Thesis (Ph.D.) - Cairo University - Faculty of Science - Department of Botany and Microbiology

Dunaliella bardawil is a halotolerant unicellular green alga isolated from El- Bardawil Lake at the northern coast of Sinai Peninsula, Arish Governorate, Egypt. This algal species is among the most studied microalgae for mass culture and is characterized by its ability to accumulate high concentrations of Ý-carotene, a fascinating biomolecule with numerous human health benefits. In this study, the effects of variable concentrations of four phytohormones, Abscisic acid (ABA), Gibberellic acid (GA3), Indol-3-acetic acid (IAA) and Kinetin (KN), on growth and accumulation of Ý-carotene and some other biomolecules in D. bardawil were investigated. In addition, the interactive effects of phytohormones and high salinity (2M & 3M NaCl) or nitrate limitation (441 & 220.5 æM) stresses were also investigated. Results revealed that under normal conditions, the phytohormonal treatments significantly increased cell density, dry biomass, and the levels of total protein, total carotenoids, and Ý-carotene of the tested alga as compared with the control culture (p{u02C2}0.05). Meanwhile, IAA and KN, at a concentration of 0.75 æM, were the most effective, especially after 15 days of growth. Interestingly, application of 0.75 æM of IAA and KN, together with salinity (2M NaCl) or nitrate limitation (220.5 æM nitrate) significantly enhanced the expression patterns of carotenogenic genes (phytoene synthase, phytoene desaturase and lycopene Ý-cyclase) and, therefore, the accumulation of Ý- carotene, compared to each of stress factors separately

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