The influence of increased solar UV-B radiation on magnesium-deficient cowpea seedlings: Changes in the photosynthetic characteristics

The influence of increased solar UV-B radiation on the photosynthetic characteristics in cowpea seedlings (Vigna unguiculata) grown at optimal (Mg-s) and low (Mg-d) 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 Mg-d 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 P-N also followed a typical inhibitory pattern as seen in photochemical activities. Concentrations of several chloroplast proteins in trifoliate leaves were significantly reduced by Mg-d 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 Mg-d seedlings, no major difference was noted for combined stress.