Effect of methylmercury chloride on the primary photosynthetic activity of higher plants

The effect of methylmercury chloride (MeHg) on the fluorescence characteristics of pea seedling leaves and thylakoids isolated from these leaves was studied by the pulse-amplitude-modulation (PAM) fluorometric method. In 3-4 days after the addition of MeHg (20 microM) to the nutritious solution, the maximal (Fv/Fm) and real (under steady state actinic light illumination) (deltaF/F'm) quantum photochemical yield of PS II decreased. The nonphotochemical fluorescence quenching coefficient in control (qN) decreased after its maximum value has been reached. In MeHg-treated samples, this decrease was not observed, possibly due to the disturbance of delta pH energy transducing processes in ATP synthase. This was confirmed by the results of experiments on isolated thylakoids. After MeHg (5 microM) treatment of thylakoids, the photophosphorylation rate and light-triggered Mg2+-dependent H+-ATPase activity were suppressed by 20-40%, depending on the duration of MeHg exposure. However, in experiments with isolated thylakoids, no decrease either in the electron transport rate or in the Fv/Fm ratio was observed. In total, the results obtained allow one to assume that MeHg at concentrations and time duration used directly damages the coupling complex. The PS II inactivation in leaves and algae cells may be a result of the oxidative stress processes.     

Modifications to the photosynthetic apparatus of higher plants in response to changes in the light environment

A brief review of the photosynthetic apparatus of higher plants is given, followed by a consideration of the modifications induced in this apparatus by changes in light intensity and light quality. Possible strategies by which plants may optimize photosynthetic activity by both long- and short-term modifications of their photosynthetic apparatus in response to changing light regimes are discussed.     

Relationships between jasmonates and auxin in regulation of some physiological processes in higher plants

Growth and development of plants are regulated by interactions among different plant growth substances. During stress conditions, both abiotic and biotic, interaction of the some hormones activates defense responses. The present review describes the interaction between jasmonates and auxin in regulation of some physiological processes in plant growth and development. Some jasmonate-induced processes reduced by auxins and some auxin stimulated physiological processes inhibited by jasmonates are the focus of this review. Therefore, the following physiological processes are described: stem cell growth, abscission, secondary abscission zone formation, tendril coiling, opening of the pulvinules in Mimosa pudica, wounding and induced gene expression, nicotine biosynthesis and auxin biosynthesis in Brassicaceae.     

Water-deficit stress-induced anatomical changes in higher plants

Water is vital for plant growth and development. Water-deficit stress, permanent or temporary, limits the growth and the distribution of natural vegetation and the performance of cultivated plants more than any other environmental factors do. Although research and practices aimed at improving water-stress resistance and water-use efficiency have been carried out for many years, the mechanism involved is still not clear. Further understanding and manipulating plant-water relations and water-stress tolerance at the scale of physiology and molecular biology can significantly improve plant productivity and environmental quality. Currently, post-genomics and metabolomics are very important to explore anti-drought gene resource in different life forms, but modern agricultural sustainable development must be combined with plant physiological measures in the field, on the basis of which post-genomics and metabolomics will have further a practical prospect. In this review, we discussed the anatomical changes and drought-tolerance strategies under drought condition in higher plants.     

Composition, architecture and dynamics of the photosynthetic apparatus in higher plants

The process of oxygenic photosynthesis enabled and still sustains aerobic life on Earth. The most elaborate form of the apparatus that carries out the primary steps of this vital process is the one present in higher plants. Here, we review the overall composition and supramolecular organization of this apparatus, as well as the complex architecture of the lamellar system within which it is harbored. Along the way, we refer to the genetic, biochemical, spectroscopic and, in particular, microscopic studies that have been employed to elucidate the structure and working of this remarkable molecular energy conversion device. As an example of the highly dynamic nature of the apparatus, we discuss the molecular and structural events that enable it to maintain high photosynthetic yields under fluctuating light conditions. We conclude the review with a summary of the hypotheses made over the years about the driving forces that underlie the partition of the lamellar system of higher plants and certain green algae into appressed and non-appressed membrane domains and the segregation of the photosynthetic protein complexes within these domains.     

