Showing papers on "Plant physiology published in 1997"

Physiological nitrogen efficiency in rice: Nitrogen utilization, photosynthesis, and yield potential

Abstract: Characteristics of rice (Oryza sativa) as a crop plant are briefly introduced, and the relationship between formation of yield potential and nitrogen (N) nutrition is described on the basis of studies using 15N as a tracer In addition, the relationship between the leaf photosynthetic capacity and leaf N, and the factors limiting leaf photosynthesis under different growth conditions are reviewed Finally, targets for improving rice yield potential are discussed with a focus on the role of increased photosynthesis efficiency in relation to leaf N status and the photosynthetic components in the leaves

Plant biochemistry and molecular biology

Abstract: Contents : 1. A leaf cell consists of several metabolic compartments -2. The use of energy from sunlight by photosynthesis -3. Photosynthesis is an electron transport process -4. ATP generation by photosynthesis -5. Mitochondria, the power stations of cell -6. Photosynthetic CO2 assimilation by the Calvin cycle -7. Photorespiration -8. Photosynthesis and water consumption -9. Polysaccharides -10. Nitrate assimilation -11. Nitrogen fixation -12. Sulfate assimilation -13. Phloem transport -14. Plant storage proteins -15. Glycerolipids -16. The function of secondary metabolites in plants -17. Isoprenoids -18. Phenylpropanoids -19. Signals regulating the growth and development of plant organs -20. The genomes of plant cells -21. Protein biosynthesis -22. Gene technology in plants.

Pea mutants with reduced sensitivity to far-red light define an important role for phytochrome A in day-length detection

Abstract: In garden pea (Pisum sativum L.), a long-day plant, long photoperiods promote flowering by reducing the synthesis or transport of a graft-transmissible inhibitor of flowering. Previous physiological studies have indicated that this promotive effect is predominantly achieved through a response that requires long exposures to light and for which far-red (FR) light is the most effective. These characteristics implicate the action of phytochrome A (phyA). To investigate this matter further, we screened ethylmethane sulfonate-mutagenized pea seedlings for FR-unresponsive, potentially phyA-deficient mutants. Two allelic, recessive mutants were isolated and were designated fun1 for FR unresponsive. The fun1-1 mutant is specifically deficient in the PHYA apoprotein and has a seedling phenotype indistinguishable from wild type when grown under white light. However, fun1-1 plants grown to maturity under long photoperiods show a highly pleiotropic phenotype, with short internodes, thickened stems, delayed flowering and senescence, longer peduncles, and higher seed yield. This phenotype results in large part from an inability of fun1-1 to detect day extensions. These results establish a crucial role for phyA in the control of flowering in pea, and show that phyA mediates responses to both red and FR light. Furthermore, grafting and epistasis studies with fun1 and dne, a mutant deficient in the floral inhibitor, show that the roles of phyA in seedling deetiolation and in day-length detection are genetically separable and that the phyA-mediated promotion of flowering results from a reduction in the synthesis or transport of the floral inhibitor.

Phytochrome regulation of seed germination

Abstract: Seed germination of many plant species is influenced by light. Of the various photoreceptor systems, phytochrome plays an especially important role in seed germination. The existence of at least five phytochrome genes has led to the proposal that different members of the family have different roles in the photoregulation of seed germination. Physiological analysis of seed germination ofArabidopsis thaliana (L.) Heynh. with phytochrome-deficient mutants showed for the first time that phytochrome A and phytochrome B modulate the timing of seed germination in distinct actions. Phytochrome A photo-irreversibly triggers the photoinduction of seed germination after irradiation with extremely low fluence light in a wide range of wavelengths, from UV-A, to visible, to far-red. In contrast, phytochrome B mediates the well-characterized photoreversible reaction, responding to red and far-red light of fluences four orders of magnitude higher than those to which PhyA responds. Wild plants, such asA. thaliana, survive under ground as dormant seeds for long periods, and the timing of seed germination is crucial for optimizing growth and reproduction. It therefore seems reasonable for plants to possess at least two different physiological systems for sensing the light environment over a wide spectral range with exquisite sensitivity of different phytochromes. This redundancy seems to enhance plant survival in a fluctuating environment.

