Invertase-mediated Interconversion of Sucrose and Hexoses During Their Translocation in Growing Pearl Millet Plant

Abstract

Metabolism of free sugars, particularly sucrose, in various plant tissues enroute from leaf sheaths to grains in growing pearl millet was studied. With the enhancement in growth, the levels of both reducing and non-reducing sugars declined in middle and basal leaf sheaths but increased in flag leaf sheath towards plant maturity. In sheath, wall-bound invertase was more active than soluble invertases and the activities of all these enzymes rose towards maturity. Besides hexoses and sucrose, some fructose polymers were also detected in the internodes. In contrast with internodes, where the levels of total free sugars declined till around anthesis, in penultimate node their levels continuously increased, but attained peak values at 65 CAS in middle- and basal nodes. In both these tissues, arriving sucrose encounters invertases but in nodes wall-bound invertase appears to be the pivotal one. On feeding (U-¹⁴C)-sucrose to the detached ear-heads a large proportion of ¹⁴C was incorporated into hexoses alone in peduncle and rachis. PCMBS and HgCl₂ inhibited the metabolism of sucrose supplied to peduncle and rachis pointing to the involvement of invertases in sucrose cleavage in these organs. Through the regulated operation of invertase(s), the nodes seem to maintain a controlled flow of free sugars from source to sink tissue.