Leaf anatomy, gas exchange and photosynthetic enzyme activity in Flaveria kochiana.

Flaveria (Asteraceae) is one of the few genera known to contain both C and C species, in addition to numerous biochemically-intermediate species. C-C and C-like intermediate photosynthesis have arisen more than once in different phylogenetic clades of Flaveria. Here, we characterise for the first time the photosynthetic pathway of the recently described species Flaveria kochiana B.L. Turner. We examined leaf anatomy, activity and localisation of key photosynthetic enzymes, and gas exchange characteristics and compared these trait values with those from related C and C-like Flaveria species. F. kochiana has Kranz anatomy that is typical of other C Flaveria species. As in the other C lineages within the Flaveria genus, the primary decarboxylating enzyme is NADP-malic enzyme. Immunolocalisation of the major C cycle enzymes, PEP carboxylase and pyruvate, orthophosphate dikinase, were restricted to the mesophyll, while Rubisco was largely localised to the bundle sheath. Gas exchange analysis demonstrated that F. kochiana operates a fully functional C pathway with little sensitivity to ambient oxygen levels. The CO compensation point (2.2 µbar) was typical for C species, and the O-response of the CO compensation point was the same as the C species F. trinervia. Notably, F. vaginata (B.L. Robinson & Greenman), a putative C-like species that is the nearest relative of F. kochiana, had an identical response of the CO compensation point to O. Furthermore, F. vaginata, exhibited a carbon isotope ratio (-15.4‰) similar to C species including F. australasica Hooker, F. trinervia Spreng. C. Mohr and the newly characterised F. kochiana. F. vaginata could be considered a C species, but additional studies are necessary to confirm this hypothesis. In addition, our results show that F. kochiana uses an efficient C cycle, with the highest initial slope of the A/C curve of any C Flaveria species.