PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Diversification and plasticity of C₄ photosynthetic pathway in Eleocharis (cyperaceae). Joćo Barroca^{*,1, 2}, Lesley Murphy¹, Vincent Franceschi¹, Raymond Lee¹, Eric Roalson¹, Gerald Edwards¹, Maurice Ku¹, ¹ School of Biological Sciences, Pullman, WA, USA² Departamento de Biologia Vegetal, Lisboa, Portugal

ABSTRACT- The genus Eleocharis, which contains C₃, C₄, and C₃-C₄ intermediate species, also has several species that exhibit varying degrees of C₄ characteristics, and genetic plasticity in changing their photosynthetic metabolism and leaf/culm anatomy depending on growth habitat. Analyses of leaf ¹³C content, anatomy, enzyme activity, and immuno-localization indicate that accession 1499 is a typical C₄ plant under terrestrial environment, with a strict compartmentation of PEPC and Rubisco in mesophyll and bundle sheath cells, respectively. Two other species (1490 and E. baldwinii) are considered leaky C₄ species when grown under terrestrial conditions, with Rubisco expressed in the chloroplasts of both cell types but a strict localization of PEPC in the mesophyll cells. Consistently, the terrestrial form of 1499 shows very little O₂ inhibition of photosynthesis (3%), whereas E. baldwinii and 1490 have substantial O₂ inhibition of photosynthesis (13% and 32%, respectively, as versus 37% in E. montevidensis, a C₃ species). When submerged, 1499 becomes a C₃-C₄ intermediate, as judged by its Kranz-like leaf anatomy and intermediate ¹³C content, between those of typical C₃ and C₄ plants. In contrast, the aquatic form of E. baldwinii remains a leaky C₄ plant, but 1490 lacks Kranz anatomy and performs C₃ photosynthesis using bicarbonate rather than CO₂ as carbon source, as demonstrated by an enriched leaf ¹³C content. Earlier studies have reported that E. vivipara is a typical C₄ plant when grown under terrestrial condition, but switches its photosynthetic mode to C₃ when submerged. These results demonstrate the great diversity of photosynthetic mechanism in Eleocharis and the genetic plasticity that some Eleocharis possess in modifying their photosynthetic metabolism in adaptation to different environments. Thus, Eleocharis is a model genus for studying the changes that may have occurred during the evolution of C₄ photosynthesis and for dissecting the novel genetic regulatory mechanisms responsible for its expression.

KEY WORDS: C₄ photosynthesis, plasticity, Eleocharis, diversity