Role of the testa epidermis in the leakage of intracellular substances from imbibing soybean seeds and its implications for seedling survival

Abstract

The effects of testa epidermal cracks on imbibition induced soybean (Glycine max [L.] Merr.) seed damage, as measured by the leakage of intracellular constituents, and on subsequent seedling survival were examined. Testa epidermal cracking increased with increasing seed surface area and this was caused by periods of dry seed hydration as short as 1 min followed by air drying. As compared to slow imbibition in germination paper, rapid imbibition of seeds caused by submersion in distilled H2O for 6 h at 25°C greatly increased the leakage of intracellular substances during imbibition and greatly decreased the survival of seeds with intact testae, testa epidermal cracks, and without testae. Seeds that were aerated during rapid hydration germinated as poorly and leached solutes as profusely as seeds not aerated. This indicates that anoxia is not a significant factor in rapid hydration effects on soybean seeds. Seeds with testa epidermal cracks had higher levels of leakage of intracellular substances and lower rates of seedling survival than seeds with intact testae. This was true regardless of rate of hydration. Testa tissues other than the epidermis had no effect on seedling survival after slow imbibition but greatly decreased seed leakage during rapid imbibition and increased subsequent survival. Studies with individual seeds indicated that the leakage of intracellular substances during rapid hydration is greatest from seeds that are killed or severely injured by imbibition or that are dead before imbibition, regardless of testa condition. These results indicate that soybean seed testa epidermis is extremely important in protecting the seed from injury by rapid and slow hydration and in maintaining seed viability.