Evidence for transcriptional and post-transcriptional control of protein synthesis in water-stressed wheat leaves: A quantitative analysis of messenger and ribosomal RNA

Although it has long been recognized that water;deficit in plants can resul t in a reduction in protein synthesis, the detailed mechanisms behind this have not been thoroughly elucidated. In the present study, experiments were conducted to investigate the effects of water stress on protein synthesis at both transcriptional and post-transcriptional levels in spring wheat lea ves (Triticum aestivum L. cv. Longchun No. 10). The results revealed that s tressing wheat seedlings in -0.5 MPa PEG solutions for 0, 24, 48 and 72 h r esulted in a progressive decrease in leaf protein synthesis as reflected by the incorporation of H-3-Leucine into chloroplast protein. Accompanying th e decrease of protein synthesis, the synthetic rate of leaf RNA, the steady state levels of cellular mRNAs and rRNAs, as well as the translatability o f poly(A)(+)-RNAs decreased significantly, indicating that water stress not only affected gene transcription and RNA accumulation in wheat leaves but impaired the messenger-like properties of mRNAs. Furthermore, as the loss o f rRNA species might result in disruption of the ribosomal subunits and tha t of mRNAs might reduce the proportion of ribosomes organized as polyriboso mes, it is conceivable that water stress also affected the translational le vel of leaf gene expression. Based on these results, the slowdown of protei n synthesis in water-stressed wheat leaves can be attributed to both transc riptional and post-transcriptional control mechanisms.