The temperature dependence of the stimulation of photosynthesis by elevated carbon dioxide in wheat and barley |
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Authors: | Bunce J |
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Institution: | Climate Stress Laboratory, USDA-ARS, Beltsville Agricultural Research Center, 10300 Baltimore Avenue, Beltsville, MD-20705-2350, USA; Fax: +1 301 504 6626; E-mail: jabunce@aol.com |
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Abstract: | The temperature dependencies of the solubility of carbon dioxide and oxygen
in water and the temperature dependency of the kinetic characteristics of
the ribulose-1,5 bisphosphate carboxylase/oxygenase (Rubisco) enzyme result
in the short-term stimulation of photosynthesis with a doubling of carbon
dioxide from 350 to 700 mol
mol-1 usually decreasing from about 90% at 30 C to about 25% at 10 C
at high photon flux. In field-grown wheat and barley, the expected values
at 30°C were observed, but also values as high as 60% at
10°C. The much larger than expected stimulation at cool
temperatures in these species also occurred in plants grown at
15°C, but not at 23°C in controlled environment chambers.
Gas exchange analysis indicated that an unusually high diffusive limitation
was not an explanation for the large response. Assessment of the apparent
in vivo specificity of Rubisco by determining the
carbon dioxide concentration at which carboxylation equalled carbon dioxide
release from oxygenation, indicated that growth at low temperatures altered
the apparent enzyme specificity in these species compared to these species
grown at the warmer temperature. Inserting the observed specificities into
a biochemical model of photosynthesis indicated that altered Rubisco
specificity was consistent with the observed rates of assimilation. Whether
altered apparent Rubisco specificity is caused by altered stoichiometry of
photorespiration or an actual change in enzyme specificity, the results
indicate that the temperature dependence of the stimulation of
photosynthesis by elevated carbon dioxide may vary greatly with species and
with prior exposure to low temperature.Keywords:
Barley, carbon dioxide, photosynthesis, temperature, wheat.
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