Changes in soluble carbohydrates, lipid peroxidation and antioxidant enzyme activities in the embryo during ageing in wheat grains

Soluble sugar contents and antioxidant enzyme activities were measured in the embryo of wheat (Triticum aestivum L., cv Charger) seeds throughout their storage under two conditions (45 °C and 100% relative humidity (RH), and 30 °C and 75% RH) to investigate whether grain deterioration during ageing was related to lipid peroxidation resulting in a decrease in the efficiency of the antioxidant defence system, and in changes in sugar metabolism. The half-viability period (P50) was only 6 d at 45 °C and 100% RH against about 3.75 months at 30 °C and 75% RH. However, sensitivity of grains to accelerated ageing carried out at 45 °C and 100% RH increased during their pre-storage at 30 °C and 75% RH. Loss of grain viability at 45 °C and 100% RH was associated with an accumulation of H2O2 which was concomitant with a progressive decrease in catalase (CAT) and superoxide dismutase (SOD) activities, and with an increase in glutathione reductase (GR) activity. However, malondialdehyde content did not change, suggesting that there was no lipid peroxidation during such an ageing. In return, ageing of grains at 30 °C and 75% RH was not associated either with strong changes in CAT, SOD and GR activities or with an accumulation of H2O2. When there was no correlation between CAT, SOD and GR activities and seed viability, there was a linear correlation between CAT activity and seed vigour evaluated by the T50 during ageing at 45 °C and 100% RH. Sugar metabolism in wheat embryo largely depended on ageing conditions. Loss of grain viability at 45 °C and 100% RH was associated with a marked decrease in sucrose (Su) and a slight increase in raffinose (Ra), and subsequently in the Ra/Su ratio. At 30 °C and 75% RH, seed ageing was associated with an increase in both sugars but with no strong increase in Su/Ra ratio. Our results suggest that ageing was associated with various mechanisms depending on the conditions of ageing, and that accelerated ageing at 45 °C and 100% RH was not the only model to consider in order to understand the mechanisms involved in seed deterioration.