Mitigation of drought-induced oxidative damage by enhanced carbon assimilation and an efficient antioxidative metabolism under high CO2 environment in pigeonpea (Cajanus cajan L.)

Abstract

In the current study, pigeonpea (Cajanus cajan L.), a promising legume food crop was assessed for its photosynthetic physiology, antioxidative system as well as C and N metabolism under elevated CO₂ and combined drought stress (DS). Pigeonpea was grown in open top chambers under elevated CO₂ (600 µmol mol^-1) and ambient CO₂ (390 ± 20 µmol mol^-1) concentrations, later subjected to DS by complete water withholding. The DS plants were re-watered and recovered (R) to gain normal physiological growth and assessed the recoverable capacity in both elevated and ambient CO₂ concentrations. The elevated CO₂ grown pigeonpea showed greater gas exchange physiology, nodule mass and total dry biomass over ambient CO₂ grown plants under well-watered (WW) and DS conditions albeit a decrease in leaf relative water content (LRWC). Glucose, fructose and sucrose levels were measured to understand the role of hexose to sucrose ratios (H:S) in mediating the drought responses. Free amino acid levels as indicative of N assimilation provided insights into C and N balance under DS and CO₂ interactions. The enzymatic and non-enzymatic antioxidants showed significant upregulation in elevated CO₂ grown plants under DS thereby protecting the plant from oxidative damage caused by the reactive oxygen species. Our results clearly demonstrated the protective role of elevated CO₂ under DS at lower LRWC and gained comparative advantage of mitigating the DS-induced damage over ambient CO₂ grown pigeonpea.

Keywords: Amino acids; Antioxidative system; Cajanus cajan; Drought stress; Elevated CO2.