Effect of Drought Stress on Photosynthetic Efficiency of Glycine max L. Plants

The current study is carried out to investigate the response of photosynthetic efficiency of soybean plant
to drought stress extended for six days. Plants exposed to water deficit, growth inhibition and chlorophyll
content losses increased. All drought treatments resulted in distinct physiological and biochemical effects
on photosynthesis in a duration dependent manner. Relatively high inhibitory effect was observed
throughout the experimental period, six days drought almost totally crushed the dynamics of chlorophyll
accumulation in soybean leaves. A marked decrease in the ratio of chlorophyll a/b occurred in 6 days
drought treated soybean leaves. Thus, a significant reduction in content of aminolaevulinic acid (ALA)
was observed after 6 days drought treatment compared with relatively less decrease after 2 and 4 days
drought treatments. The maximal photochemical efficiency of soybean leaves subjected to drought
treatment, decreased sharply in Fv/Fm values to approximately half of the corresponding control at the
end of drought duration. The photosynthetic strength of the plant indicated by Fv/F0 values showed that,
soybean leaves exposed to drought were significantly decreased especially at the end of experimental
period. Drought stressed soybean leaves showed a highly significant increase in H2O2 and MDA contents
reached about 4.5 fold increase relative to control after 6 days drought treatment. This means that drought
caused depression of photosynthetic efficiency of soybean leaves in a period-dependent manner.