Relation between photosynthetic and phenolase activities in spinach chloroplasts

During O°-storage of class I chloroplasts from spinach leaves, activation of phenolase strongly correlates with the inactivation of photosynthetic re     

Effect of copper on cellular processes in higher plants

Copper (Cu) is a heavy metal which in recent studies has been attributed an increasing role in metabolic processes of plant cells. It is an indispensable component of oxidative enzymes or of particular structural components of cells. At elevated concentrations, Cu can act strongly on chromatin, the photosynthetic apparatus, growth, and senescence processes. The mechanisms of the metal toxicity depending largely on the growth stage of treated plants are presented in this review.     

Effect of copper on cellular processes in higher plants

Copper (Cu) is a heavy metal which in recent studies has been attributed an increasing role in metabolic processes of plant cells. It is an indispensable component of oxidative enzymes or of particular structural components of cells. At elevated concentrations, Cu can act strongly on chromatin, the photosynthetic apparatus, growth, and senescence processes. The mechanisms of the metal toxicity depending largely on the growth stage of treated plants are presented in this review.     

Chemical composition of leaves and structure of photosynthetic apparatus in aquatic higher plants

Chemical composition of leaves (the content of carbon, nitrogen, nonstructural carbohydrates, organic acids, mineral substances, and water) and the structure of photosynthetic apparatus (specific leaf weight, cell volume, and the number of cells per unit leaf area) were investigated for 18 species of aquatic plants featuring various degrees of contact with aqueous environment and sediment. The rooted hydrophytes with floating leaves were characterized by comparatively high content of carbon and nitrogen (437 and 37 mg/g dry wt, respectively) and by low concentration of nonstructural carbohydrates, mineral substances, and organic acids (161, 54, and 60 mg/g dry wt, respectively). Unlike rooted plants, the free-floating nonrooted hydrophytes had characteristically higher content of nonstructural polysaccharides and mineral substances (by a factor of 1.3 and 1.6, respectively), while the leaf nitrogen content was 1.4 times lower, and the proportion of soluble carbohydrates in the total content of nonstructural carbohydrates was rather low (9%). The chemical composition of leaves in submerged rooted hydrophytes was intermediate between those for rooted hydrophytes with floating leaves and for nonrooted free plants. We found reliable positive correlations between the volume of photosynthesizing cells and the leaf content of organic acids (r = 0.69), as well as between specific leaf weight, the number of photosynthesizing cells per unit leaf area, and carbon content (r = 0.67 and r = 0.62, respectively). The content of nitrogen and nonstructural carbohydrates in hydrophytes was unrelated to structural characteristics of photosynthetic apparatus and depended on the absence or presence of plant attachment to the sediment. It is concluded that the structural traits of photosynthetic apparatus and the leaf chemical composition in hydrophytes featuring different degrees of plant contact with water and sediment reflect the specificity of plant adaptation to complex conditions of their habitats.     

Hydrogen isotope discrimination in higher plants: Correlations with photosynthetic pathway and environment

Summary The ratio of deuterium to hydrogen (expressed as D) in hydrogen released as water during the combustion of dried plant material was examined. The D value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C₃ plants show mean D values of-132 for shoots and -117 for roots; C₄ plants show mean D values of -91 for shoots and-77 for roots and CAM plants a D value of-75 for roots and shoots. The difference between the D value of shoot material from C₃ and C₄ plants was confirmed in species growing under a range of glasshouse conditions. This difference in D value between C₃ and C₄ species does not appear to be due to differences in the D value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C₃ and C₄ plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in D values are discussed. In CAM plants grown in the laboratory or collected from the field D values range from-75 to +50 and are correlated with ¹³C values. When deprived of water, the D value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different D value of available water in areas of increasing aridity. Whatever the origin of the variable D value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.     

