Turgor, Growth and Rheological Gradients of Wheat Roots Following Osmotic Stress

The growth rate of hydroponically grown wheat roots was reduced by mannitol solutions of various osmotic pressures. For example, following 24 h exposure to 0·96 MPa mannitol root elongation was reduced from 1· mm h−1 to 0·1 mm h−1 Mature cell length was reduced from 290 μm in unstressed roots to 100 μm in 0·96 MPa mannitol. This indicates a reduction in cell production rate from about 4 per h in the unstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4·5 mm in unstressed roots but became shorter as growth ceased in the proximal regions at higher levels of osmotic stress. The turgor pressure along the apical 5·0 mm of unstressed roots was between 0·5 and 0·6 MPa but declined to 0·41 MPa over the next 50 mm. Following 24 h in 0·48 (200 mol m−3) or 0·72 MPa (300 mol m−) mannitol, turgor along the apical 50 mm was indistinguishable from that of unstressed roots but turgor declined more steeply in the region 5·10 mm from the tip. At the highest level of stress (0·96 MPa or 400 mol m−3 mannitol) turgor declined steeply within the apical 20 mm.