Leaf movement of Linum usitatissimum

Abstract

A brief historical review and summary of recent work on leaf movement is presented. The leaf movements of Linum usitatissimum were studied by measurements of the angular position of the sub-opposite pair of leaves at the second node of the seedling. Oscillatory up and down movements of these leaves continue for about three days in normal light:dark cycles but cease as the leaves mature. In continuous bright light a rhythmic movement persists for two cycles. In prolonged darkness no further movement occurs after the first nyctinastic cycle. A rhythmic movement in darkness can be induced by short (4 h) periods of light and when the light is given in late subjective night the phase of the rhythmic movement is advanced; a delayed movement is induced by a short light period given in the early subjective night. These phase responses of the leaf movement rhythm are considered in relation to the mechanism of entrainment to a non-diumal (20 h) cycle of 10 h light and 10 h darkness.

Evidence is presented for the involvement of the phytochrome system in the regulation of the leaf movement. Induction of rhythmic nyctinasty by short light periods in the early part of the subjective day can be reversed by short (15 min) treatment with far-red light, which is itself reversible by subsequent red irradiation. Red light breaks during darkness will induce rhythmic nyctinasty when given at appropriate times in the subjective day.

At the close of the day the leaves are not sensitive to red light which is perceived, or darkness, but blue light delays the rising leaf movement until the rhythmic control overrides this effect of light.

These results are discussed in relation to results recently published by other workers on movement of leaves possessing pulvini. Anatomical study of the basal part of the leaf of Linum confirms the absence of a pulvinus.