Role of gamma radiation in changing phytotoxic effect of elevated level of ozone in Trifolium alexandrinum L. (Clover)

The present study was conducted on clover (Trifolium alexandrinum L. cv Wardan), to investigate the effect of ambient and elevated (ambient +10 ppb O-3) ozone (O-3) on plants grown in open top chambers (OTCs) germinated from gamma (gamma) irradiated seeds. Dry seeds were subjected to irradiation with 0, 5, 10 and 20 krad doses of gamma rays from Co-60 source. Dose dependent differential responses were observed on growth and biomass, photosynthetic pigments, metabolites, antioxidative defense system of plant. Growth parameters and biomass of plants were severely affected under elevated O-3 with increasing radiation doses, except, 5 krad which showed a reverse trend of response. Photosynthetic pigments and total soluble proteins were also reduced with higher dose of gamma radiation and elevated O-3. Reactive oxygen species formation and membrane damage increased significantly to different extents. Plants grown from seeds irradiated with low dose (5 krad) of gamma irradiation depicted more induction of antioxidants (enzymatic and non-enzymatic) than higher doses suggesting their high ameliorative capability against elevated O-3. Principal component analysis has also confirmed that plants grown from 5 krad gamma irradiated seeds performed better against O-3 depicting reduction in negative effect against elevated O-3. The experimental findings evidently showed that 5 krad gamma radiations altered the O-3 induced stress and thus minimized the loss in biomass of the test plant.