Studies in carotenogenesis. 25. The incorporation of 14CO2, [2-14C]acetate and [2-14C]mevalonate into β-carotene by illuminated etiolated maize seedlings

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Abstract
The carotenoids of etiolated maize seedlings are almost entirely xanthophylls, only traces of [beta]-carotene being present. Intact or excised etiolated seedlings synthesized [beta]-carotene and xanthophylls when illuminated. All the light-synthesized carotenoids are present in the chloroplasts which also develop on illumination. The root system of intact maize seedlings can not be penetrated by (2-C14) acetate and (2-C14) mevalonate and are thus not incorporated into the unsaponifiable matter. They are rapidly incorporated into the unsaponifiable matter of excised seedlings kept either in the dark or illuminated. There is, however only an insignificant incorporation into [beta]-carotene in illuminated excised seedlings. Into the unsaponifiable matter of illuminated intact and excised seedlings, C14O2 is rapidly incorporated and there is a very marked and preferential incorporation into [beta]-carotene. Hydroxylamine (0.001[image]) inhibits the synthesis of [beta]-carotene, chlorophyll and, presumably, chloroplast development in illuminated excised seedlings. It is concluded that the synthesis of [beta]-carotene in illuminated seedlings occurs in the chloroplasts and utilizes photosynthetically-fixed CO2; this is an integral part of the process of turning an etiolated plant into a photosynthetic plant.