HEAT ADAPTATION OF PROTEIN-SYNTHESIS IN WHEAT - A PHENOMENON BESIDES HEAT-SHOCK RESPONSE

Translational efficiency of wheat ribosomes was studied as a function of an in vivo temperature pretreatment of wheat seedlings. The ribosom es were isolated from 41 or 36-degrees-C-adapted and non-adapted (20-d egrees-C) wheat seedlings. The poly-U-dependent translational efficien cy, measured as H-3 phenylalanine incorporation into poly-Phe, was enh anced up to 3-fold in the heat-adapted ribosomes. The adaptive enhance ment was due to the large ribosomal subunit as demonstrated earlier by heterologous recombination of ribosomal subunits, obtained from the p lants pretreated by different temperatures. According to this, the pat tern of ribosomal proteins of the large subunit exhibited pronounced d ifferences as a function of preadaptation temperature: one spot increa sed markedly in the protein staining intensity on the two-dimensional polyacrylamide gels, while another almost disappeared. Two minor prote in spots disappeared at high preadaptation temperatures. An evaluation of the protein phosphorylation of ribosomal proteins yielded a decrea sed P-32-label degree in case of the small subunit of heat-adapted rib osomes. These results are considered to be an important molecular corr elation to phenotypical temperature adaptation of in vivo protein synt hesis in wheat, where the optimum temperature of C-14-leucine incorpor ation into the total protein fraction, as a measure of in vivo protein synthesis, shifts to higher grades with increasing preadaptation temp erature of the wheat seedlings. Besides Triticum aestivum L. (spring w heat; cv. Kolibri), heat adaptation potentials of T dicoccoides (tetra ploid), T. longissimum (2n), T monococcum (2n), T. speltoides (2n) and T tauschii (2n) were investigated. The temperature coefficient mu (ap parent activation energy) also underwent adaptive alterations, althoug h these changes were not unidirectional. T tauschii proved to be the s pecies with the most pronounced adaptive potential in the high tempera ture range, surpassed only by the heat adaptability of 14 d-postanthes is caryopses: its optimum temperature of in vivo protein synthesis ros e by more than 20-degrees-C after a 38-degrees-C-preadaptation period (2 d).