Regulation of Carbon Aquisition and Partitioning at Low Growth Temperatures

Damage resulting from extra-cellular ice formation during exposure to freezing temperatures is a widespread problem in nature, and in agriculture. In natural systems the prevalence, intensity and duration of freezing events affect seedling establishment and persistence as well as overall plant growth and reproductive performance, influencing both species diversity and ecosystem productivity. In agricultural systems, frost patterns affect not only the regional suitability of crops and/or cultivars, but unseasonable frosts can greatly reduce crop yields by causing vegetative injury to sensitive seedlings or by damaging particularly sensitive organs, such as flowers and fruits, leading to reduced yields without injuring vegetative growth. Therefore there are two separate, though related, questions to address when attempting to understand freezing tolerance With the view of modifying this character by breeding or genetic manipulation. First, the sensitivity to frost damage of non-acclimated plants or sensitive organs, and second the effect of prolonged exposure to low temperatures, leading to the development of freezing tolerance. Addressing the first question requires the modification of the basic frost sensitivity of non-acclimated tissues. Recent work reporting the effects of constitutive upregulation of several cold-regulated (COR) proteins’ and the over-expression of specific osmolytes such as glycinebetaine2 are exciting directions being taken to address this first question. Addressing the second question requires, in addition, an understanding of how metabolism as a whole is regulated in order that the plant can survive individual freezing events and also maintain primary productivity to fuel over-wintering and regrowth in the spring.