Synthesis of Translatable mRNA for Phytochrome during Imbibition in Embryonic Axes of Pisum sativum L.

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The activity of translatable mRNA for phytochrome was measured in excised embryonic axes of Pisum sativum L. during imbibition both in the dark and under continuous irradiation with white light. When measured in cell-free protein synthesis systems of both rabbit reticulocyte lysate and wheat germ extract, the activity of translatable mRNA for phytochrome was not detected in dry quiescent axes but increased rapidly after imbibition in the dark. After 24 h imbibition, the level of translatable mRNA for phytochrome, in terms of the incorporation of [^<35>S]methionine in the wheat germ system, was ca. 0.0034% of total translatable mRNA. In the presence of 0.5 μg ml-1 α-amanitin, the appearance of translatable mRNA for phytochrome was inhibited by 60%, while 2 μg ml-1 α-amanitin was almost completely inhibitory. This indicates that the synthesis of translatable mRNA for phytochrome in embryonic axes begins upon imbibition. When the axes were imbibed under continuous white light, the activity of phytochrome mRNA increased as rapidly during the first 3 h as in the dark. After this time, the activity was markedly lower than in the dark. Nevertheless, during the 24 h of imbibition, activity in the light was always found to be more than half of that in the dark. These results indicate that in germinating pea axes the level of translatable mRNA for phytochrome is partially repressed by light.
日本植物生理学会の論文