Dr. Zimmerman has shown that somatic embryos of carrot which have reached the globular stage of development exhibit both novel mechanisms of heat shock gene regulation and unusual physiological reactions to heat stress. Specifically, the regulation of heat shock gene expression transiently shifts from the transcriptional to the translational level, and then shifts back again. Moveover, heat shock exposure of mid-globular embryos results in the specific and irreversible arrest of development (no other embryo stage is so dramatically affected). In this proposal, she describes experiments which will extend these findings in an effort to understand the molecular mechanisms which are at work in this system and the relationship between this unusual heat shock gene regulation and the observed arrest of globular embryo development. She proposes to achieve four major objectives; 1) To understand the general mechanisms underlying the transcriptional repression and translational activation of heat shock gene expression during globular embryo development, 2) To characterize the DNA sequences of carrot heat shock genes which respond to transcriptional and translational regulation both in suspension cells and during embryo development, 3) To elucidate the relationship between globular embryo thermotolerance and developmental arrest by heat shock, and 4) To characterize the heat shock response of globular embryos at the individual cell level.
