Root growth inhibition by low temperature explains differences in sugar accumulation between spring and winter wheat

Exposure to low temperatures is associated with an increased concentration of carbohydrate (mainly sugar) in tissues of cool temperate species. Within a species, carbohydrate concentration is usually much higher in winter cultivars than in spring ones, frequently correlates well with winter survival, and is also related to the expression of several genes. It has been proposed that either a smaller reduction in carbon assimilation, or greater growth inhibition by cold in winter cultivars, might explain this differential increase in carbohydrate concentration. However, little experimental support for these hypotheses is available. In this work, carbon assimilation and growth, as related to the cold-induced increase in carbohydrate concentration, are analysed in contrasting wheat (Triticum aestivum L.) genotypes. No significant differences in the degree of cold-induced reduction of carbon assimilation between cultivar types were found. Also, shoot growth was similarly inhibited by cold in both winter and spring cultivars. However, root growth rates were lower in cold-treated winter cultivars than in spring ones, which led to much larger root systems in the latter. A simple method for quantitatively estimating the contribution of cold-induced changes in carbon fixation and growth to changes in carbohydrate concentration was developed. This analytical framework suggests that the degree of root growth inhibition by cold was the main factor in determining differences in carbohydrate content between cultivars.