Abiotic stress effects on grapevine (Vitis vinifera L.): Focus on abscisic acid-mediated consequences on secondary metabolism and berry quality
Introduction
According to the Food and Agriculture Organization of the United nations time-series and cross sectional data FAOSTAT (http://faostat3.fao.org) 69,654,925.50 tons of grapes on 7,086,021.81 ha were produced in the world in 2011. About 29 millions of wine tons were produced in 2011, two thirds of them in the Mediterranean basin; considering that the yield of the transformation of grape into wine is averagely 80%, about 36 millions of tons are destined to the winemaking, the remaining ones are fresh or dry consumed.
Regions with Mediterranean climate, where viticulture flourished since 1000 BC, are characterized by long growing seasons, with moderate to warm temperatures. Throughout the year there is little seasonal change in temperatures, and winters are generally warmer than those of maritime and continental climates. During the grapevine growing season, there is very little rain fall (most precipitation occurring in the winter months), which increases the risk of drought hazard in viticulture (Robinson, 2006), especially in sandy and gravelly soils that do not retain water (Tramontini et al., 2013).
Mediterranean climate ensures to grapevine long warm periods during the crucial phenological stages of flowering, fruit set and ripening. The physiological processes of grapevines begin when temperatures are around 10 °C. Below this temperature, vines are usually dormant. Above 35 °C, on the contrary, plant adaptation to heat stress is activated. In addition to temperature, the amount of rainfall and the need for supplemental irrigation are crucial characteristics for the definition of viticultural areas (Keller, 2010). On average, a grapevine needs around 6–7 hundreds mm of water for sustenance during the growing season, not all of which may be provided by natural rainfall. In the Mediterranean region, climate may be quite dry during the grapevine growing season and vines may require additional irrigation to limit water deficit stress (Chaves et al., 2007, Chaves et al., 2010).
Berry quality, particularly that of winegrape varieties, is largely dependent on secondary metabolites, i.e. on the accumulation of polyphenols and volatiles.
Plant secondary metabolism provides a line of defense in cellular response to abiotic stress (Cramer et al., 2011) and induces an enhancement of grape quality, as secondary metabolites contribute to color, taste and aroma of fresh and dried grapes and they are involved in wine stabilization and aging processes. In the last decades this concept has largely been addressed, by linking technological aspects (both agricultural and enological ones) with biological and molecular aspects in viticulture, resulting in an increase of the related scientific literature (Fig. 1a). Abscisic acid has been proposed as the main mediator of grapevine biological response to abiotic stress, especially drought. If, on one hand, the number of papers published on grape secondary metabolism has linearly increased during the last fifteen years, due to the progress in science applied to viticulture, on the other, it has exponentially increased when linked to abiotic stress and especially to the ABA-mediated response to stress (Fig. 1b).
In this review we address grapevine responses to the main abiotic stresses, highlighting the ABA role in controlling environmental stress effects on secondary metabolism especially in berries, but also in vegetative organs.
Section snippets
Grape ripening: an ABA-induced process crossing with abiotic stress and secondary metabolite accumulation
In Vitis vinifera berries, the onset of ripening (véraison, i.e. the onset of anthocyanin accumulation in colored-skin varieties) is proved to be tied to sugar accumulation (Gambetta et al., 2010) and it is accompanied by a marked increase in ABA concentration (Deluc et al., 2009, Gambetta et al., 2010, Owen et al., 2009).
Pirie and Mullins (1976) were the first to show a synergic effect of ABA and sucrose in grape leaf anthocyanin accumulation. The hypothesis that ABA may drive ripening in
Water stress
Grapevine performances and berry quality depend on the vine adaptability to drought (Lovisolo et al., 2010). Water deficit does not exclusively cause negative effects, but a regulated water deficit, which is the base of various agronomic practices, has largely been used to balance grapevine vegetative and reproductive growth with the aim of controlling berry quality (Chaves et al., 2010).
In grapevines a direct role of ABA in stomatal closure upon water stress was demonstrated since the 70s (Liu
Light stress
The light stress implies photosynthetic activity variations, photoinhibition, and photoxidation. In leaves light deficiency and excess induce stomatal and metabolic responses such as the accumulation of antioxidants, namely ascorbate, glutathione, flavonoids, carotenoids and of enzymes controlling their oxido-reductive state (Fini et al., 2011); in Arabidopsis thaliana leaves (Page et al., 2012) light intensity was shown to be able to influence the accumulation of anthocyanins confirming the
Temperature stress
Temperature plays an important role in the ripening of many fruits, including grape berries. Temperature trends are so determinant for grape phenology, that historical series of grape ripening have been used to reconstruct temperatures to provide insight into regional-scale climate variations (Chuine et al., 2004). In the last decade much attention has been focused on the global warming effects in many fields of agriculture (Wolfe et al., 2008) and in viticulture, as well (Hannah et al., 2013,
Stress-mediated variations of berry and must quality improve the nutraceutical value of grapes
Epidemiological data indicate a beneficial effect of Mediterranean diets on human health, especially associated to the lower incidence of cardiovascular diseases. Heinrich et al. (2005) tested in vitro Mediterranean plant extracts through different tests: four antioxidant tests (2,2-diphenyl-1-picrylhydrazyl scavenging – DDPH-, prevention of oxyhaemoglobin bleaching, prevention of lipid peroxidation, and protection from DNA damage), three enzyme inhibition tests (inhibition of xanthine oxidase,
Feeding grapevine organs with exogenous ABA: a tool to enhance grape quality and to control abiotic stress
Exogenous ABA application is moderately used in the production of table grapes, to hasten ripening, to increase berry color and to regulate other key processes such as dormancy (Zhang et al., 2011). Since few years a commercial product containing ABA was authorized in Chile and in California where it is essentially used for the enhancement of color development in table grapes. Research on the application of exogenous ABA is not so wide at present and is focalized on table grape varieties such
Conclusions
In grapevine, abiotic stress modifies growth and development of all plant organs. The response to abiotic stress at the berry level drives the accumulation in berry pulps, seeds and skins of secondary metabolites as a line of defense against cell damages. Viticultural practices can be managed to control stress plant response in order to increase secondary metabolite concentrations, reflecting on an enhancement of table grape and must quality, as secondary metabolites of grapes contribute to
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