Inhibition of light-induced stomatal opening by allyl isothiocyanate does not require guard cell cytosolic Ca2+ signaling.

Eiji Okuma,Yoshimasa Nakamura,Md Tahjib-Ul-Arif,Mohammad Saidur Rhaman,Wenxiu Ye,Eigo Ando,Yoshiyuki Murata,Toshinori Kinoshita,Ian Dodd

doi:10.1093/jxb/eraa073

Abstract

The glucosinolate–myrosinase system is a well-known defense system that has been shown to induce stomatal closure in Brassicales. Isothiocyanates are highly reactive hydrolysates of glucosinolates, and an isothiocyanate, allyl isothiocyanate (AITC), induces stomatal closure accompanied by elevation of free cytosolic Ca2+ concentration ([Ca2+]cyt) in Arabidopsis. It remains unknown whether AITC inhibits light-induced stomatal opening. This study investigated the role of Ca2+ in AITC-induced stomatal closure and inhibition of light-induced stomatal opening. AITC induced stomatal closure and inhibited light-induced stomatal opening in a dose-dependent manner. A Ca2+ channel inhibitor, La3+, a Ca2+chelator, EGTA, and an inhibitor of Ca2+ release from internal stores, nicotinamide, inhibited AITC-induced [Ca2+]cyt elevation and stomatal closure, but did not affect inhibition of light-induced stomatal opening. AITC activated non-selective Ca2+-permeable cation channels and inhibited inward-rectifying K+ (K+in) channels in a Ca2+-independent manner. AITC also inhibited stomatal opening induced by fusicoccin, a plasma membrane H+-ATPase activator, but had no significant effect on fusicoccin-induced phosphorylation of the penultimate threonine of H+-ATPase. Taken together, these results suggest that AITC induces Ca2+ influx and Ca2+ release to elevate [Ca2+]cyt, which is essential for AITC-induced stomatal closure but not for inhibition of K+in channels and light-induced stomatal opening.

Highlights

Stomata, surrounded by pairs of guard cells, function as the main window for gas exchange and are in the frontline for defense against microbe invasion in the phyllosphere
These results suggest that allyl isothiocyanate (AITC) induces Ca2+ influx and Ca2+ release to elevate [Ca2+]cyt, which is essential for AITC-induced stomatal closure but not for inhibition of K+in channels and light-induced stomatal opening
Since many ITCs including AITC are volatile, the results imply that ITCs function as signals for plant–plant interaction (Sobahan et al, 2015).To elucidate the mechanism of AITC-induced stomatal closure, it has been shown that AITC induces production of reactive oxygen species (ROS) and elevation of free cytosolic Ca2+ concentration ([Ca2+]cyt) in guard cells (Khokon et al, 2011)

Summary

Introduction

Stomata, surrounded by pairs of guard cells, function as the main window for gas exchange and are in the frontline for defense against microbe invasion in the phyllosphere. Isothiocyanates (ITCs) are highly reactive hydrolysates of glucosinolates and an ITC, allyl isothiocyanate (AITC), induces stomatal closure in Arabidopsis (Khokon et al, 2011; Hossain et al, 2014). Since many ITCs including AITC are volatile, the results imply that ITCs function as signals for plant–plant interaction (Sobahan et al, 2015).To elucidate the mechanism of AITC-induced stomatal closure, it has been shown that AITC induces production of reactive oxygen species (ROS) and elevation of free cytosolic Ca2+ concentration ([Ca2+]cyt) in guard cells (Khokon et al, 2011). Pharmacological studies indicate that ROS are essential for AITC-induced stomatal closure (Hossain et al, 2014; Sobahan et al, 2015)

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