Variations in Protein Synthesis in Different Regions of Greening Leaves of Barley Seedlings and Effects of Imposed Water Stress

Water stress, applied to the roots of six-day-old barley seedlingsmarkedly reduced the capacity of their leaves to synthesizeproteins during greening, a process that normally involves intensesynthetic activity. Upon illumination of etiolated seedlingsprotein synthesis commenced most rapidly in the basal region,and then declined in activity. Thereafter, in turn, the middleand apical regions exhibited a similar pattern of syntheticactivity; this is indicative of a ‘wave’ of proteinsynthesis progressing from the base of the leaf to the apexas greening proceeded. The synthesis of proteins varied bothquantitatively and qualitatively in different regions of theleaf during greening. For example, there was a noticeable increasein ribulose-1, 5-bisphosphate carboxylase synthesis in the apicalregion of the leaf compared to the basal region. Water stressreduced protein synthesis in all regions of the leaf, althoughmost effectively in the oldest, apical regions. Upon returnto full water status, the basal regions recovered the most rapidlyand to the greatest extent. Similar results were obtained whenboth intact greening leaves, and isolated segments from differentregions of the leaf were used. The reduction in protein synthesiselicited by water stress was not due to a selective quantitativechange in any particular protein; one protein, of an approximatemolecular weight of 60 kD, appeared to be synthesized only understress conditions. Key words: Water stress, Protein synthesis, Barley seedlings