Different CO2 acclimation strategies in juvenile and mature leaves of Ottelia alismoides

• Published in: Photosynthesis research 2018-11, Vol.138 (2), p.219-232
• Main Authors: Huang, Wen Min, Shao, Hui, Zhou, Si Ning, Zhou, Qin, Fu, Wen Long, Zhang, Ting, Jiang, Hong Sheng, Li, Wei, Gontero, Brigitte, Maberly, Stephen C.
• Format: Article
• Language: English
• Subjects: Acclimation; Acidity; Bicarbonates; Biochemistry; Biochemistry, Molecular Biology; Biomedical and Life Sciences; Carbon dioxide; Diurnal; Leaves; Life Sciences; Original Article; Ottelia alismoides; Oxygenase; Phosphoenolpyruvate carboxylase; Photosynthesis; Plant Genetics and Genomics; Plant Physiology; Plant Sciences; Ribulose-bisphosphate carboxylase; Starch
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-018-0568-y

The freshwater macrophyte, Ottelia alismoides , is a bicarbonate user performing C4 photosynthesis in the light, and crassulacean acid metabolism (CAM) when acclimated to low CO 2 . The regulation of the three mechanisms by CO 2 concentration was studied in juvenile and mature leaves. For mature leaves, the ratios of phosphoenolpyruvate carboxylase (PEPC) to ribulose-bisphosphate carboxylase/oxygenase (Rubisco) are in the range of that of C4 plants regardless of CO 2 concentration (1.5–2.5 at low CO 2 , 1.8–3.4 at high CO 2 ). In contrast, results for juvenile leaves suggest that C4 is facultative and only present under low CO 2 . pH-drift experiments showed that both juvenile and mature leaves can use bicarbonate irrespective of CO 2 concentration, but mature leaves have a significantly greater carbon-extracting ability than juvenile leaves at low CO 2 . At high CO 2 , neither juvenile nor mature leaves perform CAM as indicated by lack of diurnal acid fluctuation. However, CAM was present at low CO 2 , though the fluctuation of titratable acidity in juvenile leaves (15–17 µequiv g −1 FW) was slightly but significantly lower than in mature leaves (19–25 µequiv g −1 FW), implying that the capacity to perform CAM increases as leaves mature. The increased CAM activity is associated with elevated PEPC activity and large diel changes in starch content. These results show that in O. alismoides , carbon-dioxide concentrating mechanisms are more effective in mature compared to juvenile leaves, and C4 is facultative in juvenile leaves but constitutive in mature leaves.