The water relations of hemlock (Tsuga canadensis). II. The kinetics of water exchange between the symplast and apoplast

摘要

We present a theoretical analysis of the events that occur while a plant enclosed in a pressure bomb evolves from one equilibrium balancing pressure to another. The initial rate of efflux from any one cell in response to a pressure increment of Delta;Pequals (ALp)iDelta;P, where (ALp)iis the surface area times hydraulic conductivity of the cell's semipermeable membrane(s). If the volume changes and pressure increment are small, the cell will approach equilibrium exponentially. The half time of the exponential process is governed by (ALp)iki, wherekiis the cell constant (= the combined rate of change of osmotic and turgor pressure with the volume expressed from the cell). Experimental studies of the kinetics of water exchange between the symplast and apoplast of hemock (Tsuga canadensis) shoots in a pressure bomb reveal that the cells collectively behave as though they fall into three distinct populations which approach equilibrium with different half times.