Fig 1.
Fruit mass, expressed fruit juice osmotic potential (A) and fruit skin color (B) of developing European plum. Fruit skin color is indexed as a change in Hue angle. The vertical dashed line indicates the transition between stage II and stage III. Time (x-axis) is in days after full bloom (DAFB). Data represent means ± SE.
Fig 2.
Typical weekly time courses of change in fruit volume calculated from changes in the three orthogonal diameters of European plum fruit during stage II at 75 days after full bloom (DAFB) (A), in early stage III (103 DAFB) (B) and in late stage III (132 DAFB) (C). In the morning of the fourth day (indicated by arrow), fruit pedicels were steam-girdled (dashed line) or detached (dashed and dotted line), but all fruit remained in situ in the canopy. Un-treated fruit served as controls for comparison. Data are for a single fruit representative for the steam-girdled, detached and control treatments. D and N on the x-axis indicate day (light) and night (dark) periods.
Fig 3.
Representative diurnal time courses of xylem, phloem and transpiration flow rates in developing European plum fruit (A: Stage II, 76 days after full bloom (DAFB), B: Early stage III, 104 DAFB, C: Late stage III, 132 DAFB). The pattern of change in water vapor pressure deficit (VPD) is given for comparison. Xylem, phloem and transpiration flows were calculated from net flows determined for un-treated control fruit, steam-girdled fruit and detached fruit. For details see Materials and Methods.
Fig 4.
Daily total xylem inflow (positive), total xylem backflow (negative) and net daily xylem flow in stage II (A) and stage III (B) for European plum fruit as affected by atmospheric vapor pressure deficit (VPD). The net xylem flow was calculated as the algebraic sum of the total daily inflows plus the total daily backflows. Because fruit softening may slightly affect the measurement of fruit diameter change by a lightly spring-loaded linear variable displacement transducer, data for the last sampling period were not shown, as this is when fruit softening would have been most pronounced. Data represent means ± SE.
Fig 5.
(A) Developmental time course of the water flow rates through the skin (transpiration) and through the pedicel (xylem and phloem) of fruit of European plum. Values of atmospheric water vapor pressure deficit (VPD) are provided for comparison. (B) Xylem flow rates and (C) transpiration flow rates as affected by VPD. (D) Relationship between xylem flow rate and transpiration flow rate. The vertical dashed line in A indicates the stage II/III transition. Xylem, phloem and transpiration flows were calculated from flows determined for un-treated control fruit, steam-girdled fruit and detached fruit. Data represent means ± SE for 24 h time intervals. For details see Materials and Methods.
Fig 6.
Transpiration of developing European plum fruit.
(A) Transpiration rate (per fruit). (B) Transpiration flux density (volume per mm2 of skin and day). (C) Skin permeance (flux density per unit water vapor pressure deficit (volume per mm2 of skin and day and VPD)). Transpiration flux density was calculated by dividing the flow rate in transpiration per fruit by fruit surface area. To avoid confusion, the absolute of value of the flux density and skin permeance is shown. Skin permeance was calculated by dividing transpiration flux density by the VPD. The open symbols represent the final sampling date. Because fruit softening may slightly affect the measurement of fruit diameter change by a lightly spring-loaded linear variable displacement transducer, data for the last sampling period were excluded from the regression analysis as this is when fruit softening would have been most pronounced. Data in Fig 6A represent means ± SE.
Fig 7.
Relative contributions of xylem and phloem sap inflows to total sap inflow to fruit of developing European plums.
Total inflow (100%) was calculated as the sum of the xylem and phloem inflows. Data represent means ± SE.