Environmental regulation of photosynthetic metabolism in the amphibious sedge Eleocharis baldwinii and comparisons with related species

Abstract

The amphibious leafless sedge, Eleocharis baldwinii, expresses C 4 characteristics in the terrestrial form and intermediate characteristics between C3 and C4 photosynthesis in the submerged form. This study examined the immunocytochemical localization of C3 and C4 enzymes in culms of the two forms to elucidate the regulatory mechanism of photosynthetic metabolism and compared the activities and amounts of C3 and C4 enzymes with those in other Eleocharis species, E. vivipara and E. retroflexa, which show C 4 characteristics on land but C3 and C4 characteristics under water. The terrestrial form of E. baldwinii exhibited a C4-like pattern of enzyme localization. The submerged form exhibited a modified anatomy with well-developed mesophyll cells and small Kranz cells. The C4 enzyme levels declined conspicuously in outer mesophyll cells adjacent to the epidermis, whereas Rubisco levels increased throughout the mesophyll in the submerged form. These results suggest that intermediate photosynthesis between C3 and C4 photosynthesis in the submerged form results from the predominant operation of the C3 pathway in the outer mesophyll cells and the C4 pathway in both the inner mesophyll and Kranz cells. Differences in the degree of C4 expression in terrestrial forms of Eleocharis species may cause the differences in the expression of photosynthetic modes under water.