Showing papers on "Plant physiology published in 2005"

Response of barley grains to the interactive effect of salinity and salicylic acid

Abstract: Effect of grain soaking presowing in 1 mM salicylic acid (SA) and NaCl (0, 50, 100, 150 and 200 mM) on barley (Hordeum vulgare cv Gerbel) was studied. Increasing of NaCl level reduced the germination percentage, the growth parameters (fresh and dry weight), potassium, calcium, phosphorus and insoluble sugars content in both shoots and roots of 15-day old seedlings. Leaf relative water content (RWC) and the photosynthetic pigments (Chl a, b and carotenoids) contents also decreased with increasing NaCl concentration. On the other hand, Na, soluble sugars, soluble proteins, free amino acids including proline content and lipid peroxidation level and peroxidase activity were increased in the two plant organs with increasing of NaCl level. Electrolyte leakage from plant leaves was found to increase with salinity level. SA-pretreatment increased the RWC, fresh and dry weights, water, photosynthetic pigments, insolube saccharides, phosphorus content and peroxidase activity in the stressed seedlings. On the contrary, Na+, soluble proteins content, lipid peroxidation level, electrolyte leakage were markedly reduced under salt stress with SA than without. Under stress conditions, SA-pretreated plants exhibited less Ca2+ and more accumulation of K+, and soluble sugars in roots at the expense of these contents in the plant shoots. Exogenous application (Grain soaking presowing) of SA appeared to induce preadaptive response to salt stress leading to promoting protective reactions to the photosynthetic pigments and maintain the membranes integrity in barley plants, which reflected in improving the plant growth.

Manipulation of the Blue Light Photoreceptor Cryptochrome 2 in Tomato Affects Vegetative Development, Flowering Time, and Fruit Antioxidant Content

Abstract: Cryptochromes are blue light photoreceptors found in plants, bacteria, and animals. In Arabidopsis, cryptochrome 2 (cry2) is involved primarily in the control of flowering time and in photomorphogenesis under low-fluence light. No data on the function of cry2 are available in plants, apart from Arabidopsis (Arabidopsis thaliana). Expression of the tomato (Solanum lycopersicum) CRY2 gene was altered through a combination of transgenic overexpression and virus-induced gene silencing. Tomato CRY2 overexpressors show phenotypes similar to but distinct from their Arabidopsis counterparts (hypocotyl and internode shortening under both low- and high-fluence blue light), but also several novel ones, including a high-pigment phenotype, resulting in overproduction of anthocyanins and chlorophyll in leaves and of flavonoids and lycopene in fruits. The accumulation of lycopene in fruits is accompanied by the decreased expression of lycopene β-cyclase genes. CRY2 overexpression causes an unexpected delay in flowering, observed under both short- and long-day conditions, and an increased outgrowth of axillary branches. Virus-induced gene silencing of CRY2 results in a reversion of leaf anthocyanin accumulation, of internode shortening, and of late flowering in CRY2-overexpressing plants, whereas in wild-type plants it causes a minor internode elongation.

Ability of bacterium Bacillus subtilis to produce cytokinins and to influence the growth and endogenous hormone content of lettuce plants

Abstract: Hormone production by micro-organisms selected as antagonists of pathogenic fungi and the effect of their introduction into soil on hormone content and growth of lettuce plants were studied. Hormones in bacterial cultural media and in plant extracts were immunopurified and assayed using specific antibodies to indolyl-3-acetic acid (IAA), abscisic acid (ABA), and different cytokinins (zeatin riboside (ZR), dihydrozeatinriboside (DHZR) and isopentenyladenosine (iPA)). ZR was shown to be the main cytokinin present in bacterial cultural media as a complex with a high molecular weight component. Inoculation of lettuce plants with bacteria increased the cytokinin content of both shoots and roots. Accumulation of zeatin and its riboside was greatest in roots shortly 2 days after inoculation, when their content was 10 times higher than in control. Changes in the content of other hormones (ABA and IAA) were observed at the end of experiments only. Accumulation of cytokinins in inoculated lettuce plants was associated with an increase in plant shoot and root weight of approximately 30% over 8 days.

