Carbohydrates and Sucrose Metabolizing Enzymes in the Leaves of Vigna mungo Genotypes as Influenced by Elevated CO۲ Concentration

Effect of different CO۲ concentrations on sucrose metabolizing enzymes and on carbohydrate metabolism was studied for eight blackgram (Vigna mungo L. Hepper) genotypes grown in open top chambers under ambient (۳۸۰ µmol mol-۱) vs. elevated CO۲ (۵۵۰ and ۷۰۰ µmol mol-۱) levels. The higher acid invertase activity over neutral invertase indicated the major role of acid invertase in sucrose breakdown. Higher acid invertase activity over Sucrose Synthase (SuSy) suggested the major role of invertase in sucrose breakdown and sucrolysis. Sucrose Phosphate Synthase (SPS) activity did not match with sucrose pool sizes in mature leaves and rather varied among genotypes. Plants exposed to higher CO۲ concentrations showed higher starch and sucrose contents as compared with those exposed to ambient CO۲. Leaf starch content being found several-folds higher than sucrose throughout the study indicated its major role in regulating assimilate partitioning. Increase in glucose vs. fructose concentrations for genotypes grown under elevated CO۲ conditions ranged from ۲۰ to ۹۰% and from ۱۰ to ۱۴۰%, respectively. The hexoses/sucrose ratio for elevated CO۲ concentration was approximately ۰.۸-۱.۶, however for ambient CO۲ content it approximately amounted to unity. Genotypes IC۴۳۶۷۲۰, IC۵۱۹۸۰۵, IC۳۴۳۹۵۲, and IC۲۸۲۰۰۹ with low hexose/sucrose ratio representing high CO۲ assimilation along with high sucrose formation indicated better tolerance to elevated CO۲ for carbon partitioning and carbohydrate metabolism. The up-regulation of leaf carbohydrate metabolizing enzymes of low hexose/sucrose as well as low sucrose/starch ratios for the genotype IC۴۳۶۷۲۰ (as compared with other genotypes) improved its photosynthetic capability which coupled with its better efficiency of carbon partitioning (indicative of better acclimation to elevated CO۲) could prove beneficial to its growth and productivity in the future change of climatic conditions.

Keywords:

Enzymes , Invertase , Soluble sugars , Sucrose metabolism , Up-regulation