Changes of temperature exotherms and soluble sugars in grapevine (Vitis vinifera L.) buds during winter

Nonstructural carbohydrates (NSC), including water soluble carbohydrates (WSC) are thought to serve an important role in freezing tolerance of many plants. Raffinose family oligosaccharides (RFOs) are a-galactosyl derivatives of sucrose. The most common RFOs are the trisaccharide raffinose, the tetrasaccharide stachyose, and the pentasaccharide verbascose. RFOs are nearly ubiquitous in the plant kingdom and are found in a large variety of seeds from many different families. Severely cold winter temperatures can significantly impact grapevine productivity through tissue and organ destruction caused by freeze injury. Crop loss and the need to retrain vines after bud, cane, and trunk injury mean financial loss, often for one or more years. Buds of grapevine (Vitis vinifera L.), grown at the vineyard of the Institute of Fruit Science, Vegetable Science and Viticulture, University of Hohenheim, Germany, were sampled during winter and analyzed for their concentration of soluble sugars (i.e, glucose, fructose, sucrose, raffinose and stachyose) and thermal analysis was performed to determine their freezing points. Freezing of extracellular water was recorded from -5 to - 16 degrees C with a minimum at the beginning of January; freezing of intra-cellular water was recorded from -11 to -24 degrees C. Apical buds are very important organs as they determine further growth and development of tree species. Bud physiological state, including saccharide metabolism, determines their growth activity. The concentration of soluble sugars was highest by the end of December. Sugar concentrations in basal buds were significant higher than in buds from intermediate and apical shoot sections. A significant correlation could be proofed between sugar concentrations (i.e. raffinose and stachyose) and air temperature before sampling. But there was no correlation between freezing temperature of extra-cellular or intra-cellular water and soluble sugars in bud tissues.