Control of wheat leaf growth under saline conditions

Abstract

Water relations parameters in individual cells and the biophysical parameters controlling leaf growth were studied in context of salt stress. Various levels of NaCI, ranging from 25 to 250mo1 m^-3, were used to salinize the medium. The parameters were measured in growing zone of the first emerged leaf of wheat seedlings (cv. Flanders, a British variety). In case of leaf elongation rate a two phase response was observed i.e. an immediate decrease followed by subsequent recovery. The elongation rate decreased within 1 to 2 minutes of the stress onset and later started recovering after 1 to 2 h and was almost fully recovered after 24h for all NaCI concentrations. Turgor pressure measured in epidermal and mesophyll cells was about 0.45 MPa in control plant cells where the tissue osmotic pressure was equal to 1.1 MPa. The cell wall transpiration tension was found to be equivalent to 0.1 MPa indicating the high values of osmotic pressure of osmotically active solutes present in cell wall i.e. about 0.6 to 0.7 MPa. The turgor pressure did not change after the salt addition (0 to 150mol m^-3 NaCI), however, the osmotic pressure increased continually with time. Turgor pressure dropped when higher concentrations (200 and 250mol m^-3) of NaC1 were applied to the medium. This is presented as evidence that growing leaf cells maintained their turgor pressure in response to the salt stress by taking up the osmotically active solutes present in the cell wall. The salt stress did not have any effect on Instron tensiometric measurements (in vitro) of elastic and plastic extension of the cell wall.