Ribulose-1,5-bisphosphate regeneration limitation in rice leaf photosynthetic acclimation to elevated CO 2

Abstract

Our previous study has demonstrated that both RuBP carboxylation limitation and RuBP regeneration limitation exist simultaneously in rice grown under free-air CO 2 enrichment (FACE, about 200 μmol mol −1 above the ambient air CO 2 concentration) conditions [G.-Y. Chen, Z.-H. Yong, Y. Liao, D.-Y. Zhang, Y. Chen, H.-B. Zhang, J. Chen, J.-G. Zhu, D.-Q. Xu, Photosynthetic acclimation in rice leaves to free-air CO 2 enrichment related to both ribulose-1,5-bisphosphate carboxylase limitation and ribulose-1,5-bisphosphate regeneration limitation. Plant Cell Physiol. 46 (2005) 1036–1045]. To explore the mechanism for forming of RuBP regeneration limitation, we conducted the gas exchange measurements and some biochemical analyses in FACE-treated and ambient rice plants. Net CO 2 assimilation rate ( A net) in FACE leaves was remarkably lower than that in ambient leaves when measured at the same CO 2 concentration, indicating that photosynthetic acclimation to elevated CO 2 occurred. In the meantime the maximum electron transport rate (ETR) ( J max), maximum carboxylation rate ( V cmax) in vivo, and RuBP contents decreased significantly in FACE leaves. The whole chain electron transport rate and photophosphorylation rate reduced significantly while ETR of photosystem II (PSII) did not significantly decrease and ETR of photosystem I (PSI) was significantly increased in the chloroplasts from FACE leaves. Further, the amount of cytochrome (Cyt) f protein, a key component localized between PSII and PSI, was remarkably declined in FACE leaves. It appears that during photosynthetic acclimation the decline in the Cyt f amount is an important cause for the decreased RuBP regeneration capacity by decreasing the whole chain electron transport in FACE leaves.