INHIBITORY EFFECT OF CONTINUOUS FAR-RED PREIRRADIATION ON CHLOROPHYLL ACCUMULATION OF PHARBITIS NIL COTYLEDONS

Abstract The effect of continuous far-red (FR) preirradiation on the accumulation of chlorophyll (Chi) during a white light (WL; 500 lx) period was examined using Pharbitis nil cotyledons. The saturation level of accumulated Chi attained after prolonged exposure to WL was always lowered by continuous FR irradiation preceding the WL. The rate of Chi accumulation during the rapid increase phase (operationally defined as the amount of Chi accumulated during a 24-h WL period) was enhanced by preirradiation with up to 36 h of FR. However, when the FR preirradiation lasted longer, the rate was reduced below the dark control level. Even FR preirradiation of up to 36 h fully reduced the rate of Chi accumulation under WL when 36 h or longer darkness was spaced between the FR and the WL period.