Primary root growth dynamics and lateral root development of dark- and light grown cotton seedlin... more Primary root growth dynamics and lateral root development of dark- and light grown cotton seedlings (Gossypium hirsutum L., cv. Acala SJ-2) were studied under control and salinity stress conditions. The seedlings were grown by two methods: A) in paper-lined, vermiculite-filled beakers with the plants growing between the paper and the glass wall (Gladish and Rost, 1993), and B) in hydroponics after germination and initial growth in germination paper rolls saturated with the treatment solutions (Kent and Lauchli, 1985). After germination, daily primary root elongation rate gradually incrased to a maximum, then gradually declined to close to zero for dark-grown seedlings, or to sustained rates of about 10 mm per day for light-grown control plants. Salinity stress delayed primary root growth and reduced peak elongation rates, without changing the general primary root growth pattern. These results suggest that salinity changed the time-scale, but did not modify the normal developmental sequence. Lateral root growth was more inhibited by salinity than primary root growth. In addition, elongation of lateral roots was more inhibited by salinity than their initiation and emergence. Light exposure of the shoot favored both sustained primary root growth from 7 days after planting, and lateral root emergence and growth. Salinity effects were more severe on seedlings germinated and grown in hydroponics (method B) than on vermiculite-grown plants (method A). These results emphasize the importance of growing conditions for the NaCl-induced effects on cotton root development. In addition, the differential effects of salinity on primary and lateral roots became evident, pointing to diverse control mechanisms for the development of these root types.
The effects of NaCl salinity on the development of primary tissues of cotton seedling roots (Goss... more The effects of NaCl salinity on the development of primary tissues of cotton seedling roots (Gossypium hirsutum L. cv Acala SJ-2) were studied. Control and salinity treatments were imposed on 4-9-d-old plants grown in hydroponics in the light, with a photoperiod of 16 h. Observations were made on thin longitudinal and transverse sections from plastic embedded root samples taken at increasing distances from the root tip. Salinity induced a reduction of root growth rate and induced cells and tissues to initiate and complete maturation closer to the tip, except for the late metaxylem in the center of the stele. These responses were more pronounced with rising NaCl level in the growth medium. Roots exposed to salinity showed increased cellular vacuolation in all tissues but most strikingly in cortex and metaxylem cells. Other changes induced by salinity were the premature differentiation of protophloem sieve tube members, the dense staining of endodermal and some xylem parenchyma cells, the positional compression of the maturation of proto- and early metaxylem tracheary elements, and the induction of lateral root initiations much closer to the root tip. Possible adaptive values of some of these responses to salinity are suggested.
SummaryRoot tip excision, wounding, or cotyledon removal causes a reduction of the percentage of ... more SummaryRoot tip excision, wounding, or cotyledon removal causes a reduction of the percentage of mitotic figures in the root tip meristem. This reduction followed by recovery can be mimicked in root tip meristems of intact seedlings by treatments with methionine, Ethrel, and ethylene. Evidence is presented to suggest that this mitotic regulation is induced by wound-stimulated ethylene.
The sequence of organ emergence in embryos of S. lutescens was similar to that reported for other... more The sequence of organ emergence in embryos of S. lutescens was similar to that reported for other grasses: coleorhiza, radicle, coleoptile and first leaf. The coleorhiza emerged by forcing open a hinged flap on the lemma. Coleorhiza trichomes formed soon after emergence. The radicle protruded through the abaxial surface of the coleorhiza. The coleoptile initially elongated downwards as it passed between the lemma and palea, but immediately turned upwards. The first leaf emerged by protruding through a slit-like crease on the adaxial surface of the coleoptile. Embryos excised from dormant florets germinated as well as those from non-dormant florets. Inhibitory effects on germination of the lemma, palea and caryopsis coat were demonstrated. Cycloheximide at 10-4 M did not decrease germination percentage, but rather inhibited radicle growth but not coleoptile elongation. The significance of the observations is discussed
Journal of the American Veterinary Medical Association, 1982
During a 2-week period, 3 hanuman langurs (Presbytis entellus) died from severe fibrinopurulent a... more During a 2-week period, 3 hanuman langurs (Presbytis entellus) died from severe fibrinopurulent and proliferative peritonitis. Partially digested plant material was identified in the necrotic abdominal debris of the 1st and 2nd langurs. In the 3rd, a phytobezoar that extended 17.5 cm distally from the pyloric area had caused a 1-cm perforation. Seven months later, surgery was performed on a douc langur (Pygathrix nemaeus) to remove 1 gastric and 2 intestinal phytobezoars composed primarily of undigested Acacia sp leaves. An analysis of Acacia sp leaves consumed by these langurs revealed a high cell wall concentration (40%, dry basis), with an exceedingly high proportion of this cell wall composed of indigestible lignin. It was concluded that the species of acacia (Acacia saligna and A longifolia) fed in these cases are inappropriate browse items for langurs.
