Pulvini as the Photoreceptors in the Phytochrome Effect on Nyctinasty in Albizzia julibrissin.

The fact that far-red pretreatment slows the closing response of Albizzia julibrissin pinnules to darkness was used to locate the photoreceptor region for the role of phytochrome in nyctinasty, and to determine whether the effect is localized or translocated. Illumination of pinnule tissue alone induced no response, while illumination of an area as narrow as 1 mm, including only the tertiary pulvini and adjacent portions of rachilla and pinnules, was sufficient for a full response. This suggests that the pulvini themselves, the sites of the response, act as photoreceptors. In experiments with various shielding devices, pinnules on the same rachilla responded independently to local illumination, suggesting the absence of any translocatable effects.