Soluble sugars make a greater contribution than cell wall components to the variability of freezing tolerance in wheat cultivars.

Abstract

Wheat, the second most produced cereal globally, is primarily cultivated in cooler regions. Unexpected freezing temperatures can severely impact wheat production. Wheat and other temperate plants have a cold acclimation mechanism that enhances freezing tolerance, but reduces growth under low, non-freezing temperatures. During cold acclimation, plants break down storage polysaccharides like starch and fructan to accumulate soluble sugars such as glucose and fructose. These soluble sugars aid freezing tolerance through osmotic adjustments, membrane stabilization, and freezing point depression. However, plant cell walls, composed of insoluble polysaccharides, are the first line of defense against extracellular freezing. We analyzed the contributions of soluble sugars, storage polysaccharides, and cell wall polysaccharides to freezing tolerance and growth under cold acclimation in wheat. The study involved two Japanese winter cultivars (Yumechikara and Norin-61) and one Japanese spring cultivar (Haruyokoi). While Yumechikara showed poor growth after four weeks of cold acclimation, it exhibited higher freezing tolerance than the other cultivars. Our analysis revealed that Yumechikara accumulated higher levels of glucose, fructose, starch, and fructan than Norin-61 and Haruyokoi, whereas no significant differences in cell wall composition among the cultivars were observed. Gene expression patterns related to soluble sugar metabolism supported these findings. Additionally, the distribution of sugar changes between leaves (source) and crown (sink) correlated with the relationship between growth and freezing tolerance. These results suggest that freezing tolerance in wheat involves a balance between sugar accumulation and growth regulation during cold acclimation.