Heat shock causes destabilization of specific mRNAs and destruction of endoplasmic reticulum in barley aleurone cells.

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Abstract
In response to a phytohormone, gibberellie acid, the aleurone layers of barley seeds synthesize and secrete .alpha.-amylases, which are coded by a set of stable mRNAs. When aleurone layers are subjected to heat shock treatment, the synthesis of .alpha.-amylase is suppressed while heat shock proteins are induced. The suppression of .alpha.-amylase synthesis is not the result of translational control as reported in several other systems. Rather, the sequences of .alpha.-amylase mRNA are rapidly degraded during heat shock as shown by in vitro translation and dot blot hybridization with a cDNA probe. Upon recovery from heat shock, the tissue resumes the synthesis of .alpha.-amylase in 2-4 hr. However, in the presence of a transcription inhibitor, cordycepin, the resumption of synthesis of .alpha.-amylase does not take place, indicating that new transcription of .alpha.-amylase genes is necessary for this recovery process. The degradation of .alpha.-amylase mRNAs correlates with the rapid destruction of endoplasmic reticulum as observed by electron microscopy, a phenomenon that has not been reported previously as a heat shock response. Since .alpha.-amylase mRNA is associated with the endoplasmic reticulum via membrane-bound polyribosomes, we suggest that the destruction of the endoplasmic reticulum during heat shock causes the destabilization and the eventual degradation of .alpha.-amylase mRNA.