NMR studies of water compartmentation in carrot parenchyma tissue during drying and freezing

An analysis is presented of the effect of drying and freezing on the distribution and pulse spacing dependence of water proton transverse relaxation times in carrot parenchyma tissue. The relaxation behaviour can be interpreted by treating the effects of changing subcellular morphology with a numerical cell model and combining this with a two-site proton exchange model to take account of solutes dissolved in the vacuolar fluid. In this way it is shown that drying removes water primarily from the vacuolar compartment, causing cell shrinkage and concentration of dissolved solutes, with little change in the volume of intercellular air spaces. Freezing causes initial ice crystal formation in the vacuolar compartment which concentrates the dissolved solutes. However, even at 248 K substantial quantities of nonfreezing water are associated with the cell walls and dissolved biopolymers. Comparison is made with previous studies on apple tissue.