Inhibition of beta-amylase activity, starch degradation and sucrose formation by indole-3-acetic acid during banana ripening

In order to observe the effect of indole-3-acetic acid (IAA) on carbohydrat e metabolism, unripe banana (Musa acuminata AAA, cv. Nanicao) slices were i nfiltrated with the hormone and left to ripen under controlled conditions, The climacteric respiration burst was reduced by the action of IAA, and sta rch degradation and sucrose formation were delayed. Sucrose synthase (SuSy, EC 2.4.1.13) and sucrose-phosphate synthase (SPS, EC 2.4.1.14) activities and transcript levels were not affected. indicating that prevention of sucr ose accumulation was not related to sucrose-metabolizing enzymes. Impairmen t of sucrose synthesis could be a consequence of lack of substrate, since s tarch degradation was inhibited. The increase in activity and transcript le vel of beta -amylase was delayed. indicating that this enzyme could be impo rtant in starch-to-sucrose metabolism in bananas and that it might be, at l east partially, controlled at the transcriptional level. This is the first report showing that IAA can delay starch degradation, possibly affecting th e activity of hydrolytic enzymes such as beta -amylase (EC 3.2.1.2).