Grapevine (Vitis vinifera L.) is a non-climacteric fruit species used as table fruit, dried raisins, and for vinification (wines) and distillation (liquors). In recent years, our knowledge of the molecular basis of ripening regulation has improved. Water status, light conditions, and temperature may hasten, delay, or enhance ripening. Hormones seem to play a central role, as their concentrations change prior to and during ripening and in response to several environmental cues. The review summarizes recent data related to the molecular and hormonal control of grape berry development and ripening, with special emphasis on secondary metabolism and its response to the environment, and pinpoints some experimental limitations.

Several lines of evidence suggest that regulation of intracellular Ca²⁺ levels is crucial for adaptation of plants to environmental stress. We have cloned and characterized Arabidopsis auto-inhibited Ca²⁺-ATPase, isoform 4 (ACA4), a calmodulin-regulated Ca²⁺-ATPase. Confocal laser scanning data of a green fluorescent protein-tagged version of ACA4 as well as western-blot analysis of microsomal fractions obtained from two-phase partitioning and Suc density gradient centrifugation suggest that ACA4 is localized to small vacuoles. The N terminus of ACA4 contains an auto-inhibitory domain with a binding site for calmodulin as demonstrated through calmodulin-binding studies and complementation experiments using the calcium transport yeast mutant K616. ACA4 and PMC1, the yeast vacuolar Ca²⁺-ATPase, conferred protection against osmotic stress such as high NaCl, KCl, and mannitol when expressed in the K616 strain. An N-terminally modified form of ACA4 specifically conferred increased NaCl tolerance, whereas full-length ATPase had less effect.

Grape berry development and ripening are under complex regulation by the nutrients, hormones, and environment cues sensed by the berry. However, the biochemical and molecular mechanisms underlying these types of regulation are poorly understood. A simplified but realistic model system that enables fruit growth conditions to be modulated easily will facilitate the deciphering of these mechanisms. Here, an in vitro culture system of intact detached grape berries was developed by coupling the production of greenhouse fruiting-cuttings and in vitro organ culture techniques. ¹³C and ¹⁵N labelling experiments showed that this system enables the intact detached berries actively to absorb and utilize carbon and nitrogen from the culture medium. It was further used to study the effects of sugars on anthocyanin accumulation. A sucrose concentration >2% could induce anthocyanin synthesis in the absence of additional exogenous abscisic acid. The higher the sucrose concentration, the earlier was the induction of anthocyanin accumulation. Glucose, fructose, and sucrose increased anthocyanin accumulation, with glucose and fructose being more effective than sucrose. This increase was not due to an increase in its precursor level, since the phenylalanine content was decreased by a high sugar supply. Instead, genome-wide transcriptome analysis suggests that the sugar-induced enhancement of anthocyanin accumulation results from altered expression of regulatory and structural genes (especially UDP-glucose:anthocyanidin 3-O-glucosyltransferase), together with massive reprogramming in signalling transduction pathways. This in vitro system may serve to study the response of berry composition to nutrient factors and hormones, and their interaction with environmental factors (e.g. light and temperature), which can all be finely tuned and controlled.