Influence of plant water status on the production of C13-norisoprenoid precursors in Vitis vinifera L. Cv. Cabernet Sauvignon grape berries

The influence of irrigation strategy on grape berry carotenoids and C-13-norisoprenoid precursors was investigated for Vitis vinifera L. cv. Cabernet Sauvignon. Two irrigation treatments were compared, one in which vines received reduced irrigation applied alternately to either side of the vine (partial rootzone drying, PRD) and a second control treatment in which water was applied to both sides of the vine. Over the two years of the experiments, PRD vines received on average 66% of the water applied to the controls. Initially, the PRD treatment did not alter midday leaf (psi(L)) and stem (psi(S)) water potential relative to the control, but decreased stomatal conductance (gs). Continued exposure to the PRD treatment resulted in treated grapevines experiencing hydraulic water deficit relative to the control treatment and induced lowered midday psi(L) and psi(S), which was also reflected in decreased berry weight at harvest. In both irrigation treatments, the most abundant grape berry carotenoids, beta-carotene and lutein, followed the developmental pattern typical of other grape varieties, decreasing post-veraison. At certain points in time, as the fruit approached maturity, the concentration of these carotenoids was increased in fruit of PRD-treated vines relative to the controls. This effect was greater for lutein than for beta-carotene. PRD consistently caused increases in the concentration of hydrolytically released C-13-norisoprenoids beta-damascenone, beta-ionone, and 1,1,6-trimethyl-1,2-dihydronaphthalene in fruit at harvest (24 degrees Brix) over two seasons. The effect of the PRD treatment on the concentration of hydrolytically released C-13-norisoprenoids was greater in the second of the two seasons of the experiment and was also reflected in an increase in total C-13-norisoprenoid content per berry. This suggests that the increases in the concentration of the C-13-norisoprenoids in response to PRD were independent of water deficit induced changes in berry size and were not the result of an altered berry surface area to volume ratio.