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 , in leaf cells are water saving and homeostasis of reactants. This paper advances methods for detecting the occurrence of negative P in leaves. Biomechanical models of pressure-volume (PV) curves predict that negative P does not change the linearity of PV curve plots of inverse balance pressure, P , 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 domain because of negative P . 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 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 domain. Non-collapse means that P 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 .