Keller Markus, Smith Jason P, Bondada Bhaskar R
Irrigated Agriculture Research and Extension Center, Washington State University, 24106 N. Bunn Road, Prosser, 99350, USA.
J Exp Bot. 2006;57(11):2577-87. doi: 10.1093/jxb/erl020. Epub 2006 Jul 25.
Berry diameter was monitored during dry-down and rewatering cycles and pressurization of the root system of Vitis vinifera (cv. Merlot) and Vitis labruscana (cv. Concord) to test changes in xylem functionality during grape ripening. Prior to veraison (onset of ripening), berries maintained their size under declining soil moisture until the plants had used 80% of the transpirable soil water, began to shrink thereafter, and recovered rapidly after rewatering. By contrast, berry diameter declined slowly but steadily during post-veraison water stress and did not recover after rewatering; irrigation merely prevented further shrinking. Preconditioning vines with a period of water stress after flowering did not influence the berries' reaction to subsequent changes in transpirable soil water. Pressurizing the root system led to concomitant changes in berry diameter only prior to veraison, although some post-veraison Concord, but not Merlot, berries cracked under root pressurization. The xylem-mobile dye basic fuchsin, infused via the shoot base, moved throughout the berry vasculature before veraison, but became gradually confined to the brush area during ripening. When the dye was infused through the stylar end of attached berries, it readily moved back to the plant both before and after veraison. Our work demonstrated that berry-xylem conduits retain their capacity for water and solute transport during ripening. It is proposed here that apoplastic phloem unloading coupled with solute accumulation in the berry apoplast may be responsible for the decline in xylem water influx into ripening grape berries. Instead, the xylem may serve to recycle excess phloem water back to the shoot.
在葡萄果实脱水和复水周期以及葡萄（赤霞珠品种）和美洲葡萄（康科德品种）根系加压过程中，监测浆果直径，以测试葡萄成熟期间木质部功能的变化。在转色期（成熟开始）之前，浆果在土壤湿度下降的情况下保持其大小，直到植株消耗了80%的可蒸腾土壤水分，此后开始萎缩，并在复水后迅速恢复。相比之下，转色期后水分胁迫期间，浆果直径缓慢但稳定地下降，复水后未恢复；灌溉仅防止了进一步萎缩。开花后对葡萄藤进行一段时间的水分胁迫预处理，并不影响浆果对随后可蒸腾土壤水分变化的反应。对根系加压仅在转色期之前导致浆果直径随之发生变化，尽管转色期后一些康科德品种（而非赤霞珠品种）的浆果在根系加压下出现开裂。通过茎基部注入的木质部可移动染料碱性品红，在转色期前在整个浆果维管系统中移动，但在成熟过程中逐渐局限于果刷区域。当通过附着浆果的花柱端注入染料时，在转色期前后它都很容易回流到植株中。我们的研究表明，浆果 - 木质部导管在成熟过程中保持其水分和溶质运输能力。本文提出，质外体韧皮部卸载与浆果质外体中溶质积累相结合，可能是木质部水分流入成熟葡萄浆果减少的原因。相反，木质部可能起到将多余的韧皮部水分循环回茎的作用。
