Vascular functioning and development of the kiwifruit berry (Actinidia deliciosa)

The aim of this study was to understand kiwifruit berry development and the role of cell turgor and the phloem unloading pathway in development. Important aspects of berry development include the size of the fruit and its composition. The fresh weight growth curve of the kiwifruit berry was shown to be double sigmoid in shape. Dry weight accumulated linearly for the initial 139 days after anthesis (DAA). At this time the soluble solids concentration began to increase. Berry firmness was measured using two methods, with the penetrometer and with a new non-destructive method, utilising skinfold callipers. Both methods exhibited similar results, indicating that the skin callipers may be useful in the future for non-destructive berry rheological measurements. Cell turgor was measured indirectly from measurements of symplasmic and apoplasmic solute potentials, and the matric potential of the berry. Apoplasmic sap, required to measure the apoplasmic solute potential, was extracted using two different methods the pressure chamber and through centrifugation. Measurements of sap osmotic potential suggest that the sap extracted using the centrifuge was contaminated with symplasmic sap, resulting in a negative cell turgor estimate. However, the pressure chamber technique provided apoplasmic sap that produced a more accurate estimate of cell turgor. Direct estimates of cell turgor were only obtained from the midpoint of the growing season because of contamination with symplasmic sap, but the values obtained were comparable to literature values for developing grape and tomato berries. The phloem unloading pathway in the fruit was investigated using a symplasmic tracer dye, carboxyfluorescein diacetate coupled with 14C labelling and autoradiography. The phloem unloading pathway was symplasmic until 91 DAA when the dye was restricted to the phloem cells only, indicating a change to an apoplasmic pathway. However, due to the lack of functional unloading seen in radiolabelled samples, a change in the phloem unloading pathway could not be confirmed