structural:scholar_edition
Light sensing, light emission, and circadian biology

The photoreceptors phytochromes A, B, C, D, and E mediate red light-based phototropic response. Understanding the function of these receptors has helped plant biologists understand the signaling cascades that regulate photoperiodism, germination, de-etiolation, and shade avoidance in plants. The genes FCA, fy, fpa, LUMINIDEPENDENS (ld), fly, fve and FLOWERING LOCUS C (FLC) are involved in photoperiod triggering of flowering and vernalization. Specifically Lee et al 1994 find ld produces a homeodomain and Blazquez et al 2001 that fve produces a WD40 repeat.

The UVR8 protein detects UV-B light and mediates the response to this DNA-damaging wavelength.

A. thaliana was used extensively in the study of the genetic basis of phototropism, chloroplast alignment, and stomal aperture and other blue light-influenced processes. These traits respond to blue light, which is perceived by the phototropin light receptors. Arabidopsis has also been important in understanding the functions of another blue light receptor, cryptochrome, which is especially important for light entrainment to control the plants' circadian rhythms. When the onset of darkness is unusually early, A. thaliana reduces its metabolism of starch by an amount that effectively requires division.

Light responses were even found in roots, previously thought to be largely insensitive to light. While the gravitropic response of A. thaliana root organs is their predominant tropic response, specimens treated with mutagens and selected for the absence of gravitropic action showed negative phototropic response to blue or white light, and positive response to red light, indicating that the roots also show positive phototropism.

In 2000, Dr. Janet Braam of Rice University genetically engineered A. thaliana to glow in the dark when touched. The effect was visible to ultrasensitive cameras.

Multiple efforts, including the Glowing Plant project, have sought to use A. thaliana to increase plant luminescence intensity towards commercially viable levels.