Abstract
By pulse-labeling field-grown soybean leaves for 60 seconds at midday with 14CO2 and then sequentially harvesting, dissecting, and extracting the radioactive fruit tissues (of pod and seeds), the route, uptake kinetics, and metabolic fate of 14C-photosynthate as it was imported by 35- to 40-day-old pods were determined. As the [14C]sucrose pulse entered the pods, the seeds became radioactive immediately but a lag of nearly 30 minutes occurred before label could be detected in the pod wall pericarp.
Import of the 14C-pulse by the seeds was exclusively via the seed coats, where rapid unloading occurred. Maximum accumulation of label in the seed coat occurred in about 60 minutes at which time 59% of the total radioactivity in the fruit was in the three seed coats, whereas only 7% was in the cotyledons they enclosed. The photosynthate remained as [14C]sucrose as it passed through the seed coat, but appeared to be hydrolyzed relatively soon after uptake by the cotyledons. By 2.5 hours, 60% of the 14C-photosynthate pulse had passed into the cotyledons with only 27% remaining in the seed coats. Inasmuch as there is no vascular connection between maternal seed coat and the developing embryo, cotyledonary uptake of sucrose released from the inner seed coat surface may require specialized transport mechanisms.
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Selected References
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- Fisher D. B. Kinetics of C-14 translocation in soybean: I. Kinetics in the stem. Plant Physiol. 1970 Feb;45(2):107–113. doi: 10.1104/pp.45.2.107. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Giaquinta R. T. Phloem loading of sucrose: involvement of membrane ATPase and proton transport. Plant Physiol. 1979 Apr;63(4):744–748. doi: 10.1104/pp.63.4.744. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Giaquinta R. Source and sink leaf metabolism in relation to Phloem translocation: carbon partitioning and enzymology. Plant Physiol. 1978 Mar;61(3):380–385. doi: 10.1104/pp.61.3.380. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Housley T. L., Fisher D. B. Estimation of Osmotic Gradients in Soybean Sieve Tubes by Quantitative Autoradiography: Qualified Support for the MUnch Hypothesis. Plant Physiol. 1977 Apr;59(4):701–706. doi: 10.1104/pp.59.4.701. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Quebedeaux B., Chollet R. Growth and Development of Soybean (Glycine max [L.] Merr.) Pods: CO(2) Exchange and Enzyme Studies. Plant Physiol. 1975 Apr;55(4):745–748. doi: 10.1104/pp.55.4.745. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Servaites J. C., Schrader L. E., Jung D. M. Energy-dependent Loading of Amino Acids and Sucrose into the Phloem of Soybean. Plant Physiol. 1979 Oct;64(4):546–550. doi: 10.1104/pp.64.4.546. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wyse R. Sucrose uptake by sugar beet tap root tissue. Plant Physiol. 1979 Nov;64(5):837–841. doi: 10.1104/pp.64.5.837. [DOI] [PMC free article] [PubMed] [Google Scholar]