STRESS RESPONSES IN NICOTIANA-SYLVESTRIS CELLS TO SALINITY AND HIGH-TEMPERATURE .2. SYNTHESIS OF HEAT-SHOCK PROTEINS AND POLYPEPTIDE PHOSPHORYLATION

Synthesis of heat shock proteins (HSPs) and phosphorylation of individual polypeptides were investigated in cell suspension culture of Nicotiana sylvestris L. in relation to response to salinity and high temperature stresses. HSP synthesis was studied in wild-type cells and salt-resistant strain (N(r)E(s)-1), which possessed an increased thermotolerance as well. Labeling with S-35-methionine and electrophoretic separation of proteins was employed. The level of mRNA for HSP (mol wt of 70 kD) was estimated by northern-blot analysis of total RNA with pHSP-4.8 plasmid. Higher thermotolerance of the salt-resistant strain of Nicotiana sylvestris under normal temperature (25-degrees-C) or hyperthermia (38 or 40-degrees-C) did not correlate with HSP synthesis, but with phosphorylation of some polypeptides (47, 32 - 31, 27, and 24 - 23 kD). Their modification seemed to be important for cell resistance to both high temperature and salinity. Hence, the formation and functioning of these systems are determined by special salt-resistance mechanisms, the expression of which is constitutive.