Chlorophyll (Chl) biosynthesis intermediate compounds (like protoporphyrin-IX, Mg-protoporphyrin methyl ester and protochlorophyllide), Chl {a + h), heme, cytochrome P-450 (cyt P-450) and lipid peroxide levels as well as the activities of superoxide dismutase, catalase and lipoxygenase were studied in selenium treated mung beán seedlings. Chl (a -t- b) content and heme levels were decreased with a concomitant accumulation of all the three porphyrins studied. Se treatment enhanced the lipoxygenase activity and correspondingly increased lipid peroxide levels. Se inhibited both the antioxidant enzymes catalase and superoxide dismutase in a dose- dependent manner. However, cyt P-450 levels were enhanced under Se exposure. Hence the inhibitory effect of Se on Chl synthesis is not only by acting on constituent biosynthetic enzymes but also through lipoxygenase-mediated lipid peroxide levels and inhibition of antioxidant defence component systém.
The treatment of green algae Chlorococcum lobatum with the herbicide BASTA containing phosphinothricin lead to a significant decrease in the level of peak M2 of the chlorophyll fluorescence induction curve. This agrees with the suggestion that glutamine synthetase activity affects this region of the induction curve.
The treatment of maize {Zea mays L.) seedlings (8-d-old) with 5 and 10 gM Cd^'*’ for 24 and 48 h caused a decrease in ffesh and dry mass, in the contents of chlorophylls and carotenoids, rates of net carbon dioxide uptake (Pyj) and transpiration (E), water use efficiency (Pyj/E = WUE) and stomatal conductance (gg).
Chlorophyll fluorescence kinetics was used to investigate the effect of 1,4-dithiothreitol (DTT) on the distribution of excitation energy between photosystem 1 (PS1) and photosystem 2 (PS2) in soybean leaves under high irradiance (HI). The maximum PS2 quantum yield (Fv/Fm) was hardly affected by the presence of DTT, however, photon-saturated photosynthesis was depressed distinctly. Photochemical efficiency of open PS2 reaction centres during irradiation (Fv'/Fm') was enhanced by about 30-40 % by DTT treatment, whereas photochemical quenching (qP) was depressed by about 40 % under HI. DTT treatment caused a 30 % decrease in allocation of excitation energy to PS1 under HI and a 20 % increase to PS2. An obvious shift in the balance of excitation energy distribution between photosystems was observed in DTT-treated leaves. Though high excitation pressure (1 - qP) resulted from DTT treatment, non-photochemical quenching (qN) was lower. DTT completely inhibited the formation of zeaxanthin and also distinctly depressed the state transition (qT). The shift in the balance of excitation distribution between the two photosystems induced by DTT was mainly due to the enhancement of excitation energy capture by PS2 antenna and the inhibition of state transition. It might be the shift in the balance between the two photosystems that mainly induced the depression of photosynthesis. Thus, to keep high utilization efficiency of absorbed photon energy, it is necessary to maintain the balance of excitation distribution between PS2 and PS1. and C.-D. Jiang ... [et al.].
The rates of net photosynthesis (P^). respiration and growth of Lemna gibba L. were measured as fiinctions of tiine across ranges of temperature, irradiance and carbon dioxide concentrations. on an area basis increased with temperature up to 30 °C but decreased dramatically within a few hours of exposure to elevated CO2, when reported on a dry mass basis. Reductions in the apparent quantum efRciency, photosynthetic capacity and the affinity of ribulose-l,5-bisphosphate carboxylase/oxygenase for CO2 were observed for plants grown at elevated CO2. Starch concentration was not significantly affected by elevated CO2. Although elevated temperature increased metaboiic activity, it only partíally ídleviated the inhibition of P^. L. gibba exhibits a characteristic C3-type response to elevated CO2 and the methodology described is usefiil for fiirther elucidating the mechanism of photosynthetic acclimation to elevated CO2.
2-(alkoxycarbonylmethylthio)-6-aminobenzothiazoles (ACABTs) inhibited oxygen evolution in spinacb cbloroplasts. Tbe inhibitory activity of ACABTs increased witb tbe increasing lipopbilicity of tbe molecule. Tbe probable site of ACABT action on oxygen evolving complex is suggested.
Isoxaflutole [5-cyclopropyl-4-(2-methylsulphonyl-4-trifluromethylbenzoyl)isoxazole] is a new preemergence herbicide for broad-spectrum weed control in maize. The effect of isoxaflutole on chlorophyll (Chl) and carotenoid (Car) biosynthesis was investigated in cucumber (Cucumis sativus L.) cotyledons. Etiolated tissue was incubated with 5 mM isoxaflutole for 24 h and irradiated (60 μmol m-2 s-1). The irradiation for 3 h did not reduce Chl a, Chl b, and Car contents, but after a 28-h irradiation the contents of Chl a and Car decreased by 35 and 15 %, respectively, and the content of Chl b increased by 24 %. Increasing the concentration of isoxaflutole beyond 5 mM resulted in reduction of Chl a (71 %), Chl b (20 %), and Car (31 %) contents. Similarly, increase in irradiance from 60 to 180 μmol m-2 s-1 resulted in larger reduction of Chl and Car contents. Exogenously supplied 5-aminolevulinic acid did not reverse the isoxaflutole-inhibited Chl synthesis, whereas an exogenously supplied homogentisic acid lactone reversed the inhibition of pigment synthesis due to isoxaflutole. and S. Kushwaha, P. C. Bhowmik.
Leaf senescence can be induced by numerous factors. In order to explore the relationship between root respiration and leaf senescence, we utilized different types of phloem girdling to control the root respiration of Alhagi sparsifolia and its physiological response. Our results showed that both girdling and inhibition of root respiration led to a decline of stomatal conductance, photosynthesis, transpiration rate, chlorophyll (Chl) a, Chl b, carotenoid (Car) content, Chl a/b, Chl/Car, water potential, and Chl a fluorescence, as well as to an increase of abscisic acid (ABA), proline, and malondialdehyde content in leaves and to upregulation of senescence-associated gene expression. Our present work implied that both inhibition of root respiration and girdling can induce leaf senescence. In comparison with phloem girdling, the leaf senescence caused by inhibition of root respiration was less significant. The reason for girdling-induced senescence was ABA and carbohydrate accumulation. Senescence induced by inhibition of root respiration occurred due to leaf water stress resulting from inhibition of water absorption., G.-L. Tang, X.-Y. Li, L.-S. Lin, Y. Hu, F.-J. Zeng., and Obsahuje seznam literatury
Inner structure of isolated intact chloroplasts was observed for the first time by a method of laser scanning microscopy at the temperature of liquid nitrogen at 77 K. The microscope, based on gradient index optics, has a maximum resolution of 440 nm at the wavelength of 650 nm. Chloroplasts were excited into the Q-band of chlorophyll b by a krypton laser line at 647.6 nm and fluorescence was detected using two different interference filters. The 680 nm interference filter detects the regions where photosystem (PS) 2 mainly occurs, the 730 nm interference filter detects domains with predominant location of PS1. Since PS1 occurs mainly in stroma lamellae, whereas PS2 occurs mainly in grana regions we were able to view the structure of thylakoid membrane in isolated intact chloroplast that is the closest to in vivo state. and F. Vácha ... [et al.].