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.     

Pigment ligation to proteins of the photosynthetic apparatus in higher plants

Ligation of pigments to proteins of the thylakoid membrane is a central step in the assembly of the photosynthetic apparatus in higher plants. Because of the potentially damaging photooxidative activity of chlorophylls, it is likely that between their biosynthesis and final assembly, chlorophylls will always be bound to protein complexes in which photooxidation is prevented by quenchers such as carotenoids. Such complexes may include chlorophyll carriers and/or membrane receptors involved in protein insertion into the membrane. Many if not all pigment-protein complexes of the thylakoid are stabilised towards protease attack by bound pigments. The major light-harvesting chlorophyll a/b protein (Lhebl,2) folds into its native structure in vitro only when it binds pigments. Pigment-induced folding may also be a general feature of chlorophyll-carotenoid proteins of the photosynthetic apparatus.     

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.     

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     

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.     

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.     

Primary photosynthetic processes in Heliobacterium chlorum at 15K

Absorbance changes induced by 25-ps laser flashes were measured in membranes of Heliobacterium chlorum at 15 K. Absorbance difference spectra, measured at various times after the flash showed negative bands in the Q_y region at 812, 793 and 665 nm. The first of these bands was attributed to the formation of excited singlet states of a long-wavelength form of antenna bacteriochlorophyll g (BChl g 808). Absorbance changes of shorter wavelength absorbing antenna BChls g were at least an order of magnitude smaller, indicating rapid excitation energy transfer (i.e. within the time resolution of the apparatus) from these BChls to BChl g 808. Excited BChl g 808 showed a bi-exponential decay with time constants of 50 and 200 ps. The bands at 793 and 665 nm may be attributed to the primary charge separation and reflect the photooxidation of the primary electron donor P-798 and photoreduction of a primary electron acceptor absorbing near 670 nm, presumably a BChl c or Chl a-like pigment. The bleaching of this pigment reversed with a time constant of 300 ps at 15 K and of 800 ps at 300 K. This indicates that electron transfer from the primary to the secondary electron acceptor is approximately 2.5 times faster at 15 K than at room temperature.Abbreviations BChl bacteriochlorophyll - FWHM full width at half maximum - P-798 primary electron donor - Tris tris(hydroxymethyl)amino methane     

Ferredoxins in the evolution of photosynthetic systems from anaerobic bacteria to higher plants

Ferredoxins are present in a wide range of organisms, from the primitive anaerobic bacteria to higher plants and animals, where they function in diverse electron transfer processes. They are relatively small proteins with molecular weights of 6000 to 12000, contain 2–8 Fe atoms and an equivalent amount of inorganic sulphur per molecule, and they transfer electrons at low redox potentials.Anaerobic bacteria, like the clostridia, contain 8 Fe ferredoxins with a peptide chain of 55 amino acid residues which could be arranged in two similar halves suggesting the evolution of the molecule, from a prototype of 26 amino acid residues, by gene duplication. Since these ferredoxins contain a high predominance of certain amino acids detected in meteorites and lunar samples and synthesized under simulated prebiotic environment and since iron and sulphus could be incorporated easily into the apoprotein in anaerobic conditions, the ferredoxin molecule could have been formed in the early periods of the origin of life. From the available chemical compositions and amino acid sequences of various ferredoxins the following evolutionary scheme can be postulated: anaerobic bacteriagreen photosynthetic bacteriared photosynthetic bacteriasulphate reducing bacteriablue-green algaegreen algae and higher plants.Special Symposium on Photochemistry and the Origins of Life, Sixth International Congress on Photobiology, Bochum, Germany.