Plant Biol (Stuttg) 2000; 2(1): 107-112
DOI: 10.1055/s-2000-9459
Original Paper
Georg Thieme Verlag Stuttgart ·New York

Compartmentation of Assimilate Fluxes in Leaves

II. Apoplastic Sugar Levels in Leaves of Plants with Different Companion Cell TypesOlga V. Voitsekhovskaja 1 , Marina V. Pakhomova 1 , Anna V. Syutkina 1 , Y. V. Gamalei 1 , and U. Heber 2
  • 1 Department of Ecophysiology, Komarov Botanical Institute, St. Petersburg, Russia
  • 2 Julius-von-Sachs-Institute, University of Würzburg, Würzburg, Germany
Further Information

Publication History

July 28, 1999

November 16, 1999

Publication Date:
31 December 2000 (online)

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Abstract:

Sugar levels in the apoplast of assimilate exporting leaves were studied in two groups of plant species with contrasting structures of companion cells in minor veins. These species are termed either „symplastic” (with intermediary cells) or „apoplastic” (with transfer or ordinary cells). Sugars were measured in intercellular washing fluid after extracting the apoplast by an infiltration-centrifugation technique. During the course of a day, sugar contents in the apoplast were, in general, lower in species with intermediary cells than in species with transfer or ordinary cells. In „symplastic” species, apoplastic sucrose concentrations were between 0.3 and 1 mM. In „apoplastic” species with transfer cells, they ranged between 2 and 6 mM. Apoplastic hexose contents were between 0.3 and 1 mM irrespective of presumed transport mode. „Symplastic” and „apoplastic” plants differed markedly in their response to a’translocation block. In „symplastic” plants, inhibition of assimilate export left apoplastic concentrations of sucrose and hexoses unchanged, whereas in „apoplastic” plants sugar levels increased, the maximal increase being observed with sucrose. In these plants, concentrations of sucrose were two to six times higher in the apoplast under export inhibition than in control leaves. The data suggest a different role of the leaf apoplast in the compartmentation and export of assimilates in the two plant groups under study.