Role of Abscisic Acid in Seed Dormancy

Abstract: Seed dormancy is an adaptive trait that improves survival of the next generation by optimizing the distribution of germination over time. The agricultural and forest industries rely on seeds that exhibit high rates of germination and vigorous, synchronous growth after germination; hence dormancy is sometimes considered an undesirable trait. The forest industry encounters problems with the pronounced dormancy of some conifer seeds, a feature that can lead to non-uniform germination and poor seedling vigor. In cereal crops, an optimum balance is most sought after; some dormancy at harvest is favored because it prevents germination of the physiologically mature grain in the head prior to harvest (that is, preharvest sprouting), a phenomenon that leads to considerable damage to grain quality and is especially prominent in cool moist environments. The sesquiterpene abscisic acid (ABA) regulates key events during seed formation, such as the deposition of storage reserves, prevention of precocious germination, acquisition of desiccation tolerance, and induction of primary dormancy. Its regulatory role is achieved in part by cross-talk with other hormones and their associated signaling networks, via mechanisms that are largely unknown. Quantitative genetics and functional genomics approaches will contribute to the elucidation of genes and proteins that control seed dormancy and germination, including components of the ABA signal transduction pathway. Dynamic changes in ABA biosynthesis and catabolism elicit hormone-signaling changes that affect downstream gene expression and thereby regulate critical checkpoints at the transitions from dormancy to germination and from germination to growth. Some of the recent developments in these areas are discussed.

Physiological and Molecular Effects of 24-Epibrassinolide, a Brassinosteroid on Thermotolerance of Tomato

Abstract: Brassinosteroids are naturally occurring plant growth regulators, which exhibit structural similarities to animal steroid hormones. Recent studies have indicated that besides an essential role in plant growth and development, brassinosteroids also exert anti-stress effects on plants. We show here that tomato plants treated with 24-epibrassinolide (EBR) are more tolerant to high temperature than untreated plants. An analysis of mitochondrial small heat shock proteins (MT-sHSP) in tomato leaves by western blotting revealed that the MT-sHSP did not preferentially accumulate in EBR treated plants at 25 °C. However, treatment of plants at 38 °C induced much more accumulation of MT-sHSP in EBR treated than in untreated plants. Results of this study provide the first direct evidence for EBR induced expression of MT-sHSP, which possibly induced thermotolerance in tomato plants. EBR treated tomato plants had better photosynthetic efficiency. We also observed significantly higher in vitro pollen germination, enhanced pollen tube growth and low pollen bursting in the presence of EBR at 35 °C, a temperature high enough to induce heat-stress symptoms in tomato, indicating a possible role of EBR during plant reproduction.

The roots of carnivorous plants

Abstract: Carnivorous plants may benefit from animal-derived nutrients to supplement minerals from the soil. Therefore, the role and importance of their roots is a matter of debate. Aquatic carnivorous species lack roots completely, and many hygrophytic and epiphytic carnivorous species only have a weakly developed root system. In xerophytes, however, large, extended and/or deep-reaching roots and sub-soil shoots develop. Roots develop also in carnivorous plants in other habitats that are hostile, due to flooding, salinity or heavy metal occurance. Information about the structure and functioning of roots of carnivorous plants is limited, but this knowledge is essential for a sound understanding of the plants’ physiology and ecology. Here we compile and summarise available information on: (1) The morphology of the roots. (2) The root functions that are taken over by stems and leaves in species without roots or with poorly developed root systems; anchoring and storage occur by specialized chlorophyll-less stems; water and nutrients are taken up by the trap leaves. (3) The contribution of the roots to the nutrient supply of the plants; this varies considerably amongst the few investigated species. We compare nutrient uptake by the roots with the acquisition of nutrients via the traps. (4) The ability of the roots of some carnivorous species to tolerate stressful conditions in their habitats; e.g., lack of oxygen, saline conditions, heavy metals in the soil, heat during bushfires, drought, and flooding.kg]Key words

Effects of water stress on photosynthesis and nitrogen metabolism in vegetative and reproductive shoots of Leymus chinensis

Abstract: In Leymus chinensis, mild water stress (soil moisture 60–65 % of field capacity) had no significant effects on nitrogen metabolism, photosynthesis, and chlorophyll fluorescence. Severe water stress (35–40 %) significantly decreased the activities of nitrate reductase, glutamine synthetase, and glutamate dehydrogenase, net photosynthetic rate, stomatal conductance, transpiration rate, maximal efficiency of photosystem 2 photochemistry (Fv/Fm), actual quantum yield, and photochemical quenching, but increased the endopeptidase activity and malondialdehyde contents. The adverse effects on photosynthesis and N metabolism were markedly greater in reproductive shoots than in vegetative shoots.

