes are collectively called as non-vascular cryptogams. Bryphoytes, are highly advanced cryptogams.

The vascular plants include pteridophytes, gymnosperms and angiosperms and are collectively grouped under Tracheophytes because of the presence of tracheids. The Tracheophytes constitute a group of vast and richly varied assemblage of plants that dominate the earth today. They are characterised by.

1. A dominant sporophyte, and a highly reduced gametophyte (the microscopic pollen)

2. Presence of vascular elements that transport water and food

3. Development of variety of flowers and seeds

The tracheophyte has four sub-division as follow :

1. Psilopsida

2. Lycopsida

3. Sphenopsida

4. Pteropsida

The Pteropsida is sub-divided into ferns (seedless plants) and seed plants (gymnosperms and angiosperms). The ferns are the first vascular land plants and their body shows differentiation of root, stem and leaves.

The pteropsida are plants with protected seeds which produce exposed seeds not covered by fruits are the gymnosperm while the plants that bear true fruits are the angiosperms. The term angiosperm was coined in 1690 but it was Robert Brown (1827) who gave the meaning and significance to angiosperms and gymnosperms. These are sub-divided into two groups as shown below. A comparison of how they differ in several characters is shown in Table 1.3.

Model Plants System

A number of plants have been used as model system. The best example is Arabidiopsis because : Arabidiopsis thaliana a member of Brassicaeae, has a small genome with 1,20,000 kbp is extensively used because in comparison with rice 4,50,000 kbp. Arabidopsis can be grown easily in large numbers in plant growth chambers/greenhouse. It has a short life cycle, seed germination to production takes 6-8 weeks only. The seeds are small, 20mg each; 20,000 per plant; can be stored and large numbers of plant can be generated at will. It is easy to induce mutations by chemicals or radiations. It is easy to carry out various techniques of molecular biology. The plant genome sequencing of Arbidopsis Genome Project (AGP), was completed in December 2000. Other plant species for which genome sequences are being obtained include maize and rice etc.

Table 1.3

1.4 Life History of a Typical Plant

Alternation of Generation

The term alternation of generations was originally coined to describe the kind of life history found in the Bryophyte and Vascular Cryptogams. (Psilopsida, Sphenopsida, Lycopsida, Pteropsida). In all these groups the sporophytic the diploid generation reproduces by means of spores. These germinate and grow into a gametophytic the haploid generation which reproduces by means of male and female reproductive organs. Fertilization of the female gamete by the male gamete produces again the diploid status of the sporophyte. Apart from certain cases where either the sporophyte or gametophyte respectively can give rise vegetatively to new comparable plants the two generations must succeed each other alternately and repeatedly (Fig. 1.2).

Fig. 1.2

In these plants reduction division takes place at spore formation and there is an alternation, not only of morphologically unlike generations but also of cytologically unlike generations (diploid and haploid state).

The term alternation of generations has since been applied to all members of the plant kingdom where it is relevant, and in the case of the land plants it is possible to trace a series in which at first the gametophyte (haploid) generation is the larger (or dominant) through a succession in which the gametophyte generation becomes successively more and more reduced, until in the flowering plants it is represented by only a few nuclei. In plants below the rank of Bryophyta (i.e. Algae, Fungi) alternation of generations also exists. However, the alternation of generation is not regular. It is thus evident that the phenomenon emerged before the adoption of the land habitat, but that prior to the transmigration from water to land the alternation was not inevitably regular. In the algae there is regular alternation of morphologically similar generations, as in Dictyota, Ulva : of morphological dissimilar generations both of which are macroscopic as in Cutleria or one generation microscopic and the other macroscopic as in Laminaria. There is thus, considerable variation in alternation of generations in red algae.

Considerable acrimony as to whether the two generations (e.g. in the Bryophyta) were completely distinct entities (antithetic theory) or whether one generation had arisen from the other and there was no such distinction (homologous theory). With present day knowledge about chromosomes and the nature of the haploid and diploid nuclei, this problem is of historical interest only.

