Water relations of the grape berry and aquaporins

Berry water content during development and at harvest is a crucial parameter of the vintage quality by directly impacting the concentration of sugars and flavour compounds. In the last decade, there has been considerable progress in understanding how berry water relations are involved in the ripening process as a result of exploring and integrating developmental changes in berry hydraulic conductivity, mineral nutrient loading, phloem unloading, xylem development, functionality of xylem vessels, cell vitality, cell water relations, gene expression and the molecular biology of aquaporins (water channels). In this chapter, we review the most recent advances in our understanding of the berry water influx and efflux during development and their consequences on cell turgor and apoplast solute concentrations, taking account of the changes in cell vitality observed late in ripening in some varieties. The role of aquaporins in the regulation of berry water relations is also presented, with a particular emphasis on the varietal differences observed in aquaporin functioning. Finally, the impact of water status of the parent vine on berry ripening is discussed. From this review, it appears that the varietal differences observed at different regulatory levels of berry water status represent a great opportunity to gain a better understanding of the ripening process.S. D. Tyerman, M. M. Chaves and F. Barrie