Enzymatic and quantitative properties of Rubisco in some conifers and lycopods.

Information on the kinetic properties of Rubisco, a key enzyme for photosynthesis, is scarce in land plants that emerged early during the evolutionary process. This study examined the carboxylase activity and abundance of Rubisco in five conifers, two lycopods, and three control C crops. The turnover rates of Rubisco carboxylation (k) under saturated-CO conditions in conifers and lycopods were comparable to those in the control C crops. Rubisco carboxylase activity under CO-unsaturated conditions (v) was also measured using reaction mixtures saturated with a N gas containing CO and O at present atmospheric levels to predict the Rubisco CO affinity from the percentage of v in k. The predicted CO affinity in conifers and lycopods tended to be lower than that in the control C crops. When the control C crops and two previously examined C crops were analyzed together, the k of Rubisco with a low CO affinity tended to be high. N allocation to Rubisco with a low k tended to be high in these plants. In conifers and lycopods, the k was lower than that expected on the basis of predicted Rubisco CO affinity, unlike in the control crops. N allocation to Rubisco also tended to be lower than that expected on the basis of k. These results indicate that Rubisco in the examined conifers and lycopods is not superior in terms of both k and CO affinity and that the abundance of Rubisco is not necessarily closely related to its kinetic properties. The reason for these phenomena is discussed in terms of the molecular evolution of Rubisco.