Gamma radiation effect on Populus nigra assimilatory pigments

The influence of low intensity gamma radiation on the photosynthesis in young poplar saplings was studied. Black poplar (Populus nigra) was chosen due to its ecological importance, as fast growing tree species with many hybrids, in the frame of a polluted environment. Assimilatory pigments in the leaves of irradiated saplings were assayed using standard spectrophotometric method in acetone extract. Series of five saplings formed the experimental samples. Chlorophyll a and chlorophyll b levels appeared as diminished in exposed samples in comparison to the controls. Linear regression was established in every case, the line slope showing the higher effect in chlorophyll b. Carotene pigments presented a slight increasing tendency in the exposed samples. Assimilatory pigment sum was shown to be affected by the same decreasing tendency. Student t-test was applied (two tailed, pair type) to reveal statistical significance of observed modifications. Though not very deep, the modifications induced by exposure to gamma radiation of low intensity (comparable to the local atmospheric variations, caused by both natural and artificial sources) represent putative inhibitory factors in young plant photosynthesis. The main mechanism of radiation action seems to be water radiolysis, triggering peroxide cascade, generally producing toxic products for the cell metabolism. Nevertheless, living cell ability to repair some damages caused by external stress could be revealed in the present case by the enhancing tendency of the carotenes which sustain photosynthesis as secondary pigments. (authors)