Carbon monoxide mitigates salt-induced inhibition of root growth and suppresses programmed cell death in wheat primary roots by inhibiting superoxide anion overproduction

Abstract

In our experiments, treatment of wheat seedling roots with varying concentrations of NaCl caused the inhibition of primary root growth in a dose-dependent manner, which was consistent with the progressive DNA laddering in the primary root tips. Upon 100, and 200 mM NaCl stress, the increase of carbon monoxide (CO) release and heme oxygenase (HO) activity was observed. By contraries, treatment with 400 mM NaCl is otherwise, that the result displays a decreasing tendency. Besides DNA laddering, 200 mM NaCl treatment exhibited the induction of other programmed cell death (PCD) associated with phenomenon in the primary root tips, such as TUNEL staining, nuclear condense and deformation. Further, HO's catalytic product CO was able to dose-dependently mitigate 200 mM NaCl-induced inhibition of root growth and delay PCD. These effects were prevented strongly by incubation with DETC (a Cu/Zn-SOD inhibitor), and differentially influenced by Tiron (a scavenger of superoxide anion) and apocynin (an inhibitor of NADPH oxidase). Meanwhile, 50% CO aqueous solution inhibited the overproduction of superoxide anion, NADPH oxidase activities and corresponding transcript, and enhanced superoxide dismutase (SOD) activity, Mn-SOD and Cu/ Zn-SOD transcript. Taken together, the results suggested that CO might be involved in plant tolerance against salinity stress, and its alleviation of PCD and inhibition of root growth was related to the decrease of superoxide anion overproduction partially via up-regulation of SOD and down-regulation of NADPH oxidase expression.