North Central Forest Experiment Station, USDA Forest Service, Rhinelander, Wisconsin, USA.
Planta. 1972 Dec;107(4):301-14. doi: 10.1007/BF00386392.
Individual leaves of eastern cottonwood (Populus deltoides), representing an ontogenetic series from leaf plastochron index 0.0 to 8.0, were fed (14)CO2 photosynthetically and then harvested at times ranging from 15 to 1440 min. The lamina of each fed leaf was sectioned from tip to base into 5 parts, and each part was quantitatively assayed for (14)C activity. In young leaves, the percentage of the total (14)C fixed (expressed in dpm/mg of dry leaf tissue) was high in the lamina tip and decreased almost linearly toward the base. With increasing leaf age, the percentage of (14)C fixed decreased in the lamina tip and increased in the base. The relative activity in mature leaves was almost uniform throughout the lamina. No differences were detected in the (14)C distribution patterns within leaves over the time series.On the basis of the data presented and of anatomical observations of developing cottonwood leaves, the hypothesis that the precociously mature lamina tip may provide photosynthates to the still-expanding lamina base was shown to be invalid. It is concluded that bidirectional transport in a developing cottonwood leaf results from simultaneous import to the immature basal region and export from the mature tip.
东部棉白杨（Populus deltoides）的单个叶片，代表了从叶龄指数 0.0 到 8.0 的个体发育系列，通过光合作用喂养（14）CO2，然后在 15 到 1440 分钟的时间范围内收获。每个喂养叶片的叶板从尖端到基部分为 5 部分，每个部分都定量测定（14）C 活性。在年轻的叶片中，（14）C 固定的总百分比（以 dpm/mg 干叶组织表示）在叶板的尖端较高，并且几乎呈线性下降到基部。随着叶片年龄的增加，（14）C 固定在叶板的尖端减少，而在基部增加。在成熟叶片中，相对活性在整个叶板中几乎均匀。在整个时间序列中，叶片内的（14）C 分布模式没有差异。基于所提出的数据和发育中的棉白杨叶片的解剖观察，过早成熟的叶尖可能为仍在扩展的叶基部提供光合作用产物的假设被证明是无效的。结论是，发育中的棉白杨叶片中的双向运输是由于同时向不成熟的基部区域导入和从成熟的顶端导出。
