Comparative analysis of some biochemical responses of three indica rice varieties during polyethylene glycol-mediated water stress exhibits distinct varietal differences

Extensive investigation into plant response and adaptation to diverse osmotic stresses like high salt/dehydration/low temperature, involving a broad spectrum of cellular physiological and biochemical changes, is essential to unravel intrinsic mechanism to mitigate against such stresses. In our previous communications, we conducted biochemical analyses of indica rice varieties, subjected to exogenous salt/abscisic acid-mediated oxidative stress. The aim of this study was to compare differential biochemical responses of the salt-sensitive (IR-29), salt-tolerant (Pokkali) and aromatic (Pusa Basmati or PB) rice varieties during polyethylene glycol (PEG)-induced dehydration stress. The greater susceptibility of IR-29 and PB, to water scarcity, was reflected by the higher toxic Na⁺ and putrescine accumulation, considerable decrease in (reduced/oxidized) glutathione, maximal increment in protease activity and greater downregulation of nitrate reductase activity. On the other hand, Pokkali appeared to suffer lesser damages as evidenced from much lower endogenous Na⁺ but higher K⁺, Ca²⁺ and Mg²⁺ accumulation, registering the highest levels of osmolytes like glycinebetaine and higher polyamines (spermidine and spermine) accounting to improved relative water content, higher (reduced/oxidized) glutathione, maximal induction of the enzyme phenylalanine ammonia-lyase and practically unhindered nitrate reductase activity, following PEG treatment. The highest induction of sugars and proline in IR-29 and PB probably played the osmoprotective/antioxidative functions, enabling to a certain extent to heighten their lipoxygenase inhibition or H₂O₂ scavenging potential, more than Pokkali, to ward off oxidative damages and sustain survival under critical dehydrated situations. Thus, the salt-tolerant Pokkali also showed prominent dehydration-tolerance properties, whereas the aromatic rice PB, almost identical in their biochemical responses to IR-29, showed greater sensitivity to PEG-mediated water deficit.