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This article in CS

  1. Vol. 15 No. 1, p. 55-59
    Received: Apr 19, 1974

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14C-Photosynthate Translocation in C3 and C4 Plants as Related to Leaf Anatomy1

  1. R. N. Gallaher,
  2. D. A. Ashley and
  3. R. H. Brown2



This study was performed to investigate the relationship between 14C photosynthate translocation and phloem cross-sectional area in C3 and C4 plants. Spots 5 mm in diameter were labeled by 14CO2 exposure on fully expanded leaves of two monocots (Panicum maximum Jacq., a C4 species and Panicum milioides Nees ex. Trin., a C3 species) and two dicots (Amaranthus retroflexus L., a C4 species and Glycine max Merrill, a C3 species). The spots were removed after 3 hours of translocation and equally divided. Half of the spots were used for 14C analysis and half for anatomical study of cross sectional areas of phloem and other tissues.

In all cases percent translocation from and cross-sectional area of phloem tissue in labeled spots were higher in C4 than in C3 plants. P. maximum had 100% greater translocation out of and 96% more phloem tissue in the labeled spots than P. milioides. A. retroflexus translocated 48, 91, and 45% more 14C out of spots over the midvein, secondary, and tertiary veins, respectively, than G. max. A. retrollexus had 5, 92, and 66% more phloem tissue in the above respective spots than G. max. Photosynthesis rates were higher in C4 than in C3 plants, but differences were not as great as those in translocation.

Data from this study indicate that C4 plants have both a greater translocation capacity and larger cross-sectional area of phloem than C3 plants.

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