1.5 Plant Cell - Structure and Function

Robert Hooke (1676) first observed network of cells in a thin section from the cork and this was followed by similar observations on bacteria and protozoa by Leeuwenhoek in 1683. Robert Brown (1855) proposed the term nucleus while Purkinje (1858) proposed the term protoplasm.

For convenience the plant cell is best studied under the following heads and illustrated in Fig. 1.3.

Fig. 1.3 Diagram of a generalized plant cell and enlarged view of the nucleus

1. Protoplasmic (living) parts

(a) Nucleus

(b) Nucleous

(c) Cytoplasm

(d) Mitochondrion

(e) Plastids etc.

2. Non-Protoplasmic (non-living) parts

(a) Vacuoles

(b) Ergastic substances

(i) Starch grains

(ii) Crystals etc

(c) Cell wall

The cytoplasm is highly organised and forms the living ground substance of the all various specialized protoplasmic bodies or organell are dispersed in it (Fig. 1.4). The cytoplasm is bounded externally by the plasma membrane or plasmalemma and internally by the tonoplast or vaculor membrane. Both the plasma membrane and the tonoplast are differentially permeable membranes and hence are of great importance in various cellular activities such as osmosis. Cytoplasm is a complex colloidal substance consisting; of water (85-900%) proteins (7-10%) carbohydrates (1-0%), lipids (1.0%) and various inorganic compounds like calcium, magnesium etc. in small amounts. Evidence from electron microscopy on cell ultrastructure provides ample proof that the cytoplasm is highly organised interwoven network of endoplasmic reticulum membrane which may be smooth at the site of lipid synthesis or rough coated with ribosomes, the site of protein synthesis the endoplasmic reticulum may be perinuclear (around the nucleus) and cortical at the cell periphery. The nucleus is large spherical bounded by a two layered nuclear membrane with distinct nuclear pores indicating continuity between the outer part of the nuclear membrane and endoplasmic reticulum within the nucleus embedded in nuclear sap (nucleoplasm) are chromonemata, which later become, chromosomes during mitotis and meiotic divisions and carries genes all along its length and biochemically made up of deoxyribonucleic acid (DNA). Nuclear chromatin of DNA threads intimately forms complex with nucleo proteins are histones low, molecular weight proteins are non histone proteins. Interphase nuclei have large spherical nucleoli that contain the machinery for the production of ribosomes and apparently involved in the synthesis of nuclear ribonucleic acid (RNA) and proteins. The main functions of a chromosome are :

Fig. 1.4 Diagram illustrating (a) Cell wall layers, (b) A primary pit field, (c) Cross section of a simple pit, and (d) Cross section of a bordered pit 1. Middle lamella 2. Primary wall 3. Secondary wall 4. Cell lumen 5. Plasmodesmata

Fig. 1.5 Ultra structure of plant cell based on information obtained by light and electron microscopy

1. Transmission of genetic material from one cell to another cell and from generation to other generation

2. Control of cellular functions and development.

All living cells, both plant and animal contain small rod like or spherical double membrane structures called mitochondria referred to as the powerhouses of the cell, as they generate adenosine triphosphate (ATP) from stored food reserves carbohydrates and lipids (Fig. 1.5).

Plant cells usually contain specialised bodies called plastids. These can be of three main types on the basis of the colour. Green plastids are called, chloroplasts which contain the two green pigment chlorophyll ‘A’ and chlorophyll ‘B’. Orange and yellow plastids are called chromoplasts and contain carotene and xanthophyll. All these pigments are necessary for photosynthesis (the process where by sunlight is converted into chemical energy), Leucoplast are colourless plastids and store food such as starch (amyloplast) and oil synthesis (elaioplasts). The Goigi complex is a membrane system similar to endoplasmic reticulum but lacks ribonucleoprotein granules and designated as smooth membrane system. Peroxisomes contain catalase that removes toxic hydrogen peroxide produced during metabolism while glyoxysomes contain lipid biosynthesis enzymes.

