High irradiance (HI) effects on xanthophyll cycle pigments (XCP) and activity of violaxanthin de-epoxidase (VDE) in terms of de-epoxidation index (DEI) were studied in soybean calli. The calli from the hypocotyl segments of 5-d seedlings were induced on a solid (1.1 % agar) MS medium (pH 5.8) supplemented with 4.52 μM 2,4-dichloro-phenoxyacetic acid, 2.32 μM kinetin, and 3 % sucrose. After a 30 d cultivation, the green calli were irradiated for 24 h with "white light" (HI, 1 300 μmol m-2 s-1) and VDE was isolated from the photosystem 2 (PS2) particles. In the control (0 h irradiation) callus, the reaction of PS2 particles with VDE in the presence or absence of Tween 20 resulted in the decrease of VIO content and the increase of ZEA content. In the 24 h HI-callus, the reaction of PS2 particles in the absence of VDE led to the decrease of VIO and ANT contents and increase of ZEA content. In the control, DEIs in the presence of VDE with or without 0.1 %Tween 20 (1.04 and 1.06, respectively) were significantly higher than the DEI (0.76) in the absence of VDE. In the HI-callus, DEIs in the presence of VDE with or without 0.1 %Tween 20 (0.98 and 0.96, respectively) were similar to that (1.03) in the absence of VDE. and D. M. Pandey ... [et al.].
Sodium chloride salinity had enhanced the photosynthetic rate, photosystem 2 activity and chlorophyll synthesis in isolated leaf cells of Ipomoea pescaprae up to 200 mM NaCl. The salt treated plants did not show any shift in the mode of photosynthesis.
Aging induced loss of chlorophyll (Chl), carotenoids (Car) and proteins was studied in suspensions of isolated wheat chloroplasts incubated in the light or dark. Faster rate of pigment loss in the light was due to photodestruction of pigments. Compared to Chl, a greater loss of Car in the light was due to photoprotective action of Car towards Chl resulting in its own destruction. The total protein content was lowered more in the light than in dark. Soluble proteins of chloroplasts declined by 36 %, whereas membrane proteins showed a loss of only 8 % after 6 d of light incubation.
Quaternary ammonium salts, besides having an inhibitory effect which was studied by Králová eí al. (1992), exhibited at low concentrations a stimulating effect upon the oxygen evolution rate in spinách chloroplasts. The stimulation is caused by changes in arrangement of thylakoid membranes due to a detergent-like effect of the compoimds.
The stimulating effect of 1-alkyl-1-ethyl piperidinium bromides on the oxygen evolution rate in spinách chloroplasts was caused by rearrangement of thylakoid membrane.
The thermoluminescence signals from leaflets of the same pea plant varied gradually according to their developmental stage. The AG emission, due to a back flow of electrons towards photosystem 2 (PS2) along a cyclic/chlororespiratory pathway, was stronger in mature leaves than in the growing ones. These age-related variations could be explained by a higher capacity of cyclic electron flow in mature leaves.