Botany Department, University of California, 95616, Davis, CA, USA.
Planta. 1987 Jun;171(2):197-204. doi: 10.1007/BF00391094.
Autoradiographs obtained from discs from mature, peeled Ipomoea tricolor Cav. leaves indicated that a 15-min 2 mM p-chloromercuribenzene sulfonic acid (PCMBS) pretreatment did not prevent the accumulation of (14)CO2-derived (14)C-photosynthate within the minor veins. However, accumulation of (14)C-photosynthate within these veins was almost, or completely prevented by treatment of the leaf discs at pH 9.0. Peeled Ipomoea leaf discs were also used to study the kinetics of exogenously supplied [(14)C]sucrose; influx occurred by the combined operation of a saturable and a first-order kinetic mechanism. Both transport mechanisms were inhibited by a 15-min 2 mM PCMBS pretreatment or by treatment at pH 9.0. An analysis of autoradiographs obtained on leaf discs that had been fed exogenous [(14)C]sucrose, showed that whereas all cells of the leaf took up sucrose at pH 5.0, uptake at pH 9.0 occurred primarily into cells of the minor veins. In contrast with (14)C-photoassimilate experiments, PCMBS pretreatment, at either pH 5.0 or pH 9.0, resulted in a reduction in the radioactivity within the minor veins when the label was supplied exogenously as [(14)C]sucrose. Kinetic experiments conducted with mesophyll cells isolated enzymatically from peeled source-leaf discs indicated that [(14)C]sucrose influx also occurred by a saturable and a first-order kinetic mechanism. Comparative studies between leaf discs and isolated mesophyll cells showed that mesophyll cells could account for 75% of the total uptake occurring into the peeled leaf discs. These results indicate that the effects of PCMBS and alkaline pH on net sucrose uptake by leaf tissues are not exerted solely on phloem tissues, and that some of the effects of these treatments may be attributable to an inhibition of symplasmic transport to the minor veins.
从成熟、去皮的 Ipomoea tricolor Cav. 叶片的圆盘获得的放射自显影图表明，15 分钟 2mM 的对氯汞苯甲酸（PCMBS）预处理不能阻止 14CO2 衍生的（14）C-光合产物在小叶脉内的积累。然而，用 pH 值 9.0 处理叶圆盘几乎或完全阻止了（14）C-光合产物在这些脉内的积累。去皮的 Ipomoea 叶片圆盘也被用于研究外源供应的 [(14)C]蔗糖的动力学；流入是通过一个饱和和一级动力学机制的联合作用发生的。这两种运输机制都被 15 分钟 2mM 的 PCMBS 预处理或 pH 值 9.0 的处理所抑制。对已喂给外源 [(14)C]蔗糖的叶圆盘获得的放射自显影图的分析表明，虽然叶片的所有细胞在 pH 值 5.0 时都能吸收蔗糖，但在 pH 值 9.0 时，吸收主要发生在小叶脉的细胞中。与（14）C-光合产物实验相反，PCMBS 预处理，无论是在 pH 值 5.0 还是 pH 值 9.0，当标记物作为外源 [(14)C]蔗糖供应时，都会导致小叶脉内的放射性减少。用酶从去皮源叶圆盘分离的叶肉细胞进行的动力学实验表明，[(14)C]蔗糖的流入也通过一个饱和和一级动力学机制发生。叶圆盘和分离的叶肉细胞之间的比较研究表明，叶肉细胞可以解释 75%的总吸收进入去皮叶圆盘。这些结果表明，PCMBS 和碱性 pH 值对叶片组织净蔗糖吸收的影响不是仅作用于韧皮组织，这些处理的一些影响可能归因于对向小叶脉的共质体运输的抑制。