In Fig. 1.5 the generalised ultrastructure of cell is shown. The most important protoplasmic parts of the plant cell are vacuoles. In young cells the vacuoles are small but at maturity plant cell contains a single large vacuole which may occupy 90-95% of the total cell volume. The vacuole is seperated by a membrane the tonoplast and contains complex organic and inorganic substances. Apart from water (major component), red blue and purple anthocyanin pigments, organic acids, fats, tannins, crystals, starch, grains, amino acids, proteins and dissolved salts are the other constitutents of cell sap. This is responsible for osmotic regulation of cell.

The plant cell wall is fully permeable metabolically active wall surrounding and enclosing the protoplast as shown in Fig. 1.5. The primary wall is capable of growth in surface, varies in thickness depending upon the metabolic state and is always associated with living protoplast. Cells involved in water conduction and mechanical support have secondary walls and are often thick and consist in part of lignin or suberin. The plant cell walls are usually composed of two and rarely three distinct layer viz., 1. Middle lamella which is formed during telephase of mitosis (cell division) and act as a cementing substance between adjacent cells. 2. The primary wall, formed while the cell is still actively enlarging/elongating and 3. In some cases, the secondary wall, formed inside the primary wall at a time when the cell is nearing its maximum enlargement. The adjacent cells are interconnected by plasmodesmata pores through the wall where plasma membrane and endoplasmic reticulum connect. Everything with in the plasma membrane is termed symplast and everything outside it apoplast which is water permeable space in which hydrophilic molecules are present. The primary wall is the first finite wall layer formed by a developing cell and may be the only wall layer present in many types of all such as paenchyuma, collenchyma etc. Chemically primary wall is composed of cellulose (42%), non-cellulosic the polysaccharides (38%), hemicelluloses and pectic substances (8%) and protein (12%).

Plant cells either divide mitotically to ensure equal cell division or meiotically (reduction division) to ensure haploid condition of male/female gametes.

1.6 Biology of Algae

Algae are typically adapted for aquatic life and mostly live in water or in damp situations. They are present in all kinds of running waters, however, abundant in still waters. The aquatic algae are found either floating at the surface simply immersed in water, or attached to stones or to larger aquatic plants. The free floating algae are generally unicellular or colonial form and are called as 'plankton' The algae attached to the littoral zone are the'benthos'.

Range of plant body

The form of algae varies from a single cell to the complex giant kelps (sea weeds). Single celled Chlorella (5 - 8μm) are in the range of bacterial size whereas some seaweeds may attain a length of 60 m. The organisation of the thallus in algae is unicellular, colonial, filamentous (unbranched, branched, heterotrichous) membranous or foliose or tubular types. Unicellular motile (flagelletes) - Chlamydomonas; unicellular non-motile (coccoid habit) Chlorella; multicellular colonial motile -Volvox; multicellular aggregations - Gleocapsa; simple filamentous - Ulothrix, Oedogonium; Branched filamentous - Cladophora; Heterotrichous - Coleochaete; Siphonous - Vaucheria, Caulerpa; Parenchymatous or pseudoparencnymatous - Batracospermum, Polysiphonia. (Fig. 1.16 (a-j)).

Cell structure

Most algal cell walls are formed from cellulose sometimes impregnated with silica or calcium carbonate. Algal cells contain nuclei, mitochondria, ribosomes, golgi and chloroplasts. The internal cell structure is supported by a network of microtubules and endoplasmic reticulum. They often possess flagella that have a 9 + 2 microtubule arrangement within them, and there may be one or two per cell. The presence of eyespots near the flagella insertion point allows the cell to swim towards the light. Chloroplasts are very variable structures in the algae and can be large and single, multiple, ribbon like spiral or stellate etc.

Fig. 1.6 Range of vegetative structure. The motile type (a)-(d) and (j); (a) motile vegetative cell of Chlamydomonas', (b) vegetative colony of Pandorina sp; (c) vegetative colony of Eudorina unicocca; (d) vegetative and colony of Volvo×', (j) Motile cell of Sphaerella. The palmelloid type (e) and (f-e), colony of Tetraspora cylindrical (f) Portion of a colony of T cylindrical the coccoid type - (g-i) and (k) (g) (h) and (i) vegetative cells of Chlorococcum humicola', (k) colony of Scenedesmus sp.

