Sterol main line

A problem similar to the one with the A -bond exists with a number of other differences in plant sterols. Thus, we have the A /A ratio to explain as well as the 24a-methyl/24)8-methyl and 24-methyl/24-ethyl ratios not to mention the curious fact that 24-ethylsterols of main line plants are always of the a-configura-tion although the 24-methyl analogs are not. In view of the statistics of occurrence, such as that sitosterol is usually the major sterol in main line plants, it would appear that the ratios are rather tightly controlled. This tight control probably constitutes a fine tuning of the function(s) that the sterol pool plays. 

A > -sterol (brassicasterol) with little or no 22-dihydro derivative present. The monoenic 24-methylcholesterols, therefore, are composed almost entirely of the 24a-eplmer (campesterol). However, in the mature leaf brassicasterol has all but disappeared and the 24-methylsterols have become the usual main line mixture of campesterol with smaller amounts of 22-dihydrobrassicasterol. It appears from this that in the synthesis of Brassica seed sterols a A22-dehydrogenase is present which declines during ontogeny suggesting functionality for the sterols used and/or produced. 

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