Yamori Wataru, Noguchi Ko, Kashino Yasuhiro, Terashima Ichiro
Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
Plant Cell Physiol. 2008 Apr;49(4):583-91. doi: 10.1093/pcp/pcn030. Epub 2008 Feb 21.
The temperature response of the uncoupled whole-chain electron transport rate (ETR) in thylakoid membranes differs depending on the growth temperature. However, the steps that limit whole-chain ETR are still unclear and the question of whether the temperature dependence of whole-chain ETR reflects that of the photosynthetic rate remains unresolved. Here, we determined the whole-chain, PSI and PSII ETR in thylakoid membranes isolated from spinach leaves grown at 30 degrees C [high temperature (HT)] and 15 degrees C [low temperature (LT)]. We measured temperature dependencies of the light-saturated photosynthetic rate at 360 microl l(-1) CO2 (A360) in HT and LT leaves. Both of the temperature dependences of whole-chain ETR and of A360 were different depending on the growth temperature. Whole-chain ETR was less than the rates of PSI ETR and PSII ETR in the broad temperature range, indicating that the process was limited by diffusion processes between the PSI and PSII. However, at high temperatures, whole-chain ETR appeared to be limited by not only the diffusion processes but also PSII ETR. The C3 photosynthesis model was used to evaluate the limitations of A360 by whole-chain ETR (Pr) and ribulose bisphosphate carboxylation (Pc). In HT leaves, A360 was co-limited by Pc and Pr at low temperatures, whereas at high temperatures, A360 was limited by Pc. On the other hand, in LT leaves, A360 was solely limited by Pc over the entire temperature range. The optimum temperature for A360 was determined by Pc in both HT and LT leaves. Thus, this study showed that, at low temperatures, the limiting step of A360 was different depending on the growth temperature, but was limited by Pc at high temperatures regardless of the growth temperatures.
类囊体膜中解偶联的全链电子传递速率（ETR）的温度响应因生长温度而异。然而，限制全链ETR的步骤仍不清楚，全链ETR的温度依赖性是否反映光合速率这一问题也尚未解决。在这里，我们测定了从生长在30℃[高温（HT）]和15℃[低温（LT）]的菠菜叶片中分离出的类囊体膜中的全链、PSI和PSII的ETR。我们测量了HT和LT叶片在360 μl l(-1) CO2（A360）下光饱和光合速率的温度依赖性。全链ETR和A360的温度依赖性均因生长温度而异。在较宽的温度范围内，全链ETR低于PSI ETR和PSII ETR的速率，这表明该过程受PSI和PSII之间扩散过程的限制。然而，在高温下，全链ETR似乎不仅受扩散过程限制，还受PSII ETR限制。C3光合作用模型用于评估全链ETR（Pr）和核酮糖二磷酸羧化（Pc）对A360的限制。在HT叶片中，低温时A360受Pc和Pr共同限制，而在高温时，A360受Pc限制。另一方面，在LT叶片中，A360在整个温度范围内仅受Pc限制。HT和LT叶片中A360的最适温度均由Pc决定。因此，本研究表明，在低温下，A360的限制步骤因生长温度而异，但在高温下，无论生长温度如何，A360均受Pc限制。
