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

Abstract

Water stress, applied to the roots of six-day-old barley seedlings markedly reduced the capacity of their leaves to synthesize proteins during greening, a process that normally involves intense synthetic activity. Upon illumination of etiolated seedlings protein synthesis commenced most rapidly in the basal region, and then declined in activity. Thereafter, in turn, the middle and apical regions exhibited a similar pattern of synthetic activity; this is indicative of a ‘wave’ of protein synthesis progressing from the base of the leaf to the apex as greening proceeded. The synthesis of proteins varied both quantitatively and qualitatively in different regions of the leaf during greening. For example, there was a noticeable increase in ribulose-1, 5-bisphosphate carboxylase synthesis in the apical region of the leaf compared to the basal region. Water stress reduced protein synthesis in all regions of the leaf, although most effectively in the oldest, apical regions. Upon return to full water status, the basal regions recovered the most rapidly and to the greatest extent. Similar results were obtained when both intact greening leaves, and isolated segments from different regions of the leaf were used. The reduction in protein synthesis elicited by water stress was not due to a selective quantitative change in any particular protein; one protein, of an approximate molecular weight of 60 kD, appeared to be synthesized only under stress conditions.