Plant volatiles regulate the activities of Ca2+-permeable channels and promote cytoplasmic calcium transients in Arabidopsis leaf cells

Abstract

A variety of plant species emit volatile compounds in response to mechanical stresses such as herbivore attack. Although these volatile compounds promote gene expression leading to anti-herbivore responses, the underlying transduction mechanisms are largely unknown. While indirect evidence suggests that the cytoplasmic free Ca2+ concentration ([Ca2+]c) plays a crucial role in the volatile-sensing mechanisms in plants, these roles have not been directly demonstrated. In the present study, we used Arabidopsis leaves expressing apoaequorin, a Ca2+-sensitive luminescent protein, in combination with a luminometer, to monitor [Ca2+]c transients that occur in response to a variety of volatile compounds and to characterized the pharmacological properties of the increase in [Ca2+]c. When leaves were exposed to volatiles, [Ca2+]c was transiently raised. The [Ca2+]c increases induced by acyclic compounds were disrupted by Ruthenium Red, a potential plasma-membrane and endo-membrane Ca2+-permeable channel inhibitor, but not by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), an extracellular Ca2+-chelator, suggesting that acyclic compounds promote Ca2+-release from intracellular stores. On the other hand, the electrophilic compound (E)-2-hexenal promoted Ca2+-influx via ROS production by natural oxidation at the aquarius phase. In a gpa1-2 mutant lacking a canonical Gα subunit, the [Ca2+]c transients induced by all tested volatiles were not attenuated, suggesting that G-protein coupled receptors are not involved in the volatile-induced [Ca2+]c transients in Arabidopsis leaves.