Involvement of a Novel Peptide in the Heat Shock Response of Australian Wheats

Abstract

A low molecular weight peptide, induced by exposure of coleoptiles to heat stress at 41°C, has been detected by reversed-phase high performance liquid chromatography of extracts from coleoptiles of five wheat (Triticum aestivum) cultivars. This component is detected within 1 h of a 41°C heat shock, is not detected 48 h after cessation of the heat shock, and remains present during a continuous 24 h heat treatment. The appearance of this component is also induced by exposure of the coleoptile to 0.1 M sodium arsenite or 10% ethanol. When other species such as barley (Hordeum vulgare), soybean (Glycine max), sorghum (Sorghum bicolor), maize (Zea mays), mungbean (Vigna radiata), or rice (Oryza sativa) were examined for the presence of a component eluting in the same position, it was only detected in maize. The amino acid sequence for the heat-induced peptide from wheat was determined to be: V-L-V-P-V-P-Q-L-Q-P-Q-N-Q-P/Q. The sequence of 12 of these amino acids is the same as the N-terminal sequence of α- and β gliadins (wheat endosperm storage proteins). The production of this heat-induced peptide in aneuploids of Chinese spring wheat indicated that the peptide gene was located on the same chromosome arm as one of the gliadin genes. The presence of this gliadin-like peptide in heat-stressed coleoptiles may be due to the presence of five heat shock elements in the gene sequence of gliadins. The potential heat inducibility of the gliadin gene has important implications for end-use quality of wheat. The results also imply that seed proteins may have a function other than storage of nitrogen.