A s imple and con venient procedure was u sed for studying plant m eri st ematic tissu es. Tissue... more A s imple and con venient procedure was u sed for studying plant m eri st ematic tissu es. Tissues were fixed in 4% glutaraldehy de , d ehydrated in a t ertiary butyl alcohol series and embedded in SPURR' s m edium. Sectioning may b e done with a glass knife in an inexpen sively made holder fitted t o a rotary microtome. St a ining with 0.5 % aqueous safranin or fast green was followed b y counter st a ining in 0.2 % a queous toluidine blue a t 60°C. U sing appropriate hist ochemical methods at appropria t e stages in the process it was shown that enzymes, nucleic acid s, total proteins and polysacchar ides could b e identified.
Background The difference between indeterminate and determinate growth in plants consists of the ... more Background The difference between indeterminate and determinate growth in plants consists of the presence or absence of an active meristem in the fully developed organ. Determinate root growth implies that the root apical meristem (RAM) becomes exhausted. As a consequence, all cells in the root tip differentiate. This type of growth is widely found in roots of many angiosperm taxa and might have evolved as a developmental adaptation to water deficit (in desert Cactaceae), or low mineral content in the soil (proteoid roots in various taxa). † Scope and Conclusions This review considers the mechanisms of determinate root growth to better understand how the RAM is maintained, how it functions, and the cellular and genetic bases of these processes. The role of the quiescent centre in RAM maintenance and exhaustion will be analysed. During root ageing, the RAM becomes smaller and its organization changes; however, it remains unknown whether every root is truly determinate in the sense that its RAM becomes exhausted before senescence. We define two types of determinate growth: constitutive where determinacy is a natural part of root development; and non-constitutive where determinacy is induced usually by an environmental factor. Determinate root growth is proposed to include two phases: the indeterminate growth phase, when the RAM continuously produces new cells; and the termination growth phase, when cell production gradually decreases and eventually ceases. Finally, new concepts regarding stem cells and a stem cell niche are discussed to help comprehend how the meristem is maintained in a broad taxonomic context.
Rice (Oryza sativa L.) belongs to the family Gramineae and is the staple food for half of the wor... more Rice (Oryza sativa L.) belongs to the family Gramineae and is the staple food for half of the world's population and occupies almost one-fifth of the total land area covered under cereals. Now-a-days, the production of rice is hampered due to climatic changes. Therefore, it is essential to develop variety which is tolerant to abiotic and biotic stresses. The present investigation was conducted to establish an efficient and simple protocol for regeneration of four agronomically important indica rice varieties (Khandagiri, Udayagiri, Swarna and Pratikhya). Somatic embryogenesis were achieved from immature zygotic embryos on Murashige and Skoog (MS) medium supplemented with 3 mg/l 2,4-D (2,4dichlorophenoxyacetic acid), 1.0 mg/l kinetin and 3% (w/v) sucrose within 4 weeks of culture. The secondary somatic embryogenesis was also achieved in subsequent subculture on MS medium supplemented with 2 mg/l 2,4-D and 2.0 mg/l kinetin and 200 mg/l L-proline. The percentage of embryogenic calli proliferation were 82.4, 83.7, 88.4 and 84.4 in variety Khandagiri, Udayagiri, Swarna and Pratikhya respectively on MS basal medium supplemented with 3.0 mg/l 2,4-D, 2.0 mg/l Kinetin and 200 mg/l L-proline. Inclusion of higher concentration of L-proline (400 mg/l) in the induction medium, the growth of calli was reduced. The maximum percentage of somatic embryo germination took place in medium supplemented with 2.0 mg/l kinetin, 0.25 mg/l NAA and 50 mg/l adenine sulfate within 4 weeks of culture. The regenerated plantlets were transferred to pots for acclimatization. About 80% of plants were survived in the greenhouse condition.
With the first reports of embryogenesis from cultured somatic tissues (Reinert 1958; Steward et a... more With the first reports of embryogenesis from cultured somatic tissues (Reinert 1958; Steward et al. 1958), a new possibility arose for the study of plant embryo development. In carrot tissue culture systems, for instance, somatic embryogenesis is controlled by the presence or absence of auxin in the culture medium and it is possible to produce over one million embryos per liter of cultured cells (Sung et al. 1984). This allows for an analysis of plant embryo development at a biochemical and molecular level unattainable by studying zygotic embryogeny. In addition to their obvious potential for studies of plant developmental biology, somatic embryos are the preferred method of regeneration of plants from tissue culture. Somatic embryos develop as bipolar structures, eliminating the need for separate root- and shoot-forming media during regeneration. Also, by virtue of a presumptive single cell origin, the possibility of chimeric regenerants is reduced and the potential for obtaining identical, genetically engineered plants from manipulated cells or protoplasts can be realized.