Growth

Growth in unicellular algae is synonymous with binary fission. In most unicells, haploid or diploid nuclei undergo mitosis and the cell then divides longitudinally to form two daughter cells. Coenocytic filamentous algae grow from the tip of the filament in a way very similar to that of hyphal growth.

Nutrition

Algae are auxotrophic organisms and obtain their carbon and energy requirements by the fixation of CO2 by photosynthesis. Algae use aerobic respiration via glycolysis and citric acid cycle. Except heterocystous Cyanophycean algae, other algae cannot fix nitrogen and they obtain it in a fixed inorganic or organic form. Most algae can tolerate a wide range of pH and temeperature.

Fig. 1.7 Range Ofvegetative structure. Filamentous habit (a) heterotrichous thallus of Stigeoclonium-, (b) portion of Stigeoclonium-, (c) tubular thallus of Enteromorpha-, (d) portion of the filament of Ulothrix; (e) foliaceous thallus of Ulva; (f) habit of Cladophora (on mullusc shell); (g) a part of Cladophora thallus; (h) discoid thallus of Coleochaete.

Fig. 1.8 Range Ofvegetative structure. Siphonous type, (a) thallus of Caulerpa Cupressoides; (b) thallus of C. crassifolia; (c) thallus of C. prolifera; (d) thallus of Caulerpa sp; (e) thallus of Valonia utricularis; (f) thallus of Vaucheria sp.

Pigments

There are three kinds photoshynthetic pigments in algae : chlorophylls, carotenoids, and biloproteins (phycobilins). There are five chlorophylls : a, b, c, d and e. Chlorophyll ‘a’ is present in all algae. Chlorophyll ‘e’ is rare and has been identified in only two genera of Xanthophycophyta, Triboneara and Vaucheria. There are two kinds of carotenoids : carotenes and xanthophylls. Carotenes are linear, unsaturated hydrocarbons and xanthophylls are oxygenated derivatives of these. Biloproteins are pigment - proteins complexes and are present in two algae divisions : Rhodophycophyta and Crytophycophyta. Similarly there are two kinds of phycobilins : phycocyanin and phycoerythrin.

Motility

The motile algae have flagella occurring singly, in pairs, or in clusters at the anterior or posterior ends of the cell. There are three types of flagella : whiplash (cylinrical or smooth), tinsel (cylindrical and with hair like appendages), and ribbon or straplike. Some algae have no means of locomotion and are carried about by tides, waves and currents.

Reproduction

Reproduction in algae takes place in three ways.

1. Vegetative

2. Asexual

3. Sexual.

Vegetative

In unicellular forms the vegetative reproduction is by fission. In colonial forms it is by splitting of the mature colonies into two or more parts. In filamentous forms, parts of plant body becomes seperated and give rise to new individual by a process called fragmentation. The resting cells, formed to tide over a peirod, unfavourable for vegetative development is akinete formation.

Asexual

In asexual reproduction, a rejuvenation of the protoplast of algal cells is involved. This is associated with the division of protoplast and these escape from the parent cell and give rise to new plants (Fig. 1.9). The various methods are as follows :

Fig. 1.9 Reproduction Vegetative and Asexual, (a) filament of Hormidiunr, (b) fragments of same; (c, d & f) zoospores (swarmers) of Ulothrix; (e) akinetes of Ulothrix idiospora; (g) zoospore of Oedogonium sp.; I. autospores of Oocytis Iacustris; (h) akinetes of Oedogonium; (j, k & I), cell division in Pleurococcus sp.; (m) akinetes of Pithophora; (n) akinetes of Ulothrix oscillarina; o) Synzoospore of Vaucheria; (p) palmella stage in Ulothrix; (q) germination of cyst in Vaucheria; (r) akinetes of Botrydium.

Sexual

All form of sexual reproduction are found among algae. In these process there is a fusion of sex cells called gametes, to form a union in which blending of nuclear material occurs before new generations are formed. The union of gametes forms a zygote. (Fig. 1.10)

The gametes are identical with no visible sex determination hence, isogamous

The two gametes are unlike, differing in size (male and female) hence, heterogamous

The two sexual cells become more characteristically male and female; the large and non-motiie (ovum) and small and actively motile (sperm) hence, oogamy.

