Submitted to: Functional Plant Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/29/2007
Publication Date: 6/1/2007
Citation: Murphy, L.R., Barroca, J., Franceschi, V.R., Lee, R., Roalson, E.H., Edwards, G.E., Ku, M.S. 2007. Diversity and plasticity of C4 photosynthesis in Eleocharis (Cyperaceae). Functional Plant Biology 34: 571-580. Interpretive Summary: The genus Eleocharis contains some species of plants that can change their photosynthetic method depending on whether they are grown submerged in water or not submerged in water (terrestrially). Photosynthetic methods can be defined as C3, which is traditional photosynthesis; C4, which incorporates an appendage cycle that increases efficiency; or C3-C4 intermediate. This study looked at 3 species of Eleocharis; E. erythropoda Steudel, E. baldwinii (Torrey) Chapman, and E. vivipara Link. Additionally, there were two different populations of E. vivipara. The plants were grown in a greenhouse, both submerged and terrestrially and then studied to determine their photosynthetic method. It was found that E. erythropoda uses C3 photosynthesis regardless of growth condition. E. baldwinii switches from C4-like in terrestrial habitat to C3-C4 intermediacy when submerged. The two E. vivipara populations were different from each other and were different from previously reported E. vivipara, so were called type 2 and type 3. E. vivipara type 2 is a typical C4 plant in the terrestrial habitat, but becomes a C3-C4 intermediate under submerged conditions. E. vivipara type 3 is a C3-C4 intermediate terrestrially, but when submerged appears to use bicarbonate as its carbon source. Understanding the mechanisms that allow these plants to change their photosynthetic method may help further our understanding of the genetics of C4 photosynthesis.
Technical Abstract: Eleocharis contains many amphibious species, and displays diversity of photosynthetic mechanism (C3, C4 or C3-C4 intermediates). A unique feature of Eleocharis is the plasticity in the photosynthetic mechanism of some species in response to the environment. In this study, we have examined the culm anatomy and photosynthetic property of several Eleocharis species grown terrestrially and the changes in the newly produced culms over a short period time frame after switching from terrestrial to submerged condition. Eleocharis baldwinii (Torrey) Chapman is C4-like in terrestrial habitat, exhibiting O2 inhibition of photosynthesis with Rubisco expressed in both mesophyll and bundle sheath cells and PEPC strictly in the mesophyll cells, but switches to C3-C4 intermediacy when submerged. In addition to Eleocharis vivipara Link type 1 (which switches from C4-like to C3), two other photosynthetic types examined in this study were shown to have different responses to growth in either terrestrial or submerged conditions. E. vivipara type 2 is a typical C4 plant in the terrestrial habitat, but becomes a C3-C4 intermediate under submerged conditions. Further, terrestrially, E. vivipara type3 is a C3-C4 intermediate, but when submerged the d13C value increases to -6.7‰, indicating its use of bicarbonate as a major carbon source. The submerged form of this plant exhibited about three times higher photosynthetic O2 evolution rate, compared to the C3 species Eleocharis erythropoda Steudel. These Eleocharis species possess different molecular switches for regulating C4 gene expression in response to environmental stimuli both between different species, and in E. vivipara among different populations. The apparent expression of a bicarbonate transport system by E. vivipara type 3 while submerged represents a unique adaptation to low CO2 availability.