Leaflet movement of Mimosa pudica L. Indicative of phytochrome action

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Abstract
Closing movements of Mimosa pudica pinnae, upon change from light to darkness, depend upon the presence of phytochrome in the far-red-absorbing form. The potentiated control of closing movements by phytochrome can be repeatedly established and reversed by repeated alternations of red and far-red radiation, respectively. Action spectra were measured for the potentiation of closure and for its reversal. The response to phytochrome action is evident in 5 minutes and is fully expressed in 30 minutes. This rapid response and the more rapid potentiation with half times of less than 1 minute for several other responses to phytochrome action indicate that the primary action of phytochrome ist not gene activation, but rather metabolic control at the substrate level.