HSP70 HEAT-SHOCK PROTEIN COGNATE IS EXPRESSED AND STORED IN DEVELOPING TOMATO POLLEN

Pollen of angiosperms lacks the ability to respond to heat stress by synthesizing heat shock proteins (hsps). In tomato developing microspores were found to have 70 kDa heat shock proteins (hsp 70s) present throughout development, even in the absence of heat stress. Heat shock protein family members expressed in the absence of heat stress are called cognate (hsc 70) genes. Antisense RNA and antibody probes were used for in situ hybridizations which detected hsc 70 expression in developing pollen of immature buds. Hsc 70 mRNA transcripts and proteins were detected in nonstressed sporogenous tissues, microspores and in pre-tapetal layers during early pollen development. While immunoblot analysis detected hsc 70 proteins stored in mature pollen, heat stress could not induce the synthesis of new hsp 70 protein as measured by S-35-methionine labeling followed by immunoprecipitation.