Heat Shock Proteins in Sorghum and Pearl Millet; Ethanol, Sodium Arsenite, Sodium Malonate and the Development of Thermotolerance

Treatment of sorghum (Sorghum bicolor L. Moench) seedlings with arsenite or malonate at normal growing temperatures (35 °C) resulted in restricted synthesis of heat shock proteins (HSPs) without affecting 'normal' protein synthesis. In millet (Pennisetum glaucum (L.) R.Br.) seedlings, little alteration in the pattern of proteins synthesized was detected in the presence of these compounds. Ethanol greatly reduced in vivo protein synthesis in both species. Incubation with arsenite and malonate resulted in an increase in thermotolerance of both sorghum and millet seedlings. Additionally, HSPs were synthesized at an otherwise injurious high temperature if a pretreatment with arsenite or malonate was given. Extraction of RNA from arsenite-treated seedlings indicated that translatable RNAs encoding HSPs are present in both sorghum and millet seedlings at 35 °C and it is possible that they are not translated in vivo until an increase of temperature is also perceived by the seedling. Thus, treatment with arsenite results in both the transcription of genes encoding HSPs and in the development of thermotolerance. This provides further evidence for the involvement of HSPs, or the mRNA encoding these proteins, in thermotolerance.