Alonso-Cantabrana Hugo, von Caemmerer Susanne
Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia.
J Exp Bot. 2016 May;67(10):3109-21. doi: 10.1093/jxb/erv555. Epub 2016 Feb 8.
The presence and activity of the C4 cycle in C3-C4 intermediate species have proven difficult to analyze, especially when such activity is low. This study proposes a strategy to detect C4 activity and estimate its contribution to overall photosynthesis in intermediate plants, by using tunable diode laser absorption spectroscopy (TDLAS) coupled to gas exchange systems to simultaneously measure the CO2 responses of CO2 assimilation (A) and carbon isotope discrimination (Δ) under low O2 partial pressure. Mathematical models of C3-C4 photosynthesis and Δ are then fitted concurrently to both responses using the same set of constants. This strategy was applied to the intermediate species Flaveria floridana and F. brownii, and to F. pringlei and F. bidentis as C3 and C4 controls, respectively. Our results support the presence of a functional C4 cycle in F. floridana, that can fix 12-21% of carbon. In F. brownii, 75-100% of carbon is fixed via the C4 cycle, and the contribution of mesophyll Rubisco to overall carbon assimilation increases with CO2 partial pressure in both intermediate plants. Combined gas exchange and Δ measurement and modeling is a powerful diagnostic tool for C4 photosynthesis.
事实证明，很难分析C3 - C4中间物种中C4循环的存在和活性，尤其是当这种活性较低时。本研究提出了一种策略，通过使用可调谐二极管激光吸收光谱（TDLAS）与气体交换系统相结合，在低氧分压下同时测量二氧化碳同化（A）和碳同位素分馏（Δ）的二氧化碳响应，来检测C4活性并估计其对中间植物总光合作用的贡献。然后使用同一组常数，将C3 - C4光合作用和Δ的数学模型同时拟合到这两种响应上。该策略分别应用于中间物种佛罗里达黄顶菊（Flaveria floridana）和布朗氏黄顶菊（F. brownii），以及作为C3和C4对照的普氏黄顶菊（F. pringlei）和二齿黄顶菊（F. bidentis）。我们的结果支持佛罗里达黄顶菊中存在功能性C4循环，其可以固定12 - 21%的碳。在布朗氏黄顶菊中，75 - 100%的碳通过C4循环固定，并且在这两种中间植物中，叶肉Rubisco对总碳同化的贡献都随二氧化碳分压增加。结合气体交换和Δ测量及建模是用于C4光合作用的强大诊断工具。
