Water potential of cherry tomato (Lycopersicon esculentum Mill.) placenta and seed germination in response to desiccation during fruit development

Cherry tomato (Lycopersicon esculentum Mill.) seeds harvested from fruits at four stages of development [2, 4, 6 and 8 weeks after flowering (WAF)] were washed (1% HCl) and germinated after 72 h of desiccation at 20degreesC, and 76%, 49% or 12% RH. Seed alpha-amylase activity was determined at each stage of development and correlated with seed germination. Desiccation at 76% and 49% RH had no significant effect on the germination of seeds at 4, 6 and 8 WAF, whereas it improved germination of seeds at 2 WAF Low RH (12%) significantly reduced seed germination at all stages of development. There was a positive correlation (r = 0.68, P less than or equal to 0.05) between germination and alpha-amylase activity during seed development. Scanning electron microscopy also revealed a correlation between starch grain occurrence in the endosperm and alpha-amylase activity. Placenta water potential decreased with fruit and seed maturation, and correlated negatively with improved seed germination and alpha-amylase activity. Promotion of seed germination by desiccation in developing cherry tomato seeds was lost 4 weeks prior to mass maturity (80 +/- 3% seed water content and -2.3 +/- 0.1 MPa placenta water potential). It is proposed that the water potential differential between the placenta and the seeds influences alpha-amylase activity and germination behaviour during development.