Environmental Factors Controlling Flower Opening and Closing in aPortulacaHybrid

Abstract

To examine flower opening and closing of aPortulacahybrid, flower buds were placed in darkness for 12 h (2030–0830 h) at 20 °C and then exposed to various light-temperature conditions. Flower buds exposed to light at 25, 30 or 35 °C opened within 1 h, and wilted 10–14 h later. Flower buds exposed to light at 20 °C started to open after 4 h but opened slowly and not completely. Flower buds subjected to 25, 30 or 35 °C in darkness also opened rapidly, but did not reach full opening. Flowers opened at 30 °C in light, and partially closed and opened repeatedly in response to cycles of a 2-h exposure to 20 °C and a 2-h exposure to 30 °C at any time between 1000 to 1600 h. Similar phenomena were observed when the flowers opened at 30 °C in light and then were subjected to darkness and light alternately at 30 °C, although the effect of light was less obvious than that of alternating temperature. Flower opening and closing were not affected by relative humidity. These results indicate that a rise in temperature is required for rapid flower opening in the buds kept at 20 °C, and that light intensifies the effect of high temperature. Exposure to light without a temperature change delayed and slowed flower opening which was never complete. The involvement of an endogenous rhythm in flower opening byPortulacais indicated.