Sulfur metabolism and drought stress tolerance in plants

Abstract

Complex processes on all levels, transcripts, proteins, and metabolites, are involved in drought stress tolerance, but in a different way from species to species. Recent evidences lead to the assumption that sulfur not only acts like other macronutrients, such as nitrate and phosphate, but that an increasing demand for sulfate during metabolic adaptation reactions to drought stress reflects specific roles of sulfur-containing compounds. The biosynthesis of osmolytes and osmoprotectants, such as choline-O-sulfate and polyamines, is increased, the levels of the main antioxidant, the tripeptide glutathione, and its precursor cysteine are elevated, and 3'-phosphoadenosine 5'-phosphate (PAP), produced in secondary sulfur assimilation as a byproduct in sulfation reactions from 3'-phosphoadenosine 5'-phosphosulfate (PAPS), was recently suggested to act in retrograde signaling in drought. Data available on the protection against abiotic stress is summarized and discussed, in particular, the compartment-specific importance of glutathione in connection with the subcellular accumulation of ROS during drought stress. There is evidence that a significant co-regulation of sulfur metabolism and the biosynthesis of the drought hormone abscisic acid (ABA) operates to ensure sufficient cysteine availability for aldehyde oxidase maturation. In addition, the role of glucosinolates (Gls) in drought stress will be delineated, as the drought-induced accumulation of aliphatic Gl is related to ABA formation whereas indole and aromatic Gl decreased during drought stress, suggesting that these Gls are not involved in the plants’ response to drought.