Abstract
Light is the most important environmental factor that controls leaf shape and structure. When plants are grown under a high intensity of light, thick leaves, referred to as sun leaves, are developed. In sun leaves, palisade cells are greatly elongated in the adaxial/abaxial direction.
In Arabidopsis thaliana, three classes of photoreceptors, phytochrome, cryptochrome, and phototropin, are known. However, it remains unknown whether these photoreceptors are involved in the sun-leaf development. To investigate the effects of these photoreceptors, we examined sun-leaf formation in photoreceptor deficient mutants, phyB, cry1cry2, and phot1phot2. In the phot1phot2 mutant, the polar cell elongation was dramatically reduced. By contrast, elongation of palisade cells was observed normally in the cry1cry2 and phyB mutants. We further confirmed that blue but not red light effectively induced the elongation. These results suggest that phototropin regulates the polar cell elongation in palisade tissue in response to high intensity of light.
