9 Growth and Water Transport in Fleshy

Fruit volumetric growth is primarily the result of water accumulation, and hence maintenance of fruit growth requires coordination between long-distance water and solute transport through the vascular tissue, and short-distance water and solute uptake at the level of individual cells. One hypothesized coordinating principle is that for fruit growth to occur, there must be a favorable difference in total water potential between the fruit and the rest of the plant (e.g., Grange and Andrews, 1994). Essentially all of the previous studies of fruit water relations, including our own, have been based on whole fruit measurements of total water potential, and many of these are consistent with this principle. The current understand-ing of fruit water relations, however, particularly at the cellular level, is quite rudimentary, and it may be premature to generalize about the water relations of the fruit as a whole before we have a clear understanding of the water relations of the component cells. In this chapter we give a brief overview of the water relations of fleshy fruits as they relate to the process of fruit growth, particularly in grapes, and present experimental measure-ments of fruit water balance, whole fruit osmotic potential, and intact fruit cell turgor in the grape berry. Our turgor measurements indicate that fruit cell turgor is substantially depressed by the presence of solutes in the apoplast. The consequences that apoplastic solutes may have on water exchange between the fruit and the plant are discussed, as well as questions and directions for future research. Fleshy Fruit Growth, Expansion, and Contraction Fleshy fruit arise from a wide range of tissues (see Coombe, 1976), and in some respects the interaction between xylem and phloem transport during fruit growth is similar to that experienced by most other growing plan