Exclusive male or female thalli also exists. The two thalli may look alike but they are opposite sex types, since one produces male gametes and other ova, such plants are called unisexual (dioecious).

Plants in which gametes from the same individual can unite are said to be bisexual (monecious).

Fig. 1.10 Reproduction Sexual, (a) two gametes of same size (isogametes); (b) fusion of same (isogamy); (c, d) two gametes of different size (male and female); (e) fusion of same (anisogarmy); (f, g) male and female gametes; (h) fusion of same (oogamy); (i) anisogamy in Enteromorpha intestinalis; (j) oogamy in Volvox; (k) clump formation in Ectocarpus, large female is surrounded by male gametes; (I) oogamy in Oedogonium; (m) advanced oogamy in Polysiphonia; (n) oogamy, in Chara; (o) antherozoid of Chara; (p) oogamy in Batrachospermum

Life Cycles

Different types of life cycles have been recognised in the algae. (Fig. 1.11)

(a) Haplontic : The parent is haploid and the zygote is diploid with reduction divison Occuring at the time of germination of the zygote, (eg. Volvox, Oedogonium)

(b) Diplontic : The parent is diplont and the sexual spores constitute haploid. Reduction divison at the time of gametogenesis (eg. Diatoms)

(c) Diplo-haplontic : Alternation of diploid Sporotophyte with the haploid gametophyte. Reduction divison is effected at the time of formation of spores by the sporophyte (eg. Cladophora).

(d) Haplo-biontic : Two haploid generations (gametophyte and Carposporophyte) alternating with a diploid one represented by the zygote, (eg. Batracospermum)

(e) Diplo-biontic : Two diploid phases (Carposporophyte and tetrasporophyte) and a haploid phase (gametophyte) alternating with each other, (eg. Polysiphonia).

The general characteristics of major algal taxonomic groups are summarised in Table 1.4.

Fig. 1.11 Life-cycle patterns in algae. 1. haplontic type; 2. diplontic type; 3. isomorphic type; 4. heteromorphic type; 5. haplobiontic type; 6. diplobiontic type.

Classification

Algae are generally classified on the basis of the following characteristics :

1. Nature and properties of pigments

2. Chemistry of reserve food products

3. Type, number and morphology of flagella

4. Morphological characteristics of cells and thalli

5. Life history, reproductive structures and methods of reproduction.

According to the scheme of classification of Fritsch (1945), the algae consists of the following eleven classes as follows : Chlorophyceae, Xanthophyceae, Chrysophyceae, Bacillariophyceae, Cryptophyceae, Dinophyceae, Chloromonadinae, Englenineae, Phaeophyceae, Rhodophyeae and Myxophyceae. Subsequently, Smith (1950) recognised eleven major groups of algae and grouped them in seven divisons as follows :

Chlorophyta, Euglenophyta, Chrysophyta, Phaeophyta, Pyrrophyta, Cyanophyta, Rhodophyta.

Klein and Cronquist (1967) reviewed the classification of algae based on chemical, structural and functional criteria and recognised six divisons and classified the blue green algae with bacteria.

Economic Importance

The algae are economically very useful and important in the agriculture fields, industry and as food for human consumption.

Diatoms are used as oils filters, cleaning solvents, insulation of refrigerators, boiler, hollow tile bricks, sound proof rooms, tooth powders, bleaching powders and silver polishes.

Microcystis and Aphanizomenon produce toxic substances in to the water which are poisonous to fish, cattle etc.

1.7 Biology of Fungi

The Fungi are a group of Eukaryotic organisms devoid of chlorophyll that are of great practical and scientific interest to microbiologist. It produce green to orange color colonies on fruits, bread and cheese. Thus fungi have a diversity of morphological appearances, depending upon species. There are about 65,000 fungal species that comprise the molds, mushrooms, yeasts, rusts, smuts etc. Molds are filamentous and multicellular; yeasts are usually unicellular and eukaryotic spore bearing protists and generally reproduce both sexually and asexually.