Influence of arbuscular mycorrhizae and Rhizobium on nutrient content and water relations in drought stressed alfalfa

Abstract: The objective of this research was to study the effect of drought on nutrient content and leaf water status in alfalfa (Medicago sativa L. cv Aragon) plants inoculated with a mycorrhizal fungus and/or Rhizobium compared with noninoculated ones. The four treatments were: a) plants inoculated with Glomus fasciculatum and Rhizobium meliloti 102 F51 strain, (MR); b) plants inoculated with R. meliloti only (R); c) plants with G. fasciculatum only (M); and d) noninoculated plants (N). Nonmycorrhizal plants were supplemented with phosphorus and nonnodulated ones with nitrogen to achieve similar size and nutrient content in all treatments. Plants were drought stressed using two cycles of moisture stress and recovery. The components of total leaf water potential (osmotic and pressure potentials at full turgor), percentage of apoplastic water volume and the bulk modulus of elasticity of leaf tissue were determined. Macronutrient (N, P, K, Ca, S and Mg) and micronutrient (Co, Mo, Zn, Mn, Cu, Na, Fe and B) content per plant were also measured. Leaves of N and R plants had decreased osmotic potentials and increased pressure potentials at full turgor, with no changes either in the bulk modulus of elasticity or the percentage of apoplastic water upon drought conditions. By contrast, M and MR leaves did not vary in osmotic and turgor potentials under drought stress but had increased apoplastic water volume and cell elasticity (lowering bulk modulus). Drought stress decreased nutrient content of leaves and roots of noninoculated plants. R plants showed a decrease in nutrient content of leaves but maintained some micronutrients in roots. Leaves of M plants were similar in content of nutrients to N plants. However, roots of M and MR plants had significantly lower nutrient content. Results indicate an enhancement of nutrient content in mycorrhizal alfalfa plants during drought that affected leaf water relations during drought stress.

Effects of Cd2+ on the physiological state and photosynthetic activity of young barley plants

Abstract: Barley plants (Hordeum vulgare L. cv. Obzor) were grown as a water culture in a climatic room. One part of them was subjected to a long-term Cd2+ stress - 12 d with 5.4×10−5 M Cd. The Cd2+ stress inhibited formation of the photosynthetic apparatus and its capacity for 14C photoassimilation, decreased the content of soluble proteins, increased the dark respiration rate and the free amino acids content, disturbed plant water relations, as well as the distribution of 14C within primary photoproducts of the treated barley plants.

Plant Responses to High CO2 Concentration in the Atmosphere

Abstract: The impact of continuous rise in ambient CO2 concentration (AC) in the atmosphere on different facets of growth of crop plants is assessed. The effects of CO2 enrichment (EC) on plant growth, C3 and C4 photosynthesis, source-sink ratio, partitioning and translocation of metabolites, photosynthetic enzymes, respiratory rate, leaf area index, stomatal conductance (q s ), transpiration rate, biomass production and water use efficiency are reviewed. The CO2 fertilization effects are studied in both short-term (open top chambers) and long-term experiments. Long-term experiments suggest that ribulose-1,5-bisphosphate carboxylase is inactivated at high CO2 concentrations. Also g s is lowered. One of the conspicuous effects of EC is the closure of stomata in C3 plants. Photosystem (PS) 2 electron transport is more affected than PS1. Starch is the immediate product accumulated in the leaf of C3 plants. The “CO2 fertilization effect” does not confer any great advantage even in C3 plants.