The spacing of lateral root primordia in the primary root of Pisum sativum (cv. Alaska) seedlings... more The spacing of lateral root primordia in the primary root of Pisum sativum (cv. Alaska) seedlings is influenced by both predetermined lateral root initiation sites in the embryonic radicle and by factors present during seedling growth. When pea seeds were germinated in the presence of the mitotic inhibitor, colchicine, the triarch radicle produced three ranks of primordiomorphs indicating sites of embryonic lateral root primordia. The number of primordiomorphs was not the same along the three xylem strands in the radicle. Normally germinated seedling roots (5 days old) also showed a different number of lateral root primordia associated with the three strands. In both cases, the strand with the greatest number of primordia (or primordiomorphs) was associated with a cotyledonary trace. This indicated a possible role for the cotyledons in setting the pattern of lateral root distribution during radicle development. The spacing of lateral root primordia could be altered by the application of growth regulators. Seedling root tips (2 mm) were removed (− rt) and replaced with indoleacetic acid (+IAA), and in some instances seedlings were also treated with the auxin transport inhibitor, 3,3a-dihydro-2-(p-methoxyphenyl)-8H-pyrazolo[5, 1-α]isoindol-8-one (+DPX). In the growth regulator treatments, primary root elongation was inhibited, a greater number of lateral root primordia were initiated compared to controls, and the spacing intervals between primordia were greatly reduced. The — rt, +IAA, +DPX-treatment resulted in the closest possible spacing intervals (av. 0.4 − 0.6 mm), but resulted in fused or fasciated laterals. The — rt, + IAA-treatment produced the shortest spacing intervals which resulted in “normal” lateral roots (0.8 − 1.1 mm).
Cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) were germinated and grown in vermiculite ... more Cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) were germinated and grown in vermiculite for 7 days, at 1–150 mM NaCl salinity. Primary root samples were harvested daily, root lengths measured and, after clearing and staining, the distance from the root tip to the closest protoxylem tracheary element (PTE) secondary cell wall depositions was determined. The length of control roots correlated with the PTE distance and the root elongation rate. Initially, as roots became longer, elongation rates increased and so did the distance for PTE secondary wall depositions. The highest elongation rates and the farthest PTE distances were reached for 75–125 mm long roots. Thereafter, as root length increased, the PTE distance and growth rates dropped gradually. A high linear correlation between the distance for PTE secondary wall depositions and the root growth rate was obtained for control plants (up to 200 mm long) over the experimental period. This correlation was weakened by rising salinity. At 150 mM NaCl no such correlation was found. Salinity resulted in PTE distances closer to the tip in roots of intermediate length (50–150 mm). In longer and in shorter roots, salinity did not affect the distance from the root tip for PTE secondary wall depositions. Vermiculite-grown seedlings, 4–11 days old, were used to assess the effects of 200 mM NaCl salinity on the development of metaxylem vessel members (MVMs). In macerated stele samples from regions close to the root base, the dimensions of MVMs were measured. High salinity resulted in reductions of both width and length of MVMs, and this inhibition increased with plant age. Large, central MVMs matured mostly earlier in control plants than in salt-stressed plants.
Pruning treatment of current-year shoots-Current-year shoots of six-yearold Vitis vinifera var. C... more Pruning treatment of current-year shoots-Current-year shoots of six-yearold Vitis vinifera var. Chardonnay plants grown in the UC Davis experimental vineyard were subjected to pruning treatments during four seasons: summer (30 June), autumn (25 August) in 2004, and winter (25 January) and spring (28 March) in 2005. Pruning cuts were imposed as previously described (Sun et al., 2006) at 10-20 cm from the shoot base on three replicate shoots for each experiment, one shoot on each of three vines. In each season, all experimental shoots were treated and samples collected on the same day. Samples for day 0 were collected from the cut end of each detached shoot and fi xed immediately in formalin-acetic acid-alcohol (FAA) (Ruzin, 1999). Subsequently, samples were taken from the cut end of the attached stem at various days after pruning. At each sampling, three samples consisting of a 4-cm long stem segment including the cut end were taken and fi xed in FAA immediately for at least 48 h. For analysis, each sample was hydrated to water via an ethanol series of 50%, 40%, 30%, 20%, and 10% for 30 min each. Transverse freehand sections were made at depths of 2-10 mm from the cut, then observed under a microscope (Olympus
Xylem-dwelling pathogens become systemic, suggesting that microorganisms move efficiently in the ... more Xylem-dwelling pathogens become systemic, suggesting that microorganisms move efficiently in the xylem. To better understand xylem pathways and how bacteria move within the xylem, vessel connectivity between stems and leaves of Vitis vinifera cv. Chardonnay and Muscadinia rotundifolia cv. Cowart was studied. Three methods were used: (1) the light-producing bacterium, Yersinia enterocolitica, (Ye) strain GY5232 was loaded into petioles and followed using X-ray film, (2) fluorescent beads were loaded and followed by microscopy, and (3) low-pressure air was pumped into leaves and extruded bubbles from cuts in submerged leaves were followed. Bacteria, beads, and air moved through long and branched xylem vessels from the petiole into the veins in leaves of both varieties. From the stem, bacteria and air traveled into primary and secondary veins of leaves one, two, and three nodes above the loading point of the bacteria or air. Particles and air could move unimpeded through single xylem vessels or multiple vessels (conduits) connected possibly through broken pit membranes from within the stem axis into leaf blades. Bacteria were also able to move long distances within minutes from stem to leaf passively without having to cross pit membranes. Such complex, open xylem conduits have not been well documented before; these findings will help elucidate mechanisms involved in the systemic spread of pathogens.
