High accumulation of soluble sugars in deep supercooling Japanese white birch xylem parenchyma cells.

• Seasonal changes in the accumulation of soluble sugars in extracellular freezing cortical parenchyma cells and deep supercooling xylem parenchyma cells in Japanese white birch (Betula platyphylla var. japonica) were compared to identify the effects of soluble sugars on the mechanism of deep supercooling, which keeps the liquid state of water in cells under extremely low temperatures for long periods. • Soluble sugars in both tissues were analyzed by high-performance liquid chromatography (HPLC), and the concentrations of sugars in cells were estimated by histological observation of occupancy rates of parenchyma cells in each tissue. Relative and equilibrium melting points of parenchyma cells were measured by differential thermal analysis and cryoscanning electron microscopy, respectively. • In both xylem and cortical parenchyma cells, amounts of sucrose, raffinose and stachyose increased in winter, but amounts of fructose and glucose exhibited little change throughout the entire year. In addition, no sugars were found to be specific for either tissue. Combined results of HPLC analyses, histological observation and melting point analyses confirmed that the concentration of sugars was much higher in xylem cells than in cortical cells. • It is thought that the higher concentration of soluble sugars in xylem cells may contribute to facilitation of deep supercooling in xylem cells by depressing the nucleation temperature

Determination of resistance to low temperatures of winter buds on lateral shoot present in Karaerik (Vitis vinifera L.) grape cultivar

This study aims to determine the low temperature resistance of dormant buds at nodes with or without lateral shoots of Karaerik grape cultivar, and explain the relationship between the resistance and biochemical parameters in this grape cultivar. In this study, the mean values of high temperature exotherms (HTEs), low temperature exotherms (LTEs), water, reducing sugar, total soluble protein contents and antioxidant enzyme activities of dormant buds taken from nodes with or without lateral shoots were determined. The experiment has been found that buds in nodes with lateral shoots showed HTE and LTE at higher temperatures (HTE average -6.7 degrees C and LTE average -8.3 degrees C) than buds (HTE average -7.9 degrees C and LTE average -11.5 degrees C) in nodes without lateral shoots; therefore, buds in nodes with lateral shoots had less tolerance to low temperature. Additionally, lower sugar (average 41.05 mg g(-1)), protein (average 1.61 mg g(-1)), superoxide dismutase (average 425.27 EU g(-1) tissue), peroxidase (average 2516.1 EU g(-1) tissue) and polyphenol oxidase (average 7283.1 EU g(-1) tissue) were determined for buds taken from nodes with lateral shoots. Due to the fact that dormant buds taken from nodes with lateral shoots decreased the resistance to low temperatures, this research suggests that these lateral shoots should be excised with the summer pruning at the regions, where low temperatures caused the damages