THE PLANT CELL, Vol 1, Issue 12 1137-1146, Copyright © 1989 by American Society of Plant Biologists
Novel Regulation of Heat Shock Genes during Carrot Somatic Embryo Development
J. L. Zimmerman, N. Apuya, K. Darwish and C. O'Carroll
Department of Biological Sciences, University of Maryland Baltimore County, Catonsville, Maryland 21228
We have determined that somatic embryos of carrot exhibit a number of
interesting and unusual properties when exposed to heat shock at different
times in their development. Specifically, we have seen that mid-globular
embryos can be arrested irreversibly in their development when
heat-shocked, whereas all other stages of embryogenesis, both before and
after this stage, are fully capable of normal development after the stress.
In Investigating the molecular basis of this developmental sensitivity to
heat shock, using a cloned heat shock gene encoding a small heat shock
protein, we have determined that globular embryos both synthesize and
accumulate significantly less heat shock mRNA when compared with embryos of
any other stage or to callus suspension cells. In fact, there appears to be
no transcriptional induction of heat shock gene expression in response to
heat shock during this time period; the gene is expressed at the same
relatively low level both before and after heat shock. However, in spite of
the low level of heat shock mRNA available, globular embryos synthesize the
full complement of heat shock proteins in response to heat treatment. The
globular embryos appear to accomplish this by translating the existing heat
shock mRNAs at an elevated rate, which compensates for the low level of
available mRNA. Once the embryos have progressed beyond the globular stage
of development, regulation at the transcriptional level resumes, and the
embryos again exhibit normal development after heat shock.
