Halophyte salt tolerance mechanisms: An investigation of the role of plasma membrane lipid composition and proton-ATPase salinity responses of Spartina species.

摘要

There is an increasing demand to understand the mechanisms of salt tolerance in plants on the biochemical and molecular levels in order to successfully breed and genetically manipulate plants for increased tolerance to saline soils and water. The research presented here is an investigation of the salinity response of the halophytic plants, Spartina alterniflora and Spartina patens, with primary focus being on the latter species. Salt tolerance mechanisms were examined at the cellular, organ, and whole plant levels of organization. Plant growth, ion concentrations, and plasma membrane (PM) lipid composition of tissue and cells were analyzed, and results revealed some of the mechanisms used by S. patens to tolerate salt at the different organizational levels.; Based upon the ability to increase organic content, the salinity tolerance of the various tissues of Spartina patens could be ranked from high to low as whole plant, independently grown shoots, and callus. Whole plants and independently grown shoots could tolerate higher tissue Na{dollar}{bsol}sp+{dollar}/K{dollar}{bsol}sp+{dollar} ratios than callus, whereas ion exclusion was more evident in callus than in the whole plants and independently grown shoots.; There was a reduced NaCl permeability of the plasma membrane in response to increasing growth medium salinity for all the plant materials examined, including whole plant roots, independently grown shoots, and callus. The major lipid classes of Spartina patens plasma membranes were sterols, phospholipids, and glycolipids. Sterol species identified included sitosterol, campesterol, and trace amounts of stigmasterol. Phospholipid species resolved were composed of phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and phosphatidylglycerol. A significant amount of the molar percentages of the plasma membrane fatty acids in roots and callus were short-chain ones, including C11 and C14, whereas shoots contained the typical plant membrane fatty acids, including C16 and C18.; Callus appeared to be unique in that it had higher proportions of C11 and C14 fatty acids, higher FS/PL ratios, higher PC/PE ratios, and a higher campesterol content, than roots and shoots, all of which suggested a less permeable membrane to NaCl.; There was a significant increase of PM H{dollar}{bsol}sp+{dollar}-ATPase activity when callus was grown on media containing NaCl. The significant incremental activation in ATPase activity of S. patens cells would enable them to accommodate higher cytoplasmic NaCl concentrations when subjected to salinity. At the higher salinities, PM H{dollar}{bsol}sp+{dollar}-ATPase appeared to have a higher Vmax and lower substrate concentration (Km) to reach Vmax. NaCl inhibited PM H{dollar}{bsol}sp+{dollar}-ATPase in a noncompetitive pattern in which the enzyme had a decreased Vmax, but an unaffected Km in the presence of NaCl.