PLANT PHYSIOLOGY , Vol 110, Issue 3 893-902, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Doubling the CO2 Concentration Enhanced the Activity of Carbohydrate-Metabolism Enzymes, Source Carbohydrate Production, Photoassimilate Transport, and Sink Strength for Opuntia ficus-indica
N. Wang and P. S. Nobel
UCLA-DOE Laboratory and Department of Biology, University of California, Los Angeles, California 90024-1786
After exposure to a doubled CO2 concentration of 750 [mu]mol mol-1 air for
about 3 months glucose and starch in the chlorenchyma of basal cladodes of
Opuntia ficus-indica increased 175 and 57%, respectively, compared with the
current CO2 concentration of 370 [mu]mol mol-1, but sucrose content was
virtually unaffected. Doubling the CO2 concentration increased the
nocturnal malate production in basal cladodes by 75%, inorganic phosphate
(Pi) by 32%, soluble starch synthase activity by 30%, and sucrose-Pi
synthase activity by 146%, but did not affect the activity of hexokinase.
Doubling CO2 accelerated phloem transport of sucrose out of the basal
cladodes, resulting in a 73% higher dry weight for the daughter cladodes.
Doubling CO2 increased the glucose content in 14-d-old daughter cladodes by
167%, increased nocturnal malate production by 22%, decreased total amino
acid content by 61%, and increased soluble starch synthase activity by 30%
and sucrose synthase activity by 62%. No downward acclimation of
photosynthesis during long-term exposure to elevated CO2 concentrations
occurs for O. ficus-indica (M. Cui, P.M. Miller, P.S. Nobel [1993] Plant
Physiol 103: 519-524; P.S. Nobel, A.A. Israel [1994] J Exp Bot 45:
295-303), consistent with its higher source capacity and sink strength than
under current CO2. These changes apparently do not result in Pi limitation
of photosynthesis or suppression of genes governing photosynthesis for this
perennial Crassulacean acid metabolism species, as occur for some annual
crops.
