Growing pollen tubes of Tradescantia paludosa are protected from inhibition of growth at 41 degrees C by a prior exposure to gradually increasing temperatures. Heat shock proteins (hsps) are not synthesized by pollen tubes as determined by labeling with [(35)S]methionine and two-dimensional gel electrophoresis, during either a heat shock at 41 degrees C or a gradual temperature increase to 41 degrees C. A comparison after two-dimensional electrophoresis of silver-stained spots and radioactive spots after autoradiography of an extract of ungerminated pollen mixed with a trace amount of [(35)S]methionine-labeled vegetative tissue heat shocked at 41 degrees C to act as a hsps marker, indicates that the majority, if not all, of the major hsps are not present in the pollen grain at anthesis. The type of thermotolerance seen with pollen tubes can thus be achieved without the presence or the new synthesis of the hsps.