Write a short note on pigments of algae
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Answer:
Three major classes of photosynthetic pigments occur among the algae: chlorophylls, carotenoids (carotenes and xanthophylls) and phycobilins. The pigments are characteristic of certain algal groups as indicated below. Chlorophylls and carotenes are generally fat soluble molecules and can be extracted from thylakoid membranes with organic solvents such as acetone, methanol or DMSO. The phycobilins and peridinin, in contrast, are water soluble and can be extracted from algal tissues after the organic solvent extraction of chlorophyll in those tissues.
The rationale behind the extraction techniques is to disrupt cell integrity as much as possible, thereby removing pigment molecules from intrinsic membrane proteins. Freezing the tissue with liquid nitrogen, and grinding the still frozen tissue in with a mortar and pestle or blender, overcomes some of the problems of working with material that produces large amounts of viscous polysaccharides. “Freeze-thawing” tissue also breaks down cellular membranes, but may liberate more polysaccharides. Finely ground tissue can be then homogenized in organic solvent to further disrupt cellular membranes, and to liberate pigment molecules from the light harvesting pigment protein complexes.
Once the pigments are extracted into appropriate solvents they can be separated chromatographically by TLC or HPLC for spectral analysis and identification. Pigment concentrations in hydrocarbon solvents can be estimated; however, these formulas are predictive, and may overestimate some pigment concentrations (see Seely et al. 1972 for the development of equations). Uncoupling pigments from the pigment binding proteins can change the absorption patterns of the pigments, resulting in shifts in maxima from 10 to 50 nm, when compared with spectra measured for intact tissues.
The three major classes of pigments found in plants and algae are the chlorophylls, the carotenoids and the phycobilins. Carotenoid and phycobilins are called accessory pigments since the quanta (packets of light) absorbed by these pigments can be transferred to chlorophyll.