Photosynthesis, Water Status and K(+)/Na(+) Homeostasis of Buchoe dactyloides Responding to Salinity

Soil salinization is one of the most serious abiotic stresses restricting plant growth. Buffalograss is a C(4) perennial turfgrass and forage with an excellent resistance to harsh environments. To clarify the adaptative mechanisms of buffalograss in response to salinity, we investigated the effects of NaCl treatments on photosynthesis, water status and K(+)/Na(+) homeostasis of this species, then analyzed the expression of key genes involved in these processes using the qRT-PCR method. The results showed that NaCl treatments up to 200 mM had no obvious effects on plant growth, photosynthesis and leaf hydrate status, and even substantially stimulated root activity. Furthermore, buffalograss could retain a large amount of Na(+) in roots to restrict Na(+) overaccumulation in shoots, and increase leaf K(+) concentration to maintain a high K(+)/Na(+) ratio under NaCl stresses. After 50 and 200 mM NaCl treatments, the expressions of several genes related to chlorophyll synthesis, photosynthetic electron transport and CO(2) assimilation, as well as aquaporin genes (BdPIPs and BdTIPs) were upregulated. Notably, under NaCl treatments, the increased expression of BdSOS1, BdHKT1 and BdNHX1 in roots might have helped Na(+) exclusion by root tips, retrieval from xylem sap and accumulation in root cells, respectively; the upregulation of BdHAK5 and BdSKOR in roots likely enhanced K(+) uptake and long-distance transport from roots to shoots, respectively. This work finds that buffalograss possesses a strong ability to sustain high photosynthetic capacity, water balance and leaf K(+)/Na(+) homeostasis under salt stress, and lays a foundation for elucidating the molecular mechanism underlying the salt tolerance of buffalograss.