Expression of a plant cell wall invertase in roots of Arabidopsis leads to early flowering and an increase in whole plant biomass.

Abstract: In order to enhance sink strength, we expressed a heterologous plant cell wall invertase (CrCIN1) under the control of a root-specific promoter (ppyk10) in Arabidopsis thaliana. Slightly elevated apoplastic invertase activity resulted in apparent phenotypic changes. Transgenic plants developed more secondary roots and subsequently, possibly because of a higher capacity to acquire nutrients, a higher shoot and whole plant biomass. Furthermore, an early flowering phenotype was detected. The data presented here demonstrate that it is possible to modulate carbohydrate metabolism by ectopic expression of cell wall invertases and thereby influence sink organ size and whole plant development.

Physcomitrella patens and Ceratodon purpureus, mosses as model organisms in photosynthesis studies.

Abstract: With the discovery of targeted gene replacement, moss biology has been rapidly advancing over the last 10 years. This study demonstrates the usefulness of moss as a model organism for plant photosynthesis research. The two mosses examined in this study, Physcomitrella patens and Ceratodon purpureus, are easily cultured through vegetative propagation. Growth tests were conducted to determine carbon sources suitable for maintaining heterotrophic growth while photosynthesis was blocked. Photosynthetic parameters examined in these plants indicated that the photosynthetic activity of Ceratodon and Physcomitrella is more similar to vascular plants than cyanobacteria or green algae. Ceratodon plants grown heterotrophically appeared etiolated in that the plants were taller and plastids did not differentiate thylakoid membranes. After returning to the light, the plants developed green, photosynthetically active chloroplasts. Furthermore, UV-induced mutagenesis was used to show that photosynthesis-deficient mutant Ceratodon plants could be obtained. After screening approximately 1000 plants, we obtained a number of mutants, which could be arranged into the following categories: high fluorescence, low fluorescence, fast and slow fluorescence quenching, and fast and slow greening. Our results indicate that in vivo biophysical analysis of photosynthetic activity in the mosses can be carried out which makes both mosses useful for photosynthesis studies, and Ceratodon best sustains perturbations in photosynthetic activity.

Growth, photosynthesis, and metabolism of sugar beet at an early stage of exposure to elevated CO 2

Abstract: The effects of CO2 concentration (C a) on growth, photosynthesis, and the activity of enzymes associated with the translocation and assimilation of CO2 were studied in sugar beet (Beta vulgaris L subsp saccharifera, cv Ramonskaya) plants The plants were grown in controlled-climate chamber to the stage of 3–4 leaves and then used in experiments Experimental plants were exposed in boxes to doubled C a (700 µl/l, 2C plants), whereas control plants were kept in a chamber with ambient atmosphere (350 µl/l, 1C plants) As compared with 1C plants, in 3 and 8 days, the leaf area of 2C plants increased by 14 and 26%, respectively The rate of their photosynthesis (P n) measured in 3, 6, and 8 days increased by 85, 47, and 52%, respectively, whereas in normal air, the values of P n in 2C plants were by 12, 19, and 15% lower than in 1C plants After 8-day growth, the content of soluble carbohydrates in the leaves of 2C plants attained 72%, being by 80% greater than in 1C plants; the content of starch did not exceed 3% The total content of chlorophylls a and b in the leaves of 2C plants was by 14% greater than in 1C plants, but their ratio was essentially the same The level of protein in 2C plants was by 134% lower than in 1C plants The activity and content of Rubisco in 1C and 2C plants were similar As compared with 1C plants, in 2C plants the activity of soluble carbonic anhydrase (sCA) was lower by 34% in 3 days and by 18% in 8 days; the activity of carbonic anhydrase of membrane preparations (mCA), was lower by 24 and 77%, respectively Catalase activity in 2C plants became by 8% lower than in 1C plants only after 8 days A reduction in the photosynthetic ability of 2C plants in ambient atmosphere, a decrease in activity of sCA and, especially, of mCA observed together with invariable activity and content of Rubisco in the leaf extracts are interpreted as early symptoms of acclimation of young plants of sugar beet to elevated CO2

