8.
While seeds of
Cucurbita maxima contain both Δ
5- and Δ
7-sterols, the former, which have been described earlier, now have been found to disappear during germination. This suggests
that a function exists for the Δ
5-compounds only in the early part of the life cycle of
C. maxima, unlike most of the other higher plants studied. In contrast to the Δ
5-sterols, the level of Δ
7-sterols increased during germination as well as during seedling development and maturation. The period of transition between
germination and seedling development appeared to be of special importance in terms of sterol changes. This period represented
a surge of sterol biosynthesis with an ontogenetic shift in sterol composition from approximately equal amounts of 24α- and
24β-ethyl stereochemistry to a predominance of the former. The sterol composition of the mature plants included only about
5% of the 24β-ethylsterols. The configurational relationships were demonstrated by high resolution
1H-NMR. The sterols of the mature plants were: 25(27)-dehydrochondrillasterol, 24β-ethyl-25(27)-dehydrolathosterol, avenasterol,
spinasterol, 22-dihydrospinasterol and 24ξ-methyllathosterol. Based on the changes which occurred in the relative amounts
of the Δ
7-sterols, it did not appear that the Δ
5-components were being converted to their Δ
7-analogs.
A portion of this work was presented at the meeting of the American Oil Chemists' Society in May, 1985 in Philadelphia.
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