Drought-induced guard cell signal transduction involves sphingosine-1-phosphate

Abstract

Stomata form pores on leaf surfaces that regulate the uptake of CO2 for photosynthesis and the loss of water vapour during transpiration. An increase in the cytosolic concentration of free calcium ions ([Ca2+]cyt) is a common intermediate in many of the pathways leading to either opening or closure of the stomatal pore. This observation has prompted investigations into how specificity is controlled in calcium-based signalling systems in plants. One possible explanation is that each stimulus generates a unique increase in [Ca2+]cyt, or 'calcium signature', that dictates the outcome of the final response. It has been suggested that the key to generating a calcium signature, and hence to understanding how specificity is controlled, is the ability to access differentially the cellular machinery controlling calcium influx and release from internal stores. Here we report that sphingosine-1-phosphate is a new calcium-mobilizing molecule in plants. We show that after drought treatment sphingosine-1-phosphate levels increase, and we present evidence that this molecule is involved in the signal-transduction pathway linking the perception of abscisic acid to reductions in guard cell turgor.

Sphingosine-1-phosphate (S1P) mediates darkness-induced stomatal closure through raising cytosol pH and hydrogen peroxide (H2O2) levels in guard cells in Vicia faba

“…Lipid extraction was performed as described by Ng et al [14]. Relying on derivatization with NDA, S1P was quantified by high-performance liquid chromatography (HPLC) according to the methods of He et al [50] with some modifications.…”

“…Further, A. thaliana insertion mutants with disrupted in ∆4-desaturase genes lack any detectable ∆4-unsaturated LCBP, such as S1P, and display no perturbation to ABA-induced stomatal closure [8], suggesting that S1P is not involved in stomatal closure caused by ABA in A. thaliana. However, ∆4-unsaturated sphingolipids are abundant in some plant species, such as Glycine max and Lycopersicon esculentum [16,17], whereas research has been limited to the role of S1P in ABA signaling in A. thaliana and C. communis guard cells [5,8,14,15]. It remains unknown whether S1P mediates stomatal closure in response to other internal or external factors, including darkness.…”

“…It regulates many biological processes by binding to a family of receptors that are part of the specific cell surface G-protein-coupled receptors (GPCRs) and also serves as an intracellular second messenger in eukaryotes to regulate Ca 2+ homeostasis, cell growth, and survival [913]. In higher plants, S1P has been shown to be a new calcium-mobilizing molecule and involved in abscisic acid (ABA)-induced stomatal closure in Commelina communis [14] and Arabidopsis thaliana [5]. Worrall et al [15] have reported that the stomata of an A. thaliana LCBK mutant are less sensitive than wild type to ABA, whereas the stomata of LCBK-overexpression plants are more sensitive.…”

A new class of lipid desaturase central to sphingolipid biosynthesis and signalling

“…Analogous phosphorylated LCBs in yeast, such as dihydrosphingosine and phytosphingosine, have also been implicated (by reverse genetics) in stress responses to abiotic shock [3]. More recently, a role for S-1-P has been shown in drought stress and stomatal guard cell closure in plants, linking the phosphorylated lipid-derived signal to this Ca 2+ -mediated process [4]. Although sphingosine (the precursor of S-1-P) is present in trace amounts in higher plants [5], the levels of S-1-P were shown to increase under drought conditions.…”

“…The plant alternative oxidase is a 32 kDa homodimer that branches from the main respiratory chain at the level of the ubiquinone pool and catalyses the four-electron reduction of oxygen to water. The resultant free energy is lost as heat and oxygen reduction is not coupled to proton pumping [4][5][6][7][8]. Apart from its role in thermogenesis, the biological function of alternative oxidase is not fully understood.…”