Effect of enhanced solar uv-b (280-320nm) radiation on photosynthetic electron transport activity of some plants at different growing seasons

Depletion ozone layer and fluctuation of UV-B radiation on the earth’s surface is a most common phenomenon for last few decades. The potential impact of solar UVB radiation studied in three legume plants (Black gram, Cluster bean, Green gram) in field condition at two different seasons like summer and winter. The first season is (summer) coupled with dry weather and high temperature (35-40oC) and the second (monsoon) with rainy and slightly low temperature (28-32oC). The ambient UV-B levels in both seasons vary only marginally. The chlorophyll fluorescence induction kinetics are used to study the photosynthetic electron transport activity of the both ambient and UVB -treated plants.So the fast fluorescence transients give an overall picture of the early electron transport reactions. Enhanced UV-B radiation did not affect Fo values in all the three species. In Cluster bean, the UV-B radiation significantly affected the Fv/Fm ratio in both the season. Such reduction was very high in monsoon season than summer. This indicates a reduction in PSII efficiency and possible inhibition of energy transfer within the PSII reaction center. In Black gram UV-B radiation increased the Fv/Fm ratio in both the season. Whereas in green gram no change was noticed.This could be due to high proportion of light harvesting matrices per reaction centre