Ultrastructural features of well-preserved and injured sieve elements: minute clamps keep the phloem transport conduits free for mass flow
Ultrastructural features of well-preserved and injured sieve elements: minute clamps keep the phloem transport conduits free for mass flow
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DOI：
10.1007/bf02524265
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发表时间：
2000-01-01
期刊：
影响因子：
2.9
通讯作者：
van Bel, AJE
中科院分区：
文献类型：
--
作者：
Ehlers, K;Knoblauch, M;van Bel, AJE
对蚕豆叶片和番茄节间运输韧皮部经两种不同制备工艺的化学固定后，成熟筛分子的超微结构进行了系统的比较。温和制备的样品中的SES保存完好，而常规制备的样品中的SES普遍受损。(1)在保存完好的SE中，壁层P蛋白与SE内质网(ER)池相联系。此外，蚕豆根瘤菌具有结晶的P-蛋白，并且在泡菜根瘤菌的管腔内存在均一的丝状P-蛋白网络。在受损的SE中，P-蛋白全部弥散分布。(2)在保存完好的SE中，筛板壁上也有与P蛋白相关的堆积的内质网小池，但筛孔前的通道是自由的。受伤的SES缺乏这些有序安排的存款。相反，不规则的丝状和膜状材料堵塞了筛孔。(3)保存完好。筛孔内腔除了小的、侧向的P-蛋白涂层外，没有其他的阻塞。损伤SE的筛孔总是闭塞的。(4)在番茄SE中，SE细胞器和位于纵壁的顶层ER牢固地附着在SE的外围，并在受伤后保持在原地。稳定的顶端附着可能是通过微小的簇状结构来实现的，这些结构将SE组件的外膜彼此连接起来，或者连接到SE质膜。长约7 nm的单个直夹将SE组分直接锚定在SE质膜上。相邻SE细胞器和(或)壁层ER池之间的连接大多长达2倍(约15 nm)，且多为分支。据推测，长的分支夹是由相对的短夹相互作用构成的。关于SE功能的超微结构结果进行了讨论。
After chemical fixation following two different preparation procedures, the ultrastructure of mature sieve elements (SEs) was systematically compared in the transport phloem of Vicia faba leaves and Lycopersicon esculentum internodes. The SEs in samples obtained by gentle preparation were well preserved, while those in conventionally prepared samples were generally injured. (1) In well-preserved SEs, parietal P-proteins were associated with cisternae of the SE endoplasmic reticulum (ER). Additionally, the V. faba SEs had crystalline P-proteins, and a homogeneous network of filamentous P-proteins occurred in the lumen of the L. esculentum SEs. In injured SEs, all P-proteins were dispersed. (2) In well-preserved SEs, stacked ER cisternae associated with P-proteins lay also on the sieve-plate walls, but passages were kept free in front of the sieve pores. Injured SEs lacked these orderly arranged deposits. Instead, irregular filamentous and membranous materials occluded the: sieve pores. (3) In well-preserved SEs. the sieve-pore lumen was foe of obstructions, apart from small, lateral coatings of P-proteins. Sieve pores in injured SEs were always occluded. (4) The SE organelles and, in tomato SEs, also the parietal ER located at the longitudinal walls were firmly attached in the SE periphery and stayed in place after injury. The stable parietal attachment is likely exerted by minute, clamplike structures which link the outer membranes of the SE components with one another or to the SE plasma membrane. Single, straight clamps with a length of about 7 nm anchored the SE components directly to the SE plasma membrane. The connections between adjacent SE organelles and/or parietal ER cisternae were mostly twice as long (about 15 nm) and often were branched. Presumably, the long, branched clamps were constituted by the interaction of opposite short clamps. The ultrastructural results are discussed with respect to SE functioning.