Sivaguru M, Fujiwara T, Samaj J, Baluska F, Yang Z, Osawa H, Maeda T, Mori T, Volkmann D, Matsumoto H
Research Institute for Bioresources, Okayama University, Kurashiki 710-0046, Japan.
Plant Physiol. 2000 Nov;124(3):991-1006. doi: 10.1104/pp.124.3.991.
Symplastic intercellular transport in plants is achieved by plasmodesmata (PD). These cytoplasmic channels are well known to interconnect plant cells to facilitate intercellular movement of water, nutrients, and signaling molecules including hormones. However, it is not known whether Al may affect this cell-to-cell transport process, which is a critical feature for roots as organs of nutrient/water uptake. We have microinjected the dye lucifer yellow carbohydrazide into peripheral root cells of an Al-sensitive wheat (Triticum aestivum cv Scout 66) either before or after Al treatment and followed the cell-to-cell dye-coupling through PD. Here we show that the Al-induced root growth inhibition is closely associated with the Al-induced blockage of cell-to-cell dye coupling. Immunofluorescence combined with immuno-electron microscopic techniques using monoclonal antibodies against 1-->3-beta-D-glucan (callose) revealed circumstantial evidence that Al-induced callose deposition at PD may responsible for this blockage of symplastic transport. Use of 2-deoxy-D-glucose, a callose synthesis inhibitor, allowed us to demonstrate that a reduction in callose particles correlated well with the improved dye-coupling and reduced root growth inhibition. While assessing the tissue specificity of this Al effect, comparable responses were obtained from the dye-coupling pattern in tobacco (Nicotiana tabacum) mesophyll cells. Analyses of the Al-induced expression of PD-associated proteins, such as calreticulin and unconventional myosin VIII, showed enhanced fluorescence and co-localizations with callose deposits. These results suggest that Al-signal mediated localized alterations to calcium homeostasis may drive callose formation and PD closure. Our data demonstrate that extracellular Al-induced callose deposition at PD could effectively block symplastic transport and communication in higher plants.
植物中的共质体胞间运输是通过胞间连丝（PD）实现的。这些细胞质通道将植物细胞相互连接，以促进水、养分和包括激素在内的信号分子的细胞间移动，这是众所周知的。然而，尚不清楚铝是否会影响这种细胞间运输过程，而这一过程对于作为养分/水分吸收器官的根来说是一个关键特征。我们在铝处理之前或之后，将染料荧光素黄酰肼显微注射到对铝敏感的小麦（普通小麦品种Scout 66）的根外周细胞中，并通过胞间连丝追踪细胞间的染料偶联情况。在这里，我们表明铝诱导的根生长抑制与铝诱导的细胞间染料偶联阻断密切相关。使用针对1,3-β-D-葡聚糖（胼胝质）的单克隆抗体，结合免疫荧光和免疫电子显微镜技术，发现了一些间接证据，表明铝诱导的胼胝质在胞间连丝处沉积可能是这种共质体运输阻断的原因。使用2-脱氧-D-葡萄糖（一种胼胝质合成抑制剂），我们证明胼胝质颗粒的减少与染料偶联的改善和根生长抑制的降低密切相关。在评估这种铝效应的组织特异性时，从烟草（烟草）叶肉细胞的染料偶联模式中获得了类似的反应。对与胞间连丝相关的蛋白质（如钙网蛋白和非常规肌球蛋白VIII）的铝诱导表达分析表明，荧光增强且与胼胝质沉积物共定位。这些结果表明，铝信号介导的钙稳态局部改变可能驱动胼胝质形成和胞间连丝关闭。我们的数据表明，细胞外铝诱导的胼胝质在胞间连丝处沉积可有效阻断高等植物中的共质体运输和通讯。