Relation between pigment content and photosynthetic characteristics in a blue-green algae

1. The blue-green alga Anacystis nidulans was cultured under steady state conditions at 25 and 39°C. and under several different light intensities to give five different types of cells. 2. Cells were submitted to pigment analysis based upon acetone extracts and aqueous extracts obtained by sonic disintegration. The different cell types show a threefold range of chlorophyll content and a fourfold range of phycocyanin content with only minor changes in the chlorophyll/phycocyanin ratio. Cells of highest pigment content were estimated to contain 2.8 per cent chlorophyll a and 24 per cent phycocyanin, the latter on a total chromoproteid basis. 3. Light intensity curves of photosynthesis were obtained for each of the cell types at 25 and at 39°C. The slopes of the light-limited regions of the curves are approximately linear functions of chlorophyll and phycocyanin contents. Maximum light-saturated rates of photosynthesis at 25 and 39° show no simple relation to pigment content.     

State 1/State 2 changes in higher plants and algae

Current ideas regarding the molecular basis of State 1/State 2 transitions in higher plants and green algae are mainly centered around the view that excitation energy distribution is controlled by phosphorylation of the light-harvesting complex of photosystem II (LHC-II). The evidence supporting this view is examined and the relationship of the transitions occurring in these systems to the corresponding transitions seen in red and blue-green algae is explored.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - Chl a chlorophyll a - Chl b chlorophyll b - DAD diaminodurene - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCCD N,N-dicyclohexyl carbodiimide - DCMU 3-(3,4-dichlorophenyl)-l,l-dimethylurea (also called diuron) - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone - FSBA 5-fluorosulphonylbenzoyl adenosine - kDa kilodalton - LHC-II light-harvesting Chl a/Chl b protein - PMS phenazine methosulfate - PS I photosystem I - PS II photosystem II - SDS sodium dodecyl sulfate - TPTC triphenyl tin chloride This paper follows our new instructions for citation of references—authors are requested to follow Photosynth Res 10: 519–526 (1986)—editors.     

On the possible control of ultraviolet-B induced response in growth and photosynthetic activities in higher plants

When Vigna sinensis L.cv. Walp seedlings were grown under control (from four 40 W white fluorescent tubes) and enhanced ultraviolet-B (UV-B) radiation (four 40 W white fluorescent tubes plus one Philips 20W/12 sun lamp) a large inhibition in seedling growth, particularly shoot eelongation and leaf expansion, was observed under enhanced UV-B radiation. The UV-B radiation also reduced the overall photosynthetic activity as measured by chlorophyll fluorescence induction. In order to check whether UV-B causes any destruction of auxins, seedlings with either their shoot tip or primary leaves were covered with black paper and kept under both light conditions. Both the fully exposed and shoot tip-covered seedlings showed a similar negative response on growth characteristics and physiological activities. Leaf-covered seedlings showed well preserved photosynthetic activity under both light conditions. However, in these seedlings the pigment content decreased more than under other treatment conditions.
Our experiments provide evidence for distinguishing between the UV-B induced responses on growth and physiological activities; while the former may be controlled through auxins, the latter is probably by direct action on the organelles.     

A possible mechanism of ammonium ion regulation of photosynthetic carbon flow in higher plants

Addition of NH₄⁺ to the photosynthesizing leaf cells of Dolichos lab lab L. var. Lignosis Prain and leaf discs of Vigna sinensis L. savi ex Hassk caused a significant increase in the flow of photosynthetic carbon toward amino acids with a concomitant decrease toward sugars without affecting the over-all photosynthetic rate. Similar diversion of photosynthetic carbon away from sugars was also observed in the photosynthesizing isolated chloroplasts of V. sinensis, but the latter differed in that they accumulated organic acids rather than amino acids. In an effort to understand the mechanism of NH₄⁺-mediated regulation, the specific and total activities of NAD(P)-glutamate dehydrogenase, glutamine synthetase, pyruvate kinase, alkaline fructose 1,6-bisphosphatase, and NAD(P)-glyceraldehyde-3-phosphate dehydrogenase of the cells of D. lab lab were checked but none was affected by the added ammonium salts even after prolonged incubation. At certain concentrations, ammonium ions abolished the light activation of NADP-glyceraldehyde-3-phosphate dehydrogenase and alkaline fructose 1,6-bisphosphatase in isolated chloroplasts from dark-adapted Vigna leaves without interfering with the basal dark activity of these enzymes. Based on these observations, a possible mechanism of action of NH₄⁺ in regulating the photosynthetic carbon flow is postulated.