Differences between wheat and rice in the enzymic properties of ribulose-1,5-bisphosphate carboxylase/oxygenase and the relationship to photosynthetic gas exchange

Abstract

The kinetic parameters of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (EC 4.1.1.39) in wheat (Triticum aestivum L.) and rice (Oryza sativa L.) were determined by rapidly assaying the leaf extracts. The respective K m and V max values for carboxylase and oxygenase activities were significantly higher for wheat than for rice. In particular, the differences in the V max values between the two species were greater. When the net activity of CO2 exchange was calculated at the physiological CO2-O2 concentration from these kinetic parameters, it was 22% greater in wheat than in rice. This difference in the in-vitro RuBP-carboxylase/oxygenase activity between the two species reflected a difference in the CO2-assimilation rate per unit of RuBP-carboxylase protein. However, there was no apparent difference in the CO2-assimilation rate for a given leaf-nitrogen content between the two species. When the RuBP-carboxylase/oxygenase activity was estimated at the intercellular CO2 pressure from the enzyme content and kinetic parameters, these estimated enzyme activities in wheat and rice were similar to each other for the same rate of CO2 assimilation. These results indicate that the difference in the kinetic parameters of RuBP carboxylase between the two species was offset by the differences in RuBP-carboxylase content and conductance for a given leaf-nitrogen content.

Photosynthesis, Grain Yield, and Nitrogen Utilization in Rice and Wheat

“…Rice allocates 25% to 30% of leaf N to Rubisco with higher affinity for CO 2 (20% lower K m for CO 2 ) than wheat, whereas wheat allocates 20% to 25% of leaf N to Rubisco with greater k cat (50% higher V max for carboxylation) than rice (Makino et al, 1988). The CO 2 /O 2 specificity for carboxylation and oxygenation does not differ between the two species.…”

“…As described above, since the photosynthetic system of rice may have evolved to adapt to warm and hot environments, engineering C 4 photosynthesis may not necessarily be suitable in some points. Rice has greater Rubisco content of the low K m (CO 2 )/low k cat form (Makino et al, 1988). In addition, rice mesophyll cells are specialized to effectively scavenge photorespired CO 2 (Sage and Sage, 2009).…”

Effects of Nitrogen Nutrition on Nitrogen Partitioning between Chloroplasts and Mitochondria in Pea and Wheat

“…The rates of CO2 and water-vapor exchange were measured with an open gas-exchange system using a temperature-controlled chamber equipped with two fans (23 …”

Changes in Photosynthetic Activity and Export of Carbon by Overexpressing a Maize Sucrose-Phosphate Synthase Gene under Elevated C02in Transgenic Rice

“…For the elevated [C0 2 ] treatment, CO 2 was injected into a controlled~environment chamber (Eyelatron FLI~ 30lNHCL, Eyela, Tokyo, Japan), which could control [C0 2 ] within ± 5 Pa. To select transgenic rice plants from the seedlings, we sampled the 3rd leaves when the 4th or the 5th leaves were fully expanded, and performed Western blot analysis against anti~maize SPS antibody. Transgenic and wild~type plants were transplanted into 3 L pots (three plants/pot) and grown hydroponically with the nutrient solution described by Makino et al (1988), except that NH 4 N0 3 was replaced by KN0 3 under the conditions described above for seedlings growth. The solution was renewed every 7 days.…”