Experimental evidence for negative turgor pressure in small leaf cells of Robinia pseudoacacia L versus large cells of Metasequoia glyptostroboides Hu et W.C. Cheng. 2. Höfler diagrams below the volume of zero turgor and the theoretical implication for pressure‐volume curves of living cells

The physiological advantages of negative turgor pressure, P t , in leaf cells are water saving and homeostasis of reactants. This paper advances methods for detecting the occurrence of negative P t in leaves. Biomechanical models of pressure‐volume (PV) curves predict that negative P t does not change the linearity of PV curve plots of inverse balance pressure, P B , versus relative water loss, but it does predict changes in either the y ‐intercept or the x ‐intercept of the plots depending on where cell collapse occurs in the P B domain because of negative P t . PV curve analysis of Robinia leaves revealed a shift in the x ‐intercept ( x ‐axis is relative water loss) of PV curves, caused by negative P t of palisade cells. The low x ‐intercept of the PV curve was explained by the non‐collapse of palisade cells in Robinia in the P B domain. Non‐collapse means that P t smoothly falls from positive to negative values with decreasing cell volume without a dramatic change in slope. The magnitude of negative turgor in non‐collapsing living cells was as low as −1.3 MPa and the relative volume of the non‐collapsing cell equaled 58% of the total leaf cell volume. This study adds to the growing evidence for negative P t .