A Circuit Analog Model for Studying Quantitative Water Relations of Plant Tissues

Using arrays of resistors and capacitors, a lumped circuit analog of plant tissue is developed. The circuit elements of the analog are identified in terms of physiological variables (hydraulic conductivities, water capacities, and cell dimensions) which can be measured in the laboratory. With the aid of a circuit simulation subroutine, the model was solved to predict water potential distributions as a function of position and time in plant tissues of three, six, and nine cells. Results presented for the six-cell case indicate that local equilibrium may or may not occur depending on the actual values of tissue hydraulic conductivities, water capacities, and the rate of change of water potential at the tissue boundaries. However, present measurements and estimates of tissue parameters suggest that local equilibrium is more the rule than the exception. Membrane resistance is an especially important parameter because it serves to isolate the vacuoles from the cell walls in addition to increasing the natural vacuole response time to changes in water potential.The proposed model should be useful in studying water transport processes in roots, stems, and leaves. Nonhomogeneity can be taken into account easily. Nonlinearity (changes in circuit parameter values with potential) which is known to occur in plant tissues could be incorporated also if the required information were available.