THE SALT SECRETION PHYSIOLOGY OF A CHLORIDOID GRASS, CYNODON DACTYLON (L.) PERS., AND ITS IMPLICATIONS

Abstract

Leaves and branches of bermuda grass, Cynodon dactylon (L.)
Pers., were exposed to various concentrations of NaCI and KCI salt solutions and were examined using light microscopy, electron microscopy and atomic absorption spectrophotometer. Salt secretion was observed first as droplets and later on as salt crystals. Even though salt was secreted at both sides of the leaf, most of the secretion occurred at the abaxial side of the leaf. The salt was secreted by salt glands which are distributed on· the adaxial and abaxial leaf
surfaces. Each gland consists of two cells: the basal cell and the cap cell. This plant bears salt glands with a mean density of 765 cm·2• Amount of secretion was influenced by the external salt concentration. The amount of sodium secretion increased following an increase in the external NaCl concentration of up to 0.2 M. Leaves secreted more than 50 percent more under a higher relative humidity than under a lower relative humidity at higher NaCI concentrations. This suggests the influence of water stress on secretion. The secretion mechanism was found
to be selective for sodium against potassium. Mixed treatment of NaC} and KCI markedly reduced secretion of sodium while the effect on potassium was less significant. Salt secretion of C. dactylon has an ecological significance in maintaining low salt levels in the shoot. It could play perhaps an important role in the rehabilitation of saline soils.