Abstract:
The effects of indoleacetic acid, indolebutyric acid, gibberellic acid and kinetin on growth and biomass productivity of Chlorella sorokiniana and Spirulina platensis were investigated. The optimum concentration of the phytohormones for Chlorella sorokiniana cell enlargement was 20ppm for GA3, Kinetin, IAA, and IBA. At this concentration, the Chlorella cell sizes were 81.07µm, 78.67μm, 78 .07μm and 66.90μm respectively. The effectiveness of the phytohormones in increasing the size of the cells can be ranked as GA3 > kinetin > IAA > IBA. Treatment with IAA at concentration of 10ppm had the highest effect on Chlorella sorokiniana cell number with a value of 7.94x 109 cells/ml, followed by IBA at 15ppm with a value of 4.36 x 109 cells/ml. GA3 and kinetin had no significant effects (P< 0.05) on cell number. The effects of the phytohormones on dry cell weight of the two microalgae species followed the same trend as the cell number with 10ppm of IAA giving the highest value of 4.825g/l in Chlorella sorokiniana and 1.10g/l in Spirulina platensis. The optimal concentrations of the phytohormones for Chlorella chlorophyll contents were 15ppm for IAA, GA3, IBA and kinetin. At these concentrations, the values of extractable chlorophyll were 594.20 mg/g, 238.60 mg/g, 141.65 mg/g and 140.90 mg/g respectively. The effectiveness of the phytohormones on chlorophyll contents can be ranked as IAA > GA3 > IBA > kinetin. In the case of Spirulina platensis, the optimal concentrations were 10ppm for IAA and 15ppm for GA3. At these concentrations, the extractable chlorophyll contents were 444.14 mg/g and 156.92 mg/g respectively. There were no significant effects (P > 0.05) of phytohormones on protein content of the two strains of microalgae in all the treatments. Combination of the phytohormones exhibited synergistic effect on growth and productivity of Chlorella sorokiniana. IBA (12.5ppm) + GA (2.5ppm), IBA (10ppm) + GA (5ppm), and IAA (12.5ppm) + GA (2.5ppm) gave the highest dry cell weight of 3.368g/l, 3.02g/l and 1.688g/l respectively. These values were much higher than the 0.552g/l obtained in the control experiment (without phytohormone). The optimal concentrations of the combined pyhtohormones for Chlorella chlorophyll contents were IBA(12.5ppm) + GA(2.5ppm), IAA(7.5ppm ) + kinetin(7.5ppm) and IAA(5ppm) + kinetin(10ppm.). At these concentrations, the chlorophyll contents were 425 mg/g, 136.26 mg/g and 122.60 mg/g respectively
