Salt stress induces Kranz anatomy and expression of C4 photosynthetic enzymes in the amphibious sedge Eleocharis vivipara.

Eleocharis vivipara Link is a unique amphibious leafless plant of the Cyperaceae. The terrestrial form develops culms with Kranz anatomy and C4-like traits, while the submerged form does culms with non-Kranz anatomy and C3 traits. The submerged form develops new culms with C4-like mode when exposed to air or exogenous abscisic acid. In this study, we investigated whether salt stress (0.05-0.3 M NaCl) has a similar effect. When the submerged form was grown for one month in solutions of 0.1 M NaCl and more, culm growth was strongly suppressed. However, these plants slowly developed new culms that had Kranz anatomy with chloroplast-abundant Kranz bundle sheath cells. Although the culms of the submerged form had only few stomata, culms grown in the NaCl solution had many stomata. The NaCl-grown culms also accumulated large amounts of C4 photosynthetic enzymes (phosphoenolpyruvate carboxylase and pyruvate Pi dikinase), and the cellular localization patterns of these enzymes and ribulose 1,5-bisphosphate carboxylase/oxygenase were similar to those in terrestrial culms. Accumulation of C4 enzymes increased in mature culms of the submerged form (with non-Kranz anatomy) when exposed to 0.2 M NaCl solution for one week. These results suggest that salt stress induces development of Kranz anatomy and expression of C4 photosynthetic enzymes in the submerged C3 form of E. vivipara, whereas the anatomical and biochemical traits of C4 photosynthesis appear to be regulated independently.