Effects of high temperature on the ultrastructure and microtubule organization of interphase and dividing cells of the seagrass Cymodocea nodosa

Short-time temperature effects (34-40 degrees C) on microtubule (MT) organization and on cell structure of young epidermal leaf cells of the seagrass Cymodocea nodosa were investigated under laboratory conditions using transmission electron microscopy (TEM) and tubulin immunofluorescence. The interphase MT network was affected by the increased temperature, the effect being time dependent and expressed in both the form and the orientation of the MT bundles. After 1 h at 38 degrees C, there was also a severe disturbance in dividing cells with thick and short MTs in the mitotic spindle and atypically organized phragmoplasts, while after 2 h at 38 degrees C the mitotic index was tenfold reduced compared with the control material. After 6 h at 38 degrees C, a large number of telophase cells were observed, meaning that cytokinesis was blocked. TEM observation revealed cells with uncompleted cell plates consisting of swollen vesicles and branched cisternae, with no phragmoplast MTs. These cells bear a nucleolus with segregated fibrillar and granular zones, an increased number of swollen mitochondria, and numerous parallel arrays of endoplasmic reticulum cisternae in the cortical cytoplasm. The possible relationship of these changes in C. nodosa with a response mechanism in order to face elevated temperature effects of climate change is discussed.