摘要：
[Objective] Phloem unloading and postphloem transport play pivotal parts in the regulation of the distribution of sucrose in the storage organs and maintenance the sink of fruit,and largely determine the yield and quality of the crop.The objective of this study was to clarify the mechanism of phloem unloading and glucose metabolism in the phloem of blueberry.[Method] Vaccinium corymbosum‘ Sierra’ (5-year-old Highbush blueberry) was used for observation of the ultrastructure of the phloem of blueberry in each development period.Fluorescent dye tracer and laser scanning confocal microscopy were used to observe the unloading path of the phloem in the fruit timely.Determination of soluble sugar content and related metabolic enzyme activity in blueberry fruit by HPLC.[Result] An ultrastructural investigation of phloem tissue in blueberry fruit showed that the fruit phloem SE/CC complex is symplasmically isolated from surrounding parenchyma cells over fruit development,whereas a large number of piasmodesma exist between parenchyma cells and pulp cells.Confocal laser scanning images of carboxyfluorescein unloading showed that the dye remained confined to the phloem strands,not spread to the surrounding parenchyma cells,during the whole fruit development.These results provided a clear evidence for the predominance method of the assimilation of blueberry fruit is the unloading pathway over blueberry fruit development and symplasmic pathway present in postphloem transport.A large number of cells are beneficial to the material exchange between parenchyma cells,parenchyma cells and flesh cells.Activity assay showed that,invertase activity remained at a high level,it provides evidence to confirm the apoplasmic phloem unloading pathway at blueberry fruit development.In addition,carbohydrate metabolism related enzyme activity assay shows that a great amount of glucose and fructose primarily accumulated during blueberry ripening and sucrose enzyme decomposition activity was always greater than synthetic activity.During the late stage of fruit development,the activity of soluble acid invertase and neutral invertase was increased,the activity of sucrose decomposition,transformation and storage in the fruit pulp cell was revealed,the accumulation process is positively correlated with the activities of invertase,sucrose synthase and sucrose phosphate synthase enzymes.In the process of fruit development,the comprehensive effect of sucrose metabolism related enzymes is an important factor affecting the accumulation of soluble sugar in blueberry fruit.[Conclusion] These results provided clear evidence for the predominance method of the assimilation of blueberry fruit is the unloading pathway over blueberry fruit development and symplasmic pathway present in postphloem transport.A large amount of glucose and fructose primarily accumulated in blueberry and sugar accumulation was positively correlated with invertase,sucrose synthase and sucrose phosphate synthase.%[目的]韧皮部卸载和韧皮部后运输在调节蔗糖在库器官间的分配、维持果实的库强方面起着至关重要的作用,而且很大程度上决定着果实的产量和质量.本文研究目的是明确蓝莓同化物韧皮部卸载的机制与糖代谢机制.[方法]以5年生高丛蓝莓品种‘喜来’(‘Sierra’)为研究对象,对各个发育时期的蓝莓果实韧皮部的超微结构进行观察,并综合运用荧光染料活细胞示踪与激光共聚焦扫描显微镜技术实时观察果实内韧皮部同化物卸载路径,运用高效液相色谱等技术,测定分析蓝莓果实可溶性糖含量及相关代谢酶的活性变化等.[结果]对韧皮部细胞进行的超微结构观察显示,在蓝莓果实整个发育期,果实韧皮部SE/CC(筛管伴胞复合体)与周围薄壁细胞之间均未发现胞间连丝,从而形成了共质体隔离,但在薄壁细胞之间、薄壁细胞与果肉细胞之间存在大量胞间连丝.荧光染料CF[5(6)-羧基荧光素]的活细胞示踪试验表明,果实发育过程中,CF均被严格限制在韧皮部中,没有扩散到周围的薄壁细胞.这些结果证实蓝莓果实同化物以质外体卸载途径为主,韧皮部后运输存在着活跃的共质体途径,大量胞间连丝的存在有利于薄壁细胞之间以及薄壁细胞与果肉细胞之间的物质交换.进一步酶活性测定结果显示,在蓝莓果实的整个发育期,转化酶活性保持在较高水平,为证实蓝莓果实同化物以质外体卸载为主提供了证据.对糖代谢相关酶活性分析显示,在果实发育的各个阶段,蓝莓果实的可溶性糖主要以积累果糖和葡萄糖为主,蔗糖酶的分解活性始终大于合成活性;在果实发育中后期,可溶性酸性转化酶和中性转化酶活性进一步升高,显示果实发育后期果肉细胞内进行着活跃的蔗糖分解、转化及贮藏过程,且糖积累与转化酶、蔗糖合酶和蔗糖磷酸合酶等酶活性成正相关.在蓝莓果实发育过程中,蔗糖代谢相关酶的综合作用是影响蓝莓果实中可溶性糖积累的重要因子.[结论]蓝莓果实同化物以质外体卸载途径为主,韧皮部后运输存在着活跃的共质体途径.蓝莓果实主要以积累果糖和葡萄糖为主,且糖积累与转化酶、蔗糖合酶和蔗糖磷酸合酶等酶活性成正相关.
