The major portion of the lipid fraction of green tissues of plants consists of three glycolipids : galactosyl diglyceride, digalactosyl diglyceride and the sulfolipid, 6-sulfoquinovosyl diglyceride (l-7). There is good evidence that these lipids are involved in the photosynthetic mechanism of chloroplasts (7-10). They are also of interest, however, in connection with the fermentation of pasture herbage in the rumen because of their possible surface-active properties. It has been postulated that the chloroplast lipids can act as antifoaming agents in preventing the foam which results in bloat in cattle (11). A method for the measurement of total lipid-bound sugar has already been developed in this laboratory (12). However, since the sulfolipid would be expected to possess much greater surfactant properties compared to the galactolipids, it is likely to have the greatest effect in the rumen particularly with regard to foam formation. Therefore it is of some importance to be able to measure the level of this particular lipid in plant tissue and to follow its fluctuation during a growing season. The main problem associated with any analytical scheme is to free the sulfolipid and its hydrolysis products from the large excess of galactolipids and their hydrolysis products. The methods used so far for the measurement of sulfolipid concentrations are either too complex (4) or too time consuming ( 14) and would not be suitable for routine use.
This paper describes a method for measuring concurrently the level of lipid-bound sulfoquinovose and lipid-bound galactose. The method, developed from the isolation procedure of the sulfolipid ( 14)) is suitable for batchwise routine use and can be fitted into the type of analysis scheme commonly used for measuring the concentration of plant carbohydrates. Results obtained for the concentrations of lipid-bound sulfoquinovose and lipid-bound galactose in several pasture plants are given.