Species differences in seed water status during seed maturation and germination

Maize (Zea mays L., cv. B73 x Mo17), wheat (Triticum aestivum L., cv. Clark), and soybean (Glycine max L. Merrill, cv. Elgin 87) were grown in the field and seed samples were collected at frequent intervals for the determination of seed fresh and dry weight and water potential of excised embryos (maize and wheat) and axes (soybean). Seed water concentration declined during seed development and the concentration at physiological maturity (PM, maximum seed dry weight) was highest in soybean (550-590 g kg(-1) FW), lowest in maize (326-377 g kg(-1)) and intermediate in wheat (437 g kg(-1)). The embryo/axis water potential was relatively constant during much of seed filling before decreasing rapidly as the seeds approached PM and there was little variation among species (soybean -1.52 to -1.63 MPa, maize -1.61 to -1.99 MPa and wheat -1.66 MPa). Seed water concentration when 10% of the seeds germinated (radicle greater than or equal to 3 mm) was highest in soybean (514 g kg(-1)), lowest in maize (332 g kg(-1)) and intermediate in wheat (345 g kg(-1)) while the water potential of the embryo/axis varied from -2.07 to -2.20 MPa across the three species. There was Little variation in the water potential of the embryo/axis among species at the end of seed growth (PM) or at the beginning of germination. This similarity is consistent with the suggestion that the water status of critical seed structures may play a regulatory role in seed growth and germination.