Nataliya Shcherbatyuk* and Markus Keller
*Washington State University, 24106 N. Bunn Rd., Prosser, WA 99350 (n.shcherbatyuk@wsu.edu)

Plants can transport water from roots in wet soil to roots in dry soil. Such hydraulic redistribution is thought to occur via the xylem and root parenchyma. However, it is unknown how the phloem contributes to overall water transport during this process. Our hypothesis is that hydraulic redistribution in grapevines is in part due to water movement to the leaves via the xylem and recycling from the leaves to the roots via the phloem. This study used deuterium-labeled water (2H2O) as a tracer of water flow. Own-rooted Vitis vinifera L. cv. Merlot grapevines were grown in pots with a three-way split root design. One of the three compartments was irrigated with 2H2O and the other two were left to dry. The trunk in one of the dry compartments was girdled and the other one was left intact to distinguish xylem and phloem water movement. Xylem sap and phloem sap, trunk and root tissue, and soil samples were collected. Water from each sample was extracted via a cryogenic method and analyzed for deuterium enrichment (δ2H). Preliminary results show deuterium enrichment in both xylem and phloem sap collected from the same petioles. The δ2H values were six times higher in root tissues collected from the irrigated compartment compared with samples from the dry compartments. Root tissue samples from the dry/intact compartment had δ2H values two times higher than samples from the dry/girdled compartment. These preliminary results show that under drought stress, some water flows from the wet roots to the leaves via the xylem and is then recycled from the leaves to the dry roots via the phloem. A better understanding of phloem function in whole-plant water transport will help to understand the plant mechanisms involved in the irrigation strategy termed partial root-zone drying.

Funding Support: Ste. Michelle Distinguished professorship; WA State Grape and Wine Research Program; Washington State University