Water Stress and Protein Synthesis

Responses of the drought-tolerant moss, Tortula ruralis, to steady state water stress have been studied. A decrease in fresh weight, an inhibition of amino acid incorporation into protein, and a decline in polysome population occur with increasing degree of water stress. Cyclohexirnide treatment prevents the stress-induced loss of polysomes. Ribonuclease activity increases during stress and this increase is partially prevented by cycloheximide. There is a lack of correlation between ribonuclease activity and polysome levels. During stress, the decrease in polysome level and the increase in ribonuclease activity do not coincide in time, the former occurring earlier. Furthermore, ribosomes from the stressed moss do not appear to be complexed with mRNA fragments, as indicated by their inability to effect the formation of a peptide bond. It is concluded that the primary cause of polysome loss during water stress is the run-off of ribosomes from mRNA coupled with their failure to reinitiate.