Plant power for a thirsty planet

Plants can respond sensitively to drying soil, with leaf growth inhibition and partial stomatal closure preceding any quantitative difference in leaf water potential, or visual difference in leaf turgor, by several days. Attention has focused on soil drying induced synthesis and metabolism of phytohormones, which can change tissue hormone concentrations and xylem sap composition. The advent of multi-analyte phytohormone analyses, with xylem sap sampling at sap flow rates approximating transpiration, allows their role as sensors of soil drying to be investigated. Whether these changes in xylem sap affect tissue phytohormone concentrations, and are due to local or long- distance processes, can be investigated by self- and reciprocal-grafting of mutants that are deficient in or overexpress selected phytohormone groups, and stem girdling techniques. Ultimately, this fundamental knowledge can be used to inform biotechnological and/or agronomic approaches to improve crop water use efficiency, which has applications in both UK and developing world contexts.

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