Prostaglandins and related substances in plants

Abstract: Prostaglandins (PGs) have been detected in many different plants and certain microorganisms. A few prostaglandin-like compounds have also been shown to occur in plants such as flax,Chromolaena morii, and aquatic sedge; and direct precursors (arachidonic acid, di-homo-γ-linolenic acid and eicosapentaenoic acid) have been detected in a variety of plants and microorganisms, including certain red algae, brown algae, green algae, and saltwater diatoms. Furthermore, arachidonic acid has been found in mosses and a liverwort. It has also been reported that arachidonic acid occurs in certain angiosperms, namely, poplar (Populus balsamifera), wheat germ oil,Aloe vera, andAllium sativum (garlic). In our studies on the possible physiological effects of prostaglandins we found that a PG possibly has an effect on the flowering of the short-day plantPharbitis nil. It has hastened flower formation by 28 days as compared with controls under inductive conditions (short days), and certain inhibitors of PG-biosynthesis inhibited flowering to a greater or lesser extent. In other physiological studies of prostaglandins, it was found that they have an effect on such aspects as GA3-controlled responses in barley endosperm, inhibition of crown gall tumor formation on potato discs, and certain electron-flow reactions in isolated chloroplasts. In corn leaf segments it has an effect on photosynthesis, nucleic acid metabolism, and protein synthesis. The effect on four plant bioassay systems was negligible. It has also been reported that PGs play a role in the regulation of cell membrane permeability.

A method for measuring whole plant photosynthesis in Arabidopsis thaliana

Abstract: Measurement of photosynthesis of intact leaves of Arabidopsis thaliana has been prohibitive due to the small leaf size and prostrate growth habit. Because of the widespread use of Arabidopsis for plant science research it is important to have a procedure for accurate, nondestructive measurement of its photosynthesis. We developed and tested a method for analysis of photosynthesis in whole plants of Arabidopsis. Net carbon assimilation and stomatal conductance were measured with an open gas exchange system and photosynthetic oxygen evolution was determined from chlorophyll fluorescence parameters. Individual plants were grown in 50 cubic centimeter tubes that were attached with an air tight seal to an enclosed gas exchange chamber for measurement of carbon dioxide and water exchange by the whole plant. Chlorophyll fluorescence from intact leaves was simultaneously measured with a pulse modulated fluorometer. Photosynthetic CO2 assimilation and stomatal conductance rates were calculated with established gas exchange procedures and O2 evolution was determined from chlorophyll fluorescence measurement of Photosystem II yield. Carbon assimilation and oxygen evolution in response to light intensity and ambient CO2 concentration was measured and is presented here to demonstrate the potential use of this method for investigation of photosynthesis of Arabidopsis plants in controlled environment conditions.

Effects of constant and fluctuating temperature on time to budburst in Betula pubescens and its relation to bud respiration

Abstract: Effects of fluctuating and constant temperatures on budburst time, and respiration in winter buds were studied in Betula pubescens Ehrh. Dormant seedlings were chilled at 0°C for 4 months and then allowed to sprout in long days (LD, 24 h) at constant temperatures of 6, 9, 12, 15, 18 and 21°C, and at diurnally fluctuating temperatures (12/12 h, LD 24 h) with means of 9, 12, 15 and 18°C. No difference in thermal time requirements for budburst was found between plants receiving constant and fluctuating temperatures. The base temperature for thermal time accumulation was estimated to 1°C. Respiration in post-dormant (dormancy fully released) excised winter buds from an adult tree increased exponentially with temperature and was 20 times as high at 30°C than at 0°C. However, respiration in buds without scales was 30% higher at 0°C, and it was 2.7 times higher at 24°C than in intact buds. Thus, the tight bud scales probably constrain respiration and growth and are likely to delay budburst in spring. Arrhenius plots of the respiration data were biphasic with breaks at 13–15°C. However, this phase transition is unlikely to be associated with chilling sensitivity since the present species is hardy and adapted to a boreal climate.

