Phloem sap proteins from Cucurbita maxima and Ricinus communis have the capacity to traffic cell to cell through plasmodesmata
Phloem sap proteins from Cucurbita maxima and Ricinus communis have the capacity to traffic cell to cell through plasmodesmata
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DOI：
10.1073/pnas.94.25.14150
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发表时间：
1997-12-09
影响因子：
11.1
通讯作者：
Lucas, WJ
中科院分区：
文献类型：
--
作者：
Balachandran, S;Xiang, Y;Lucas, WJ
在被子植物中，韧皮部的功能性去核筛管系统似乎由周围的伴细胞维持。在这项研究中，我测试了这样的假设：韧皮部汁液中存在的多肽通过胞间连丝从合成它们的伴随细胞运输到细胞之间，进入筛管。将荧光标记的葡聚糖与尺寸分级的葫芦韧皮部蛋白（尺寸范围为 10 至 200 kDa）共注射，以及注射单个荧光标记的韧皮部蛋白，提供了明确的证据，证明这些蛋白质具有与葫芦子叶中的叶肉胞间连丝相互作用的能力，从而诱导尺寸排除限制和细胞间运输的增加。无论注射蛋白质的大小如何，质连丝尺寸排除极限增加至大于 20 kDa，但小于 40 kDa，表明部分蛋白质解折叠可能是运输的必要条件。 20-100 nM 范围内的阈值浓度 nas 需要远距离细胞间运输，表明韧皮部蛋白对叶肉胞间连丝结合位点具有高亲和力。使用谷氧还蛋白和半胱氨酸蛋白酶抑制剂（来自蓖麻的韧皮部汁液蛋白）进行的平行实验表明，这些蛋白也可以通过葫芦叶肉胞间连丝运输。这些结果根据伴随细胞和筛管系统之间调节蛋白质运输的要求进行讨论。由于韧皮部汁液蛋白的胞间连丝运输的阈值与许多植物激素处于同一范围内，因此讨论了其中一些蛋白可能充当长距离信号分子的可能性。
In angiosperms, the functional enucleate sieve tube system of the phloem appears to be maintained by the surrounding companion cells. In this study, me tested the hypothesis that polypeptides present within the phloem sap traffic cell to cell from the companion cells, where they are synthesized, into the sieve tube via plasmodesmata. Coinjection of fluorescently labeled dextrans along with size-fractionated Cucurbita maxima phloem proteins, ranging in size from 10 to 200 kDa, as well as injection of individual fluorescently labeled phloem proteins, provided unambiguous evidence that these proteins have the capacity to interact with mesophyll plasmodesmata in cucurbit cotyledons to induce an increase in size exclusion limit and traffic cell to cell. Plasmodesmal size exclusion limit increased to greater than 20 kDa, hut less than 40 kDa, irrespective of the size of the injected protein, indicating that partial protein unfolding may be a requirement for transport. A threshold concentration in the 20-100 nM range nas required far cell-to-cell transport indicating that phloem proteins have a high affinity for the mesophyll plasmodesmata binding site(s). Parallel experiments with glutaredoxin and cystatin, phloem sap proteins from Ricinus communis, established, that these proteins can also traffic through cucurbit mesophyll plasmodesmata. These results are discussed in terms of the requirements for regulated protein trafficking between companion cells and the sieve tube system. As the threshold value fur plasmodesmal transport of phloem sap proteins falls within the same range as many plant hormones, the possibility is discussed that some of these proteins may act as long-distance signaling molecules.