Water-deficit-induced translational control in Nicotiana tabacum

The effect of prolonged water deficit on mRNA translation was quantitatively analysed in apical and basal leaves of whole tobacco (Nicotiana tabacum) plants. The level of large polysomes (six or more ribosomes per mRNA) was significantly higher in apical than basal leaves under well-watered conditions. In both young and old leaves, water deficit caused a progressive reduction in levels of polysomes with concomitant increases in 80S monosomes, indicative of reduced initiation of translation. Despite the global reduction in polysome formation over 144 h of water deficit, the water-deficit-induced putative lipid transfer protein (ltp) mRNA was associated with large polysomes and LTP content increased. Osmotin (osm) mRNA, another water-deficit-induced transcript, also remained associated with large polysomes during prolonged water deficit. In contrast, mRNAs encoding the non-stress proteins ribulose bisphosphate carboxylase/oxygenase small subunit (rbcS) and eukaryotic initiation factor 4A (eIF4A) decreased in abundance and shifted to small polysomes and non-polysomal complexes, indicating that initiation of translation of these mRNAs was impaired by water deficit. These results show that translational regulation is a component of the water-deficit response and the differential translation of individual mRNAs is distinct in leaves of different age.