Physiological Responses of Gamma-Irradiated Onion Bulbs during Storage

Abstract

The present study aimed to evaluate the effects of different doses ofgamma radiation on some physiological characters of oniongenotypes and the expression of PAL gene in the best interaction ofgamma irradiation dose and onion genotype treatment. To this aim,four onion genotypes (White-Qom, White-Neyshabour, Red-RidgeLump, 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) andperoxidase (POD) were investigated. In addition, the expression ofPAL gene in the best interaction of gamma irradiation dose andonion genotype treatment was assessed. The result indicated thatPOD activity was increased by most of the gamma irradiationlevels; however, the protein content and PAL activity weredecreased. Moreover, dry matter content was found to be highlygenotype-dependent. A linear regression (R2= 0.82) between PALactivity and gamma irradiation levels, was observed. PAL activitydecreased with increasing in gamma irradiation level, while theexpression rate of PAL gene was not significantly changed betweenirradiated and non-irradiated control, indicating that the radiationmight not have direct effects on the gene regulatory elements. Theseresults suggest that gamma irradiation could reduce the PAL activitypossibly by controlling abiotic stress sources such as fungal andbacterial stresses.