Changes in the content of pigments and rate of photosynthesis in Azolla microphylla Kaulf. fronds were measured during growth under solar and ultraviolet-C (UV-C) supplemented solar radiation. Maximum content of total chlorophyll (Chl) was observed on the 13th day (termination of the experiment) of treatment in both control and treated plants. The treated plants had significantly lower total Chl and carotenoid contents than the control plants during the 1st day of growth. After the 4th day of exposure to UV-C supplemented solar radiation, the Chl and carotenoids accumulation increased in treated plants, so that the pigment concentration in the treated fronds was nearer to the control values after the 13th day of treatment. Significant increase in UV absorbing pigments, anthocyanins, and flavonoids was observed at the 13th day of treatment. In spite of the roughly similar photosynthetic pigment concentration, the photosynthetic activity measured as the rate of electron transport at photosystem 2 was only 65 % of the control values after 13 d of UV-C exposure. and M. Jayakumar ... [et al.].
The influence of increased solar UV-B radiation on the photosynthetic characteristics in cowpea seedlings (Vigna unguiculata) grown at optimal (Mgs) and low (Mgd) Mg levels were studied. Both higher UV-B and Mgd treatments caused significant drops of photochemical activities and net CO2 uptake rates (PN). Yet the UV-B-induced decrease in the photosynthetic efficiency was lesser in Mgd seedlings. The leaf Chl a fluorescence measurements proved that after receiving an enhanced UV-B radiation these seedlings showed a significant enhancement in their variable parts. The PSM oscillation of slow fluorescence kinetics was remarkably altered by both treatments. The PN also followed a typical inhibitory pattern as seen in photochemical activities. Concentrations of several chloroplast proteins in trifoliate leaves were significantly reduced by Mgd treatment and unaffected by the other two treatments. Whereas the contents of 43-47 kDa polypeptides in primary leaves were markedly reduced with a maximal effect in Mgd seedlings, no major difference was noted for combined stress. and A. Premkumar, G. Kulandaivelu.