Drought-Enhanced Xylem Sap Sulfate Closes Stomata by Affecting ALMT12 and Guard Cell ABA Synthesis

Abstract

Water limitation of plants causes stomatal closure to prevent water loss by transpiration. For this purpose, progressing soil water deficit is communicated from roots to shoots. Abscisic acid (ABA) is the key signal in stress-induced stomatal closure, but ABA as an early xylem-delivered signal is still a matter of debate. In this study, poplar plants () were exposed to water stress to investigate xylem sap sulfate and ABA, stomatal conductance, and sulfate transporter () expression. In addition, stomatal behavior and expression of ABA receptors, drought-responsive genes, transcription factors, and were studied after feeding sulfate and ABA to detached poplar leaves and epidermal peels of Arabidopsis (). The results show that increased xylem sap sulfate is achieved upon drought by reduced xylem unloading by PtaSULTR3;3a and PtaSULTR1;1, and by enhanced loading from parenchyma cells into the xylem via PtaALMT3b. Sulfate application caused stomatal closure in excised leaves and peeled epidermis. In the loss of sulfate-channel function mutant, At, sulfate-triggered stomatal closure was impaired. The QUAC1/ALMT12 anion channel heterologous expressed in oocytes was gated open by extracellular sulfate. Sulfate up-regulated the expression of , a key step of ABA synthesis, in guard cells. In conclusion, xylem-derived sulfate seems to be a chemical signal of drought that induces stomatal closure via QUAC1/ALMT12 and/or guard cell ABA synthesis.

An Overview of Hazardous Impacts of Soil Salinity in Crops, Tolerance Mechanisms, and Amelioration through Selenium Supplementation

“…Therefore, selenate and small amounts of SeMet and selenomethionine Se-oxide (SeOMet) have been considered important Se species in the plant xylem [116]. The family of aluminum-activated malate transporter (ALMT) genes are thought to be responsible for carrying selenate in the shoot xylem sap [117], whereas, following the delivery of selenate from root to shoot via the xylem, the members of the Sulfate transporters (SULTRs) family take it to leaf cells [118], where it is stored in the cell vacuoles [114]. In addition to inorganic Se, plant uptake of organic Se is known to occur and has been reported at much higher rates (20-100 fold greater) than the uptake of inorganic species [108].…”

Small Pores with a Big Impact

“…Malcheska et al (2017) describe a potential role for sulfate, delivered via the xylem in poplar, as a signal that affects anion channel gating of the guard cells. Jalakas et al (2017) revisit the role of the ERA1 farnesyl transferase to show that its actions extend well beyond abscisic acid signaling.…”

Plastid Sulfate Transporters Open Doors to Abiotic Stress Resistance

“…1). Despite the limited nutrient uptake from the soil during drought, SO 4 22 quickly accumulates in the xylem sap, is transported toward green tissues, is imported into the chloroplasts, and ultimately causes an increase in ABA and stomatal closure (Malcheska et al, 2017;Batool et al, 2018). Chen et al (2019) now show that this rapid drought response depends on all five SULTR3 transporters, resulting in an 80% reduction in ABA levels in the quintuple mutant compared with wildtype plants.…”

“…) quickly accumulates in the xylem upon drought stress and is therefore thought to fulfill this role as a signaling molecule (Malcheska et al, 2017). Several classes of SO 4 22 transporters (SULTRs) are responsible for SO 4 22 uptake from the soil (rootlocalized SULTR1;1 and SULTR1;2) and transport into the xylem and toward the shoot (SULTR2;1 and SULTR2;2) or into the phloem and back to the roots (SULTR1;3; Fig.…”