PLANT PHYSIOLOGY , Vol 106, Issue 2 591-600, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Modeling Carbon Export Out of Mature Peach Leaves
A. Moing, A. Escobar-Gutierrez and J. P. Gaudillere
Institut National de la Recherche Agronomique, Station de Recherches Fruitieres, Centre de Recherches de Bordeaux, BP81 F-33883 Villenave d'Ornon, France (A.M.)
The characteristics of sorbitol and sucrose export out of mature leaves in
seedlings of peach (Prunus persica L. Batsch cv GF 305) were investigated
by simulating carbon fluxes through the leaf. Three treatments were
employed: a control treatment and two treatments modifying leaf export, the
latter using either shading or girdling. Photosynthesis and 14C
partitioning into sorbitol and sucrose were measured during carbohydrate
pool buildup at the beginning of the photoperiod, and the export rate of
sorbitol and sucrose was modeled using a PSPICE (Simulation Program with
Integrated Circuit Emphasis) simulator. The simulation allowed prediction
of the resulting sorbitol and sucrose contents, which were compared to
experimental carbohydrate contents. The apparent Km for sorbitol and
sucrose phloem loading, estimated by carbon flux modeling, was 6.6 and 4
mol m-3, respectively. The predicted export capacity of the leaf,
characterized by the estimated Vmax values for phloem loading of sorbitol
and sucrose, was similar to the photosynthetic carbon flux measured under
the leaf growth conditions. This export capacity was enhanced in plants in
which all leaves except those studied were shaded. The mature leaf had a
higher storage capacity for sorbitol than for sucrose in control plants,
especially in the girdled treatment. Sucrose content appears to be tightly
regulated.
