Physiological Responses of Gamma-Irradiated Onion Bulbs during Storage

The present study aimed to evaluate the effects of different doses of  gamma radiation on some physiological characters of onion  genotypes and the expression of PAL gene in the best interaction of  gamma irradiation dose and onion genotype treatment. To this aim,  four onion genotypes (White-Qom, White-Neyshabour, Red-Ridge- Lump, and Red-Ray-Corrugated) irradiated at 0, 30, 60, 90, 120,  and 150 Gy. After four months of storage (at 10-15 °C and 70%  relative humidity), the effects of gamma rays on the dry matter  (DM), protein content, phenylalanine ammonia lyase (PAL) and  peroxidase (POD) were investigated. In addition, the expression of  PAL gene in the best interaction of gamma irradiation dose and  onion genotype treatment was assessed. The result indicated that  POD activity was increased by most of the gamma irradiation  levels; however, the protein content and PAL activity were  decreased. Moreover, dry matter content was found to be highly  genotype-dependent. A linear regression (R2= 0.82) between PAL  activity and gamma irradiation levels, was observed. PAL activity  decreased with increasing in gamma irradiation level, while the  expression rate of PAL gene was not significantly changed between  irradiated and non-irradiated control, indicating that the radiation  might not have direct effects on the gene regulatory elements. These  results suggest that gamma irradiation could reduce the PAL activity  possibly by controlling abiotic stress sources such as fungal and  bacterial stresses.