Vascular functioning and the water balance of ripening kiwifruit (Actinidia chinensis) berries

Abstract

Indirect evidence suggests that water supply to fleshy fruits during the final stages of development occurs through the phloem, with the xylem providing little water, or acting as a pathway for water loss back to the plant. This inference was tested by examining the water balance and vascular functioning of ripening kiwifruit berries (Actinidia chinensis var. chinensis ‘Hort16A’) exhibiting a pre-harvest ‘shrivel’ disorder in California, and normal development in New Zealand. Dye labelling and mass balance experiments indicated that the xylem and phloem were both functional and contributed approximately equally to the fruit water supply during this stage of development. The modelled fruit water balance was dominated by transpiration, with net water loss under high vapour pressure deficit (Da) conditions in California, but a net gain under cooler New Zealand conditions. Direct measurement of pedicel sap flow under controlled conditions confirmed inward flows in both the phloem and xylem under conditions of both low and high Da. Phloem flows were required for growth, with gradual recovery after a step increase in Da. Xylem flows alone were unable to support growth, but did supply transpiration and were responsive to Da-induced pressure fluctuations. The results suggest that the shrivel disorder was a consequence of a high fruit transpiration rate, and that the perception of complete loss or reversal of inward xylem flows in ripening fruits should be re-examined.

Fruit calcium accumulation coupled and uncoupled from its transpiration in kiwifruit

“…Reduction of the evaporative destiny at lowered VPD agreed with previous observation in kiwifruit (Morandi et al, 2010a). Clearwater et al (2012) compared over a 30-day period the effect of microclimate (dry or humid) of the growing environment on water budget in a ripening fruit of a closely related species (Actinidia chinensis) showing that at the wetter environment transpirational water losses were a less dominant feature of the water balance. It is unfortunate that in these papers the physiological implication of changed water budget on fruit Ca accumulation was not examined.…”

“…The main fruit quality traits focussed by carbon and water balance models relate to size, dry matter and sugars content, and fraction of edible tissue sometimes under contrasting environmental (temperature, air vapour pressure deficit) and plant conditions (fruit load and fruit position) (Lescourret and Génard, 2005;Liu et al, 2007;Clearwater et al, 2012). In that context, the importance of water potential, osmotic potential and turgor pressure of fruit and environmental conditions as driving force of water import have been emphasized along with variations of hydraulic resistance of fruit and stalk and skin conductance Montanaro et al, 2012;Mazzeo et al, 2013).…”

“…The various components of the fruit water budget (xylem, phloem, transpiration and growth) have been analysed in detail (Lang and Thorpe, 1989;Fishman and Génard, 1998) also in relation to the functionality of the vasculature (Clearwater et al, 2012) and, interestingly, to the VPD of the surrounding environment even if with contrasting conclusions. For example, in tomato increased VPD reduced fruit xylem inflows while phloem flow was almost unaffected, similarly, in young kiwifruit, increased VPD increased xylem and transpiration, but does not affect phloem imports (Guichard et al, 2005;Morandi et al, 2012).…”

Integrating Physiology and Architecture in Models of Fruit Expansion

“…In kiwifruit and other fleshy fruit such as grape vine (Rogiers et al, 2004), a shrivel disorder at the final stages of growth appears as a longitudinal pattern of softening and shrinkage starting at the stylar (blossom) end (Thorp et al, 2007). The cause of this disorder may be a consequence of reduced xylem density or hydraulic conductance that prevents adequate supply of water to the stylar end (Clearwater et al, 2012). At the fruit's surface, the pattern and the density of cuticular cracks (Gibert et al, 2007, 2010) together with the microclimate surrounding the fruit (Li et al, 2001; Saudreau et al, 2007) may impact water loss due to transpiration.…”

Vascular anatomy of kiwi fruit and its implications for the origin of carpels

“…The growth of fleshy fruits involves a balance between the supply or withdrawal of water via the vascular tissue, and losses to transpiration (Morandi et al, 2007; Clearwater et al, 2011). Kiwi fruit is of great agricultural, botanical, and economic interest.…”