The chlorophylls are the essential components for photosynthesis, and occur in chloroplasts as green pigments in all photosynthetic plant tissues. They are bound loosely to proteins but are readily extracted in organic solvents such as acetone or ether. Chemically, each chlorophyll molecule contains a porphyrin (tetrapyrole) nucleus with a chelated magnesium atom at the centre and a long-chain hydrocarbon (phytyl) side chain attached through a carboxylic acid group. There are at least five types of chlorophylls in plants. Chlorophylls a and b occur in higher plants, ferns and mosses. Chlorophylls c, d and e are only found in algae and in certain bacteria.
Chlorophyll is extracted in 80% acetone and the absorption at 663nm and 645nm areread in a spectrophotometer. Using the absorption coefficients, the amount of chlorophyll is calculated.
» Dilute analytical grade acetone to 80% acetone (prechilled).
Calculate the amount of chlorophyll present in the extract mg chlorophyll per g tissue using the following equations:
A = absorbance at specific wavelengths,
V = final volume of chlorophyll extract in 80% acetone and
W = fresh weight of tissue extracted.
The amount of tissue taken for extraction may be varied. Accordingly amount of 80% acetone used may be altered so that the final extract has a volume based on 10mg plant material extracted in 1mL of acetone.
1. Arnon, D I (1949) Plant Physiol 24 1.
2. Witham, F H, Blaydes, D F and Devlin, R M (1971) Experiments in Plant Physiology Van Nostrand New York p 245.
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