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 chara cteristics 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 rat es (PN) Yet the UV-B-induced decrease in the photosynthetic efficiency was lesser in Mg-d seedlings. The leaf Chl a fluorescence measurements proved t hat after receiving an enhanced UV-B radiation these seedlings showed a sig nificant enhancement in their variable parts. The PSM oscillation of slow f luorescence kinetics was remarkably altered by both treatments. The P-N als o 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 tre atments. Whereas the contents of 43-47 kDa polypeptides in primary leaves w ere markedly reduced with a maximal effect in Mg-d seedlings, no major diff erence was noted for combined stress.