Schmalstig J G, Geiger D R
Biology Department, University of Dayton, Dayton, Ohio 45469-0001.
Plant Physiol. 1985 Sep;79(1):237-41. doi: 10.1104/pp.79.1.237.
Physiological and transport data are presented in support of a symplastic pathway of phloem unloading in importing leaves of Beta vulgaris L. (;Klein E multigerm'). The sulfhydryl reagent p-chloromercuribenzene sulfonic acid (PCMBS) at concentration of 10 millimolar inhibited uptake of exogenous [(14)C]sucrose by sink leaf tissue over sucrose concentrations of 0.1 to 5.0 millimolar. Inhibited uptake was 24% of controls. The same PCMBS treatment did not affect import of (14)C-label into sink leaves during steady state labeling of a source leaf with (14)CO(2). Lack of inhibition of import implies that sucrose did not pass through the free space during unloading. A passively transported xenobiotic sugar, l-[(14)C]glucose, imported by a sink leaf through the phloem, was evenly distributed throughout the leaf as seen by whole-leaf autoradiography. In contrast, l-[(14)C]glucose supplied to the apoplast through the cut petiole or into a vein of a sink leaf collected mainly in the vicinity of the major veins with little entering the mesophyll. These patterns are best explained by transport through the symplast from phloem to mesophyll.
本文展示了生理学和运输数据，以支持甜菜（Beta vulgaris L.，品种为Klein E multigerm）输入叶中韧皮部卸载的共质体途径。浓度为10毫摩尔的巯基试剂对氯汞苯磺酸（PCMBS）在0.1至5.0毫摩尔的蔗糖浓度范围内抑制了库叶组织对外源[¹⁴C]蔗糖的吸收。抑制后的吸收量为对照的24%。在用¹⁴CO₂对源叶进行稳态标记期间，相同的PCMBS处理不影响¹⁴C标记物向库叶的输入。对输入的抑制缺乏表明蔗糖在卸载过程中未穿过自由空间。通过韧皮部由库叶导入的被动运输的外源性糖l-[¹⁴C]葡萄糖，通过全叶放射自显影可见其在整个叶片中均匀分布。相比之下，通过切割叶柄供应到质外体或供应到库叶叶脉中的l-[¹⁴C]葡萄糖主要聚集在主叶脉附近，很少进入叶肉。这些模式最好用从韧皮部到叶肉通过共质体的运输来解释。
