Physiological effects of glycinebetaine on gamma-irradiated stressed fenugreek plants

Abstract

Irradiation stress adversely affects plant growth and development. The radio protective activity by glycinebetaine in plants has not been reported, and its mechanism has not been known. Gamma rays at doses 0.0, 25, 50, 100, and 150 Gray (Gy) when applied pre-sowingly to dry seeds of fenugreek from a cobalt source (60Co) with strength of 500 Ci and the dose rate of 0.54 Gy/min significantly reduced chlorophyll content, total protein, photosynthetic efficiency (14CO2-fixation), total dry weight, the accumulation of reducing, non-reducing and total soluble sugars in comparison with un-irradiated control. It also significantly repressed the activities of hydrolytic enzymes (α-amylase and invertase), the carboxylating enzyme (ribulose-1,5-bisphosphate-carboxylase/oxygenase) in the developed fenugreek plants. Soaking irradiated seeds with glycinebetaine (50 mM) for 24 h partially alleviated the depression effects of irradiation in these parameters. γ-irradiation treatment increased significantly H2O2 content. Presoaking irradiated seeds with GB decreased significantly the H2O2 level. The magnitude of the reversal decreased with increasing the irradiation dose. γ-irradiation induced a significant decrease in the level of nucleic acids (DNA and RNA) accompanied by a corresponding induction of hydrolytic activities of DNase and RNase in the developed plants in comparison with un-irradiated control. Those changes were more significant at higher γ-ray doses. Post-treatment of irradiated seeds with GB partially alleviated the adverse effects of radiation. It significantly increased nucleic acid levels and repressed the activities of DNase and RNase. The protective role played by glycinebetaine was more significant at lower γ-ray doses. Pretreatment of seeds with GB may play an effective role in the radio-repair mechanism.