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Chapter. New temperature response parameters for wheat Rubisco

By: Silva-Pérez, V.
Contributor(s): Condon, T | Furbank, R | Reynolds, M.P | Molero, G | Evans, J.R.
Material type: materialTypeLabelChapterPublisher: Mexico : CIMMYT, USAID, MASAGRO, SAGARPA, CONACYT, 2015Subject(s): Wheat | RuBisCO AGROVOC In: Proceedings of the International TRIGO Wheat Yield Potential p. 50-53Summary: In order to select for improved photosynthesis, it is first necessary to identify genetic variation. The photosynthetic rate of an unstressed young leaf under high light and ambient CO2 reflects, firstly, the underlying content and characteristics of photosynthetic enzymes and, secondly, the ease with which CO2 can reach the sites of carboxylation from the atmosphere. The first constraint is related to the nitrogen content per unit leaf area, its allocation to photosynthetic enzymes such as Rubisco and the kinetic properties of the enzymes. The second constraint is associated with stomatal and mesophyll conductances. By analyzing gas exchange data with the standard Farquhar, von Caemmerer and Berry C3 photosynthesis model (Von Caemmerer and Farquhar 1981), it is possible to identify the underlying components that are associated with variation in the measured photosynthetic rate. However, to measure a sufficiently detailed CO2 response curve in the field requires about 30 minutes limiting how many genotypes can be screened. We have been developing a higher throughput method for assessing photosynthetic properties of wheat leaves using reflectance spectra. This was calibrated in the field against CO2 response curves measured with conventional gas exchange. While the LI6400 is able to control leaf temperature to some extent, it was not always possible to achieve a common temperature of 25 C in the field (especially when ambient temperature was above 30 C combined with high irradiance). In fact, leaf temperatures for the experiments conducted in Australia and Mexico ranged between 20 and 34 C. Checks were made by repeated measurement of several leaves through a day at different temperatures. When the standard Farquhar, von Caemmerer and Berry C3 photosynthesis model was applied, we found that the derived Rubisco activity corrected to 25 C was not constant. This prompted us to conduct an experiment where CO2 response curves were measured repeatedly with the same leaf over a range of temperatures. From these measurements, we have derived a set of activation energies and values for Rubisco kinetic parameters at 25 C.
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Book CIMMYT Knowledge Center: John Woolston Library

Lic. Jose Juan Caballero Flores

 

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In order to select for improved photosynthesis, it is first necessary to identify genetic variation. The photosynthetic rate of an unstressed young leaf under high light and ambient CO2 reflects, firstly, the underlying content and characteristics of photosynthetic enzymes and, secondly, the ease with which CO2 can reach the sites of carboxylation from the atmosphere. The first constraint is related to the nitrogen content per unit leaf area, its allocation to photosynthetic enzymes such as Rubisco and the kinetic properties of the enzymes. The second constraint is associated with stomatal and mesophyll conductances. By analyzing gas exchange data with the standard Farquhar, von Caemmerer and Berry C3 photosynthesis model (Von Caemmerer and Farquhar 1981), it is possible to identify the underlying components that are associated with variation in the measured photosynthetic rate. However, to measure a sufficiently detailed CO2 response curve in the field requires about 30 minutes limiting how many genotypes can be screened. We have been developing a higher throughput method for assessing photosynthetic properties of wheat leaves using reflectance spectra. This was calibrated in the field against CO2 response curves measured with conventional gas exchange. While the LI6400 is able to control leaf temperature to some extent, it was not always possible to achieve a common temperature of 25 C in the field (especially when ambient temperature was above 30 C combined with high irradiance). In fact, leaf temperatures for the experiments conducted in Australia and Mexico ranged between 20 and 34 C. Checks were made by repeated measurement of several leaves through a day at different temperatures. When the standard Farquhar, von Caemmerer and Berry C3 photosynthesis model was applied, we found that the derived Rubisco activity corrected to 25 C was not constant. This prompted us to conduct an experiment where CO2 response curves were measured repeatedly with the same leaf over a range of temperatures. From these measurements, we have derived a set of activation energies and values for Rubisco kinetic parameters at 25 C.

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