Heat shock induced changes of plant cell ultrastructure and autoradiographic localization of heat shock proteins.

Treating tomato cell cultures and leaves by a physiological heat shock (hs) at 35 to 39 degrees C results in a progressive disintegration of the nucleolus and the assembly of cytoplasmic hs granules. Other ultrastructural changes are not observed. The alterations of the nucleoli coincide with an immediate stop of the processing and with a strongly decreased synthesis of pre-rRNA. Both hs effects are reversed after shift-down to normal temperature conditions (25 degrees C). Assembly of cytoplasmic hs granules depends on the accumulation of the newly forming hs proteins and on supraoptimal temperatures. It is not observed in preinduced cultures synthesizing hs proteins at 25 degrees C. Autoradiographic studies reveal the preferential accumulation of hsp in the nucleoli and hs granules. Furthermore uridine labeling points to the presence of RNA in electron dense particles of both subcellular components. A survey on the state of hsp synthesis and structural binding as well as on the ultrastructural changes is given for 12 selected hs regimes.