Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 18.104.22.168) (RubisCO) was quantified in 7-day-old leaves of barley (Hordeum vulgare L., var. Alfa) treated with NaCl using polyacrylamide gel electrophoresis. The treated plants showed a decrease in the level of RubisCO. In the presence of 100 mM NaCl the level of total soluble protein on a fresh weight basis was about 64% of the control, whereas the level of RubisCO was only about 20% that of control plants.
Salinity induced marked quantitative and qualitative changes in polypeptide profiles of soluble leaf proteins. Enhanced levels of 76, 60, 47, 43 and 30 kD polypeptides and reduced levels of 55 and 15 kD polypeptides were observed in NaCl-treated plants. The appearance of one new polypeptide of 26-25 kD was found in NaCl-treated samples.
The influence of salinity on the synthesis of RubisCO was followed by in vivo labeling with a 14C-amino acid mixture (14C-AAM). The results demonstrate that salinity inhibits the synthesis of total soluble protein with a more pronounced inhibition of synthesis of RubisCO.