The strategy of Na+ compartmentation and growth of Atriplex centralasiatica in adaptation to saline environments

Abstract

In this study, we investigated the adaptation strategy employed by Atriplex centralasiatica Iljin in response to high salinity. When grown in high saline environments (100–200 mM NaCl), A. centralasiatica plants were larger and more succulent. This increased growth and water uptake was correlated with a large and specific cellular accumulation of sodium, demonstrating that in A. centralasiatica Na+ is beneficial rather than toxic. More than 95% of Na+ absorbed by salt-treated A. centralasiatica plants accumulated in shoots, especially in leaves; approximately 98% of Na+ that accumulated in leaves was localized in leaf protoplasts, a situation that was responsible for the decreased photosynthetic rate observed with increasing salt concentration. Because of the greater leaf area per plant found under saline conditions, no reduction in biomass of individual plants was observed. Measurements on isolated tonoplast-enriched membrane vesicles derived from the leaves of A. centralasiatica revealed increased V-H+-ATPase hydrolytic activity and V-H+-ATPase proton pump activity in salt-treated leaves compared with controls. These results suggest that, as an adaptation to saline environments, A. centralasiatica can efficiently sequester Na+ into vacuoles, thereby increasing leaf area to maintain its CO2 assimilation capabilities.