Antioxidant systems in sunflower (Helianthus annuus L.) seeds as affected by priming

Priming treatment of sunflower (Helianthus annuus L., cv Briosol) seeds for 7 days at 15 degrees C with a polyethylene glycol solution at -2.0 MPa strongly improved their subsequent germination at 15 degrees C on water. This stimulatory effect of priming remained after drying back the seeds at 20 degrees C for 3 days. Malondialdehyde (MDA) and activities of superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) were measured in control unprimed seeds, primed seeds, seeds primed then dried, and after 3 and 6 hours of imbibition of control and dried primed seeds in order to determine whether the cell antioxidant systems were involved in the beneficial effect of priming. The osmotreatment resulted in a strong increase in SOD and CAT activities but did not markedly affect MDA and GR activity. Following the 3 days of drying, MDA increased and the enzyme activities became similar to those measured in dry unprimed seeds, although the stimulatory effect of priming on germination remained. Imbibition of control dry seeds was associated with an increase in MDA and a decrease in CAT and GR activities, whereas reimbibition of dried primed seeds resulted in a decrease in MDA and an increase in SOD, CAT and GR activities. Isoform patterns on native gels showed no difference between treated (priming with or without subsequent drying) and control seeds for SOD (7 isoforms) and GR (5 isoforms), but the osmotreatment did induce a second isoform of CAT. The results obtained indicate that the CAT isoform pattern might be used as an indicator of the priming treatment that promotes germination. Involvement of the antioxidant systems in seed vigour is discussed.