Plant growth

Callus induction from petiole explants has been achieved in Alocasia micholitziana `Green Velvet'. The highest percentage (71%) of explants inducing callus was obtained on MS medium supplemented with 0.5 μM 2,4-D and 0.5 μM kinetin in the dark after 4 months of culture. Shoots were regenerated at the highest frequency of 33.3% under light condition when 0.5 μM BA was added to MS medium with the average of 7.8±2.3 shoots per callus explant. The callus-derived shoots rooted on hormone free MS medium and within 4 weeks the plantlets were ready for acclimatization. The regenerated plants appeared morphologically similar to mother plants.

Root herbivores and plant mutualists, such as arbuscular mycorrhizal fungi (AMF), have a significant effect on the structure and dynamic of plant communities. Nevertheless, the interactions between the two groups of organisms in natural ecosystems are far from understood. We carried out an inoculation experiment to examine the effect of two root herbivores, Pratylenchus penetrans and P. dunensis (Nematoda), on the composition of the AMF communities associated with two populations of the dune grass Ammophila arenaria. The outcome of the interaction in terms of plant and nematode performance was also analyzed. The total percentage of AMF colonization was not affected by the presence of root-feeders, but they did alter the composition of the AMF communities inside the roots. These changes were dependent on the root-feeder species and the original AMF community: the most severe alterations were observed in the mycorrhizal plants from Wales attacked by P. penetrans. Plant growth was impaired in plants from Wales inoculated with AMF and P. dunensis, which suggests a highly species-specific synergistic interaction with negative consequences for the plant. Root infection by the nematodes was reduced in all mycorrhizal plants when compared to non-mycorrhizal plants. However, a significant reduction of the final number of nematodes was observed only in the mycorrhizal plants from one population.

The present study investigated the dynamics of nutrient utilization and various growth and physiological parameters during in vitro proliferation of apple root stock 'M9 EMLA' in two different bioreactor systems, i.e. temporary and continuous immersions. Individual shoots obtained from temporary immersion system had higher dry mass and were of better quality than those obtained from continuous immersion. In continuous immersion bioreactor, apple shoots appeared to utilize more nutrients from liquid culture medium than that from temporary immersion. The shoot growth was limited by the availability of phosphate and nitrogen in continuous immersion system. The shoots produced in temporary immersion bioreactor showed higher photosynthetic rate, maximum quantum yield of photosystem-II and slow but steady rate of nutrient absorption, indicating the occurrence of higher photomixotrophic metabolism. The study also showed that high level of antioxidant scavenging enzymes in shoots grown in continuous immersion system induced physiological changes to foster adaptation to stresses.

A regional sorghum head-bug and grain mold resistance trial was conducted in 1996 and 1997 at 15 and 13 research stations located in 10 West and Central African countries, respectively. Two cultivars namely IS 14384 and CGM 39/17-2-2 exhibited consistently high levels of resistance both to head-bugs and grain molds over years and localities. Eurystylus oldi was the dominant head-bug species at all localities except in Benin, Chad and Guinea. Sorghum grain mycoflora varied little between sites with genera Phoma and Fusarium dominating, followed by Curvularia. Efficiency of the insecticidal treatment on head-bug incidence partially confirmed the critical role played by head-bugs in aggravating mold infection.

Tobacco (Nicotiana tabacum L.) is a tolerant species that accumulates cadmium. We studied the effect of Cd (0, 10, 25, 50, 100 lM) on growth parameters, chlorophyll and proline contents, enzymatic antioxidative response and lipid peroxidation of tobacco plants grown in hydroponic culture for 11 days to clarify the strategy of plant response against oxidative stress caused by this heavy metal. Cadmium accumulated more in roots than in shoots. Plant growth was not significantly affected by the cadmium concentrations used. Young leaves were more affected, showing visible chlorosis and a significant decrease in chlorophyll content at high Cd concentrations. Dry weight of both leaves and roots increased indicating a lower capacity for roots to absorb water. An increase in malondialdehyde levels was observed, indicating that lipid peroxidation occurred as a result of ROS formation. The activity of guaiacol peroxidase in leaves increased, indicating that it was very important in the scavenging of H 2 O 2 , while superoxide dismutase activity only increased in old leaves. Ascorbate peroxidase showed constant activity levels in tobacco leaves, suggesting that the ascorbate-glutathione pathway was less important as a defense mechanism.

African smallholder farmers face perennial food shortages due to low crop yields. The major cause of poor crop yields is soil fertility decline. The diversity of sites and soils between African farming systems is<span class=GramE>great,</span>therefore strategies to solve soil fertility problems should suit the opportunities and problems encountered in the different climatic regions. This thesis characterizes the semi-arid regions of south-western Zimbabwe and explores some of the strategies that can be used to provide farmers with more options for soil fertility improvement.<o:p></o:p></span>Resource flow maps were used to study the characteristics of the semi-arid farming system of Tsholotsho (Mkhubazi)in south-western<st1:place w:st="on"><st1:country-region w:st="on">Zimbabwe. The results revealed that farmers in the region face perennial cereal grain shortages, but the poorly-resourced farmers are the most affected. N...

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Two greenhouse experiments were focused on the application of arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) in planting of high-biomass crops on reclaimed spoil banks. In the first experiment, we tested the effects of different organic amendments on growth of alfalfa and on the introduced microorganisms. While growth of plants was supported in substrate with compost amendment, mycorrhizal colonization was suppressed. Lignocellulose papermill waste had no negative effects on AMF, but did not positively affect growth of plants. The mixture of these two amendments was found to be optimal in both respects, plant growth and mycorrhizal development. Decreasing doses of this mixture amendment were used in the second experiment, where the effects of microbial inoculation (assumed to compensate for reduced doses of organic matter) on growth of two high-biomass crops, hemp and reed canarygrass, were studied. Plant growth response to microbial inoculation was either positive or negative, depending on the dose of the applied amendment and plant species.

