PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

The balance between capacities of RuBP carboxylation and RuBP regeneration: Interspecific variation in response to seasonal environment. Yusuke Onoda^*,1, Kouki Hikosaka¹, Tadaki Hirose¹, ¹ Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan

ABSTRACT- Light-saturated rates of photosynthesis at ambient CO₂ (P_max) are limited by either RuBP (ribulose-1,5-bisphosphate) carboxylation and RuBP regeneration, and the two capacities (V_cmax and J_max, respectively) affect temperature dependence of P_max. Some species increase the ratio of J_max/V_cmax (measured at a constant temperature) when they are grown at lower temperature. However, other species do not show such change. To elucidate the cause of interspecific difference in the response of J_max/V_cmax to growth temperature, we analyzed the temperature dependence of V_cmax and J_max in Polygonum cuspidatum and Fagus crenata. P. cuspidatum had a higher ratio of J_max/V_cmax in spring and autumn than in summer, while F. crenata did not show such change. The two species had similar activation energies of V_cmax (H_aV) across seasons, but P. cuspidatum had a higher activation energy of J_max (H_aJ) than F. crenata. Reconstruction of the P_max-temperature curve with these parameters showed that the higher ratio of H_aJ/H_aV in P. cuspidatum brought about a shift of limiting steps of photosynthesis along temperature: P_max was limited by RuBP regeneration at low temperature and limited by RuBP carboxylation at high temperature. On the other hand, in F. crenata, P_max was always limited by RuBP carboxylation. The higher ratio of J_max/V_cmax at low temperature in P. cuspidatum was found to relieve the limitation by RuBP regeneration, and consequently kept P_max at relatively high levels at low temperature. These results suggest that the J_max/V_cmax ratio changes when it improves imbalance between capacities of RuBP carboxylation and RuBP.

KEY WORDS: Farquhar's model, temperature acclimation, seasonality, interspecific variation