Physiological changes in maize seed (Zea mays L.) quality associated with genotype, drying temperature and aging

摘要

A limited number of harvest days coupled with threats of early frost often require harvesting seeds at high moisture and artificially drying to approximately 120 g H2O kg-1 fw (fresh weight) moisture content for safe storage. Further, a substantial amount of seed is carried over in storage for more than one year. These practices often result in a loss of seed quality. This study was conducted to determine the effects of drying temperature and aging on seed quality parameters in A632 and B73 hybrids differing in sensitivity to drying temperature and to identify the physiological and biochemical parameters or processes associated with drying and/or aging damage. Compared to 35°C, drying at 45°C reduced seedling vigor of B73 harvested at 450 g H2O kg-1 fw moisture whereas A632 was relatively tolerant. Greater reductions in seedling vigor for both hybrids were found in axes from seeds following four years of storage. Reductions in ATP, EC and GTP levels were demonstrated in both fresh and aged axes from seeds harvested at 450 g H2O kg-1 fw moisture and dried at 45°C. Oxygen and (1-14C)- or (6-14C)-glucose uptake, and the evolution of 14CO2 from (1-14C)- or (6-14C)-glucose in axes from seeds harvested at 450 g H2O kg-1 fw moisture was reduced by high temperature drying or high temperature drying followed by four years of storage. Electron microscopy of axis tissues showed high temperature drying followed by storage resulted in a developmental delay and damage to mitochondria as shown by the presence of electronic dense aggregates in conserved mitochondrial matrix. Loss of cell membrane integrity during high temperature drying or drying followed by storage was also reflected by the increased individual seed conductivity values. Both a developmental delay in mitochondria and the loss of cell membrane integrity contribute to the reductions in metabolic activity. Insufficient energy production due to the decline in metabolic activity further results in a reduction in seedling vigor.