EFFECT OF COLD-EXPOSURE ON CORTICAL MICROTUBULES OF RYE (SECALE-CEREALE) AS OBSERVED BY IMMUNOCYTOCHEMISTRY

The responses of cortical microtubules to sub-zero temperatures were e xamined in non-acclimated (NA) and cold-acclimated (CA) rye (Secale ce reale L. cv. Voima) leaf and root cells, and in protoplasts isolated e nzymatically from leaves. Responses of leaf and root cells to hyperton ic solutions equivalent to the dehydration response of freezing (P. L. Steponkus and D. V. Lynch 1989. J. Bioenerg. Biomembr. 21: 21-41) wer e also examined. At the respective growth temperatures both NA and CA leaf and root cells had typical organization and abundance of cortical microtubules as observed by indirect immunofluorescence (IIF) stainin g. Unchanged microtubule arrays were still present in CA leaf cells af ter -4 degrees C treatment, while in leaf cells of NA plants and in th e root cells of both NA and CA plants microtubules were shorter and le ss abundant. After -10 degrees C treatment the cortical microtubules w ere almost totally depolymerized in both types of root cells and in le af cells of NA plants, while CA leaf cells still had abundant cortical microtubule arrays. Semiquantitative analyses of cortical microtubule s (MTs) of protoplasts confirmed the findings with intact leaf cells. Hypertonic treatment of NA and CA leaf cells gave similar effects as e xposure of cells to sub-zero temperatures. However, after the hyperton ic treatment, more microtubules remained present in the CA root cells than in the NA root cells, suggesting that also in root cells cold acc limation increases the dehydration stability of MTs. In conclusion, co ld acclimation induces both greater frost stability and greater osmoti c tolerance in the cortical microtubules of the leaf cells, and greate r osmotic tolerance in the microtubules of the root cells in winter ry e.