ANTI-OXIDATIVE ENZYMES AND VIGOR OF MAIZE SEEDS INDUCED BY HYDROPRIMING

PC’ maize seeds subjected to either hydropriming or artificial accelerated aging were investigated. The relationship between germination and lipid peroxidation (indicated by malondialdehyde (MDA) content was monitored. The changes in germination, anti-oxidative enzyme activities, and hydrogen peroxide (H2O2) during hydropriming for 6-30 h were determined. The germination of the seeds treated by artificial accelerated aging for 4-8 days was gradually decreased. The MDA content was not significantly different from the control seeds. In contrast, germination of seeds hydroprimed beyond 24-30 h significantly declined with a reduction of MDA content. Therefore, the ambiguous MDA content might need to be intensively monitored during accelerated aging treatment, imbibition, or the redrying processes. H2O2 decreased germination of seeds hydroprimed up to 24 h. Catalase (CAT) and superoxide dismutase (SOD) appeared to be the main antioxidative enzymes involved in germination loss of hydroprimed seeds. The activities of ascorbate peroxidase (APX) and peroxidase (POD) did not correspond to the changes in hydroprimed seed germination. When the hydroprimed seeds were subjected to stress conditions, the greatest germination observed was with the seeds primed for 6 h. Therefore, the activities of SOD and CAT could partly correspond to induce hydroprimed seed vigor. In contrast, the reduction in hydroprimed seed germination corresponded to the decline of SOD and CAT activities, and probably involved H2O2. INTRODUCTION Priming techniques are known to considerably improve seed quality by enhancing germination rates and seedling uniformity (Bradford, 1986). There are three types of priming comprising hydropriming, osmotic priming, and matrix priming. Hydropriming is the easiest and cheapest compared with the other methods. Moreover, there is no risk from chemical compounds because the samples are only placed in water and dried back to their original moisture content. Germination and vigor are enhanced by an appropriate priming time and the method reported in sunflower (Bailly et al., 2000) and tomato (ELAraby and Hegazi, 2004). Hydropriming was also observed to improve seedling emergence in rice (Farooq et al., 2010), and to decrease the germination time and increase the seedling vigor in wheat (Basra et al., 2003). Both hydroand osmo-priming improved mean emergence time and final germination in sunflower (Hussain et al., 2006). Harris et al. (1999) reported that primed maize seeds showed better crop establishment and growth, earlier flowering, and greater yields. Metabolic events inducing vigor of primed seeds are protein synthesis (Wahid et al., 2008), DNA repair (Balestrazzi et al., 2011), and/or mRNA expression (Gurusinghe et al., 2002). Moreover, a greater activity of anti-oxidative enzymes was reported to increase the emergence percentage in primed sweet corn seeds (Chiu et al., 2002). The enhanced peroxidase (POD) and catalase (CAT) activities caused by priming were related to lower malondialdehyde (MDA) content, leading to increased chilling tolerance in maize Proc. IC on Postharvest Pest & Disease Mgt. Exporting Hort. Crops Eds.: C. Hale and P. Jitareerat Acta Hort. 973, ISHS 2013