Ethanol breaks dormancy of the potato tuber apical bud

Growing potato tubers or freshly harvested mature tubers have a dormant apical bud. Normally, this dormancy is spontaneously broken after a period of maturation of the tuber, resulting in the growth of a new sprout. Here it is shown that in in vitro-cultured growing and maturing tubers, ethanol can rapidly break this dormancy and re-induce growth of the apical bud. The in vivo promoter activity of selected genes during this secondary growth of the apical bud was monitored, using luciferase as a reporter. In response to ethanol, the expression of carbohydrate-storage, protein-storage, and cell division-related genes are rapidly down-regulated in tuber tissue. It was shown that dormancy was broken by primary but not by secondary alcohols, and the effect of ethanol on sprouting and gene expression in tuber tissue was blocked by an inhibitor of alcohol dehydrogenase. By contrast, products derived from alcohol dehydrogenase activity (acetaldehyde and acetic acid) did not induce sprouting, nor did they affect luciferase reporter gene activity in the tuber tissue. Application of an inhibitor of gibberellin biosynthesis had no effect on ethanol-induced sprouting. It is suggested that ethanol-induced sprouting may be related to an alcohol dehydrogenase-mediated increase in the catabolic redox charge [NADH/(NADH+NAD+)].