Effect of long periods of low temperature exposure on protein synthesis activity in wheat seedlings

Long periods of low temperature exposure induce complex changes in the metabolism of nucleic acids and protein molecules in plants: i.e. new proteins; new tRNA isoacceptors and new mRNAs appear with altered minor nucleotide contents, implying that the components of the protein synthesising system change during cold treatment. To study the effect of changes in the RNA pool on the intensity of protein synthesis, different homologous and heterologous cell-free protein synthesising systems were constructed with polysome fractions and tRNAs isolated from non-treated wheat seedlings and from seedlings cold treated for a long period. The homologous cell-free protein synthesising systems contained polysome fractions from non-treated samples of the wheat cultivar Martonvasari 15 and from samples treated for 1, 5 or 7 weeks together with their own tRNA. Heterologous systems were constructed from the tRNA fractions of cold-treated seedlings with S-23 fractions of non-treated ones and vice versa. Cell-free protein synthesis was carried out at 4 and 30 degrees C. The results demonstrate that independently of the length of the cold period the intensity of protein synthesis in homologous cold-treated systems at 4 degrees C was as high as the intensity of homologous non-treated systems at 30 degrees C. Combinations of cold-treated S-23 fractions with cold-treated tRNAs were about 30% more effective than cold-treated S-23 fractions with non-treated tRNAs at 4 degrees C, while combinations of cold-treated tRNAs with non-treated S-23 fractions resulted in only a slight decrease in activity at 30 degrees C. It can thus be concluded that long-term cold exposure leads to changes in the protein synthesising system, resulting in optimal synthesising capacity under the altered conditions. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.