Plants often respond to elevated atmospheric CO2 levels with reduced tissue nitrogen concentrations relative to ambient CO2-grown plants when comparisons are made at a common time. Another common response to enriched COz atmospheres is an acceleration in plant growth rates. Because plant nitrogen concentrations are often highest in seedlings and subsequently decrease during growth, comparisons between ambient and elevated CO2-grown plants made at a common time may not demonstrate CO2-induced reductions in plant nitrogen concentration per se. Rather, this comparison may be highlighting differences in nitrogen concentration between bigger, more developed plants and smaller, less developed plants. In this study, we directly examined whether elevated CO2 environments reduce plant nitrogen concentrations independent of changes in plant growth rates. We grew two annual plant species, Abutilon theophrasti (C3 photosynthetic pathway) and Amaranthus retroflexus (C4 photosynthetic pathway), from seed in glass-sided growth chambers with atmospheric CO2 levels of 350 gmol-mol-1 or 700 gmol 9 mol-1 and with high or low fertilizer applications. Individual plants were harvested every 2 days starting 3 days after germination to determine plant biomass and nitrogen concentration. We found: 1. High CO2-grown plants had reduced nitrogen concentrations and increased biomass relative to ambient CO2-grown plants when compared at a common time; 2. Tissue nitrogen concentrations did not vary as a function of CO2 level when plants were compared at a common size; and 3. The rate of biomass accumulation per rate of increase in plant nitrogen was unaffected by CO2 availability, but was altered by nutrient availability. These results indicate that a CO2-induced reduction in plant nitrogen concentration may not be due to physiological changes in plant nitrogen use efficiency, but is probably a size-dependent phenomenon resulting from accelerated plant growth.

Inorganic arsenicals have been used in agriculture as pesticides or defoliants for many years and, in localized areas, oxides of arsenic have contaminated soils as a result of fallout from ore-smelting operations and coal-fired power plants. Use of inorganic arsenicals is no longer permitted in most agricultural operations, and recent air pollution controls have markedly reduced contamination from smelters. Thus, this paper will concentrate on the effect of past applications on arsenic accumulation in soil, phytotoxicity to and uptake by plants as influenced by soil properties, and alleviation of the deleterious effects of arsenic. Once incorporated into the soil, inorganic arsenical pesticides and arsenic oxides revert to arsenates, except where the soil is under reducing conditions. The arsenate ion has properties similar to that of orthophosphate, and is readily sorbed by iron and aluminum components. This reaction greatly restricts the downward movement (leaching) of arsenic in soils and the availability of arsenic to plants. Several methods of estimating plant available arsenic in soils have been developed. They involve extraction of the soil with reagents used to estimate phosphorus availability. This extractable arsenic is reasonably well correlated with reduced plant growth by, and plant uptake of arsenic. For most plants, levels of arsenic in the edible portion of the plant are well below the critical concentration for animal or human consumption, even when severe phytotoxicity occurs. Alleviation of arsenic phytotoxicity has been attempted by increasing the soil pH, by use of iron or aluminum sulfate, by desorbing arsenate with phosphate and subsequent leaching, and by cultural practices such as deep plowing. Only limited benefits have accrued from these procedures the cost of which is often prohibitively high. Since attempts to reduce arsenic toxicity have not been very successful, its excessive accumulation in soils should be avoided.

Quantitative information on growing organs is required to better understand morphogenesis in both plants and animals. however, detailed analyses of growth patterns at cellular resolution have remained elusive. We developed an approach, multiangle image acquisition, three-dimensional reconstruction and cell segmentation-automated lineage tracking (mArs-Alt), in which we imaged whole organs from multiple angles, computationally merged and segmented these images to provide accurate cell identification in three dimensions and automatically tracked cell lineages through multiple rounds of cell division during development. using these methods, we quantitatively analyzed Arabidopsis thaliana flower development at cell resolution, which revealed differential growth patterns of key regions during early stages of floral morphogenesis. lastly, using rice roots, we demonstrated that this approach is both generic and scalable.

Ethylene (ET) plays a critical role in the activation of plant defenses against different biotic stresses through its participation in a complex signaling network that includes jasmonic acid (JA), salicylic acid (SA), and abscisic acid (ABA). Pathogen attack, wounding, and herbivory trigger asymmetric activation of this defense signaling network, thereby affecting the final balance of interactions between its components and establishing a targeted response to the initial threat. Ethylene’s contribution to the modulation of this defense network relies on the complexity of the regulation of multigene families involved in ET biosynthesis, signal transduction, and crosstalk and enables the plant to fine-tune its response. The function of the members of these multigene families is tightly regulated at transcriptional, post-transcriptional, and post-translational levels. It is generally accepted that ET cooperates with JA in the activation of defenses against necrotrophic pathogens and antagonizes SA-dependent resistance against biotrophic pathogens. However, this is likely an oversimplified view, because cooperative interactions between ET and SA pathways have been reported and ET has been implicated in the activation of defenses against some biotrophic and hemibiotrophic pathogens. Therefore, deciphering ET’s place in this hormonal network is essential to understanding how the cell orchestrates an optimal response to a specific biotic stress.

