Sucrose Accumulation and Internodal Soluble Invertase Isoenzymes in Plant and Ratoon Crops of Sugarcane

Abstract

Accumulation pattern of sucrose and hexoses in relation to activities of invertases in stem tissue of plant and ratoon crops of CoJ88 (mid maturing variety) has been investigated at different physiological stages of cane growth. At each stage of crop development, sucrose content was relatively more in ratoon crop than plant crop, whereas the reducing sugar content was relatively less in ratoon crop than plant crop. The activity of soluble acid invertase in stem was found to be highest at stem elongation stage and declined thereafter in both plant and ratoon crops. The activity of soluble acid invertase (pH 5.5) was markedly lower in ratoon crop as compared to plant crop at each stage of crop development. Higher level of sucrose and lower level of acid invertase in ratoon crop indicates higher sink strength and better juice quality of ratoon crop. The activity of neutral invertase (pH 7.0) increased with the advancement of the cane growth in both the crops. Three isoenzymes of soluble acid invertase in plant crop namely A-I, A-II and A-III and two isoforms of this enzyme in ratoon crop namely A-I and A-II were identified at stem elongation stage. Neutral invertase isoenzyme was not detected in both the crops at this stage. At maturation stage, one acid invertase isoform i.e. A-I was obtained in both the crops along with four neutral invertase isoenzymes in plant crop i.e. N-I, N-II, N-III and N-IV and two isoforms of this enzyme in ratoon crop i.e. N-I and N-II. These invertase isoforms differed with respect to their Km and Vmax values. From the temperature effect on Km and Vmax values, the energy of activation (Ea) and enthalpy change (∆H) of invertase isoenzymes were calculated at stem elongation and maturity stages and compared among isoenzymes of plant and ratoon crops in relation to sucrose accumulation.