Plant shading increases lipid peroxidation and intensifies senescence-induced changes in photosynthesis and activities of ascorbate peroxidase and glutathione reductase in wheat

Abstract: Plants of spring wheat (Triticum aestivum L. cv. Saxana) were grown during the autumn. Over the growth phase of three leaves (37 d after sowing), some of the plants were shaded and the plants were grown at 100 (control without shading), 70, and 40 % photosynthetically active radiation. Over 12 d, chlorophyll (Chl) and total protein (TP) contents, rate of CO2 assimilation (PN), maximal efficiency of photosystem 2 photochemistry (FV/FP), level of lipid peroxidation, and activities of antioxidative enzymes ascorbate peroxidase (APX) and glutathione reductase (GR) were followed in the 1st, 2nd, and 3rd leaves (counted according to their emergence). In un-shaded plants, the Chl and TP contents, PN, and FV/FP decreased during plant ageing. Further, lipid peroxidation increased, while the APX and GR activities related to the fresh mass (FM) decreased. The APX activity related to the TP content increased in the 3rd leaves. The plant shading accelerated senescence including the increase in lipid peroxidation especially in the 1st leaves and intensified the changes in APX and GR activities. We suggest that in the 2nd and 3rd leaves a degradation of APX was slowed down, which could reflect a tendency to maintain the antioxidant protection in chloroplasts of these leaves.

The Effects of Cold Acclimation of Winter Wheat Plants on Changes in CO 2 Exchange and Phenolic Compound Formation

Abstract: We studied CO2 exchange and phenolic compound production in various organs of unhardened and hardened winter wheat (Triticum aestivum L.) plants. The rates of CO2 assimilation at saturating illumination (photosynthesis) and CO2 evolution in darkness (respiration) declined substantially at the autumnal decrease of ambient temperature. However, because of a higher cold resistance of photosynthesis, the ratio of photosynthesis to respiration rates increased 1.5-fold. These gas exchange changes were accompanied by the accumulation of total soluble phenolics in leaves and a polymeric phenolic compound lignin in roots. We did not observe any changes in the production of either soluble or polymeric (lignin) phenolics in crowns.

Effect of Light Quality on Nitrogen Metabolism of Radish Plants

Abstract: The long-term action of blue or red light on nitrogen metabolism was studied in radish (Raphanus sativus L.) plants. The potential activity of nitrate reductase (NR) in vivo and its maximum activity in vitro, the content of soluble protein and free amino acids were determined in the course of the growth of a third leaf of radish plants. The effect of light quality on NR activity was found to depend significantly on the stage of leaf development. Blue light (BL) stimulated NR activity in leaves, when their areas were about 11–13% of the fully developed leaves. The efficiency of red light (RL) was significantly lower, because the maximum NR activity was observed in the leaves developed to the stage, when their areas were 38–40% of the final one. The comparative analysis of the pool of free amino acids in expanding leaves of BL- or RL-grown plants revealed significant changes in the contents of individual amino acids. Despite a higher accumulation of two amino acids in the leaves of BL-grown plants, namely, Asp (27% as compared to 13–16% in the RL-grown leaves) and Gly (5% against 2.5% in RL-grown leaves), the BL-grown leaves also demonstrated a significant decrease in Ala (10% as compared to 23% in the RL-grown leaves) and some decrease in the amounts of Ser and Gly. The content of soluble protein in a juvenile BL-grown leaf was observed to decrease gradually during leaf development. However, the protein content in the BL-grown leaf was always higher than in the RL-grown leaf of the same age. We concluded that the photoregulatory action of BL on NR activity determined the different rates of nitrogen assimilation in BL- and RL-grown plants.

Physiological and biochemical aspects and molecular mechanisms of plant adaptation to the elevated concentration of atmospheric CO2

Abstract: The review of publications concerning the impact of increasing CO2 concentration in the Earth’s atmosphere (Ca) on higher terrestrial plants. The physiological changes in plants induced by increasing Ca, including growth and biochemical composition, the characteristics of photosynthesis and respiration, as well as the molecular mechanisms of the regulation of the activity of most important biosynthetic enzymes at early and late stages of the exposure to elevated Ca are under consideration. Various concepts of metabolic regulation during acclimation to increasing CO2 concentration are critically reviewed. The pathways of possible involvement of carbonic anhydrase-mediated systems of CO2 transport and concentration during C3 photosynthesis of higher plants, the metabolic and signal mechanisms of photosynthesis inhibition by carbohydrates and the role of ethylene at elevated Ca are presented. The effect of elevated Ca on plant development and source-sink relations, as well as its interaction with other environmental factors, such as mineral, primarily nitrogen nutrition, light, temperature, and water regime, are discussed in with the context of potential forecasting of the consequences of increase in Ca and temperature for the activities of various higher plant forms in the rapidly changing climate.

