Reversible Photoreaction Controlling Expansion of Etiolated Bean-Leaf Disks

Abstract
Disks of 5 mm diam. from unexpanded, dark grown, simple leaves of garden bean were placed in petri dishes on filter paper treated with 5 ml of solution of 3% D-glucose and 0.08M KNO3, pH 5.6. Manipulation of disks except the final measurements were in dim green safelight. Various exposures of the leaf disks to red light (6500 A) from various sources promoted expansion of the etiolated disks and this promotion was reversed by subsequent exposure to far-red (7300 A) irradiation. Measurements were made at 48 hrs. and continuous red irradiation was more effective in promoting expansion than a short exposure.