Effects of gibberellic acid on Hill reaction, photosynthetic Pigment and phenolic compounds in Moldavian dragonhead (Dracocephalum moldavica L.)in different drought stress levels

Drought stress stimulates reactive oxygen species production in plant chloroplast and reactive oxygen species cause peroxidation of lipid membrane and destruction of cell membrane. Moldavian dragonhead Dracocephalum moldavica L. is one of the aromatic and medicinal plants which use as healing of wound. In this research gibberlin use in order to control oxidative stress to tolerate water shortage and fluctuation in leaf pigments and total phenol were investigated. Therefore, an experiment was conducted in factorial design based on completely randomized design with four replications. Irrigation factor were in three level Fc (without stress), 2/3FC (moderate stress) and 1/3FC (severe stress) and gibberellic acid were in two level including and 100 mM. The results of experiment showed that by increasing of stress severity chlorophyll a, b and a+b content decreased. However, flavonoid, anthocynin and phenol content increased. Because of dehydration effect, β-carotene and xanthophyll content increased only in moderate stess. Gibberellic acid increased cholorophyll content, Hill reaction rate and phenol content. But There was no considerable change in Flavonoid and anthocyanin amount. According to result, exogenous gibberellic acid increased drought response of Moldavian dragonhead with various mechanism and trigger to increase phtosythesis rate in plant.