Phenotypical Temperature Adaptation of Protein Synthesis in Wheat Seedlings : QUALITATIVE ASPECTS. INVOLVEMENT OF AMINOACID:tRNA-LIGASES.

Phenotypical temperature adaptation of protein synthesis in wheat (Triticum aestivum L.) seedlings is not affected by darkness (etiolation), by partial inhibition of protein biosynthesis (10(-3)m fluorophenylalanine), or by changing the amino acid precursor and the radioisotope ([(3)H]valine instead of [(14)C]leucine). The temperature coefficient (mu), as well as the optimum temperature of in vivo protein synthesis, increases with rising preadaptation temperature, as normally observed. Protein turnover studies revealed that only proteins with a short half-life time (t((1/2)) = 2 to 4 hours) are labeled to a measurable extent during the temperature adaptation experiments. A heat-labile protein has been detected and partially characterized by means of polyacrylamide gradient gels. Leucine:tRNA-ligase (EC 6.1 1.4) from heat-pretreated wheat seedlings exhibits enhanced thermal stability. In Arrhenius curves, the upper transition point shifts from 30 to 34 degrees C, depending on preadaptation temperature. Only the leucine:tRNA-ligase extracted from heat-adapted plants is stable when the enzyme extracts are subjected to a 34 degrees C heat treatment.