Carbohydrate metabolism in grapevine (cv. Malbec) leaves exposed to different radiation regimes

Abstract

Radiation is one of the main environmental variables that determine leaf microclimate within the vine, and consequently its photosynthesis and carbohydrate metabolism. The objective of this study was to comprehend the relationships among photosynthetic performance, carbohydrate metabolism, and related gene expression of grapevine leaves grown under different radiation regimes. During 2012/13 growing season, an experiment was conducted at INTA Mendoza Experimental Station on a Malbec vineyard (Vitis vinifera L.) in which four exposure regimes were established in the leaves: i) East, ii) West, iii) Sun, and iv) Shade. Plastic screens were installed to generate the different radiation regimes. Leaf microclimate (photosynthetic photon flux density and temperature) was continuously monitored during the day. Diurnal dynamics of photosynthesis and non-structural carbohydrates (starch and soluble sugars) were measured at different days of the growing season and leaf daily carbon production and exportation rates calculated. Transcript profiles of leaf sugar transporters (VvHT1, VvHT3, VvHT5, VvSUC12, VvSUC27 and VvCWI) were measured at different times of the day. Leaf starch accumulation and sugar exportation rate had similar patterns in Sun, East and West exposure regimes, increasing during the day until the afternoon when a plateau was reached. Leaf net photosynthetic rate was close to zero in Shade and therefore no starch was accumulated and soluble sugars were not exported. Transcripts of hexoses and sucrose transporters were expressed even under shaded conditions indicating a regulation of the short-distance sugar transport in those leaves. These results allow us to better understand the physiological and molecular behavior of leaves under different exposure regimes and the effects of vineyard cultural management practices (e.g., row orientation).