Differential leakage of substances from two soybean genotypes during imbibition is influenced by seed coat pore characteristics

Soybean (Glycine max [L.] Merrill) seed coat and embryo damage is the major cause of excessive electrolyte leakage during imbibition. No studies have examined the influence of seed coat pore morphology on differential leakage between soybean genotypes. The objective of this study was to characterize substances leaking from two soybean genotypes [Ohio Food Grade 1 (OFG1) and an experimental line, 9544544] which differ in seed coat pore characteristics. Mature (10 to 11% water content, fresh mass) field produced seeds were observed for seed coat damage and pore characteristics under light and scanning electron microscopes following 7 to 10 d storage in a cold room (4 degrees C, 47% RH). Leachates from seeds in Petri dishes lined with moistened germination blotting paper were examined at 2 h intervals until 30 h imbibition for substances including metabolites, UV absorbing substances and malate dehydrogenase activity. An increase in leakage of all substances with time was observed until radicle protrusion. The pattern of leakage was the same in both genotypes, but OFG1 consistently showed higher leakage than 9544544. Although a general decline in leakage of all substances occurred after radicle protrusion, suggesting an increased metabolite mobilization during seedling growth, the pattern of leakage was not linear. In conclusion, this study demonstrates that during soybean seed imbibition 1) most compounds examined leaked more followed by a reduction in leakage after radicle protrusion, 2) a differential leakage in soluble carbohydrates was observed where free cyclitols > reducing sugars > oligosaccharides > galactosyl cyclitols and 3) these leakage characteristics may be attributed to genotype and seed coat pore characteristics. It is also suggested that osmolality could be a useful measure of seed leaching.