作 者 ：Zhang Da-peng and Luo Guo-guang
Keywords:Fruit of grapevine, Water movement, Water potential, Pressure potential, Solute potential,
Abstract:The experiment was carried out during the ripening of grape (Vitis vinifera L. and V. vinifera × V. labrusca) fruits using the technique of dye tracing and measurement of water potential. Under the natural conditions of sufficient soil water supply and those of a high evapotranspiration potentiality on clear days, the water in fruits was transfered, during the morning and afternoon, out of the clusters and into the xylem of shoots; but the fruits capture water in the late afternoon and evening from the xylem of shoots. The diurnal variations of the water exchange between fruits and the xylem of shoots have been described and these variations seemed to be relevant not only to the differences of water potential between leaves and fruits but also to the hydraulic status of fruits. Under the mild water stress, the variations of the diurnal "fruits-shoots" water exchange were similar to those under the conditions of ample water supply, but the rate of "fruits-shoots" water exchange in the lightly stressed vine was decreased as compared with the fully watered vines. After a certain period of severe water stress, the fruits possessed a great capacity of conserving their water and an equilibrium in water potential was set up between leaves and fruits so that the fruits did not lose any more water. Under a sudden severe water stress, the fruits lost water at a higher outflux rate than when the water supply was sufficient. However, this water loss ceased rapidly. The water flowing out from the fruits was privileged to pass in the lateral shoots located above and on the same side of the fruits, and then the water might enter the primary shoot leaves situated above and on the same side of the fruits. Water captured by the fruits of the well watered vines in the evening came from the roots while under severe stress water might be obtained from the roots and also from the leaves as well. The fruit cell water potential, solute potential and pressure potential were different from those of leaves, mainly in the more important differences of water potential necessitated for the volume changes of fruit cell after incipient plasmolysis in com parison with leaves. Finally the relationships between water exchange and water potential dif ferences between "fruits-shoots", associated with the fruits hydraulic status, have been discussed. The possible relationships between water "sink-source" of fruits and the fruit development have been analysed.
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