Plant Physiol.
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Plant Physiology 75:881-886 (1984)
© 1984 American Society of Plant Biologists

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Articles

Effect of Shortened Photosynthetic Period on 14C-Assimilate Translocation and Partitioning in Reproductive Soyeans 1

Dale R. Carlson and William A. Brun

Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55108

Starch accumulation rate in leaves of vegetative soybeans is inversely related to the length of the daily photosynthetic period. However, it is not known whether a similar response would be observed during reproductive growth. Soybeans (Glycine max L. Merr. cv Amsoy 71) were grown to three stages of reproductive growth (beginning seed, mid seed-fill, and late seed-fill) under 12-hour daylengths, and then shifted to 6-hour photosynthetic periods (12-hour photoperiods) for 4 days. One and 4 days after treatment, a mid-canopy leaf was pulsed with 14CO2, and sampled for radiolabeled starch and water-soluble compounds at 0.5, 1, 3, 9, and 21 hours after labeling.

Plants exposed to the 6-hour photosynthetic periods at the beginning seed stage retained and incorporated significantly more label as starch than did those given 12-hour photosynthetic periods. However, plants exposed to the shortened photosynthetic periods at the late seed-fill stage partitioned less label into starch. Plants exposed at mid seed-fill gave a variable response.

Shortened photosynthetic periods resulted in preferential partitioning of recently fixed carbon to the seed at the expense of the pod wall. The results of these experiments suggest that the increased sink demand present during late reproductive growth may be of greater importance in control of leaf starch accumulation than is the length of the daily photosynthetic period.

1 Supported in part by a grant from the Minnesota Soybean Research and Promotion Council, and also in part by the Science and Education Administration of the United States Department of Agriculture under Grant 82-CRRC-1-1077 from the Competitive Research Grants Office. Contribution from the University of Minnesota Agricultural Experimental Station, St. Paul, MN 55108. Paper no. 13,602, Scientific Journal Series.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1984 by the American Society of Plant Biologists