Influence of supplemental UV-B radiation on photosynthetic characteristics of rice plants

Abstract: In a field experiment with rice (Oryza sativa L. cv. Saket 4) grown under ambient and supplemental ultraviolet-B (UV-B) radiation at 20 % ozone depletion, differences in gas exchange, concentrations of photosynthetic pigments, anthocyanins and flavonoids, biomass accumulation, catalase and peroxidase activities, and contents of ascorbic acid and phenol were determined. Decline in photosynthesis was associated with reductions in stomatal conductance and concentrations of photosynthetic pigments. Enhanced UV-B radiation (eUV-B) increased the contents of flavonoid and phenolic compounds in leaves. Peroxidase activity increased and catalase activity was always lower at eUV-B. The total plant biomass decreased at eUV-B.

Regulation of photosynthesis in developing leaves of soybean chlorophyll-deficient mutants

Abstract: In this report we examine the factors that regulate photosynthesis during leaf ontogeny in y3y3 and Y11y11, two chlorophyll-deficient mutants of soybean. Photosynthetic rates were similar during wild type and Y11y11 leaf development, but the senescence decline in photosynthesis was accelerated in y3y3. Photosynthetic rates fell more rapidly than chlorophyll concentrations during senescence in wild type leaves, indicating that light harvesting is not strongly limiting for photosynthesis during this phase of leaf development. Chlorophyll concentrations in Y11y11, though significantly lower than normal, were able to support normal photosynthetic rates throughout leaf ontogeny. Chlorophyll a/b ratios were constant during leaf development in the wild type, but in the mutants they progressively increased (y3y3) or decreased (Y11y11). In all three sets of plants, photosynthetic rates were directly proportional to Rubisco contents and activities, suggesting that Rubisco plays a dominant role in regulating photosynthesis throughout leaf ontogeny in these plants. The expression of some photosynthetic proteins, such as Rubisco activase, was coordinately regulated with that of Rubisco in all three genotypes, i.e. an early increase, coincident with leaf expansion, followed by a senescence decline in the fully-expanded leaf. On the other hand, the light harvesting chlorophyll a/b-binding proteins of PS II (the CAB proteins), while they showed a profile similar to that of Rubisco in the wild type and y3y3, progressively increased in amount during Y11y11 leaf development. We conclude that Y11y11 may be defective in the accumulation of a component required for LHC II assembly or function, while y3y3 has more global effects and may be a regulatory factor that controls the duration of senescence.

Molecular mechanism of phytochrome action.

Abstract: Studies on phytochrome have been revolutionized by two pioneering works: isolation of Iong-hypocotyl mutants of Arabidopsis (Koornneef et al. 1980) and molecular cloning of a phytochrome cDNA (Hershey et al. 1985). The former work introduced a powerful genetic approach into the field of photomorphogenesis, which had been mainly a world of physiology and biophysics. Isolation of a de-et iolat ion mutant (Chory et al. 1988) changed the paradigm of photomorphogenesis, and initiated a series of studies which has led to the discovery of nearly a dozen components in the light signaling pathway. The isolation of phytochrome genes has opened the way to create transgenic plants harboring the wild-type or mutant phytochrome transgenes. Combination of the two approaches has made it possible to dissect physiological responses in photomorphogenesis in a totally different manner, which we could not have envisaged just 15 years ago. We are in the midst of the expanding frontier of photomorphogenesis research, and its limit seems far beyond our imagination. We therefore organized a symposium in the Annual Meeting of the Botanical Society of Japan held in Kanazawa, 1995, in order to discuss the recent achievements in the field of photomorphogenesis and evaluate the limit of the current approaches and formulate future plans. The JPR Symposium is composed of contributions by speakers at the Symposium. Though Prof. R. E. Kendrick did not attend the Symposium in Kanazawa, he kindly contributed his paper to this issue. We hope that this series of papers will evoke the readers interest. I am very much indebted to Profs. M. lino, Y. Komeda, K. Manabe, A. Nagatani and M. Sugai for organizing the symposium in Kanazawa.