Abstract:
Effect of different CO2 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 (380 µmol mol-1) vs. elevated CO2
(550 and 700 µmol mol-1) 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 CO2
concentrations showed higher starch and sucrose contents as compared with
those exposed to ambient CO2
. 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 CO2
conditions ranged from 20 to 90% and from 10 to 140%, respectively. The
hexoses/sucrose ratio for elevated CO2
concentration was approximately 0.8-1.6, however
for ambient CO2
content it approximately amounted to unity. Genotypes IC436720,
IC519805, IC343952, and IC282009 with low hexose/sucrose ratio representing high CO2
assimilation along with high sucrose formation indicated better tolerance to elevated CO2
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 IC436720 (as compared with other genotypes) improved its
photosynthetic capability which coupled with its better efficiency of carbon partitioning
(indicative of better acclimation to elevated CO2
) could prove beneficial to its growth and
productivity in the future change of climatic conditions.
Keywords: Enzymes, Invertase, Soluble sugars, Sucrose metabolism, Up-regulation
