Changes in the ultrastructures of crown cells of winter wheat during wintering under snow

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Abstract
Electron microscopic studies were carried out to examine cytological events in crown cells of wheat during wintering under snow. Two cultiyars of winter wheat were used for the ultrastructural studies: Triticum aestivum L. cv. Horoshirikomugi and Norin 61. In October and November, the cells of these cultivars had similar ultrastructure which was characteristic of cells engaged in protein synthesis and proliferation of organelles. After this period, the two cultivars exhibited different changes in ultrastructure. The changes in the Horoshirikomugi cultivar could be divided into four phases: 1) an active, growing phase in the fall; 2) a second phase, initiated when the field was covered with snow; 3) a third phase that commenced in late February; and 4) a fourth phase that could be detected in June under conditions that simulated wintering. The second and third phases in the process were apparently absent in Norin 61 and the cellular events in this cultivar seemed to proceed directly from the initial growing phase to the fourth phase under snow. The ultra-structures of cells in the second and third phases appeared to be related to cellular organization, such that lower levels of reserved carbohydrates are used up and, therefore, the Horoshirikomugi cultivar is able to husband its reserves of hexose during cultivation under snow. At the final stage of life under snow (Norin 61 in late February and Horoshirikomugi in August or September under simulated wintering) both cultivars exhibited a similar disorganized ultrastrucure of the crown cells.