ALGAL PIGMENTS AND FOOD RESERVES

ALGAL PIGMENTS AND FOOD RESERVES

The colour of the algal thallus which varies in different classes of algae is due to the presence of definite chemical compounds in their cells. These are called pigments. Each pigment has its own characteristic colour. The particular colour that a thallus has is due to the predominance of one pigment in combination with several others. For example brown algae have predominance of Fucoxanthin and phycophenin while red algae and blue green algae have phycoerythrin and phycocyanin respectively.  Each group of algae has its own particular combination of pigments and characteristic colour which is not found in other group.

The photosynthetic pigments of algae are of three kinds –

 Chlorophylls, Carotenoids and Phycobillins or Billoproteins.

Chlorophyll pigments are fat soluble compounds and are of five different types, i.e., chlorophyll a, b, c, d and e. Out of these, chlorophyll a is universally present in all the groups of algae whereas chlorophyll b, c, d and e have restricted distribution.

Carotenoids are fat soluble yellow coloured pigments and are sub-divided into carotene, xanthophylls and carotenoidacids.

Phycobillins are water soluble blue (phycocyanin) and red (phycoerythrin) coloured pigments and are present in Cyanophyceae and Rhodophyceae.

The primary product which accumulates as food reserve in algae is the polysaccharides. Polysaccharides however vary in different algal groups. They may be found as starch, lamanarian paramylon and leucosin.

True starch is a typical food reserve of only two algal divisions namely, Chlorophyta and Charophyta. The two other kinds of characteristic starches are Cyanophycean starch and Floridean starch. The former is the characteristic food reserve of Cyanophyta and the later is the characteristic food reserve of Rhodophyta. Lamanarianis a food reserve found in brown algae. Paramylon is a characteristic food reserve of Euglenoids and Leucosin is peculiar to Xanthophyta, Bacillariophyta and Chrysophyta.

Besides polysaccharides, a proteinaceous compound Cyanophycin is found only in the cells of blue-green algae. Manitol, is a food reserve which was primarily considered to be unique to the brown algae has recently been reported to occur in few red algae.

Fats occur as food reserve in appreciable amount in the cells of Xanthophyta, Bacillariophyta and Chrysophyta.

             (Both pigments and food reserves has its occurrence in different divisions of algae and thus provide the key source for the classification of algae.)