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

Abstract

In response to a phytohormone, gibberellic acid, the aleurone layers of barley seeds synthesize and secrete α-amylases, which are coded by a set of stable mRNAs. When aleurone layers are subjected to heat shock treatment, the synthesis of α-amylase is suppressed while heat shock proteins are induced. The suppression of α-amylase synthesis is not the result of translational control as reported in several other systems. Rather, the sequences of α-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 α-amylase in 2-4 hr. However, in the presence of a transcription inhibitor, cordycepin, the resumption of synthesis of α-amylase does not take place, indicating that new transcription of α-amylase genes is necessary for this recovery process. The degradation of α-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 α-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 α-amylase mRNA.