Pfr PHYTOCHROME AND SUCROSE REQUIREMENT FOR RHYTHMIC LEAFLET MOVEMENT IN ALBIZZIA

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Abstract
Abstract— Albizzia leaflets open and close with a circadian periodicity without damping during extended dark periods if supplied with sucrose and irradiated with red each rhythmic cycle. In the absence of a carbohydrate source, the rhythm damps irrespective of phytochrome status and the differential effects of red and far‐red light treatments tend to disappear after 2 or 3 cycles. The rhythm also damps if leaflets are exposed to red only once, or if they are exposed to far‐red once or cyclically. Sucrose does not prevent such damping but affects the stable angle assumed; the rhythm damps in the closed position in the presence of sucrose, and in the partially open position in its absence. Sucrose appears to have two distinct effects; it interacts with Pfr to promote manifestation of the rhythm and it reduces the average angle, whether the Pfr level is low or high.