Tyloses form in xylem vessels in response to various environmental stimuli, but little is known o... more Tyloses form in xylem vessels in response to various environmental stimuli, but little is known of the kinetics or regulation of their development. Preliminary investigations indicated that wounds seal quickly with tyloses after pruning of grapevine shoots. In this study, tylose development was analyzed qualitatively and quantitatively at different depths and times from pruning cuts along current-year shoots of grapevines at basal, middle, and apical stem regions. Tyloses developed simultaneously within a single vessel but much separated in time among vessels. Pruning caused prodigious tylosis in vessels of grape stems, extending to approximately 1 cm deep and to 7 d after wounding, but about half of the vessels did not become completely occluded. The fraction of vessels forming tyloses was greatest in basal (85%) and least in apical (50%) regions. The depth of maximum density of tyloses was 4 mm from the cut in the basal region and 2 mm from the cut in the middle and apical regions. Tylose development was faster in the basal and middle than in the apical region. The pattern of tylose development is discussed in the context of wound repair and pathogen movement in grapevines.
The seeds of 20 legume species were grown in the greenhouse or in growth chambers at different te... more The seeds of 20 legume species were grown in the greenhouse or in growth chambers at different temperatures. Under warm temperature conditions (above 15°C). six species, pea (Pisum satiuum), broadbean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinaris), wild lupine (Lupinus latifolius), and soybean (Glycine m a d , formed cavities in the vascular cylinder of their primary roots, which in turn became filled by the ingrowth of specialized parenchyma cells (SP cells). When these species were grown at low temperature (below 15 "C), however, a "normal" vascular cylinder formed in the primary roots with late-maturing metaxylem vessel members differentiating in the center. These species were all cool-season legumes except soybean, a warm-season legume, which sometimes also formed cavities and SP cell ingrowths. The occurrence of cavities and SP cells therefore was restricted to the coolseason legumes (except soybean) when they were grown under warm temperature conditions. The position and size of cavities varied among these species. Pea and broadbean usually formed large, axially elongated cavities in the central vascular cylinder, or in the xylem poles. Others formed smaller cavities of various lengths.
Root apical organization in Arabidopsis thaliana ecotype 'WS' and a c o m m e n t on root cap str... more Root apical organization in Arabidopsis thaliana ecotype 'WS' and a c o m m e n t on root cap structure
The first morphogenetic events of lateral root primordium (LRP) formation in the Arabidopsis thal... more The first morphogenetic events of lateral root primordium (LRP) formation in the Arabidopsis thaliana (L.) Heynh. pericycle occur soon after cells of the primary root complete elongation. Pericycle cells in direct contact with underlying protoxylem cells participate in LRP formation. Two types of LRP initiation were found, longitudinal uni- and bi-cellular. These occur when a single or two pericycle cells within a file, respectively, become founder cells for the entire longitudinal extent of the LRP. Histochemical and cytological analysis suggests that three is the minimum number of cells required to initiate an LRP. In young primordia comprising less than 32 cells, the average cell-doubling time was 3.7 h, indicating a drastic acceleration of cell cycle progression after lateral root initiation. Early in LRP development, cell growth is limited and therefore cytokinesis leads to a reduction of cell volume, similar to cleavage division cycles during animal and plant embryogenesis. The striking coordination of proliferation between pericycle cells in adjacent files in direct contact with the underlying protoxylem implies that intercellular signaling mechanisms act in the root apical meristem or later in development.
It has been hypothesized that the substantial reductions in xylemic water flow occurring at verai... more It has been hypothesized that the substantial reductions in xylemic water flow occurring at veraison are due to physical disruption (breaking) of the xylem as a result of renewed berry growth. In a companion paper, evidence was presented that the vast majority of xylem tracheary elements remained intact despite the growth of the berry, and it was proposed that existing tracheary elements stretch to accommodate growth and that additional elements may also differentiate after veraison. Measurements of the intergyre distance of tracheary elements in macerated tissue were used to test for stretching, and the numbers of tracheary elements per vascular bundle and of branch points of the peripheral xylem network were analysed to test for continued differentiation from 18 to 120 d after anthesis in Chardonnay berries. The distance between the epidermis and the vasculature increased substantially from pre-to post-veraison, potentially increasing the amount of skin available for analysis of compounds important for winemaking. Tracheary elements continued to differentiate within the existing vascular bundles throughout berry development. Additional vascular bundles also appeared until after veraison, thereby increasing the complexity of the peripheral vascular network. The results also confirmed that tracheary elements stretched by ;20%, but this was not as much as that predicted based on the growth of the vascular diameter (40%). These results complete a comprehensive evaluation of grape berry peripheral xylem during its development and show that tracheary development continues further into berry maturation than previously thought.
