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 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).
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.