Abstract
We have reported that submergence decreases the osmotic concentration of cell sap by decreasing the levels of sugars and amino acids, thereby inhibiting elongation growth in azuki bean epicotyls. The present study was undertaken to elucidate the mechanisms by which submergence decreases the levels of sugars and amino acids in epicotyls by examining the effect of submergence on the activities of proton symport, which is involved in the unloading of these osmotica. The levels of protons in apoplastic solutions of epicotyls grown underwater were significantly lower than those grown in air. Also, under water, the levels of ATP in epicotyl cells decreased by half. These results suggest that submergence decreases activities of proton pumps by decreasing the levels of ATP in epicotyl cells. Such a decrease in activities of proton pumps may be involved in inhibition of the unloading of both sugars and amino acids into epicotyl cells under submergence.