Primary root growth dynamics and lateral root development of dark- and light grown cotton seedlin... more Primary root growth dynamics and lateral root development of dark- and light grown cotton seedlings (Gossypium hirsutum L., cv. Acala SJ-2) were studied under control and salinity stress conditions. The seedlings were grown by two methods: A) in paper-lined, vermiculite-filled beakers with the plants growing between the paper and the glass wall (Gladish and Rost, 1993), and B) in hydroponics after germination and initial growth in germination paper rolls saturated with the treatment solutions (Kent and Lauchli, 1985). After germination, daily primary root elongation rate gradually incrased to a maximum, then gradually declined to close to zero for dark-grown seedlings, or to sustained rates of about 10 mm per day for light-grown control plants. Salinity stress delayed primary root growth and reduced peak elongation rates, without changing the general primary root growth pattern. These results suggest that salinity changed the time-scale, but did not modify the normal developmental sequence. Lateral root growth was more inhibited by salinity than primary root growth. In addition, elongation of lateral roots was more inhibited by salinity than their initiation and emergence. Light exposure of the shoot favored both sustained primary root growth from 7 days after planting, and lateral root emergence and growth. Salinity effects were more severe on seedlings germinated and grown in hydroponics (method B) than on vermiculite-grown plants (method A). These results emphasize the importance of growing conditions for the NaCl-induced effects on cotton root development. In addition, the differential effects of salinity on primary and lateral roots became evident, pointing to diverse control mechanisms for the development of these root types.
The effects of NaCl salinity on the development of primary tissues of cotton seedling roots (Goss... more The effects of NaCl salinity on the development of primary tissues of cotton seedling roots (Gossypium hirsutum L. cv Acala SJ-2) were studied. Control and salinity treatments were imposed on 4-9-d-old plants grown in hydroponics in the light, with a photoperiod of 16 h. Observations were made on thin longitudinal and transverse sections from plastic embedded root samples taken at increasing distances from the root tip. Salinity induced a reduction of root growth rate and induced cells and tissues to initiate and complete maturation closer to the tip, except for the late metaxylem in the center of the stele. These responses were more pronounced with rising NaCl level in the growth medium. Roots exposed to salinity showed increased cellular vacuolation in all tissues but most strikingly in cortex and metaxylem cells. Other changes induced by salinity were the premature differentiation of protophloem sieve tube members, the dense staining of endodermal and some xylem parenchyma cells, the positional compression of the maturation of proto- and early metaxylem tracheary elements, and the induction of lateral root initiations much closer to the root tip. Possible adaptive values of some of these responses to salinity are suggested.
SummaryRoot tip excision, wounding, or cotyledon removal causes a reduction of the percentage of ... more SummaryRoot tip excision, wounding, or cotyledon removal causes a reduction of the percentage of mitotic figures in the root tip meristem. This reduction followed by recovery can be mimicked in root tip meristems of intact seedlings by treatments with methionine, Ethrel, and ethylene. Evidence is presented to suggest that this mitotic regulation is induced by wound-stimulated ethylene.
The sequence of organ emergence in embryos of S. lutescens was similar to that reported for other... more The sequence of organ emergence in embryos of S. lutescens was similar to that reported for other grasses: coleorhiza, radicle, coleoptile and first leaf. The coleorhiza emerged by forcing open a hinged flap on the lemma. Coleorhiza trichomes formed soon after emergence. The radicle protruded through the abaxial surface of the coleorhiza. The coleoptile initially elongated downwards as it passed between the lemma and palea, but immediately turned upwards. The first leaf emerged by protruding through a slit-like crease on the adaxial surface of the coleoptile. Embryos excised from dormant florets germinated as well as those from non-dormant florets. Inhibitory effects on germination of the lemma, palea and caryopsis coat were demonstrated. Cycloheximide at 10-4 M did not decrease germination percentage, but rather inhibited radicle growth but not coleoptile elongation. The significance of the observations is discussed
Journal of the American Veterinary Medical Association, 1982
During a 2-week period, 3 hanuman langurs (Presbytis entellus) died from severe fibrinopurulent a... more During a 2-week period, 3 hanuman langurs (Presbytis entellus) died from severe fibrinopurulent and proliferative peritonitis. Partially digested plant material was identified in the necrotic abdominal debris of the 1st and 2nd langurs. In the 3rd, a phytobezoar that extended 17.5 cm distally from the pyloric area had caused a 1-cm perforation. Seven months later, surgery was performed on a douc langur (Pygathrix nemaeus) to remove 1 gastric and 2 intestinal phytobezoars composed primarily of undigested Acacia sp leaves. An analysis of Acacia sp leaves consumed by these langurs revealed a high cell wall concentration (40%, dry basis), with an exceedingly high proportion of this cell wall composed of indigestible lignin. It was concluded that the species of acacia (Acacia saligna and A longifolia) fed in these cases are inappropriate browse items for langurs.
