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Effects of Elevated CO₂ on Growth, Carbon Assimilation, Photosynthate Accumulation and Related Enzymes in Rice Leaves during Sink-Source Transition
- Li, Jun-Ying, Liu, Xing-Hua, Cai, Qing-Sheng, Gu, Hui, Zhang, Shan-Shan, Wu, Yan-Yan, Wang, Chun-Jiao
- Journal of integrative plant biology 2008 v.50 no.6 pp. 723-732
- Oryza sativa, biomass production, carbon, carbon dioxide, enzyme activity, leaves, rice, starch, sucrose, sucrose synthase, sucrose-phosphate synthase
- To study the effects of growing rice (Oryza sativa L.) leaves under the treatment of the short-term elevated CO₂ during the period of sink-source transition, several physiological processes such as dynamic changes in photosynthesis, photosynthate accumulation, enzyme activities (sucrose phosphate synthase (SPS), and sucrose synthase (SS)), and their specific gene (sps1 and RSus1) expressions in both mature and developing leaf were measured. Rice seedlings with fully expanded sixth leaf (marked as the source leaf, L6) were kept in elevated (700 μmol/mol) and ambient (350 mol/L) CO₂ until the 7th leaf (marked as the sink leaf, L7) fully expanded. The results demonstrated that elevated CO₂ significantly increased the rate of leaf elongation and biomass accumulation of L7 during the treatment without affecting the growth of L6. However, in both developing and mature leaves, net photosynthetic assimilation rate (A), all kinds of photosynthate contents such as starch, sucrose and hexose, activities of SPS and SS and transcript levels of sps1 and RSus1 were significantly increased under elevated CO₂ condition. Results suggested that the elevated CO₂ had facilitated photosynthate assimilation, and increased photosynthate supplies from the source leaf to the sink leaf, which accelerated the growth and sink-source transition in new developing sink leaves. The mechanisms of SPS regulation by the elevated CO₂ was also discussed.