Dipartimento delle Culture Europee e del Mediterraneo, Architettura, Ambiente, Patrimoni Culturali DiCEM, Università degli Studi della Basilicata, Italy.
Ann Bot. 2013 Jul;112(1):197-205. doi: 10.1093/aob/mct101. Epub 2013 May 8.
Xylem flows into most fruits decline as the fruit develop, with important effects on mineral and carbohydrate accumulation. It has been hypothesized that an increase in xylem hydraulic resistance (RT) contributes to this process. This study examined changes in RT that occur during development of the berry of kiwifruit (Actinidia deliciosa), identified the region within the fruit where changes were occurring, and tested whether a decrease in irradiance during fruit development caused an increase in RT, potentially contributing to decreased mineral accumulation in shaded fruit.
RT was measured using pressure chamber and flow meter methods, the two methods were compared, and the flow meter was also used to partition RT between the pedicel, receptacle and proximal and distal portions of the berry. Dye was used as a tracer for xylem function. Artificial shading was used to test the effect of light on RT, dye entry and mineral accumulation.
RT decreased during the early phase of rapid fruit growth, but increased again as the fruit transitioned to a final period of slower growth. The most significant changes in resistance occurred in the receptacle, which initially contributed 20 % to RT, increasing to 90 % later in development. Dye also ceased moving beyond the receptacle from 70 d after anthesis. The two methods for measuring RT agreed in terms of the direction and timing of developmental changes in RT, but pressure chamber measurements were consistently higher than flow meter estimates of RT, prompting questions regarding which method is most appropriate for measuring fruit RT. Shading had no effect on berry growth but increased RT and decreased dye movement and calcium concentration.
Increased RT in the receptacle zone coincides with slowing fresh weight growth, reduced transpiration and rapid starch accumulation by the fruit. Developmental changes in RT may be connected to changes in phloem functioning and the maintenance of water potential gradients between the stem and the fruit. The effect of shade on RT extends earlier reports that shading can affect fruit vascular differentiation, xylem flows and mineral accumulation independently of effects on transpiration.
木质部液流在大多数果实发育过程中都会减少，这对矿质和碳水化合物的积累有重要影响。有人假设木质部水力阻力（RT）的增加对此过程有贡献。本研究检测了猕猴桃果实发育过程中 RT 的变化，确定了果实中发生变化的区域，并检验了果实发育过程中光照减少是否会导致 RT 增加，从而可能导致遮荫果实中矿质积累减少。
使用压力室和流量计法测量 RT，比较了两种方法，并使用流量计将 RT 分配到果柄、果托和果实近端和远端。使用染料作为木质部功能的示踪剂。人工遮荫用于测试光照对 RT、染料进入和矿质积累的影响。
RT 在果实快速生长的早期阶段下降，但在果实进入生长缓慢的最后阶段时再次上升。阻力的最大变化发生在果托，果托最初对 RT 的贡献为 20%，在发育后期增加到 90%。从开花后 70 天起，染料也不再向果托外移动。两种测量 RT 的方法在 RT 发育变化的方向和时间上一致，但压力室测量值始终高于流量计估计的 RT 值，这引发了关于哪种方法最适合测量果实 RT 的问题。遮荫对果实生长没有影响，但增加了 RT，减少了染料的移动和钙浓度。
果托区 RT 的增加与果实鲜重生长减缓、蒸腾减少和淀粉快速积累相吻合。RT 的发育变化可能与韧皮部功能的变化以及茎与果实之间水势梯度的维持有关。遮荫对 RT 的影响扩展了先前的报道，即遮荫可以独立于对蒸腾的影响影响果实的血管分化、木质部流动和矿质积累。
