HEAT-STRESS AFFECTS THE ORGANIZATION OF MICROTUBULES AND CELL-DIVISION IN NICOTIANA-TABACUM CELLS

To investigate the effects of heat stress on the plant cytoskeleton, t he structure of microtubule arrays In N. tabacum suspension cells incu bated at 38 or 42 degrees C was analysed, Whilst incubation at 42 degr ees C resulted in the disruption of the majority of cellular microtubu les after 30 min, in cells exposed to 38 degrees C all the microtubule arrays were preserved even after 12 h of incubation, although their o rganization was altered, The most susceptible were the microtubules of the mitotic spindle and the phragmoplast, Several abnormalities mere observed: (i) splitting of the spindle into several parts; (ii) elonga tion of the spindles; (iii) formation of microtubule asters in mitotic cells, and (iv) elongation of phragmoplast microtubules, Exposure of cells to 38 degrees C caused a decrease in the mitotic index but an ac cumulation of telophase cells. The recovery of normal microtubule orga nization occurred after 12 h, Treatment of the cells subjected to hear stress conditions with an inhibitor of protein synthesis, cycloheximi de, did not prevent either the alterations of microtubule organization or accumulation of cells containing phragmoplasts. Therefore, heat sh ock proteins do not seem to be directly responsible for the microtubul e disorganization induced by heat stress.