Relationships between ultrastructure of embryo cells and biochemical variations during ageing of oat (Avena sativa L.) seeds with different moisture content

This experiment was designed to determine the relationship between the ultrastructure of the embryo cells and the changes in antioxidant enzymatic activities and lipid peroxidation in oat (Avena sativa L.) seeds with different moisture contents (4, 10 and 16 %) that were aged for 0, 8, 16, 24, 32 and 40 days in 45 degrees C. The results showed that the declining in the germination percentage and integrity of cell ultrastructure in oat aged seeds were presented during the aged process, and these changes would be enhanced by the higher moisture content. There were consequent changes for biochemical reactions and lipid peroxidation exhibited. For oat seeds with 4 and 10 % moisture content, SOD and CAT were much more sensitive than APX at the early stages of imbibition after mild ageing, the activities of SOD, CAT, APX and MDHAR at 4 h of imbibition decreased significantly (P < 0.05) after being aged from 32 to 40 days. On the contrary, MDA and H2O2 contents both did not increase further. Upon imbibition the activities of DHAR and GR increased after mild ageing, declined after further ageing and maintained a stable level after ageing from 24 to 40 days at those moisture levels. Both activities were higher after ageing at 4 % moisture content than at 10 %. The decline in integrity of ultrastructural cells was related with accumulation of H2O2 during seed ageing, and favoured by the decrease of SOD, CAT, APX and MDHAR activities after imbibition. The activities of antioxidant enzymes and contents of MDA and H2O2 in oat seeds with 16 % moisture content all gradually decreased after ageing from 8 to 40 days, also the ultrastructure of embryo cells was severely damaged. Its ultrastructure was destroyed much more quickly in the seeds with higher moisture content. The level of moisture content could accelerate the seed deterioration, and mitochondrial damages were probably the main reason for oat seed ageing. However, the activities of antioxidant enzymes were the key factor to repair the damage from lipid peroxidation and to maintain the integrity of cell ultrastructure for oat aged seeds during imbibition.