EFFECTS OF TEMPERATURE ON CYTOMORPHOGENESIS AND ULTRASTRUCTURE OF MICRASTERIAS-DENTICULATA BREB

Exposure of growing Micrasterias cells to high (32°-36°C) and low (3°-10°C) temperatures produces changes in morphology that are accompanied by several ultrastructural alterations. Whereas low temperatures essentially cause simplification of cell ornamentation, a variety of cell malformations result from high temperature treatment. These are the loss of cell symmetry leading to markedly aberrant cell shapes and an increase of "main lobes" with reduced degree of differentiation. Preliminary studies indicate that a shift in the distribution of membrane-associated Ca2+ by elevated temperatures probably underlies these abnormal cytomorphogenetic events. Both, low and high temperature cause a reduction in size of the young half cell and affect cytoplasmic streaming. Moreover, nuclear migration is retarded and chloroplast arrangement is influenced by temperature treatment at both ranges. Growth velocity of primary wall responsible for cell shaping is increased at high and slowed down at low temperatures compared to cells grown at 20°C. The main ultrastructural alterations induced by high temperatures are an increase in amount and length of ER cisternae, the appearance of "heat shock granule" aggregations localized in the cytoplasm, a reduced number of ribosomes and polysomes, the presence of oil bodies in growing cells and a varying thickness of the primary wall. Influences of low temperatures on ultrastructure are less pronounced. They are manifested in the formation of large aggregations of ER cisternae slightly differing from those found in untreated cells, a disturbed arrangement of the microtubule system surrounding the nucleus and a decrease of the number of cell wall forming cytoplasmic vesicles. It is thought that most of the temperature effects are due to an influence on membranes probably an alteration of ionic currents and, in addition, a modulation of normal protein synthesis. © 1990 Springer-Verlag.