ABSTRACT
The primary obstacle to plant survival at low temperatures is coping with ice formation and the accompanying dehydrative stress. Ice apparently first crystallizes within the xylem vessels and intercellular spaces. Several studies have related the presence or absence of low temperature exotherms with the distribution of woody plants. Large ice crystals form within the bark cortical tissues of woody plants, and adjacent cells appear dehydrated. The supercooling of water within xylem ray parenchyma cells has been compared to the freezing of water droplets in model systems. Although much of the circumstantial evidence suggests that the low temperature exotherm represents the lethal freezing of intracellular water, there is no direct evidence that intracellular ice formation is responsible for injury. Investigations of the deep supercooling phenomena have examined cellular and tissue characteristics in an effort to determine what features facilitate supercooling. The possible role of cell wall microcapillaries in deep supercooling has been investigated.
