Roberts A. G., Cruz S. S., Roberts I. M., Prior DAM., Turgeon R., Oparka K. J.
Unit of Cell Biology, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom.
Plant Cell. 1997 Aug;9(8):1381-1396. doi: 10.1105/tpc.9.8.1381.
Using noninvasive imaging techniques, we compared phloem unloading of the membrane-impermeant, fluorescent solute carboxyfluorescein (CF) with that of potato virus X expressing the gene for the green fluorescent protein. Although systemic virus transport took considerably longer to occur than did CF transport, unloading of both solute and virus occurred predominantly from the class III vein network, a highly branched veinal system found between class II veins. The minor veins (classes IV and V) played no role in solute or virus import but were shown to be functional in xylem transport at the time of import by labeling with Texas Red dextran. After virus exit from the class III phloem, the minor veins eventually became infected by cell-to-cell virus movement from the mesophyll. During the sink/source transition, phloem unloading of CF was inhibited from class III veins before the cessation of phloem import through them, suggesting a symplastic isolation of the phloem in class III veins before its involvement in export. The progression of the sink/source transition for carbon was unaffected by the presence of the virus in the sink leaf. However, the virus was unable to cross the sink/source boundary for carbon that was present at the time of viral entry, suggesting a limited capacity for cell-to-cell virus movement into the apical (source) region of the leaf. A functional model of the sink/source transition in Nicotiana benthamiana is presented. This model provides a framework for the analysis of solute and virus movement in leaves.
我们使用非侵入性成像技术，比较了膜不透性荧光溶质羧基荧光素（CF）与表达绿色荧光蛋白基因的马铃薯X病毒的韧皮部卸载情况。尽管系统性病毒运输比CF运输发生的时间要长得多，但溶质和病毒的卸载主要发生在III级叶脉网络，这是一种在II级叶脉之间发现的高度分支的叶脉系统。小叶脉（IV级和V级）在溶质或病毒的导入中不起作用，但通过用德克萨斯红葡聚糖标记表明，在导入时它们在木质部运输中发挥作用。病毒从III级韧皮部出来后，小叶脉最终通过叶肉细胞间的病毒移动而被感染。在库/源转变期间，在通过III级叶脉的韧皮部导入停止之前，CF从III级叶脉的韧皮部卸载就受到抑制，这表明在III级叶脉参与输出之前，其韧皮部存在共质体隔离。碳的库/源转变进程不受库叶中病毒存在的影响。然而，病毒无法跨越病毒进入时存在的碳的库/源边界，这表明细胞间病毒移动到叶顶端（源）区域的能力有限。本文提出了本氏烟草库/源转变的功能模型。该模型为分析叶片中溶质和病毒的移动提供了一个框架。
