Possible involvement of mechanosensitive Ca²⁺-permeable channels in cytoplasimic Ca²⁺-increases induced by changes in gravity vector.

Abstract

Plants regulate their morphology in response to gravity, known as gravitropism. In the process of gravitropism, gravity sensing forms the critical earliest event and gravistimulation will be transduced into certain intracellular signals. Previous studies showed that changes in gravity vector induced transient increases in the cytoplasmic calcium concentration ([Ca²⁺]_c). To clarify the molecular mechanisms for the [Ca²⁺]_c-increase induced by gravistimulation, we measured [Ca²⁺]_c in Arabidopsis thaliana seedlings expressing aequorin using various inhibitors. The [Ca²⁺]_c-increase was reversibly inhibited by potential mechanosensitive Ca²⁺-permeable channel blockers (La³⁺, Gd³⁺) an endomembrane Ca²⁺-channel blocker (ruthenium red) and a Ca²⁺-chelator (BAPTA), suggesting that it arose from Ca²⁺-influx via mechanosensitive Ca²⁺-permeable channels in the plasma membrane and Ca²⁺-release from intracellular Ca²⁺-stores. Furthermore, the [Ca²⁺]_c-increase was attenuated by actin-disrupting drugs (latrunculin B, cytochalasin B) but not by microtubule-disrupting drugs (oryzalin, nocodazole), suggesting that actin filaments were partially involved in the activation of the Ca²⁺-permeable channels.