This paper describes an attempt to model soil moisture over the Australian continent with an integrated system of dynamic models and a Geographic Information System (GIS) data base. A land surface scheme with improved treatment of soil hydrological processes is described. The non-linear relationships between soil hydraulic conductivity, matric potential and soil moisture are derived from the Broadbridge and White soil model. For a single location, the prediction of the scheme is in good agreement with the measurements of the Hydrological and Atmospheric Pilot Experiment (HAPEX). High resolution atmospheric and geographic data are used in soil moisture prediction over the Australian continent. The importance of reliable land surface parameters is emphasized and details are given for deriving the parameters from a GIS. Predicted soil moisture patterns over the Australian continent in summer, with a 50 km spatial resolution, are found to be closely related to the distribution of soil types, apart from isolated areas and times under the influence of precipitation. This is consistent with the notion that the Australian continent in summer is generally under water stress. In contrast, predicted soil temperatures are more closely related to radiation patterns and changes in atmospheric circulation. The simulation can provide details of soil moisture evolution both in space and time, that are very useful for studies of land use sustainability, such as plant growth modelling and soil erosion prediction.

Background and Objectives: The quality of irrigation water affected by salinity and high concentration of soluble salts is one of the important problems of pistachio areas in recent years.
In this regard, the gradual increase in the concentration of soil magnesium in pistachio areas which irrigated with inappropriate and salty quality groundwater has become one of the most serious challenges ahead. Since there are very few studies on the effect of high concentrations of magnesium on soil properties and vegetative traits of pistachio, so this study investigates soil properties and growth characteristics of two bases of pistachio Badami Zarand and Ghazvini, under the influence of different concentrations of magnesium in irrigation water, as well as selection the superior and more resistant bases to high concentrations of magnesium.

Materials and Methods: The experiment was split plot based on a randomized complete block design with two factors each with three replications. The first factor consists of two pistachio bases including Badami Zarand and Ghazvini and the second factor was made of five levels of magnesium in water (0, 0.5, 1, 2, 3 mM from magnesium sulfate source). vegetative traits were measured before the treatments (end of the eighth week) and after 6 months from the beginning of the treatment, and their changes were investigated during the application of the treatments, dry weight of the aerial parts (leaf and stem) and root, concentration of some The nutrient elements of the plant leaf and the soil chemical properties of the pots, such as electrical conductivity, pH, concentration of sodium, potassium, calcium, magnesium, soluble phosphorus and calcium to magnesium ratio were measured at the end of the experiment.

Results: Results showed that in general the effect of different levels of magnesium in the irrigation water was significant on soil EC and the concentrations of calcium, magnesium and sodium in the soil solution. In addition, at concentrations of 0.5 and 1 mM magnesium sulfate, the growth of pistachio plant (vegetative shoot and shoot dry weight plus roots) improved while by increasing the concentration of magnesium in the irrigation water (level 2 to 3 mM Mg), shoot growth and root dry weight, shoot+root weight reduced compared to the control. Also, soil soluble calcium to magnesium ratio showed significant difference at 0 mM magnesium of irrigated water compared to other treatments. The results showed that changes in soil pH, absorbable potassium and available phosphorus in the soil experienced no significant influence by pistachio base, magnesium levels in water and their interactions effect.
Conclusion: The results of this study revealed that for two bases of Badami Zarand and Ghazvini, there is a threshold value of magnesium concentration. It was found that under the influence of different concentrations of magnesium in the irrigation water, the best growth in both pistachio bases was observed at 0.5 and 1 mM magnesium sulfate. With increasing the concentration from 2 to 3 mM, both bases showed a decline in growth. Overall, the results of this study indicated that the concentration of magnesium in irrigation water mare than 2 mM can reduce pistachio growth and lead to the complexity of the leaf, and burn margins and tips of the leaves, which can be considered by researchers and farmers.

There remains conflicting evidence on the relationship between P supply and biological N 2-fixation rates, particularly N 2-fixing plant adaptive strategies under P limitation. This is important, as edaphic conditions inherent to many economically and ecologically important semi-arid leguminous tree species, such as Acacia senegal, are P deficient. Our research objective was to verify N acquisition strategies under phosphorus limitations using isotopic techniques. Acacia senegal var. senegal was cultivated in sand culture with three levels of exponentially supplied phosphorus [low (200 mol of P seedling −1 over 12 weeks), mid (400 mol) and high (600 mol)] to achieve steady-state nutrition over the growth period. Uniform additions of N were also supplied. Plant growth and nutrition were evaluated. Seedlings exhibited significantly greater total biomass under high P supply compared to low P supply. Both P and N content significantly increased with increasing P supply. Similarly, N derived from solution increased with elevated P availability. However, both the number of nodules and the N derived from atmosphere, determined by the 15 N natural abundance method, did not increase along the P gradient. Phosphorus stimulated growth and increased mineral N uptake from solution without affecting the amount of N derived from the atmosphere. We conclude that, under non-limiting N conditions, A. senegal N acquisition strategies change with P supply, with less reliance on N 2-fixation when the rhizosphere achieves a sufficient N uptake zone.

