Abstract
Light is an important factor that influences the growth and photosynthetic efficiency of microalgae; however, little is known about how light intensity together with the wavelength affect the photosynthetic capacity and growth of marine microalgae. In the present study, the growth of the marine green microalga Dunaliella parva was studied and optimized under different light intensities (25 ~ 70 μmol m-2 s-1) and qualities (blue, green, and red) in comparison with white light at 40 μmol m-2 s-1 as a control. The growth was monitored by counting the cell number, pigment content, Chl a, Chl b, and carotenoids concentrations. The optimal growth and highest photosynthetic efficiency (Fv/Fm) were recorded at a light intensity of 40 μ mol m-2 s-1, white light, and 1.25 M NaCl (1.47 and 0.678×106 cell mL-1, respectively). The activity of antioxidant enzymes, including catalase and peroxidase, as well as ascorbate content, showed the highest values of 0.190 µM/min.mg Chl, 0.434 and 13.3 mg/g f.wt. respectively, under the green light, which confirmed the presence of environmental stresses.
Highlights
The halotolerant, unicellular biflagellate green alga Dunaliella is distinguished morphologically by the absence of a rigid cell wall, contractile vacuoles, and its large pyrenoid
Effect of light intensity on growth parameters Table 1 shows the effect of light intensity (25 and 70 μmol m-2 s-1) on the growth parameters of Dunaliella parva
It is clear from the results that there was a decrease in cell number at a light intensity of 25 μmol m-2 s-1, which amounted to 14.39 %, and a slight decrease (3.03%) at 70 μmol m-2 s-1 as compared with control, the decrease in cell number at (25 μmol m-2 s-1) was accompanied by a decrease in the relative growth (K'), the number of recycling, and the mean growth rate (R')
Summary
The halotolerant, unicellular biflagellate green alga Dunaliella is distinguished morphologically by the absence of a rigid cell wall, contractile vacuoles, and its large pyrenoid. It has two equal flagella, one cup-shaped chloroplast, an anterior nucleus, an eye-spot [1]. Light is the most important factor influencing the growth of all photosynthetic organisms, including Dunaliella sp. It is well known that Dunaliella salina is significantly affected by the light intensity, which is an important factor regulating pigment production in the cells. Coesel et al, [5] observed a linear increase in the total carotenoids content of Dunaliella salina when light intensity increased
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