Flower opening and closing ofOxalis martiana

Abstract

Flowers ofOxalis martiana open in the morning and close in the afternoon repeatedly for 3–5 days in May–July under natural conditions. Both in light and in darkness, the closed flowers opened in reponse to a rise in temperature (thermonasty), but not under the constant temperatures. Transfer from darkness to light along with temperature rise caused rapid flower opening, and at 20 C or higher temperatures, exposure to light caused flower opening even without changing temperature (photonasty). Therefore, the temperature of the night before opening is critical in determining whether the flower opening under natural conditions depends on thermonasty or photonasty. The opened flowers closed about 8–11 hr after the beginning of opening both under natural conditions and constant light-temperature conditions, which suggests that the time of flower closing is determined by endogenous factors. Length of the perianth increased greatly during opening and slightly during closing. Application of actionomycin D or cycloheximide inhibited both the flower opening and closing, probably by suppressing the perianth growth.