Physiological and metabolic responses of winter wheat to prolonged freezing stress

Survival and cold hardiness declined gradually when cold-hardened Fredrick winter wheat (Triticum aestivum L.) was maintained at −6°C for several weeks. Moisture content of crown and root tissue did not change significantly during this period. Uptake of O₂ and accumulation of ⁸⁶Rb by root tissue declined abruptly upon exposure to −6°C, whereas a concomitant negative effect of freezing on these metabolic processes was not observed in crown tissue. Electron spin resonance spectroscopic analysis of microsomal membrane preparations from crown tissue revealed no evidence of gross changes in the physical properties of the bulk lipids even when seedlings were killed. The results provide biochemical evidence that seedling damage due to prolonged exposure to a mild freezing stress is due to disruption of key metabolic process in the root while cells within the crown remain viable.