Primary production on semiarid floodplains supports a diverse local and regional fauna. Reduced flooding from water resource development (WRD) may affect floodplain production by decreasing water and nutrient supply.We investigated the effects of reduced wetting on soil fertility by performing a regional soil survey across a gradient of flood frequency. Soil nitrogen (N), phosphorus (P) and carbon (C) were recorded over a soil-wetting event where heavy rainfall and flooding coincided.Soil nutrient concentrations indicate N limits plant growth and P does not.No spatial patterns in soil P were detected across the floodplain, suggesting that the principal mechanism controlling P fertility is the concentration of P in floodplain source material, and that flood mediated import and export of P are minor processes.Soil N concentrations rose following rainfall and flooding and the greatest increased occurred in flooded areas. Flood deposition of N accounted for only 9% of the boost in soil N in flooded areas, and N concentrations continued to rise when the floods and rains ceased. Elevated soil N levels do not appear to persist because at the start of a growth cycle, when soils were dry, soil N did not vary significantly with flood frequency. This suggests most of the boost in soil N was due to N-fixation, with the subsequent loss of N likely to have resulted from in situ processes such as denitrification.Agricultural export of nutrients appears to not be a significant process in the context of the high phosphorus fertility of floodplain source material and the apparently high rates of in situ processing of nitrogen.Synthesis and applications. Our data suggest that floodplain soil fertility is controlled by mechanisms other than flood frequency or agricultural export, meaning that WRD is unlikely to affect soil fertility; however, the biological implications of the brief pulse in soil N associated with wetting need further investigation.

Increasing evidences have indicated that humic substances can induce plant growth and productivity by functioning as an environmental source of auxinic activity. Here we comparatively evaluate the effects of indole-3-acetic acid (IAA) and humic acids (HA) isolated from two different soils (Inseptsol and Ultisol) and two different organic residues (vermicompost and sewage sludge) on root development and on activities of plasmalemma and tonoplast H+ pumps from maize roots. The data show that HA isolated from these different sources as well as low IAA concentrations (10−10 and 10−15 M) improve root growth through a markedly proliferation of lateral roots along with a differential activation not only of the plasmalemma but also of vacuolar H+-ATPases and H+-pyrophosphatase. Further, the vacuolar H+-ATPase had a peak of stimulation in a range from 10−8 to 10−10 M IAA, whereas the H+-pyrophosphatase was sensitive to a much broader range of IAA concentrations from 10−3 to 10−15 M. It is proposed a complementary view of the acid growth mechanism in which a concerted activation of the plasmalemma and tonoplast H+ pumps plays a key role in the root cell expansion process driven by environment-derived molecules endowed with auxinic activity, such as that of humic substances.

This study describes an experimental analysis of a five-fold plant-insect interaction, with the primary aim of determining the net effect of insect-insect interactions on the host plant. The participlants are the extrafloral nectary-bearing host plant Acacia decurrens; the resident sap-sucking membracid treehopper Sextius virescens; the ant Iridomyrmex sp. which attends both EFN and treehoppers; external herbivores including grasshoppers and gall wasps; and predators and parasitoids of the membracids. The main results are as follows. 1. The membracids alone decrease plant growth and seed set. 2. In the absence of membracids, the ants defend the plant against external herbivores, and their presence increases plant growth and seed set. 3. The interaction between ants and membracids exerts an overall negative effect on plant growth and seed set. This has not been demonstrated for any system previously and is the main result of the study. 4. Ant attendance does not increase membracid populations or feeding rates significantly, or reduce mid-season mortality. 5. Ant attendance decreases late-season membracid mortality significantly. This has been shown previously for Lepidoptera and nymphal Homoptera only. 6. The mechanism of the interactive effect in (3) is apparently that the honeydewsecreting membracids attract the ants away from the EFN and decrease the efficacy of the plant's ant defence.

Phosphorus (P) is one of the major constituents in energy metabolism and biosynthesis of nucleic acids and cell membranes with an important role in regulation of a number of enzymes. Soil phosphorous is an important macronutrient for plant growth. Phosphorus deficiency in soil is a major problem for agricultural production. Total soil P occurs in either organic or in organic form. Phytic acid as phytate (salts of phytic acid) is the major form of organic phosphorus in soil and it is not readily available to plants as a source of phosphorus because it either forms a complex with cations or adsorbs to various soil components. Phosphate solubilizing microorganisms are ubiquitous in soils and could play an important role in supplying P to plants. Microorganisms utilizing phytate are found in cultivated soils as well as in wetland, grassland and forest soils. Various fungi and bacteria (including plant growth promoting rhizobacteria) hydrolyze this organic form of phosphorus secreting phosphatases such as phytases and acidic/alkaline phosphatases. A large number of transgenic plants have been developed which were able to utilize sodium phytate as sole source of phosphorus. However, the recombinant phytases were similar to their wild type counterparts in terms of their properties. Increased phytase/phosphatase activity in transgenic plants may be an effective approach to promote their phytate-phosphorus utilization. The extracellular phytase activity of transgenic plant roots is a significant factor in the utilization of phosphorus from phytate. Furthermore, this indicated that an opportunity exists for using gene technology to improve the ability of plants to utilize accumulated forms of soil organic phosphorus. This review is focused on the role of phytases and phytase producing microbes in promoting the growth of different plants.

To explain patterns and variations in concentration of defence-related carbon-based secondary compounds in plant tissues, different complementary and in some parts contradictory plant-defence hypotheses were developed since several years. These conceptual hypotheses cannot be fully evaluated without a plant growth simulation model and consequently, the discussion about adequacy of plantdefence hypotheses neglects to a large extent the dynamics of plant growth. To get a more realistic view of the volatile dynamics of plant internal source and sink strengths of carbon and nitrogen during different phenological growth stages, a modelling approach for allocation of carbohydrates to a pool of carbon-based secondary compounds was integrated into the functional generic plant growth model PLATHO. In this paper, we explain the fundamental assumptions of our modelling approach and present the results of a simulation study for juvenile beech and spruce trees growing in mono-and mixed cultures under ambient and elevated atmospheric CO 2 .