A s imple and con venient procedure was u sed for studying plant m eri st ematic tissu es. Tissue... more A s imple and con venient procedure was u sed for studying plant m eri st ematic tissu es. Tissues were fixed in 4% glutaraldehy de , d ehydrated in a t ertiary butyl alcohol series and embedded in SPURR' s m edium. Sectioning may b e done with a glass knife in an inexpen sively made holder fitted t o a rotary microtome. St a ining with 0.5 % aqueous safranin or fast green was followed b y counter st a ining in 0.2 % a queous toluidine blue a t 60°C. U sing appropriate hist ochemical methods at appropria t e stages in the process it was shown that enzymes, nucleic acid s, total proteins and polysacchar ides could b e identified.
Background The difference between indeterminate and determinate growth in plants consists of the ... more Background The difference between indeterminate and determinate growth in plants consists of the presence or absence of an active meristem in the fully developed organ. Determinate root growth implies that the root apical meristem (RAM) becomes exhausted. As a consequence, all cells in the root tip differentiate. This type of growth is widely found in roots of many angiosperm taxa and might have evolved as a developmental adaptation to water deficit (in desert Cactaceae), or low mineral content in the soil (proteoid roots in various taxa). † Scope and Conclusions This review considers the mechanisms of determinate root growth to better understand how the RAM is maintained, how it functions, and the cellular and genetic bases of these processes. The role of the quiescent centre in RAM maintenance and exhaustion will be analysed. During root ageing, the RAM becomes smaller and its organization changes; however, it remains unknown whether every root is truly determinate in the sense that its RAM becomes exhausted before senescence. We define two types of determinate growth: constitutive where determinacy is a natural part of root development; and non-constitutive where determinacy is induced usually by an environmental factor. Determinate root growth is proposed to include two phases: the indeterminate growth phase, when the RAM continuously produces new cells; and the termination growth phase, when cell production gradually decreases and eventually ceases. Finally, new concepts regarding stem cells and a stem cell niche are discussed to help comprehend how the meristem is maintained in a broad taxonomic context.
Rice (Oryza sativa L.) belongs to the family Gramineae and is the staple food for half of the wor... more Rice (Oryza sativa L.) belongs to the family Gramineae and is the staple food for half of the world's population and occupies almost one-fifth of the total land area covered under cereals. Now-a-days, the production of rice is hampered due to climatic changes. Therefore, it is essential to develop variety which is tolerant to abiotic and biotic stresses. The present investigation was conducted to establish an efficient and simple protocol for regeneration of four agronomically important indica rice varieties (Khandagiri, Udayagiri, Swarna and Pratikhya). Somatic embryogenesis were achieved from immature zygotic embryos on Murashige and Skoog (MS) medium supplemented with 3 mg/l 2,4-D (2,4dichlorophenoxyacetic acid), 1.0 mg/l kinetin and 3% (w/v) sucrose within 4 weeks of culture. The secondary somatic embryogenesis was also achieved in subsequent subculture on MS medium supplemented with 2 mg/l 2,4-D and 2.0 mg/l kinetin and 200 mg/l L-proline. The percentage of embryogenic calli proliferation were 82.4, 83.7, 88.4 and 84.4 in variety Khandagiri, Udayagiri, Swarna and Pratikhya respectively on MS basal medium supplemented with 3.0 mg/l 2,4-D, 2.0 mg/l Kinetin and 200 mg/l L-proline. Inclusion of higher concentration of L-proline (400 mg/l) in the induction medium, the growth of calli was reduced. The maximum percentage of somatic embryo germination took place in medium supplemented with 2.0 mg/l kinetin, 0.25 mg/l NAA and 50 mg/l adenine sulfate within 4 weeks of culture. The regenerated plantlets were transferred to pots for acclimatization. About 80% of plants were survived in the greenhouse condition.
With the first reports of embryogenesis from cultured somatic tissues (Reinert 1958; Steward et a... more With the first reports of embryogenesis from cultured somatic tissues (Reinert 1958; Steward et al. 1958), a new possibility arose for the study of plant embryo development. In carrot tissue culture systems, for instance, somatic embryogenesis is controlled by the presence or absence of auxin in the culture medium and it is possible to produce over one million embryos per liter of cultured cells (Sung et al. 1984). This allows for an analysis of plant embryo development at a biochemical and molecular level unattainable by studying zygotic embryogeny. In addition to their obvious potential for studies of plant developmental biology, somatic embryos are the preferred method of regeneration of plants from tissue culture. Somatic embryos develop as bipolar structures, eliminating the need for separate root- and shoot-forming media during regeneration. Also, by virtue of a presumptive single cell origin, the possibility of chimeric regenerants is reduced and the potential for obtaining identical, genetically engineered plants from manipulated cells or protoplasts can be realized.
