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首页> 美国卫生研究院文献>Plant Physiology >Sucrose Transport and Phloem Unloading in Stem of Vicia faba: Possible Involvement of a Sucrose Carrier and Osmotic Regulation
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Sucrose Transport and Phloem Unloading in Stem of Vicia faba: Possible Involvement of a Sucrose Carrier and Osmotic Regulation

机译：蚕豆茎中的蔗糖运输和韧皮部卸荷：蔗糖载体的可能参与和渗透调节

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Stems of Vicia faba plants were used to study phloem unloading because they are hollow and have a simple anatomical structure that facilitates access to the unloading site. After pulse labeling of a source leaf with 14CO2, stem sections were cut and the efflux characteristics of 14C-labeled sugars into various buffered solutions were determined. Radiolabeled sucrose was shown to remain localized in the phloem and adjacent phloem parenchyma tissues after a 2-hour chase. Therefore, sucrose leakage from stem segments prepared following a 75-minute chase period was assumed to be characteristic of phloem unloading. The efflux of 14C assimilates from the phloem was enhanced by 1 millimolar p-chloromercuribenzene sulfonic acid (PCMBS) and by 5 micromolar carbonyl cyanide m-chlorophenly hydrazone (CCCP). However, PCMBS inhibited and CCCP enhanced general leakage of nonradioactive sugars from the stem segments. Sucrose at concentrations of 50 millimolar in the free space increased efflux of [14C]sucrose, presumably through an exchange mechanism. This exchange was inhibited by PCMBS and abolished by 0.2 molar mannitol. Increasing the osmotic concentration of the efflux medium with mannitol reduced [14C]sucrose efflux. However, this inhibition seems not to be specific to sucrose unloading since leakage of total sugars, nonlabeled sucrose, glucose, and amino acids from the bulk of the tissue was reduced in a similar manner. The data suggest that phloem unloading in cut stem segments is consistent with passive efflux of sucrose from the phloem to the apoplast and that sucrose exchange via a membrane carrier may be involved. This is consistent with the known conductive function of the stem tissues, and contrasts with the apparent nature and function of unloading in developing seeds.
机译：蚕豆蚕豆的茎被用于研究韧皮部的卸载，因为它们是空心的，并且具有简单的解剖结构，便于进入卸载部位。用 14 CO2脉冲标记源叶片后，将茎切开，并测定 14 C标记的糖在各种缓冲溶液中的流出特性。在经过2小时的追踪后，放射性标记的蔗糖显示仍保留在韧皮部和邻近韧皮部薄壁组织中。因此，在追赶75分钟后，茎段中的蔗糖泄漏被认为是韧皮部卸载的特征。 1毫摩尔对氯汞苯磺酸（PCMBS）和5微摩尔羰基氰化物间氯苯乙（（CCCP）增强了韧皮部 14 同化物的流出。但是，PCMBS抑制并且CCCP增强了茎段中非放射性糖的总体泄漏。在自由空间中浓度为50毫摩尔的蔗糖可能通过交换机制增加了[ 14 C]蔗糖的外排。该交换被PCMBS抑制并且被0.2摩尔甘露醇废除。用甘露醇提高外排培养基的渗透浓度可降低[ 14 C]蔗糖外排。但是，这种抑制作用似乎并不是蔗糖卸载所特有的，因为以类似的方式减少了总糖，未标记的蔗糖，葡萄糖和氨基酸从组织大部分中的渗漏。数据表明，切茎段中的韧皮部卸载与蔗糖从韧皮部到质外体的被动流出相一致，并且可能涉及通过膜载体交换蔗糖。这与茎组织的已知传导功能一致，并且与发育中的种子的表观性质和卸载功能相反。

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