Translocation and distribution of assimilated carbon in peanut plant

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Abstract
An attempt was made to monitor 13C that had been photosynthetically assimilated in the foliage of the main stem and branches of peanut plant, as well as in a single leaf at different positions on a branch. When the foliage of the main stem or branch was supplied with 13CO2 for 8 h at the vegetative stage, 13C assimilated in the branches was detected in the roots and nodules in addition to the foliage immediately after the exposure, whereas when the main stem was supplied with 13CO2, 13C was not detected in the roots and nodules immediately after 13CO2 feeding. At the reproductive stage, 13C assimilated in the main stem or branch was found in the leaves, stems, fruit (shell, seed coat, and seed), roots, and nodules immediately after assimilation. Photoassimilates from each leaf of the branch at the reproductive stage were exported to the fruit and leaves that were attached to the same branch. Namely, photoassimilates in the leaves of odd nodes were mainly translocated to the fruits attached to the first node, whereas such photoassimilates from the leaf of even nodes were mainly translocated to the fruit attached to the second node. When the foliage of a branch had been fed 13CO2 at the vegetative stage, the loss of the assimilated 13C by respiration was about 40% of the total assimilated 13C within 23 d and about 65% within 93 d after the exposure, and a small amount of photoassimilates was detected in the fruit. On the other hand, at the seed-filling stage, about 35% of the photoassimilates were utilized for seed growth within 10 d after the end of exposure. These results suggest that in the peanut plant, the carbon source of nodules mainly depends on the branch, and the main stem plays an important role as carbon source for the fruit, that a sink organ for carbon is connected with a specific sources leaf by the vascular bundles, and that most of the carbon sources for the growth of peanut fruit depend on the photoassimilates at the reproductive stage.