Fungi are heterophilic organisms and require organic compounds for nutrition. When they feed on dead organic matter they are known as saprophytes.

The saprophytes decompose complex plant and animal remains breaking them by increasing its fertility, thus they can be quite beneficial to humans. They decompose, textiles, food and other materials. Saprophytic fungi are also important in industrial fermentations. eg. : brewing of beer, wine making, production of antibiotics such as penicillin etc. The making of dough and the ripening of some cheeses depend on fungal activity. As parasites, fungi cause disease in plants, humans and animals. Most of them cause plant diseases and are responsible for loss of agriculture yields.

Characteristics of Fungi

Fungi are chemoorganotrophic organisms and devoid of chlorophyll.

The fungal body (thallus) consists of single cell or filamentous structure (hence dimorphic).

Morphology

Yeast cells are larger than bacteria in size and width as well as in length. They are commonly egg shaped, elongated, have no flagella. Molds consists essentially of two components.

(a) Mycelium, and

(b) Spores

The mycelium is a complex of several filaments called hyphae. New hyphae generally arise from spore which on germination puts out a germ tube or tubes, the germ tubes get elongated to form hyphae. The hyphae are composed of an outer tube like wall surrounding a cavity, the lumen, which is filled by protoplasm, between the protoplasm and the wall is the plasmalemma; which is a double - layered membrane. The wall matrix material in which the microfibrils are embedded consists of protein, lipids and other substances. The young hyphae may become divided into cells by cross walls which are formed by centripetal invagination. Sometimes the hyphae are separated by septa formation; but some of them are non-septate and cell structures filled by more nuclei forming coenocytic condition (Fig. 1.12 & 1.13). Mycelia can be either vegetative or reproductive but in mushrooms the compact fruiting structure is seen.

Fig. 1.12 Gross appearance of Mucor rouxii arthrospores. (a) Light microscopy showing extensive arthrospore formation. (b) High - magnification light microscopy showing variation in arthrospore size and shape. (c) Transmission electron micro-graph of arthrospore chain.

Fig. 1.13 Three types of (a) Non-septate coenocytic (b) septate uninucleate cells, (c) with multinucleate cells

The function of asexual spores is to disseminate the species, which are produced in large numbers. There are many kinds of asexual spores. (Fig. 1.14)

1. Sporangiospores : Single celled spores formed with in sacs (sporangium).

2. Conidiospores or Conidia : Small single celled conidia, called microconidia; multicelled conidia are called macroconidia.

3. Oidia or orthrospores : Single celled spores formed by disjointing of hyphal cells.

4. Chlamydospores : Thick walled single celled spores highly resistant to adverse condition.

5. Blastospores : Spores formed by budding.

Sexual Reproduction

Sexual reproduction (Fig. 1.15) is carried out by fusion of the compatible nuclei of two parent cells. The process of sexual reproduction begins with the joining of two cells and fusion of their protoplasts (plasmogamy) thus enabling the two haploid nuclei of two mating types to fuse together (karyogamy) to form a diploid nucleus (Fig. 1.16).

Fig. 1.14 Asexual spores in fungi

Fig. 1.15 Some sexual spore types and the structure of the corresponding reproductive mycelia in fungi. (a) Ascospores. Nuclear fusion takes place in the ascus. The diploid zygote nucleus divides by meiosis almost immediately after fusion, and produces four haploid nuclei. These haploid nuclei divide once more by mitosis, forming the eight ascospores which are typically produced in each ascus. (b) Basidiospores. Nuclear fusion and meiosis take place in the basidium. Basidiospores are then formed exogenously at the tips of the special outgrowths called sterigmata (singular, sterigma). Usually four spores are formed, one at the tip of each sterigma, but if meiosis is followed by amitotic division then eight basidial nuclei are formed (although rarely do all develop into basidiospores).

The sex organs of fungi called gametangia, male gametangia is ‘antheridium^ and female gametangia is oogonium. Sexual spores, which are produced by the fusion of two nuclei, occur less frequently, later and in smaller numbers than do asexual spores, they are :

1. Ascospores : These are single celled spores are produced in a sac called an ascus usually 4-8 ascospores are producecd in an ascus.

