The main amino acids in xylem sap of <em>Vitis vinifera</em> L. var. Cabernet Franc during the vegetative cycle. Search for an amino acid marker

Numerous studies have been carried out on the vine, must and wine, but few on sap. Main phenological stages i.e. bud burst, the flowering period, veraison and the ripening period have been well described. However, at the present time, no study is available identifying the main amino acids of the xylem sap, at the formentioned periods. Located within the « Graves de Pessac-Léognan » vineyard, the plot area studied has a clayey-chalky soil with a small amount of sand present. The cultivar Cabernet franc was grafted on the Fercal rootstock. Planted in June 1982, the vine was trained with Guyot pruning and no tillage. The density of the plantation was 5.550 vines per ha. Four rows of 21 vines were sampled. Analysis of xylem sap, by H.P.L.C., at the four stages, taken from several vintages, showed that the global content of amino acids varied year to year (LARCHEVÊQUE, 1998). The experiment reported on herein was carried out in order to determine both the main amino acids in the xylem sap and to identify a marker amongst them, having the same evolution as that of the global amino acid content from one phenological stage to the next. A pool of eight amino acids, all present in large quantities (about 80 p. cent of total amino acid content), was always noted : asparagine/glutamine, tyrosine, arginine, aspartic acid, glutamic acid, histidine and proline. Concentration levels of these components differed in sap, depending on the vintage, at the same phenological stage. At bud burst, as at the flowering period, the sap had a similar qualitative composition. It was noteworthy that aspartic acid evidenced the same evolution that of the total amino acid content (i.e. the same variation in percentage) from one phenological stage to the next. Aspartic acid should therefore be regarded as a « marker » of total amino acid content evolution during the vegetative cycle.