Light is one of important environmental sources required for plant development. Plants obtain energy and information from light. Light informations such as wavelength, intensity, day length, and direction can be converted into biological information by photoreceptors. Photoreceptors are divided largely into three groups: phytochromes, cryptochromes, and phototropins. Phytochromes are red and far-red light photoreceptors. There are five phytochromes termed phytochrome A to phytochrome E. They undergoes photoconversion between two spectrally distinct forms, a red light absorbing form (Pr) and a far-red light absorbing form (Pfr). When phytochromes are irradiated with red light, they are converted into Pfr forms. And the Pfr forms are converted into Pr forms by irradiating far-red light. This photoconversion is reversible. In this study, the role of phytochromes in regulating leaf curling was investigated. And also the role of phytochromes in integrating wavelength, intensity, day length, and direction information was investigated. In long days (LD), some leaves of phytochrome mutants were flat shape, whereas most of wild type leaves were dome-like shape. In short days (SD), the upward curling was more severe than in LD. Some leaves of phytochrome mutants showed roll-like shape, and all of wild type leaves were flat shape. These data indicate that phytochromes mediate day length information to regulate leaf curvature. To know whether intensity also affects the leaf curling, light intensity was varied both in LD and SD. When light intensity was reduced half in LD, the degree of upward curling was increased. When light intensity was increased double in SD, the curling degree was weak. These data indicate that phytochromes integrate day length and light intensity information to regulate leaf curling. To understand the cause of leaf curling, leaf tissues such as epidermis and palisade were investigated. In SD, the epidermal cell sizes of both adaxial and abaxi...