itric oxide triggers a concentration-dependentdifferential modulation of superoxide dismutase(FeSOD and Cu/ZnSOD) activity in sunflowerseedling roots and cotyledons as an early andlong distance signaling response to NaCl stress

摘要

Dark-grown sunflower (Helianthus annuusL.) seedlings exhibit modulation of total superoxide dismutase (SOD,EC1.15.1.1) activity in roots and cotyledons (10,000g supernatant) in response to salt stress (NaCl, 120 mM) through adifferential, zymographically detectable, whole tissue activity of FeSOD and Cu/ZnSOD. Confocal laser scanningmicroscopic imaging (CLSM) has further shown that NaCl stress significantly influences differential spatial distribution ofCu/ZnSOD and MnSOD isoforms in an inverse manner. Dual action of nitric oxide (NO) is evident in its crosstalk withFeSOD and Cu/ZnSOD in seedling roots and cotyledons in control and NaCl?stress conditions. Cu/ZnSOD activity in theroots of 2 d old NaCl?stressed seedlings is enhanced in the presence of 125–1000mM of NO donor (sodiumnitroprusside, SNP) indicating salt sensitivity of the enzyme activity. Quenching of endogenous NO by cPTIO treatment(500, 1000mM) lowers FeSOD activity in roots (-NaCl). Cotyledons from control seedlings show an upregulation ofFeSOD activity with increasing availability of SNP (125–1000mM) in the Hoagland irrigation medium. Quenching of NOby cPTIO provides evidence for an inverse correlation between NO availability and FeSOD activity in seedlingcotyledons irrespectiveof NaCl stress. Variable response due to NO on SOD isoforms in sunflower seedlings reflects itsconcentration-dependent biphasic (pro- and antioxidant) nature of action. Differential induction of SOD isoforms by NOindicates separate intracellular signaling pathways (associated with their respective functional separation) operative inseedling roots as an early salt stress mechanism and in cotyledons as an early long-distance NaCl stress sensingmechanism.