PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Photosynthetic acclimation in rice leaves to free-air CO₂ enrichment (FACE) related to both RuBP carboxylation limitation and RuBP regeneration limitation. Gen-Yun Chen¹, Zhen-Hua Yong², Yi Liao³, Yue Chen⁴, Dao-Yun Zhang⁵, Hai-Bo Zhang⁶, Jian-Guo Zhu⁷, Da-Quan Xu^*,, ¹ 300 Fengling Road, Shanghai, China² 300 Fengling Road, Shanghai, China³ 300 Fengling Road, China⁴ 300 Fengling Road, China⁵ 300 Fengling Road, China⁶ 300 Fengling Road, China⁷ 71 Beijing east Road, Nanjing, China

ABSTRACT- Net photosynthetic rates (Pn) in rice leaves were compared in situ between the plants grown in free-air CO₂ enrichment (FACE, 580 umol mol^-1) treated and ambient air (380 umol mol^-1) control rings. FACE leaves had significantly decreased Pn measured at a same CO₂ concentration, indicating that acclimation or down-regulation of photosynthesis occurs in FACE leaves. Although stomatal conductance (Gs) in FACE leaves was markedly lower than that in ambient leaves, intercellular CO₂ concentration (Ci) was almost same in FACE and ambient leaves, indicating that the photosynthetic down-regulation is not caused by the decrease in Gs. Furthermore, soluble protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and Rubisco activase as well as ATP contents and sucrose phosphate synthase (SPS) activity decreased significantly while sucrose, fructose, glucose and inorganic phosphate (Pi) contents increased in FACE leaves. Interestingly, chlorophyll content was increased, but the area of single flag leaf was reduced in FACE leaves. It appears that the photosynthetic acclimation in rice leaves to FACE is related to both RuBP carboxylation limitation, via the decreased amount and activity of Rubisco induced by soluble sugar accumulation, ATP shortage and Rubisco activase loss, and RuBP regeneration limitation, via ATP shortage.

KEY WORDS: FACE, Acclimation, rice, CO2