Changes in Δ5‐ and Δ7‐sterols during germination and seedling development ofCucurbita maximaduring germination and seedling development ofCucurbita maxima

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Abstract
While seeds ofCucurbita maxima contain both Δ5‐ and Δ7‐sterols, the former, which have been described earlier, now have been found to disappear during germination. This suggests that a function exists for the Δ5‐compounds only in the early part of the life cycle ofC. maxima, unlike most of the other higher plants studied. In contrast to the Δ5‐sterols, the level of Δ7‐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 resolution1H‐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 Δ7‐sterols, it did not appear that the Δ5‐components were being converted to their Δ7‐analogs.