Salt glands of recretohalophyte Tamarix under salinity: Their evolution and adaptation

Here, we studied the evolution of salt glands in 11 species ofTamarixand determined their role in adaptation to saline environments by measuring the effect of NaCl on plant growth and salt gland characteristics. Cluster analysis dividedTamarixspecies into three types (types I-III) according to salt-gland characteristics. A phylogenetic tree based on ITS sequences indicated an evolutionary relationship consistent with the geographical distribution ofTamarix. We measured growth under different NaCl conditions (0, 100, 200, and 300 mM) for 40 days in three species (T. gallica,T. ramosissima,andT. laxa) representing the threeTamarixtypes. With increasing NaCl concentration, the biomass of all species was significantly reduced, especially that ofT. gallica. Salt secretion ability and salt-gland density showed similar trends in three types. The order of salt tolerance was type I > type II > type III. We conclude that duringTamarixadaptation to salinity, salt-gland evolution followed two directions: one increasing salt-gland density, and the other increasing salt secretion rate per salt-gland. This study provides a basis for potential mechanisms of recretohalophyte adaptation to salinity.