Effect of the plant sink/source balance on the chemical content of red table grapes (Vitis vinifera L.).

Abstract

PPhloem transport of assimilates provides the materials needed for the growth and development of reproductive structures, storage and developing organs, and has long been recognized as a major determinant in crop yield. Thus, the understanding of the mechanisms and regulations of sugar transport into sink tissues has an important basic and applied relevance. The grapevine is a good example of a crop where sugar accumulation in the fruit has an important economic role. Massive sugar transport and compartmentation into the grape berry mesocarp cells (up to 1 M glucose and fructose) start at veraison and continues until the harvest. Sucrose transported in the phloem is cleaved into hexoses by invertases and stored in the vacuole. The sugar content determines the sweetness of table grapes and regulates gene expression, including, for example, several genes involved in the synthesis of secondary metabolites which contribute to grape quality. Many viticultural practices affect source/sink relationships, thus altering sugar concentration in the berry.  Considering this, the aim of this work was determined the effect of change of source/sink relations by using treatments of cluster thinning, cane girdling and leaf removal, on anthocyanin and volatile composition in grape berries during ripening. Berry grapes from varieties Red Globe and TimcoTM, cultivated in the same place under the 3 agronomical treatments (cluster thinning, cane girdling and leaf removal) were sampled from veraison to commercial maturity each ≈10-12 days. The anthocyanin composition was analyzed spectrophotometrically and by HPLC-DAD [1]. The volatile profiles from grapes were analyzed employing for the extraction solid-phase microextraction and gas chromatography coupled with mass spectrometry [2]. For both varieties, cluster thinning affect the concentration of total soluble solids and some anthocyanins in relation with the control, increasing their concentration. In relation with volatile compounds forty-one volatile compounds were determined in the two grape varieties analyzed. Among them, the terpene chemical group was the most abundant (qualitatively), accounting for 14 compounds, followed by aldehydes (13), alcohols (9), ketones (3), C13-norisoprenoids (1), and acids (1). Both varieties presented a different behavior in the evolution for the total volatiles during ripening, with a decrease during ripening for Red Globe and an increase in the case of TimcoTM berries. Except for esters with an increase in the treatment with cluster thinning and cane girdling respect the control for TimcoTM samples at commercial maturity, no effect was observed for the rest of the volatile chemical groups among the treatments. Data suggest that use of some of the plant management practices studied may improve berry color, but with a very low and/or inconsistent impact of the plant sink/source on the berry volatile fraction.

References

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