Effects of gamma irradiation on biochemical and antioxidant defense system in wheat (Triticum aestivum L.) seedlings

This investigation was carried out to determine the effect of gamma radiation on germination and physiological characteristics of wheat seedlings. For this purpose soaked grains were irradiated with 60Co at dose of 0.5, 1, 2, and 5 KGy. The germination percentages as well as the growth parameters of wheat seedling (shoot and root fresh and dry weights, and shoot length) were significantly decreased by increasing the irradiation dose. Non-enzymatic Amadori products content was increased in germinating grains in response to the increase of ?-irradiation dose. Increasing of gamma irradiation dose lead to the decrease of the relative water content (RWC) and the membrane integrity (MI) of wheat leaves. There was a gradual decline in leaf chlorophyll content with increasing irradiation dose. In contrast, there was a significant increase of carotenoids content and Carot./Chl.a + Chl.b ratio. Gamma rays induced a distortion of the pattern of grana and thylakoids, dilation of nuclear membrane and chromatin materials as well as a gradually degeneration of mitochondria. Antioxidant enzymes (superoxide dismutase, and peroxidase) activities were significantly increased in wheat leaves with increasing gamma doses, whereas catalase activity was decreased. Total phenolics and flavonoids content were significantly increased in wheat leaves in response to ?-irradiation which was associated with a significant increase of PAL activity. There was a significant increase in superoxide radicals, malondialdehyde content, and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging ability in accordance with high doses of ?-radiation.