ENVIRONMENTAL-FACTORS CONTROLLING FLOWER OPENING AND CLOSING IN A PORTULACA HYBRID

To examine flower opening and closing of a Portulaca hybrid, flower bu ds were placed in darkness for 12 h (2030-0830 h) at 20 degrees C and then exposed to various light-temperature conditions. Flower buds expo sed to light at 25, 30 or 35 degrees C opened within 1 h, and wilted 1 0-14 h later. Flower buds exposed to light at 20 degrees C started to open after 4 h but opened slowly and not completely. Flower buds subje cted to 25, 30 or 35 degrees C in darkness also opened rapidly, but di d not reach full opening. Flowers opened at 30 degrees C in light, and partially closed and opened repeatedly in response to cycles of a 2-h exposure to 20 degrees C and a 2-h exposure to 30 degrees C at any ti me between 1000 to 1600 h. Similar phenomena were observed when the fl owers opened at 30 degrees C in light and then were subjected to darkn ess and light alternately at 30 degrees C, although the effect of ligh t was less obvious than that of alternating temperature. Flower openin g and closing were not affected by relative humidity. These results in dicate that a rise in temperature is required for rapid flower opening in the buds kept at 20 degrees C, and that light intensifies the effe ct of high temperature. Exposure to light without a temperature change delayed and slowed flower opening which was never complete. The invol vement of an endogenous rhythm in flower opening by Portulaca is indic ated. (C) 1998 Annals of Botany Company.