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

Mechanisms of temperature acclimation for photosynthesis in spinach leaves. Wataru Yamori^*,1, Yukari Asakura², Masato Nakai², Ko Noguchi¹, Ichiro Terashima¹, ¹ 1Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka, Japan² 2Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, Japan

ABSTRACT- When plant growth temperature changes, optimum temperature for leaf photosynthesis also shifts. Farquhar & von Caemmerer (1982) suggested that the shift of the optimum temperature for photosynthesis would be caused by a change in a ratio of the capacity of RuBP regeneration to RuBP carboxylation. On the other hand, it is recently indicated that the growth temperature changed not only the relative capacities of these partial reactions but also the temperature dependencies of RuBP regeneration and, to a lesser extent, RuBP carboxylation. To clarify mechanisms of the temperature acclimation for photosynthesis, various photosynthetic properties were analyzed in leaves of spinach (Spinacia oleracea) grown at 15/10°C or 30/25°C Moreover, we also analyzed the leaves of the plants that were transferred from high to low temperature. The growth temperature affected the optimum temperature of photosynthesis at 360 L L^-1 CO₂. From gas-exchange analyses of partial reactions of photosynthesis, the temperature dependence and the optimum temperature of RuBP regeneration changed depending on the growth temperature. The optimum temperature of RuBP carboxylation drastically changed depending on the growth temperature, although kinetic properties of Rubisco are generally considered to be similar among higher plants and growth temperatures. Results of two-dimensional gel electrophoresis of partially-purified Rubisco revealed significant differences in the isoelectric point in Rubisco small subunits (SSU) depending on the growth temperature. Moreover, the electrophoretic difference increased with the length of 15/10°C treatment. These data suggest that, in spinach grown at lower temperature, expressions of isozyme(s) of SSU having greater activity at lower temperature or some post-translational modifications of SSU contribute to the downward shift in the optimum temperature for photosynthesis.

KEY WORDS: RuBP carboxylation, temperature acclimation, Rubisco, RuBP regeneration