A xylem sap retrieval pathway in rice leaf blades: evidence of a role for endocytosis?
A xylem sap retrieval pathway in rice leaf blades: evidence of a role for endocytosis?
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DOI：
10.1093/jxb/ern150
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发表时间：
2008-08-01
影响因子：
6.9
通讯作者：
White, R. G.
中科院分区：
文献类型：
--
作者：
Botha, C. E. J.;Aoki, N.;White, R. G.
本文研究了位于次生木质部和木质部薄壁细胞界面上的纹孔膜的结构和运输特性，以及这些纹孔膜在溶质向韧皮部转移中的可能作用。电子显微镜观察发现，在水稻（Oryza sativa）叶片束木质部导管和木质部薄壁组织之间的纹孔膜结构中，存在一种纤维状的、几乎是管状的基质。这些纹孔主要参与调节水流向周围木质部薄壁细胞。维管薄壁细胞含有大量的线粒体、大量的网质体、内膜复合体和靠近纹孔膜的小泡。总的来说，这表明内吞作用可能发生在该界面。将5，6-羧基荧光素二乙酸酯（5，6-CFDA）的弱溶液施加到叶的切割末端，并且在最少30分钟后，使用共聚焦显微镜观察荧光切割产物5，6-羧基荧光素（5，6-CF）的分布。5，6-CFDA在木质部薄壁细胞内发生裂解，然后非极性的5，6-CF共质体运输到其他薄壁细胞，并最终通过许多孔胞间连丝运输到相邻的厚壁筛管。应用荧光黄，和，分别，德克萨斯红标记的葡聚糖（10 kDa）的蒸腾流，证实这些膜不渗透的探针只能从木质部通过木质部导管木质部薄壁细胞的坑膜卸载，这表明这些膜不渗透的荧光团的胞吞跨膜转移。厚壁筛管内的积累，但不是在薄壁筛管，证实了共质韧皮部加载途径的存在下，通过木质部薄壁组织和厚壁筛管之间的孔胞间连丝，但不是薄壁筛管。
The structure and transport properties of pit membranes at the interface between the metaxylem and xylem parenchyma cells and the possible role of these pit membranes in solute transfer to the phloem were investigated. Electron microscopy revealed a fibrillar, almost tubular matrix within the pit membrane structure between the xylem vessels and xylem parenchyma of leaf blade bundles in rice (Oryza sativa). These pits are involved primarily with regulating water flux to the surrounding xylem parenchyma cells. Vascular parenchyma cells contain large mitochondrial populations, numerous dictyosomes, endomembrane complexes, and vesicles in close proximity to the pit membrane. Taken collectively, this suggests that endocytosis may occur at this interface. A weak solution of 5,6-carboxyfluorescein diacetate (5,6-CFDA) was applied to cut ends of leaves and, after a minimum of 30 min, the distribution of the fluorescent cleavage product, 5,6-carboxyfluorescein (5,6-CF), was observed using confocal microscopy. Cleavage of 5,6-CFDA occurred within the xylem parenchyma cells, and the non-polar 5,6-CF was then symplasmically transported to other parenchyma elements and ultimately, via numerous pore plasmodesmata, to adjacent thick-walled sieve tubes. Application of Lucifer Yellow, and, separately, Texas Red-labelled dextran (10 kDa) to the transpiration stream, confirmed that these membrane-impermeant probes could only have been offloaded from the xylem via the xylem vessel-xylem parenchyma pit membranes, suggesting endocytotic transmembrane transfer of these membrane-impermeant fluorophores. Accumulation within the thick-walled sieve tubes, but not in thin-walled sieve tubes, confirms the presence of a symplasmic phloem loading pathway, via pore plasmodesmata between xylem parenchyma and thick-walled sieve tubes, but not thin-walled sieve tubes.