Summary
Individual leaves of eastern cottonwood (Populus deltoides), representing an ontogenetic series from leaf plastochron index 0.0 to 8.0, were fed 14CO2 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 14C activity. In young leaves, the percentage of the total 14C 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 14C 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 14C 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.
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Larson, P.R., Isebrands, J.G. & Dickson, R.E. Fixation patterns of 14C within developing leaves of eastern cottonwood. Planta 107, 301–314 (1972). https://doi.org/10.1007/BF00386392
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DOI: https://doi.org/10.1007/BF00386392