Sektion Biowissenschaften der Martin-Luther-Universität, Wissenschaftsbereich Pflanzenphysiologie, Am Kirchtor 1, O-4020, Halle (Saale), Federal Republic of Germany.
Planta. 1990 Nov;182(4):480-5. doi: 10.1007/BF02341021.
In contrast to hexoses (fructose, glucose, 3-oxymethylglucose) sucrose is preferentially taken up by isolated conducting tissue ofCyclamen persicum Mill. Sucrose absorption follows a biphasic kinetic, with a saturable component (Km=5.2 mM; Vmax = 4.2 μmol · g FW(-1) · h(-1)) in the lower range (<20 mM) and a linear component in the upper range (20-400 mM). The saturable, carrier-mediated uptake operates against the concentration gradient without attaining any equilibrium over 6 h. It is characterized by a pH optimum at 4.5 and sensitivity to the protonophore CCCP (carbonylcyanidem-chlorophenylhydrazone). The activity of the saturable uptake increases with decreasing turgor and it is independent of the presence of hexoses. There is no effect of pH or CCCP on linear sucrose uptake at high external concentrations. Hexose uptake between 0.25 and 20 mM shows a entirely linear kinetic. Leakage after preincubation with 1 mM sucrose exhibits a minimum at pH 5.0 and enters a steady state within 100 min. Furthermore, it was found to be independent of the osmolarity of the external solution. Results are discussed in terms of apoplastic leakage and reabsorption along the phloem path: efflux of sucrose is compensated by a specific, carrier-mediated influx, which is qualitatively similar to apoplastic phloem loading accomplished by proton cotransport. In according with the balanced efflux and influx it should be considered rather as a retrieval than a loading mechanism.
与己糖（果糖、葡萄糖、3-氧甲基葡萄糖）不同，蔗糖优先被樱草鳞茎的分离传导组织吸收。蔗糖吸收遵循双相动力学，在较低浓度范围内（<20 mM）存在可饱和成分（Km=5.2 mM；Vmax=4.2 μmol·g FW(-1)·h(-1)），在较高浓度范围内（20-400 mM）呈线性。可饱和、载体介导的摄取是在没有达到任何平衡的情况下逆浓度梯度进行的，作用持续 6 小时。其特征为 pH 最佳值为 4.5，对质子载体 CCCP（羰基氰化物-氯代苯腙）敏感。可饱和摄取的活性随膨压降低而增加，且与己糖的存在无关。在高外部浓度下，pH 或 CCCP 对线性蔗糖摄取没有影响。0.25-20 mM 之间的己糖摄取呈现完全线性动力学。用 1 mM 蔗糖预孵育后的渗漏在 pH 5.0 时达到最小值，并在 100 分钟内进入稳定状态。此外，它被发现与外部溶液的渗透压无关。结果从质外体渗漏和韧皮部途径再吸收的角度进行了讨论：蔗糖的外排由特定的载体介导的内流补偿，这与质子共转运完成的质外体韧皮部加载在性质上相似。根据平衡的外排和内流，它应该被认为是一种检索机制，而不是加载机制。
