Flux and Chemical Composition of Xylem Exudates From Chardonnay Grapevines: Temporal Evolution and Effect of Recut

Abstract

Six-year-old <i>Vitis vinifera</i> L. Chardonnay grapevines grown under controlled conditions were investigated with regard to both qualitative and quantitative temporal evolution of the xylem sap composition. Xylem exudates were collected by pruning the spurs just before bud burst. Potassium was the main mineral ion found in the sap (7300 µ<i>M</i>), followed by calcium (2600 µ<i>M</i>), phosphate (2500 µ<i>M</i>), nitrate (2300 µ<i>M</i>), sulfate (1600 µ<i>M</i>), magnesium (500 µ<i>M</i>), and chloride (150 µ<i>M</i>). The major organic compounds were amino acids (5500 µ<i>M</i>) and amides (mainly glutamine, 4000 µ<i>M</i>), organic acids (3500 µ<i>M</i>, mainly malate), and soluble carbohydrates (500 µ<i>M</i>) including glucose, fructose, and sucrose. Over a one-week time course, water flux increased from the first four hours of exudation until 52 hours and then diminished steadily. Mineral ion concentrations remained fairly constant from the onset of the exudation to the end of the collection period, except for potassium which increased continuously and nitrate whose concentration reached a plateau after 24 hours. The high xylem levels of soluble organic compounds (amino acids and soluble carbohydrates), that were found initially, dropped rapidly and then increased reaching a maximum at 52 hours. Finally, the concentration decreased until the end of the exudation period. Furthermore, attention was paid to the effect on the xylem sap composition of recutting the spurs. The data obtained revealed that water flux and soluble carbohydrate release were enhanced, as a result of the recut, up to the maximum level previously reached at 52 hours.