1. Biology Department, Area 9, University of York, PO Box 373, York YO10 5YW, UK
2. Biology Department, Lancaster Environment Centre, University of Lancaster, Lancaster LA1 4YQ, UK
3. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK

Correspondence to: Dale Sanders¹ Correspondence and requests for materials should be addressed to D.S. (Email: ds10@york.ac.uk).
Sequence of A. thaliana Col-0 TPC1 is deposited in GenBank under accession number AF360372.

Abstract

Cytosolic free calcium ([Ca²⁺]_cyt) is a ubiquitous signalling component in plant cells¹. Numerous stimuli trigger sustained or transient elevations of [Ca²⁺]_cyt that evoke downstream stimulus-specific responses. Generation of [Ca²⁺]_cyt signals is effected through stimulus-induced opening of Ca²⁺-permeable ion channels that catalyse a flux of Ca²⁺ into the cytosol from extracellular or intracellular stores. Many classes of Ca²⁺ current have been characterized electrophysiologically in plant membranes². However, the identity of the ion channels that underlie these currents has until now remained obscure. Here we show that the TPC1 ('two-pore channel 1') gene of Arabidopsis thaliana encodes a class of Ca²⁺-dependent Ca²⁺-release channel that is known from numerous electrophysiological studies as the slow vacuolar channel^{3, 4, 5}. Slow vacuolar channels are ubiquitous in plant vacuoles, where they form the dominant conductance at micromolar [Ca²⁺]_cyt. We show that a tpc1 knockout mutant lacks functional slow vacuolar channel activity and is defective in both abscisic acid-induced repression of germination and in the response of stomata to extracellular calcium. These studies unequivocally demonstrate a critical role of intracellular Ca²⁺-release channels in the physiological processes of plants.

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