Investigating the Effect of Hydrogen Peroxide on Biomass and Morphophysiological Indices of Microalga Dunaliella Salina Pretreated by Four Phytohormones: Auxin, Gibberellin, Cytokinin, and Salicylic Acid

Under unfavorable conditions, Reactive Oxygen Species (ROS) are produced inside living cells. Oxidant molecules such as H2O2 could be used to study the microorganism responses to oxidative stress. The treatment of algae with phytohormones can improve their physiological indices. In this study, the effect of H2O2 on unicellular green alga Dunaliella salina, pretreated by IAA (auxin), GA3 (gibberellin), Cyt (cytokinin), and SA (salicylic acid) was studied at three concentrations.

A 23-days algal culture was treated by phytohormones (in three repetitions) at three concentrations, and two days later (day 25), H2O2 (0.1 mM) treatment was performed. Two controls were considered without hormone and without H2O2, respectively. Evaluation of the growth and number of cells, fresh and dry weights, cell size (length, width, and volume), Chl a and b, beta-carotene, soluble carbohydrate, and protein were performed in days 25 and 27.

Hormones in most cases significantly improved the Indices (compared to the hormone-free control sample) (p <0.05). H2O2 treatment, two days after pre-treatment with hormones, caused the improvement of indices in most cases, except for protein and beta carotene. In contrast to the protein, the amount of carbohydrate was not sensitive to H2O2. The best results were obtained with IAA at medium concentration, GA3 at high concentration, Cyt and SA at low concentration.

H2O2 positively influenced the effects of the four phytohormones on algae cells, especially in relation to increased algal biomass and cell division. The positive effect of H2O2 treatment on both pretreated with or without hormones was probably due to its concentration which was lower than the toxicity level. Therefore, algal cells have benefited more from the useful and signaling effects of this molecule.