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

Abstract

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 Mg(d) treatments caused significant drops of photochemical activities and net CO2 uptake rates (P(N)). 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 there 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.