H+-ATPases Regulated by Auxin and ABA Mediate Acid Growth of Soybean Embryonic Axis During Germination

Soybean seeds (Glycine max) are of great economic and nutritional importance due to their high oil and protein content. Seed germination is an essential process that influences crop yield and quality. The seed embryo resumes growth when it imbibes, which induces the expression of genes related to cell expansion. The role of acid growth in the embryonic axis during germination is not well characterized. Thus, the aim of this study was to verify the contribution of acid growth in the soybean embryonic axis germination. Acid growth is mediated by the acidification of extracellular medium due to the action of H+-ATPases, which activate expansins. We found that the expression of expansins was significantly increased throughout the germination. The expression of H+-ATPases was significantly increased at 3 and 24 h after imbibition (HAI), with major pumping activity at 24 HAI. The auxin and ABA signaling cascades during soybean germination suggest that these hormones are involved with the regulation of H+-ATPase in germinating soybean. To verify the influence of auxin and ABA on H+-ATPase functioning during germination, we treated seeds with IAA, 2,4D, ABA, and ATPase inhibitor, and germinated them in purple agar medium. We observed that IAA, 2,4D, and ABA affected H+-ATPase functioning, by delaying or inhibiting soybean germination. Our results indicate the role of acid growth controlled by H+-ATPase and its regulators—auxin and ABA—in the soybean embryonic axis during germination.