effect of postharvest pulse treatment of salicylic acid on phenylalanine ammonia-lyase activity (pal), lignin formation and stem bending disorder of gerbera cut flowers

the most important postharvest disorder of cut gerbera is stem bending disorder, which occurs below the capitulum. stem strength and lignification is one of important phenomenon and causes of gerbera stem bending. therefore, this experiment was conducted to evaluate the effects of salicylic acid (sa) on phenylalanine ammonia-lyase enzyme activity (pal), as an important enzyme in phenylpropanoids pathway, consequently lignin formation and stem bending disorder of cut gerberas, with different pulse treatment of sa (0,0.25,0.5,0.75 and 1 mm) on two gerbera cultivars with different stem bending percentages. based on the results, cultivar, sa and their interaction effects, showed significant effects on ion leakage, stem bending, pal activity and lignification. the results showed a direct and negative correlation between pal activity and stem bending. accordingly, ‘double dutch’ as a resistant cultivar to stem break showed 2 times higher pal activity than ‘ecco’ with high stem bending. sa effect depending on cultivar and concentration, had significant effect on pal, lignification and stem bending; so that, the highest enzyme activity in ‘double dutch’ and ‘ecco’ cultivars was observed at 0.5 and 0.25mm concentrations, respectively. the results showed that, sa in low concentrations with increasing of stem lignification led to decreasing of stem bending disorder in both cultivars.