Phytochrome Effects in the Nyctinastic Leaf Movements

Summnary. Participation of phytochrome 'is evident in the nyctinastic responise of leaves of Albizzia julibrissin (silk-tree), Albizzia lophantha, Leucaena glauca, Poinciana gilliesi and Calliandra inequilatera; closure of excised pairs of pinnules upon darkening is rapid following red illumination and slow following far-red. Under good conditions the difiference is obvious within 10 minutes. These observations conifirm a report by Fondeville, Borthwick, and Hendricks on the sensitive plant, Mimosa pudica, but indicate that the efifect bears no necessary relationship to the anomalous sensitivity of Mimosa. In A. julibrissin, phytochrome control is mnarked in experiments conducted early in the daily 12-hour light period and appears absent, or nearly so, toward the end of the light period, perhaps due to interaction with an endogenous circadian rhythm. Effects of leaf maturity and of the position of a pinnule-pair within a leaf are also evident. Tih-ese results are not easily reconciled with hypotheses of phytochrome action through gene activation and nucleic acid synthesis, but are consistent with hypothess ibased onl permeability changes and membrane properties. The mgnitude and reproducibility of the response in A. jutlibrissin suggest its use as a lajboratory exercise; this and related systems should prove valuable for eventuai identification of the mechanism of phytochrome action.