The spacing of lateral root primordia in the primary root of Pisum sativum (cv. Alaska) seedlings... more The spacing of lateral root primordia in the primary root of Pisum sativum (cv. Alaska) seedlings is influenced by both predetermined lateral root initiation sites in the embryonic radicle and by factors present during seedling growth. When pea seeds were germinated in the presence of the mitotic inhibitor, colchicine, the triarch radicle produced three ranks of primordiomorphs indicating sites of embryonic lateral root primordia. The number of primordiomorphs was not the same along the three xylem strands in the radicle. Normally germinated seedling roots (5 days old) also showed a different number of lateral root primordia associated with the three strands. In both cases, the strand with the greatest number of primordia (or primordiomorphs) was associated with a cotyledonary trace. This indicated a possible role for the cotyledons in setting the pattern of lateral root distribution during radicle development. The spacing of lateral root primordia could be altered by the application of growth regulators. Seedling root tips (2 mm) were removed (− rt) and replaced with indoleacetic acid (+IAA), and in some instances seedlings were also treated with the auxin transport inhibitor, 3,3a-dihydro-2-(p-methoxyphenyl)-8H-pyrazolo[5, 1-α]isoindol-8-one (+DPX). In the growth regulator treatments, primary root elongation was inhibited, a greater number of lateral root primordia were initiated compared to controls, and the spacing intervals between primordia were greatly reduced. The — rt, +IAA, +DPX-treatment resulted in the closest possible spacing intervals (av. 0.4 − 0.6 mm), but resulted in fused or fasciated laterals. The — rt, + IAA-treatment produced the shortest spacing intervals which resulted in “normal” lateral roots (0.8 − 1.1 mm).
Cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) were germinated and grown in vermiculite ... more Cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) were germinated and grown in vermiculite for 7 days, at 1–150 mM NaCl salinity. Primary root samples were harvested daily, root lengths measured and, after clearing and staining, the distance from the root tip to the closest protoxylem tracheary element (PTE) secondary cell wall depositions was determined. The length of control roots correlated with the PTE distance and the root elongation rate. Initially, as roots became longer, elongation rates increased and so did the distance for PTE secondary wall depositions. The highest elongation rates and the farthest PTE distances were reached for 75–125 mm long roots. Thereafter, as root length increased, the PTE distance and growth rates dropped gradually. A high linear correlation between the distance for PTE secondary wall depositions and the root growth rate was obtained for control plants (up to 200 mm long) over the experimental period. This correlation was weakened by rising salinity. At 150 mM NaCl no such correlation was found. Salinity resulted in PTE distances closer to the tip in roots of intermediate length (50–150 mm). In longer and in shorter roots, salinity did not affect the distance from the root tip for PTE secondary wall depositions. Vermiculite-grown seedlings, 4–11 days old, were used to assess the effects of 200 mM NaCl salinity on the development of metaxylem vessel members (MVMs). In macerated stele samples from regions close to the root base, the dimensions of MVMs were measured. High salinity resulted in reductions of both width and length of MVMs, and this inhibition increased with plant age. Large, central MVMs matured mostly earlier in control plants than in salt-stressed plants.
Pruning treatment of current-year shoots-Current-year shoots of six-yearold Vitis vinifera var. C... more Pruning treatment of current-year shoots-Current-year shoots of six-yearold Vitis vinifera var. Chardonnay plants grown in the UC Davis experimental vineyard were subjected to pruning treatments during four seasons: summer (30 June), autumn (25 August) in 2004, and winter (25 January) and spring (28 March) in 2005. Pruning cuts were imposed as previously described (Sun et al., 2006) at 10-20 cm from the shoot base on three replicate shoots for each experiment, one shoot on each of three vines. In each season, all experimental shoots were treated and samples collected on the same day. Samples for day 0 were collected from the cut end of each detached shoot and fi xed immediately in formalin-acetic acid-alcohol (FAA) (Ruzin, 1999). Subsequently, samples were taken from the cut end of the attached stem at various days after pruning. At each sampling, three samples consisting of a 4-cm long stem segment including the cut end were taken and fi xed in FAA immediately for at least 48 h. For analysis, each sample was hydrated to water via an ethanol series of 50%, 40%, 30%, 20%, and 10% for 30 min each. Transverse freehand sections were made at depths of 2-10 mm from the cut, then observed under a microscope (Olympus
Xylem-dwelling pathogens become systemic, suggesting that microorganisms move efficiently in the ... more Xylem-dwelling pathogens become systemic, suggesting that microorganisms move efficiently in the xylem. To better understand xylem pathways and how bacteria move within the xylem, vessel connectivity between stems and leaves of Vitis vinifera cv. Chardonnay and Muscadinia rotundifolia cv. Cowart was studied. Three methods were used: (1) the light-producing bacterium, Yersinia enterocolitica, (Ye) strain GY5232 was loaded into petioles and followed using X-ray film, (2) fluorescent beads were loaded and followed by microscopy, and (3) low-pressure air was pumped into leaves and extruded bubbles from cuts in submerged leaves were followed. Bacteria, beads, and air moved through long and branched xylem vessels from the petiole into the veins in leaves of both varieties. From the stem, bacteria and air traveled into primary and secondary veins of leaves one, two, and three nodes above the loading point of the bacteria or air. Particles and air could move unimpeded through single xylem vessels or multiple vessels (conduits) connected possibly through broken pit membranes from within the stem axis into leaf blades. Bacteria were also able to move long distances within minutes from stem to leaf passively without having to cross pit membranes. Such complex, open xylem conduits have not been well documented before; these findings will help elucidate mechanisms involved in the systemic spread of pathogens.
