1. The syntheses of ubiquinone-9 and plastoquinone-9 were used as parameters respectively of mitochondrial and proplastid development in the germinating wheat grain. 2. The changes in the amounts of the tocopherols were also studied and the possible biological significance of these changes is discussed. During germination, the dimethyl tocopherols of the resting grain are probably not utilized for the synthesis of α-tocopherol. 3. It was demonstrated that ubiquinone synthesis, and hence probably mitochondrial development, in the aleurone cells during germination, is independent of control by gibberellic acid from the embryo. 4. The influence of light on the syntheses of the isoprenoid quinones in the etiolated wheat shoot was investigated. In particular, illumination did not stimulate the synthesis of either α-tocopherol or α-tocopherolquinone.

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