activation of lignin biosynthetic enzymes during internodal development of aeluropus littoralis exposed to nacl

lignin is one of the major characteristics of plant secondary cell wall that provides structural rigidity for the cells and tissues and hydrophobicity to tracheary elements. internode tissues of aeluropus littoralis as a halophyte grass were sampled at different developmental stages (from the first to the fifth internodes ) and under different nacl concentrations. the influences of nacl and internode maturity on lignin content and activities of phenylalanine ammonia-lyase (pal) and cinnamyl alcohol dehydrogenase (cad) were investigated. salt stress induced the activities of pal and cad and increased the lignin content. data indicated that the highest level of pal activity was found at the first internode and cad activity in the apical and young parts of stem was higher than the old and basal parts of it. lignin accumulation correlated positively with pal and cad activities under salt stress, but during internodal maturation lignification correlated negatively with pal and cad activity. the results suggest that induction of pal and cad activities and consequently increasing of lignin deposition at internode tissues can be a strategy for high salinity tolerance in this halophyte.