Does light-promoted export from Commelina benghalensis leaves result from differential light-sensitivity of the cells in the mesophyll-to-sieve tube path? |
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Authors: | Aart J E van Bel ries J Koops Tom Dueck |
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Institution: | Dept of Plant Physiology, Rijkuniversiteit Utrecht, Lange Nieuwstraal 106, 3512 PN Utrecht, The Netherlands. |
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Abstract: | In contrast to the light-promoted uptake by mesophyll cells, light slightly inhibited sucrose uptake by stripped leaf disks of Commelina benghalensis L. This phenomenon appeared to result from a light-promoted vein-associated release, as light stimulated photosynthate release from stripped disks and inhibited that from mesophyll cells. In the -presence of the resorption-blocker p -chloromercuriphenylsulfonic acid, (PCMBS) the release of preloaded 14C]-sugars (sucrose, glucose) and 14C]-amino acids (alanine, asparagine, proline, valine, α-aminoisobutyric acid) from stripped disks was doubled in the light. Illumination enhanced by 20 to 60% the release of endogenous leaf cell compounds (sucrose, H2PO-4, K+, Mg2+, Ca2+) from stripped disks in the presence of PCMBS. Light also increased the export of 14C]-assimilates from intact leaves by 20% after pulse-labelling with 14CO2. A model for loading is proposed, based on the differential light sensitivities of the plasma membranes in the mesophyll-to-sieve tube path. |
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Keywords: | Assimilate export assimilate release phloem loading sucrose release |
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