The influence of de‐etiolation on the sensitivity of Avena coleoptiles to the far‐red absorbing form of phytochrome

In photoresponses regulated by phytochrome the effect of a red irradiation is not always reversed by far‐red. This applies for instance to the influence of red light on the geotropic reactionsof Avena coleoptiles. We could induce red/far‐red reversibility by a short de‐etiolating exposure to red light about 20 h prior to the experimental irradiations. This, was due to a decrease of the sensitivity to the low level of the far‐red absorbing form of phytochrome that is established by far‐red. Since etiolated plants react also to a wavelength of 520 nm (green light), it is advisable to expose the coleoptiles to a de‐etiolating irradiation prior to manipulations in green safelight in order to prevent the plants from reacting to the green light.