The effect of synergy between sediment organic enrichment and lack of night oxygen renewal in the water column on growth and survival of Zostera marina, and how it is reflected in the sulfur parameters in the plants (δ 34 S, TS and S 0 ) was studied experimentally. An experiment consisting of Z. marina mesocosms with different levels of organic enrichment and water column aeration was established, and the effects on sediment conditions, sulfide invasion and growth and survival of Z. marina were examined over a 4 week period. Shoots growing in Ambient Organic matter-sediments showed signs of sulfide invasion, as TS increased in all plant compartments and δ 34 S of the plant tissues decreased during the experiment, but neither growth rate nor survival were significantly affected. The lack of night oxygen renewal had no evident effects in non-enriched sediments as porewater sulfide concentrations, AVS-and CRS-pools were not different from the corresponding 24 h aeration treatment. Plant growth rate and survival were neither different from the corresponding 24 h aeration treatment. On the contrary, shoots growing on High Organic matter-sediments suffered a massive sulfide invasion and it was directly correlated to the observed decrease in growth rates. Even though the lack of night oxygen renewal had no evident effects on sediment variables there were, however, strong indications that the different aeration levels affected plant performance, suggesting a lower sulfide oxidation capacity and confirming that low water column oxygen concentrations reduces the defense capacity of the shoots against sulfide invasion. Although δ 34 S, TS and S 0 concentrations together provided a powerful set of indicators to detect the invasion of sulfide in Z. marina shoots, this study enlightens the need for a deeper investigation of sulfide intrusion in seagrasses and the relation between plant sulfur parameters and sediment conditions.

In the present study, rice seedlings were exposed to a range of Cd concentrations (0.1 M, 1 M, 10 M, 100 M and 1 mM) for 15 days and a combination of different molecular approaches were used to evidence Cd effects and to assess the plants' ability to counteract metal toxicity. At a macroscopical level, only the highest Cd concentration (1 mM) caused a complete plant growth inhibition, whereas the lowest concentrations seemed to stimulate growth. At genome level, the amplified fragment length polymorphism (AFLP) technique was applied to detect DNA sequence changes in root cells, showing that all the Cd concentrations induced significant DNA polymorphisms in a dose-dependent manner. Data also evidenced the absence of preferential mutation sites.

Many available methodologies for in vitro regeneration of commercial tomato varieties promote not only the production of normal shoots but also individual leaves, shoots without apical meristems and vitrified structures. All these abnormal formations influence and diminish the regeneration efficiency. At the basis of this phenomenon lies callus development. We optimized an alternative procedure by which the regeneration occurs without abnormal shoot formation. The portion including the proximal part of hypocotyls and the radicle was cultured on medium consisting of Murashige and Skoog salts, 4 mg/L thiamine, 100 mg/L mio-inositol and 3% sucrose. After twothree weeks, 60% explants showed adventitious shoot formation. No changes in the morphological characteristics of regenerated plants and fruits were observed as compared with parents. Karyotypic analysis of regenerated plants showed no variations in chromosome number. The optimized procedure offers the advantage of tomato plant regeneration avoiding callus formation, which enables normal plant recovery with an efficiency ranging from 1.45 ± 0.05 to 2.57 ± 0.06 shoots per explant in Campbell-28, Amalia, Lignon, and Floradel cultivars.

Effective controlled-environment and field screening techniques were developed and refined to identify resistance to Ascochyta blight (AB), caused by Ascochyta rabiei (Pass.) Labr. in chickpea. A controlled environment plant growth room facility developed for AB evaluation at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, India was modified to evaluate chickpea genotypes for resistance to AB. Controlled environment screening techniques, such as a seedling screening technique using 10-day-old seedlings and cut-twig screening techniques using excised twigs (10-15 cm long) were developed. Components of the screening techniques were optimized in the controlled environmentplant growth room. The controlled environment screening techniques were found to be rapid, reliable and reproducible and a positive correlation was found between the seedling and cut-twig screening techniques (r=0.94). The cut-twig screening technique was quicker than the seedling screening technique and is particularly useful in screening segregating breeding lines derived from wild Cicer spp. Results of the controlled environment screening techniques were compared with results of field screening trials carried out at Dhaulakuan and Ludhiana in India, where the pathogen is endemic. A significant positive correlation was found between results from the controlled environment and field screening techniques (r=0.88). Using these resistance screening techniques, 150 elite chickpea breeding lines were evaluated and 29 lines with high and stable resistance to AB were identified.

Field studies with pigeonpea (Cajanus cajan (L.) Millsp.) were conducted at four locations in Kenya varying in altitude and where temperature decreased with increase in altitude. Warm temperatures (most inductive temperatures, mean 23.58C) hastened the times from sowing to¯owering (f) and maturity (m), and between¯owering and maturity (fm). Cool temperatures (17.88C) delayed f, m, and fm but the delay was most pronounced for fm. In the least inductive cool environment, variation in f, m and fm was greatest among 63 lines developed in India. Compared to the most inductive temperature, the delay in cool environment was 2.2 for f, 3.1 for m, and 5.5 for fm, which indicates that fm is the most sensitive phase to low (sub-optimal) temperatures. Equations that describe the rates of development (1/f, 1/m, and 1/fm) were used to determine progress to different stages of development. Results revealed that optimum temperature for fastest time to¯owering varied from 23.1 to 26.18C. The 1/f at mean temperature of 26.88C was slower, indicating that the mean temperature experienced was supra-optimal. Since the mean temperature of 26.88C was not very different from the range considered optimal, further analysis revealed that this was mainly due to the high night temperatures. The 1/fm was strong and positive in the range of temperature tested indicating that warm temperatures shortened the duration between¯owering and maturity. The optimum temperature range for this effect varied from 24 to 328C. Cool temperatures at Kabete retarded plant growth while warm temperatures enhanced it.

