Update on C4 Photosynthesis Environmental Regulation of C3 and C4 Differentiation in the Amphibious Sedge Eleocharis vivipara

The biochemical and physiological characteristics of C4 photosynthesis have been researched and clarified in detail. We now know that the differentiation of two cell types, mesophyll cells (MC) and bundle sheath cells (BSC), is required for efficient C4 photosynthesis. Thus, the leaves of C4 plants have more complicated structural and functional features than those of C3 plants (Hatch, 1999; Kanai and Edwards, 1999). Current studies are focused on elucidating the regulatory mechanisms of genetic and developmental events in C4 photosynthesis, but most of them are as yet poorly understood (Dengler and Nelson, 1999; Sheen, 1999). There is much indirect evidence that C4 plants have evolved in parallel from C3 plants among diverse taxonomic groups (Kellogg, 1999). Some C3-C4 intermediate plants, such as Flaveria spp., provide a suitable system for studying the possible process of evolution of C4 plants (Ku et al., 1991; Westhoff et al., 1997). It is becoming clear that there is diversity not only in the structural and biochemical features, but also in the genetic and developmental aspects of C4 photosynthesis (Dengler and Nelson, 1999; Sheen, 1999; Edwards et al., 2001). This article reviews the available data on the differentiation of photosynthetic characteristics in some amphibious species of Eleocharis in the Cyperaceae, with particular reference to the sedge Eleocharis vivipara. E. vivipara has a unique nature that expresses C4 characteristics under terrestrial conditions and C3 characteristics under submerged aquatic conditions (Ueno et al., 1988). This characteristic is unknown in other C4 plants, and this plant provides an excellent opportunity to investigate the development of C4 photosynthesis in response to environmental factors. The amphibious species of Eleocharis are also useful for increasing our understanding of the ecological and adaptive aspects of C4 plants. C3 AND C4 PHOTOSYNTHESIS