Subcortical rotation in Xenopus eggs: a preliminary study of its mechanochemical basis

The amphibian egg undergoes a 30 degree rotation of its subcortical contents relative to its surface during the first cell cycle, a displacement of 350 micron in 50 min. This is directly visualized by following the movement of an array of Nile blue (a subcortical stain) spots applied to the egg periphery (Vincent, Oster, and Gerhart: Dev Bio 113:484-500, '86). We have investigated the mechanochemical basis of this unusual cell motility. Subcortical rotation depends on microtubule integrity during its entire course and is insensitive to inhibitors of microfilament assembly. It does not depend on newly synthesized proteins for its operation or timing, and it does not involve calcium-dependent processes. Finally, we show that vegetal fragments of the egg can complete rotation on their own, indicating that mechanochemical components can operate locally in this hemisphere.     

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.