Soilless plant growth systems are widely used as a means to save irrigation water and to reduce groundwater contamination. While nutrient concentrations in the growth medium are depleted due to uptake by the plants, salinity and toxic substances accumulate due to transpiration. A theoretical model is suggested, to simulate nutrient uptake by plants grown in soilless cultures with recycled solutions. The model accounts for salinity accumulation with time and plant growth, and its effects on uptake of the different nutrients by means of interaction with Na and Cl ions. The sink term occurs due to uptake by a growing root system. Influx as a function of the ion concentration is according to Michaelis-Menten active mechanisms for K + , NO 3 − -N, NH 4 + -N, PO 4 -P, Ca 2+ , Mg 2+ and SO 4 2− , whose influx parameters are affected by Na and Cl − , but not with time (age). Sodium influx is passive above a critical concentration. Sum of cations-anions concentrations is balanced by Cl − to maintain electro-neutrality of the growth solution. Salinity (by means of Na concentration) suppresses root and leaf growth, which further effect uptake and transpiration. The model accounts for instantaneous transpiration losses, during daytime only and its effect on uptake of nutrients and plant development due to salt accumulation. The model was tested against NO 3 − and K + uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. Deviations from observed K + uptake should be attributed to the salinity tolerance of the plants. In a study with data obtained from published literature, the model indicated that nutrient depletion and salinity buildup might be completely different with fully grown-up plants (that do not grow) and plants that grow with time. Depletion of different nutrients are according to their initial concentration and plant uptake rate, but also affected by their interactions with Na and Cl ions.

Caffeic acid (CA), which is ubiquitously present in plants, is a potent phytotoxin affecting plant growth and physiology. The aim of our study was to investigate whether CA-induced inhibition of adventitious root formation (ARF) in mung bean {Vigna radiata (L.) Wilczek [Phaseolus aureus Roxb.]} involves the induction of conventional stress responses. The effect of CA (0–1000 μM) on ARF in mung bean was determined by measuring the generation of reactive oxygen species (ROS) in terms of malondialdehyde and hydrogen peroxide (H2O2) content, root oxidizability and changes in levels of antioxidant enzymes. Our results show that CA significantly enhanced MDA content, indicating severe lipid peroxidation, and increased H2O2 accumulation and root oxidizability in the lower rooted hypocotylar region (LRHR) of mung bean, thereby inducing oxidative stress and cellular damage. In response to CA, there was a significant upregulation in the activities of scavenging enzymes, such as superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, catalase and glutathione reductase, in LRHRs of mung bean. Based on these results, we conclude that CA inhibits ARF in mung bean hypocotyls by inducing ROS-generated oxidative stress and upregulating the activities of antioxidant enzymes.

The influence of NaCl salinity on growth, dry-matter production and leaf photosynthesis of seedlings of Eucalyptus camaldulensis Dehnh. and Dalbergia sissoo Roxb. was studied by imposing 4 levels (40, 80, 120 and 160 mM) of NaCl in pot culture. Salinity up to 160 mM did not affect plant survival, but did affect plant growth and dry-matter production depending upon the species and salt concentration. NaCl reduced leaf number and dry-weight of all the plant components, but increased stem dry-weight, especially in E. camaldulensis. Salinization also stimulated total dry-matter production at all the salinity levels in E. camaldulensis but only at 40 mM in D. sissoo. The two species varied in protein and chlorophyll concentration and in leaf photosynthetic rate. Protein and chlorophyll concentration of the plants fell at all the levels of NaCl, except at 40 mM, where stimulation in the photosynthetic carbon assimilation of the plants occurred. However, no distinct relationship between leaf photosynthetic rate and dry-matter production was found. The study indicated that low salt concentrations generally stimulated growth, biomass production and rate of photosynthesis in both the species, and E. camaldulensis appeared more NaCl salt-tolerant than D. sissoo.

1] Agricultural land uses impact leachable nitrogen (N) and erosion, indicators of the potential for nitrate and sediment contamination of water resources. This paper evaluates the potential impact of alternative land uses on leachable N, soil organic nitrogen (SON) and erosion in western Iowa watersheds using a combination of widely available models and georeferenced data. The alternative land uses increase land area under perennial cover, integrate livestock with cropping systems, and reduce inorganic fertilizer use. We used the Water Erosion Prediction Program (WEPP) to estimate erosion and a N-budget model to estimate leachable N and changes in SON. The N model described here is widely applicable because it utilizes commonly available georeferenced data on soils, crops, and livestock. Maximum annual erosion rates were estimated to be 22 Mg ha À1 under current conditions, double the regional maximum at which soil is maintained as a medium for plant growth (T). Under alternative land uses, erosion was between 1.1 Mg ha À1 and 5.5 Mg ha À1 , well below T. Annual leachable N was as much as 43 kg ha À1 for current conditions, but consistently less than15 kg ha À1 under alternative land uses. Maximum SON losses were 23 kg N ha À1 under current conditions while SON increased by as much as 18 kg N ha À1 under alternative land uses. These results indicate that erosion may be minimized, leachable N could be decreased and SON may be increased by better accounting of N inputs and altering the distribution and species composition of crop and pasture systems. Citation: Burkart, M., D. James, M. Liebman, and C. Herndl (2005), Impacts of integrated crop-livestock systems on nitrogen dynamics and soil erosion in western Iowa watersheds,

Harry T. Whelan, MD1a,2,3, John M Houle, BS1a, Noel T. Whelan1a,3, Deborah L. Donohoe, AS, LATG1a, Joan Cwiklinski, MSN, CPNP1a, Meic H. Schmidt, MD1c, Lisa Gould, MD, PhD.1b, David Larson, MD1b, Glenn A. Meyer, MD1a, Vita Cevenini3, Helen ...

