United States Department of Agriculture, Agricultural Research Service, Utah State University, UMC 63, Logan, Utah 84322.
Plant Physiol. 1986 Dec;82(4):962-6. doi: 10.1104/pp.82.4.962.
The effect of gibberellic acid (GA(3)) on sucrose export from source leaves was studied in broad bean (Vicia faba L.) plants trimmed of all but one source and one sink leaf. GA(3) (10 micromolar) applied to the source leaf, enhanced export of [(14)C]sucrose (generated by (14)CO(2) fixation) to the root and to the sink leaf. Enhanced export was observed with GA treatments as short as 35 minutes. When GA(3) was applied 24 hours prior to the (14)CO(2) pulse, the enhancement of sucrose transport toward the root was abolished but transport toward the upper sink leaf was unchanged. The enhanced sucrose export was not due to increased photosynthetic rate or to changes in the starch/sucrose ratio within the source leaf; rather, GA(3) increased the proportion of sucrose exported. After a 10-min exposure to [(14)C]GA(3), radioactivity was found only in the source leaf. Following a 2 hour exposure to [(14)C]GA(3), radioactivity was distributed along the entire stem and was present in both the roots and sink leaf. Extraction and partitioning of GA metabolites by thin layer chromatography indicated that there was a decline in [(14)C]GA(3) in the lower stem and root, but not in the upper stem. This pattern of metabolism is consistent with the disappearance of the GA(3) effect in the lower stem with time after treatment. We conclude that in the short term, GA(3) enhances assimilate export from source leaves by increasing phloem loading. In the long term (24 hours), the effect of GA(3) is outside the source leaf. GA(3) accumulates in the apical region resulting in enhanced growth and thus greater sink strength. Conversely, GA(3) is rapidly metabolized in the lower stem thus attenuating any GA effect.
赤霉素（GA(3)）对除去一片源叶和一片库叶的蚕豆（Vicia faba L.）植株源叶中蔗糖输出的影响。将 10 微摩尔赤霉素（GA(3)）施加到源叶上，增强了[(14)C]蔗糖（由(14)CO(2)固定生成）向根和库叶的输出。在 35 分钟的短时间内，就观察到了增强的出口效果。当 GA(3)在(14)CO(2)脉冲前 24 小时施加时，根向蔗糖的转运增强被废除，但向上部库叶的转运保持不变。增强的蔗糖输出不是由于光合作用速率的增加或源叶内淀粉/蔗糖比的变化；相反，GA(3)增加了蔗糖输出的比例。经过 10 分钟的[(14)C]GA(3)暴露，放射性仅出现在源叶中。经过 2 小时的[(14)C]GA(3)暴露，放射性沿着整个茎分布，并存在于根和库叶中。薄层层析提取和分配 GA 代谢物表明，在下部茎和根中[(14)C]GA(3)减少，但在上部茎中没有。这种代谢模式与处理后随着时间的推移，下部茎中 GA(3)效应的消失一致。我们得出结论，短期内，GA(3)通过增加韧皮部装载来增强源叶中同化产物的输出。从长远来看（24 小时），GA(3)的作用超出了源叶。GA(3)在顶端区域积累，导致生长增强，从而增强了库的强度。相反，GA(3)在下部茎中迅速代谢，从而减弱了任何 GA 效应。