2. Basidiospores : These are single-celled spores, are borne of a club shaped structure called a basidium, usually 4 ascospores are produced.

3. Zygospores : They are large thick walled spores.

4. Oospores : These are formed within a special female structure, the oogonium, where fertilization of the egg takes place.

Asexual and sexual spores may be surrounded by highly organized protective structures called fruiting bodies. Asexual fruiting bodies are called acervulus and pycnidium. The sexual fruiting bodies are called perithecium and apothecium which contains spores.

Fig. 1.16 Some sexual mechanisms in fungi moetic copulation : the fusion in pairs of sexual gametes, formed in specialized sporangia like (b) gamete-gametangial copulation : the fusion of entiated gamete-gametangial copulation: the fusion of entiated gamete of one sex with a gametangium of other sex; (c) gametangial copulation : the dired of gametangia without differentiation of gametes matic copulation : the sexual fusion of undifferential vegetative cells; e) spermatization : spermatia with receptive hyphae of the opposite (compatible) strain.

Physiology

Fungi are able to withstand extreme environmental condition than most other microorganisms. Yeasts and molds can grow on substrate or medium containing concentrations of sugars that inhibit most bacteria. eg : jams and jellies may be spoiled by molds. Some yeasts are facultative, can grow under both aerobic and anaerobic conditions. Fungi grow over a wide range of temperature, with the optimum for saprophytic species from 22-30 oC. Pathogenic species prefer a higher temperatures optimum generally 30-37 oC. Some fungi also grow at 0 oC. Fungi are capable of using a wide variety of materials for nutrition (heterotrophic). They cannot use inorganic compounds like CO2, but they use, ammonium salt etc.

Cultivation

Molds and yeasts can be studied by the same general cultural methods. Nearly all of them grow aerobically on the usual bacteriological culture media at temperature ranging from 20 - 30 oC. They grow slowly than bacteria on SDA (Sabourauds Dextrose Agar), and this medium is widely used to grow various pathogenic fungi.

Classification

Fungal classification is based primarily on the spore types and type of life cycles.

They are divided into perfect and imperfect fungi and they are provisionally placed in Deuteromycetes, Ascomycetes and Basidiomycetes. The classification scheme was proposed by Alexopoulus.

Some Fungi of Special Interest

The characteristics and activities of Deutromycetes fungi are described as under :

1. Synchytrium : More than 100 species of genus are parasitic on flowering plants. The most serious parasite is S. endobioticum. eg : black wort disease of potato. It forms warts, they are galls on which the host cells have been stimulated the divide by the fungus. The zoospores released from sporangium are capable of swimming for about 2 hrs in soil water until a new host tubes is found to infect. The zygote then encysts on the surface on the host epidermis and penetrates the host cell to infect it. The host cell reacts by undergoing hypertrophy i.e. increased cell volume.

2. Saprolegnia : This is the most common fungus in soil and fresh water, hence commonly called as water molds.

3. Mucor : This occurs abundantly on soil, fruits, vegetable and starchy foods. Some cause food spoilage; others are used for manufacture of foods. Sporangiospores may be branched, columellae are present. No stolons or rhizoids are produced.

4. Rhizopus : These are the common bread molds which cause much food spoilage, grow on vegetables, fruits, and other food products. Morphologically are non septate, cottony, mycelia with sporangiophores arising at the nodes where the rhizoids form.

Ascomycetes

5. Schizosacchoromyces : Yeasts belong to this genus. They reproduce by transverse division and also with ascospores. The best known species is S. octosporus which has been isolated from honey.

6. Saccharomyces : There are 30 species of Saccharomyces. The best known species is S. cerevisiae. This is found in nature on ripe fruits. Reproduction is by budding. The fusion normally occurs only between cells of differing types called legitimate copulation.

7. Neurospora: This fungus is an Ascomycete : N.crassa and N. sitophila are common species. Some of them are responsible for food spoilage and some are used in fermentations.

