EFFECT OF 2,4-DICHLOROPHENOXYACETIC ACID ON THE DARK-INDUCED AND LIGHT-INDUCED PULVINAR MOVEMENTS IN CASSIA-FASCICULATA MICHX

2,4-dichlorophenoxyacetic (2,4-D) applied to excised leaves of Cassia fasciculata modified the dark-induced (scotonasty) and light-induced ( photonasty) leaflet movements, showing that this compound acts on rapi d turgor variation and the concomitant ion migrations, in particular K +. 2,4-D inhibited the scotonastic closure in a dose-dependent manner from 10(-8) M to 10(-5) M sind promoted the photonastic opening in the same range of concentrations. The compound acted rapidly since a trea tment as short as 5 min gave an obvious effect on the motile reaction; however, a lag period of 45-60 min was needed to observe its effect. Although 2,4-D is a weak acid, its greatest physiological efficiency w as obtained with pH values close to neutrality. The physiological resu lts are discussed in relation to the chemical properties acid the char acteristics of transport of the molecule.