Pfr PHYTOCHROME AND SUCROSE REQUIREMENT FOR RHYTHMIC LEAFLET MOVEMENT IN ALBIZZIA

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 P _fr to promote manifestation of the rhythm and it reduces the average angle, whether the P _fr level is low or high.