Relationship between wintering ability of winter wheat and the extent of depression of carbohydrate reserves: Basal metabolic rate under snow determines longevity of plants

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Abstract
Differences in metabolic activities of winter wheat (Triticum aestivum L.) under snow were assessed in two cultivars, Horoshirikomugi and Norin 61, which exhibit different longevity during wintering. From October, through winter to spring, changes in the levels of carbohydrates, sugar phosphates, glutathione, amino acids, inorganic ions, and osmotic pressure were monitored. When the ground was covered with snow, autotrophic metabolism in wheat ceased. The expenditure of stored carbohydrates, mainly fructans and sucrose, in the tissues appeared to be controlled to such an extent in the two respective cultivars that it proceeded at rates commensurate with the demands of the cells; the difference in the extent of consumption (1.3 to 1.7 μmol in the stem of Horoshirikomugi during the period from February 16 to March 16 and 10 μmol in that of Norin 61 from December 26 to January 18, g-1 fresh weight day-1was directly related to the longevity of the plants under snow. The difference may arise from the functional sequence of metabolic events in the plants that provides energy and materials to meet fundamental demands under snow. The trend towards the maintenance of the substrates, such as glucose-6-phosphate (G6P) and glutathione (GSH), at functional levels inside cells for a long period appeared to be common to both cultivars and was evident even under conditions where the amount of the reserve carbohydrates reached critical levels for potential regrowth and the wheat plants lost osmotic functions.