Tyloses form in xylem vessels in response to various environmental stimuli, but little is known o... more Tyloses form in xylem vessels in response to various environmental stimuli, but little is known of the kinetics or regulation of their development. Preliminary investigations indicated that wounds seal quickly with tyloses after pruning of grapevine shoots. In this study, tylose development was analyzed qualitatively and quantitatively at different depths and times from pruning cuts along current-year shoots of grapevines at basal, middle, and apical stem regions. Tyloses developed simultaneously within a single vessel but much separated in time among vessels. Pruning caused prodigious tylosis in vessels of grape stems, extending to approximately 1 cm deep and to 7 d after wounding, but about half of the vessels did not become completely occluded. The fraction of vessels forming tyloses was greatest in basal (85%) and least in apical (50%) regions. The depth of maximum density of tyloses was 4 mm from the cut in the basal region and 2 mm from the cut in the middle and apical regions. Tylose development was faster in the basal and middle than in the apical region. The pattern of tylose development is discussed in the context of wound repair and pathogen movement in grapevines.
The seeds of 20 legume species were grown in the greenhouse or in growth chambers at different te... more The seeds of 20 legume species were grown in the greenhouse or in growth chambers at different temperatures. Under warm temperature conditions (above 15°C). six species, pea (Pisum satiuum), broadbean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinaris), wild lupine (Lupinus latifolius), and soybean (Glycine m a d , formed cavities in the vascular cylinder of their primary roots, which in turn became filled by the ingrowth of specialized parenchyma cells (SP cells). When these species were grown at low temperature (below 15 "C), however, a "normal" vascular cylinder formed in the primary roots with late-maturing metaxylem vessel members differentiating in the center. These species were all cool-season legumes except soybean, a warm-season legume, which sometimes also formed cavities and SP cell ingrowths. The occurrence of cavities and SP cells therefore was restricted to the coolseason legumes (except soybean) when they were grown under warm temperature conditions. The position and size of cavities varied among these species. Pea and broadbean usually formed large, axially elongated cavities in the central vascular cylinder, or in the xylem poles. Others formed smaller cavities of various lengths.
Root apical organization in Arabidopsis thaliana ecotype 'WS' and a c o m m e n t on root cap str... more Root apical organization in Arabidopsis thaliana ecotype 'WS' and a c o m m e n t on root cap structure
The first morphogenetic events of lateral root primordium (LRP) formation in the Arabidopsis thal... more The first morphogenetic events of lateral root primordium (LRP) formation in the Arabidopsis thaliana (L.) Heynh. pericycle occur soon after cells of the primary root complete elongation. Pericycle cells in direct contact with underlying protoxylem cells participate in LRP formation. Two types of LRP initiation were found, longitudinal uni- and bi-cellular. These occur when a single or two pericycle cells within a file, respectively, become founder cells for the entire longitudinal extent of the LRP. Histochemical and cytological analysis suggests that three is the minimum number of cells required to initiate an LRP. In young primordia comprising less than 32 cells, the average cell-doubling time was 3.7 h, indicating a drastic acceleration of cell cycle progression after lateral root initiation. Early in LRP development, cell growth is limited and therefore cytokinesis leads to a reduction of cell volume, similar to cleavage division cycles during animal and plant embryogenesis. The striking coordination of proliferation between pericycle cells in adjacent files in direct contact with the underlying protoxylem implies that intercellular signaling mechanisms act in the root apical meristem or later in development.
It has been hypothesized that the substantial reductions in xylemic water flow occurring at verai... more It has been hypothesized that the substantial reductions in xylemic water flow occurring at veraison are due to physical disruption (breaking) of the xylem as a result of renewed berry growth. In a companion paper, evidence was presented that the vast majority of xylem tracheary elements remained intact despite the growth of the berry, and it was proposed that existing tracheary elements stretch to accommodate growth and that additional elements may also differentiate after veraison. Measurements of the intergyre distance of tracheary elements in macerated tissue were used to test for stretching, and the numbers of tracheary elements per vascular bundle and of branch points of the peripheral xylem network were analysed to test for continued differentiation from 18 to 120 d after anthesis in Chardonnay berries. The distance between the epidermis and the vasculature increased substantially from pre-to post-veraison, potentially increasing the amount of skin available for analysis of compounds important for winemaking. Tracheary elements continued to differentiate within the existing vascular bundles throughout berry development. Additional vascular bundles also appeared until after veraison, thereby increasing the complexity of the peripheral vascular network. The results also confirmed that tracheary elements stretched by ;20%, but this was not as much as that predicted based on the growth of the vascular diameter (40%). These results complete a comprehensive evaluation of grape berry peripheral xylem during its development and show that tracheary development continues further into berry maturation than previously thought.
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