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

Sreeharsha, Rachapudi Venkata, Mudalkar, Shalini, Sengupta, Debashree, Unnikrishnan, Divya K., Reddy, Attipalli Ramachandra
Photosynthesis research 2019 v.139 no.1-3 pp. 425-439
Cajanus cajan, biomass, carbon dioxide, carbon dioxide enrichment, carbon dioxide fixation, drought, food crops, free amino acids, fructose, gas exchange, glucose, leaves, photosynthesis, pigeon peas, protective effect, reactive oxygen species, sucrose, water content, water stress
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.