Influence of UV-radiation on the photosynthesis and photosynthetic carbon metabolism in high mountainous plants

Abstract: The influence of UV-radiation on the 14CO2 assimilation rate of three high mountainous plants (Heracleum lehmannianum Bunge, Prangos pabularia Lind L. and Lathyrus mulkak Lipsky) with different photosynthetic intensity and directivity of photosynthetic carbon metabolism was studied. The investigation was carried out in the Biological Station of The Institute of Plant Physiology and Genetics (Academy of Sciences of Republic of Tajikistan), located on an austral decline (2350 m above sea level) of the Hissar valley (Tajikistan). It is proved, that plants show different responses to dissecting away of UV-rays. Almost tenfold fall in the intensity of 14CO2 fixation (during 30 sec) is noted for H. lehmannianum; in P. pabularia there was twofold fall in depression, and in L. mulkak the dissecting away of UV-rays resulted in the minor rising of the photosynthetic rate. Under both film dropping UV-rays and in open area, we have not revealed essential differences in the 14CO2 assimilation rate in all three plants. The experiments were carried out in three variants: 1. Control – open place. 2. The plants were covered with polyethylene film. 3. The plants were covered with polyethylene film enriched with 2-oxi-4-alcoxibenzophenol (0.65%), cutting off the UV part of solar spectrum. The study of 14C incorporation into the products of photosynthesis has manifested essential differences between investigated plants. From the control experiment, using the Heracleum leaves, more than 65% of a label was included into the intermediates of the Calvin cycle (among them about 20% into PGA). The dissecting away of UV-radiation resulted in a depression of 14C incorporation into PGA and PES. The key products, which, at 30 sec exposure, concentrated the most part of label were sugars, predominantly sucrose. Intermediates of the glycolic pathway concentrated a small part of 14C (22%). The depressing of CO2 photosynthetic assimilation in Prangos was accompanied by a sharp slump of 14C incorporation into intermediates of the Calvin cycle. The label was found out in sugars predominantly and in intermediates of the glycolic pathway. In control plants we detected an increase of 14C lobe in monosaccharides. The content of label in intermediates of glycolic pathway decreased. In Lathyrus leaves under investigation we revealed intensive label incorporation into intermediates of the Calvin cycle and its decrease in the metabolites of the glycolic pathway. We found minor quantities of 14C contents in sugars and PEP-products. It is supposed that the UV-rays influence the activity of RUBISCO and other enzymes of the Calvin cycle. The mechanisms of UV-rays influence on carboxylation system and the possibility of their regulatory role in high mountainous plants are under discussion.

Aggregates formed as a result of the expression of yeast Met2 gene in transgenic tobacco plants, stimulate the production of stress-protective metabolites and increased the plants tolerance to heat stress

Abstract: Methionine biosynthesis has taken different evolutionary pathways in bacteria, fungi and plants. To gain insight into these differences and to search for new ways of manipulating methionine biosynthesis in plants, the yeast (Saccharomyces cerevisiae) Met2 gene and the bacteria (Leptospira meyeri) MetX gene, both encoding homoserine O-acetyltransferase, were expressed in tobacco plants. We found protein aggregates in extracts of these transgenic plants, whose levels were much higher in plants grown at 35 °C than at 25 °C. It appears that the yeast and the bacterial proteins are heat labile and tend to change their intracellular conformation. These conformational changes of the transgenic proteins were more prominent at high temperature and most probably triggered aggregation of the yeast and the bacterial proteins. Moreover, plants expressing the yeast gene that grew at 35 °C over-accumulated stress-associated metabolites, such as phenolic compounds, including tannins, as well as the amino acid arginine. In addition, the transgenic plants expressing high levels of the foreign genes show growth retardation, which further suggests that, these plants suffer from internal stress. The changes in protein conformation and the consequent triggering of stress response may account for the ability of these transgenic plants to tolerate more extreme heat stress (60 °C) than the wild-type plants.