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Crop Science Abstract -

Effect of Altered Intraraceme Competition on Carbon-14-Labeled Assimilate and Abscisic Acid in Soybean1


This article in CS

  1. Vol. 26 No. 6, p. 1216-1219
    Received: Oct 15, 1985

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  1. W. G. Spollen,
  2. W. J. Wiebold and
  3. Scott Glenn2



Abscission probability varies among floral positions within soybean [Glycine max (L.) Merr.] racemes. Field (1982, Beltsville silt loam, Typic Fragiudult; 1983, Mattapeake silt loam, Typic Hapludult) grown soybean plants (‘Williams’) were used to determinee the distribution of translocated l4C-labeled photosynthate and abscisic acid (ABA) among reproductive structures differing for abscission probability. The effect of proximal pods on translocation of 14C-labeled photosynthate to and ABA concentration in distal pods (floral positions 3 and above) was also evaluated. Treatments consisted of removing or not removing the two proximal pods (floral positions 1 and 2) from the major racemes at nodes 8 and 10 in 1982 and 8, 10, and 12 in 1983. Six days after treatment in 1982 and 12 days after treatment in 1983, 14C-translocation from the leaf at the node of interest was determined after exposure to 14CO2. On the same day, distal pods were collected for determination of ABA by gas chromatography. For untreated plants, proximal and distal pods accounted for 50 and 7% of the translocated 14C, respectively. Proximal pod removal had no effect on 14C retained by the source leaf (72%) or the concentration of ABA in seeds. Concentration of ABA in pod walls of distal pods was increased by proximal pod removal in only one instance. Amount of 14C translocated to distal pods and distal pod specific activity were not altered by proximal pod removal in 1982 but were increased in 1983. The different treatment effect between years may indicate that distal pods undergo a period of adjustment after proximal pod removal. An understanding of processes that occur during the adjustment period may be necessary before the mechanism of soybean reproductive abscission is known.

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