Glucose escalates PSII activity, dynamics between anabolic and catabolic pathways, redox and elemental status to promote the growth of Brassica juncea

Abstract

Glucose (Glc), a monosaccharide, accumulates in plants as a minor product of photosynthesis as well as a breakdown product of sucrose. Glucose regulates various physiological processes in plants; therefore, the present experiment was carried out to assess its role in mustard plants. Seeds of Brassica juncea were sown into pots filled with soil and farmyard manure. Glc treatments were provided as a foliar spray at the 25-day stage of growth for 5 days consecutively. Plants were sampled at the 30, 45 and 60-day stage of growth to assess various biological and biochemical parameters. Glc promoted the growth of plants in the following order of concentration: 30 mM > 20 mM > 40 mM > 10 mM > 50 mM > 0 mM. Glc treatment augmented photosynthetic efficiency by elevating primary photochemistry, stomatal movement and conductance, internal CO2 concentration, transpiration rate, and net photosynthetic rate leading to enhanced synthesis of carbohydrate. A decline in photosynthesis at higher sugar accumulation was prevented by its utilization during respiration. Moreover, the activity of photosynthetic (rubisco and carbonic anhydrase) and respiratory enzymes (hexokinase, succinate dehydrogenase, and fumarase) also increased, which suggests that Glc-mediated growth promotion depends on the dynamics between anabolic and catabolic pathways. Generation of reactive oxygen species, antioxidant enzyme activity, and elemental status, which affect the rate of photosynthesis, were also regulated in Glc-treated plants.