The effect of isoprenoid growth regulators on avocado (Persea americana Mill. cv Hass) fruit growth and mesocarp 3-hydroxy-3- methylglutaryl coenzyme A reductase (HMCR) activity was inves- tigated during the course of fruit ontogeny. Both normal and small- fruit phenotypes were used to probe the interaction between the end products of isoprenoid biosynthesis and the activity of HMCR in the metabolic

Root-associated bacteria can have beneficial effects on their host plants. Microbial products can promote and stimulate plant growth or lead to bioprotection against pathogens. This study aimed to isolate putatively beneficial bacteria from traditional cereals grown by subsistence farmers in the Kavango of Namibia. Bacteria were isolated from surface-sterilized roots of Pennisetum glaucum, Sorghum bicolor, and Zea mays, and subjected to phenotypic and phylogenetic analyses. A total of 44 root-associated bacterial strains were isolated. From 33 distinct isolates, 22 belonged to Firmicutes and Actinobacteria, while 11 were Proteobacteria. Eleven novel phylotypes were among the isolates. Features known to contribute to plant growth-promotion and biocontrol were tested in vitro and revealed promising candidates with multiple beneficial characteristics. This is the first report on the characterization of native isolates associated with important agriculture crops in the Kavango region of Namibia. Such isolates have the potential for application as inoculants adapted to poor soils and local crops. Desiccation-tolerant or sporulating Gram-positive bacteria are of particular interest for this region, which is characterized by a long dry season.

Plant growth depends upon the activity of numerous types of organisms within the environment. The recycling of nutrients in the forest floor involves the interaction of a vast diversity of bacteria, fungi, protozoa, and invertebrates. Arthropods are integral to the initial shredding of the litter, which exposes nutrients to microbial digestion. Hundreds of California species either feed directly upon decomposer microorganisms or prey upon microbivorous taxa. Microbivory enhances the succession of microbial taxa with different enzymatic capabilities for processing soil resources. The final step of recycling, the entry of soil nutrients back into a root, is largely the result of invertebrates feeding upon microbes which have immobilized nutrients within the rhizosphere. Forest management practices can significantly alter soil foodwebs, which may in turn have significant effects on long-term soil productivity. Because arthropods facilitate a number of different soil processes, assays of soil arthropod abundance and community composition may prove to be useful in developing an understanding of the effects of forest management on nutrient cycles in forest soils.

In order to clarify the response of antioxidant systems in various cellular organelles to photo-oxidative stress, the activities of superoxide dismutase (SOD) and enzymes of the ascorbateglutathione (AsA-GSH) cycle were investigated in chloroplasts, mitochondria and cytosol of cucumber leaves subjected to methyl viologen (MV) treatment. Photo-oxidation by MV resulted in significant reductions in net photosynthetic rate (Pn) and increases in the ratio of the quantum efficiency of photosystem II (PSII), U PSII to that of the quantum efficiency of CO 2 fixation (U CO 2), followed by increased activities of SOD, and a general increase of AsA-GSH cycle enzymes in chloroplasts, mitochondria and cytosol. These increases were however, most significant in chloroplasts. There were also significant increases in dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) except that the content of ascorbate (AsA) in chloroplasts and cytosol was slightly decreased and little effected, respectively. However, GSSG in mitochondria and GSH in cytosol were little influenced by the MV treatment. The activity of ascorbate oxidase (AO) in these organelles was independent of the MV treatment while the activity of L-galactono-1,4lactone dehydrogenase (GLDH) in mitochondria was slightly inhibited by MV treatment. These results indicate that disturbance of electron transport in chloroplasts by MV influenced the metabolism of whole cell by a crosstalk signaling system and that the AsA-GSH cycle played a primary role in sustaining the levels of AsA.

Many species of Western Australian Cyperaceae (sedges) are vital components of the indigenous flora but commonly display low seed set, poor seed quality and intractable seed dormancy. We report the effects of incubation temperature and in vitro growth media on whole seed germination compared with extracted zygotic embryo growth in Tetraria capillaris, T. octandra, Lepidosperma drummondii and L. tenue. No germination was observed from intact whole seeds of all test species regardless of the treatment evaluated. In contrast, excised zygotic embryos of all study species exhibited significant increases in growth when cultured at 15°C compared to embryos incubated at 25°C; however, optimal media for embryo growth were genera specific. Extracted embryos of T. capillaris and T. octandra exhibited maximum percentage growth (30 and 40%, respectively) at 15°C on MS medium with no plant growth regulators required. In the case of L. drummondii and L. tenue 1 lM thidiazuron was a necessary addition to the MS medium resulting in 40 and 77% growth of embryos (at 15°C), respectively. Incubation of extracted embryos at 25°C (regardless of medium treatment) resulted in \10% embryo growth for T. octandra and L. tenue, while the remaining two species (L. drummondii, T. capillaris) showed no embryo growth at 25°C on any medium treatment. Keywords Lepidosperma drummondii Á Lepidosperma tenue Á Temperature Á Tetraria capillaris Á Tetraria octandra Á Seed germination Abbreviations 2,4-D 2,4-Dichlorophenoxyacetic acid. TDZ Thidiazuron K Kinetin (6-furfurylaminopurine) BA 6-Benzylaminopurine MES 2-(N-morpholino) ethanesulfonic acid TTC Triphenyl tetrazolium chloride Ca(OCl) 2 Calcium hypochlorite

