Abstract
Agricultural practices in grapevines management include water restrictions due to its positive effect on wine quality, especially when applied at fruit ripening. Although the effects of water stress in some groups of phytohormones have already been described in leaves and whole grapes, information regarding tissue-specific variations in hormones during ripening in grapes is scarce. Field-grown grapevines from the cv. “Merlot” were subjected to two differential water supplies, including only rainfed, non-irrigated vines (T0) and vines additionally irrigated with 25Lweek−1 vine−1 (T1). Tissue-specific variations in the hormonal profiling of grapes [including changes in the contents of abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), the ethylene precursor 1-amino-cyclopropane-1-carboxylic acid (ACC), the auxin indole-3-acetic acid, gibberellins 1, 3, 4, and 7 (GA1, GA3, GA4, and GA7), the cytokinins trans-zeatin, and 2-isopentenyl adenine, including as well their respective ribosylated forms] were periodically evaluated from veraison to harvest. The hormonal profiling in leaves was also measured at the beginning and end of the season for comparison. Results showed that grape growth dynamics were transiently affected by the differences in water regimes, the increased water supply leading to an accelerated growth, slightly reduced accumulation of sugars, and transiently lowered pH, although grape quality did not differ between treatments at harvest. Hormonal profiling of whole berries did not reveal any difference in the endogenous contents of phytohormones between treatments, except for a transient decrease in GA4 contents in T1 compared to T0 vines, which was not confirmed at the tissular level. Hormonal profiling at the tissue level highlighted a differential accumulation of phytohormones during ripening in berry tissues, with pulps being particularly poor in ABA, JA, and SA contents, seeds particularly accumulating ACC, gibberellins, and zeatin-type cytokinins, and the skin being particularly rich in auxin and active cytokinins. Changes in water supply led to very small and transient changes in the endogenous contents of phytohormones in the seeds, pulp, and skin of berries, the most remarkable variations being observed in cytokinin contents, which increased earlier [between 5 and 12days after veraison (DAV)] but later kept more constant in the skin from T1 compared to T0 vines and were also 3-fold higher at 40 DAV in seeds of T1 compared to T0 vines. It is concluded that small changes in water supply can trigger hormonal-driven physiological adjustments at the tissular level affecting the evolution of fruit growth and quality throughout grape berry ripening.
Highlights
Wine grape (Vitis vinifera L.) is one of the most important fruit crops worldwide for both economic and cultural reasons, having Spain the largest cultivated area, positioned itself as the third in product turnover, and the main exporter of wines, based on volume, around the world (OIV, 2019)
The positive effect of water management in grapes production has been mostly attributed to endogenous increases of abscisic acid (ABA), which is considered as an important signal to trigger the onset of ripening in grape berries and has proved to have a key role in the modulation of secondary metabolism, for example, by the induction of gene expression of enzymes related to the phenylpropanoid pathway (Berli et al, 2015; Yukari et al, 2015; Villalobos-González et al, 2016; Ramírez et al, 2018)
Water irrigation improved leaf water contents at 40 days after veraison (DAV) in T1 vines compared to T0 vines, while it did not influence proline contents, leaf mass area (LMA), and Fv/Fm ratios (Supplementary Figure S1)
Summary
Wine grape (Vitis vinifera L.) is one of the most important fruit crops worldwide for both economic and cultural reasons, having Spain the largest cultivated area, positioned itself as the third in product turnover, and the main exporter of wines, based on volume, around the world (OIV, 2019). Agricultural practices in grapevines include various types of water management, such as regulated water-deficit, which is considered a key factor in many viticultural regions, especially in warm areas when applied at fruit ripening after veraison (Chaves et al, 2010; Cáceres-Mella et al, 2018) Water deficit during this period has shown to have positive effects on the quality of red wine grape varieties, since it improves the microclimate of fruit zone, reduces the size of berries, and increases the skin to pulp ratio, among other physiological responses that enhance phenolic compounds concentration, which improves wine color, astringency, mouthfeel, bitterness, stability, and antioxidant activity (Santos et al, 2005; Castellarin et al, 2007; Deluc et al, 2009; Chaves et al, 2010). The positive effect of water management in grapes production has been mostly attributed to endogenous increases of abscisic acid (ABA), which is considered as an important signal to trigger the onset of ripening in grape berries and has proved to have a key role in the modulation of secondary metabolism, for example, by the induction of gene expression of enzymes related to the phenylpropanoid pathway (Berli et al, 2015; Yukari et al, 2015; Villalobos-González et al, 2016; Ramírez et al, 2018)
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