Basidiomycetes

Approximately 12,000 species are known. None was implicated in human disease until recent times. eg : Cryptococcus neoformans now it is called Filobasidetla neoformans is a human pathogen, causing generalized mycotic (systemic infection) involving the blood stream as well as the lungs, and other organs.

8. Agaricus : Commonly known as mushroom. Pink coloration of the young gills is due to cytoplasmic pigment in the spores.

9. Aspergillus : This is a common fungus in nature, being found on fruits, vegetables, etc. They are economically important because they are used in industrial fermentations.

10. Penicillium : This is common in nature and is used in the ripening of cheese and in industrial fermentations. Fungus produces brush like conidiospores hence the name Penicillium.

11. Candida : Candida albicans is often isolated from warm blooded animals. It exists as normal flora. But sometimes this becomes pathogenic causing candidiasis called thrush.

Molds and their Association with other organisms

There are some interesting partnerships in nature involving a mold and some other organism. These associations are the partners of dependent (fungi) and independent (algae) nature of organism.

eg : Lichens, fungi and nematodes, fungi as parasites of insects, mycorrhiza.

1.8 Biology of Lichens

Lichens are the most familiar and wide spread of the stable self supporting symbioses involving an alga (phycobiont or photobiont) and fungus (mycobiont). They have a morphology, physiology and ecology which is unlike that of either the mycobiont or phycobiont component.

The lichens grown on wide ecological range soils, rocks, and tree trunks and are found in such diverse habitats as deserts, sea shores, tropical rain forests, arid deserts, mountain peaks of arctic regions, that are barred to many other life forms. Infact they occur in all continents particularly southern hemisphere. Lichen thallus structures varies from crustose forms which are tightly appressed to the substrate to leafy (foliose) forms and highly branched (fructicose) species. Reindeer moss (Cladonia species) a fructose lichen which grows to a height of 20-30 cm occurs over root areas of the arctic tundra and is a important for reindeer and caribou. Of the 70,000 species of fungi known approximately 25% are lichenised. Fungi that have become lichenised to diverse taxonomic groups and the algae that have been identified within them belong to 27 different genera comprising about 24,000 species. There are about 1000 lichen species.

Lichens may be divided into three distinct morphological groups based on their thallus growth habit (Fig. 1.17).

1. Crustose type : Crustose lichens are closely associated with stones and rocks and it is impossible to dislogic it with out breaking it. These lichens grow embedded in their substrate, the thallus is insignificant in size and without distinct lobes. The thallus lacks a lower cortex fungal layer.

e.g., Graphic scripta, Haematoma puniceium.

Fig. 1.17 (a-e) Lichens. Three fundamental types of lichen thalli.

a) crustose lichen (b) Foliose lichen (c) Fructicose lichen (d) Cross section of lichen thallus. Algal cells are intermingled with fungus hyphae in the upper part of the thallus (e) Fungal hyphae in close contact with the surface of the algal.

Fig. 1.17 (f) Cross-section of a typical foliose lichen showing the release of soredia. Aglal cells in the thallus are localized in the upper part of the medulla. Rhizines are bun dles of fungal hyphae that anchor the thallus to the substrate and conduct water by capillary aciton.

Fig. 1.17 (g - j) A trend in evolution from parasitism to mutalism in the lichens. In some primitive lichens the fungi actually penetrate the algal cells, as in diagram. In the more advanced species the two organism live in greater harmony for mutual benefit, as in i and j (After Odum. 1963)

2. Foliose type : Foliose lichens are more striking, flat, circular or lobed and grow loosely or only centrally attached to their substrates. The thallus has a lower cortex and often provided with specialized attaching filamentous structures called rhizinae.

e.g., Xanthoria, Physcia, Peltigera, Parmelia, Certraria.

3. Fructose types : These lichens are most conspicuous, upright or pendent and attached to the substrate only at their base by a flattened disc. They may be ribbon shaped, cylindrical, ropey and shrobby in form, forming extensive and attractive growths standing out from the rocks, foliage and branches of trees.

e.g., Cladonia, Usnea, Ramalina.

Chimeroid