Evidence clearly shows that cationic micronutrients in spray solutions reduce the herbicidal effectiveness of glyphosate for weed control due to the formation of metal-glyphosate complexes. The formation of these glyphosate-metal complexes in plant tissue may also impair micronutrient nutrition of nontarget plants when exposed to glyphosate drift or glyphosate residues in soil. In the present study, the effects of simulated glyphosate drift on plant growth and uptake, translocation, and accumulation (tissue concentration) of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were investigated in sunflower (Helianthus annuus L.) plants grown in nutrient solution under controlled environmental conditions. Glyphosate was sprayed on plant shoots at different rates between 1.25 and 6.0% of the recommended dosage (i.e., 0.39 and 1.89 mM glyphosate isopropylamine salt). Glyphosate applications significantly decreased root and shoot dry matter production and chlorophyll concentrations of young leaves and shoot tips. The basal parts of the youngest leaves and shoot tips were severely chlorotic. These effects became apparent within 48 h after the glyphosate spray. Glyphosate also caused substantial decreases in leaf concentration of Fe and Mn while the concentration of Zn and Cu was less affected. In short-term uptake experiments with radiolabeled Fe (59 Fe), Mn (54 Mn), and Zn (65 Zn), root uptake of 59 Fe and 54 Mn was significantly reduced in 12 and 24 h after application of 6% of the recommended dosage of glyphosate, respectively. Glyphosate resulted in almost complete inhibition of root-to-shoot translocation of 59 Fe within 12 h and 54 Mn within 24 h after application. These results suggest that glyphosate residues or drift may result in severe impairments in Fe and Mn nutrition of nontarget plants, possibly due to the formation of poorly soluble glyphosate-metal complexes in plant tissues and/or rhizosphere interactions.

The potential problems and their consequences due to fly ash disposal have been well studied around the world. Ash pond is a common available disposal facility for thermal power plants. The pond ash is subjected to weathering and the ions present in ash migrate to the soil ...

Trade-offs between acquisition capacities for aboveground and belowground resources were investigated by studying the phenotypic plasticity of leaf and root traits in response to different irradiance levels at low nutrient supply. Two congeneric grasses with contrasting light requirements, Dactylis glomerata and D. polygama, were used. The aim was to analyze phenotypic covariation in components of leaf area and root length in response to above-and belowground resource limitation and the consequences of this variation for resource acquisition and plant growth. At intermediate shading (30 and 20% of full sunlight) the plants were able to maintain their total root length, despite a strongly increased total leaf area and a reduced biomass allocation to roots. This was associated with an unaltered or slightly increased nutrient uptake and growth. At 5.5% relative irradiance, growth was severely reduced, especially in the shade-tolerant D. polygama. The results show that constraints on acquisition capacities for aboveground and belowground resources, caused by biomass allocation, may be alleviated by plasticity in other traits such as tissue-mass density and thickness of roots and leaves. The results also suggest different adaptive constraints for phenotypic plasticity and for genetically determined interspecific variation. Phenotypic plasticity tends to maximize resource acquisition and growth rate in the short term, whereas the higher tissue-mass density and the longer leaf life-span of shade-tolerant species indicate reduced loss rates as a more advantageous speciesspecific adaptation to shade in the long term.

The steady state growth rates of three species of marine phytoplankton, Thalassiosira weisflogii, Isochrysis galbana, and Prorocentrum micans, were followed in turbidostat culture. At each growth irradiance, photosynthesis and respiration were measured by following changes in oxygen. Together with measurements of optical absorption cross sections, cellular chlorophyll, carbon and nitrogen, and excretion rates as well as knowledge of the quantum flux, the quantum requirement for growth (l/&J and photosynthesis (l/&J were calculated. Our results suggest that variations in growth rate caused by changes in irradiance may be related to changes in respiration rates relative to growth as well as changes in optical absorption cross sections for a given species. Interspecific differences in growth rate at a given irradiance are not related to changes in respiration however, but are primarily attributable to differences in optical absorption cross sections normalized to chlorophyll a and differences in chlorophyll : carbon-ratios.

Polar transport of the phytohormone auxin mediates various processes in plant growth and development, such as apical dominance, tropisms, vascular patterning and axis formation. This view is based largely on the effects of polar auxin transport inhibitors. These compounds disrupt auxin efflux from the cell but their mode of action is unknown. It is thought that polar auxin flux is caused by the asymmetric distribution of efflux carriers acting at the plasma membrane. The polar localization of efflux carrier candidate PIN1 supports this model. Here we show that the seemingly static localization of PIN1 results from rapid actin-dependent cycling between the plasma membrane and endosomal compartments. Auxin transport inhibitors block PIN1 cycling and inhibit trafficking of membrane proteins that are unrelated to auxin transport. Our data suggest that PIN1 cycling is of central importance for auxin transport and that auxin transport inhibitors affect efflux by generally interfering with...

Marco António Teixeira Zullo1,*, Ladislav Kohout2 and Mariangela de Burgos Martins de Azevedo1 1Phytochemistry Laboratory, Instituto Agronômico (IAC), PO Box 28, CEP 13001-970 Campinas, SP, Brazil; 2Institute of Organic Chemistry and Biochemistry, Academy of ...