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  1. Vol. 15 No. 1, p. 75-77
     
    Received: May 28, 1974
    Published: Jan, 1975


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doi:10.2135/cropsci1975.0011183X001500010021x

Translocation Patterns in Soybeans Exposed to 14CO2 at Four Different Time Periods of the Day1

  1. W. J. Russell and
  2. D. R. Johnson2

Abstract

Abstract

Field grown soybeans [Glydne max (L.) Merr.] were exposed at the mid.bloom stage to 14CO2 for 1 hour beginning at either 9 AM, 11 AM, 1 PM, or 3 PM CDT to evaluate the effects of time of day when exposed to 14CO2 on the translocation and distribution of labeled assimilates. Plants were harvested 0, 1, 3, 6, and 24 hours after labeling. By the end of the labeling period, 16.9% of the total recovered 14C had been exported from the leaves and 36.9% had been exported by the end of 24 hours (averaged over the four exposure times).

Leaves labeled during the time periods associated with the highest net C fixation rates (11 to 12 AM and 3 to 4 PM) assimilated more 14C, translocated more to the stems and roots, and exhibited a higher rate of export from the leaves. Percent 14C recovered in each component (except nodules) was significantly different between the 9 to 10 AM and 3 to 4 PM exposure periods. Differences between the two midday exposures were relatively small, averaged over all harvest times and increased only when compared immediately and 24 hours after labeling.

Carbon-14 labeling and translocation experiments should be conducted during relatively constant time periods to allow nonconfounded intercomparisons between data when experimental technique dictates multiple times of exposure to 14C, especially between the early morning and late afternoon exposure periods.

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