Morphological responses of Arabidopsis thaliana wild type and photoreceptor genotypes to narrowband UV radiation generated by LEDs.

Abstract

Sensing and responding to light signals are critical factors for plant survival. Plants have photoreceptors which coordinate morphological responses through divergent yet overlapping signalling networks. This study aims to identify how Arabidopsis thaliana fine-tunes its architecture in response to different wavelengths of UV radiation. Using narrow wavelength UV-emitting LEDs, in combination with a set of photoreceptor genotypes, enabled investigation of photoreceptor-dependent effects on leaf morphology. Eight Arabidopsis genotypes, including wildtype Col-0, uvr8-6, cry1, cry2, cry1cry2, phot1, phot2 and phot1phot2, were exposed to ~45 μW cm^-2 narrowband UV, with emission peaks at 310, 325, 340 or 365 nm. (a) UV-B wavelengths have a strong inhibitory effect on petiole elongation, with modest effects on leaf blade width and area. (b) Inhibitory effects of narrowband UV-B on petiole elongation are mediated by UVR8. Phototropins and cryptochromes antagonise this effect, implying that these photoreceptors perceive and mediate responses to UV-B. (c) Short wavelength UV-A also induces dwarfing of petioles, but not leaf blades, and this is mediated by UVR8. Cryptochromes impede dwarfing under short wavelength UV-A. (d) Longer wavelength UV-A responses are mediated by both phototropins and cryptochromes, with opposing effects on petiole elongation. (e) Although no UVR8-mediated morphological effect was measured under longer UV-A wavelengths, UVR8 affects gene expression throughout the UV-A and UV-B spectral zones. UVR8, cryptochromes and phototropins are all active across all UV-B and UV-A wavelengths, controlling multiple interactive morphological and/or gene expression effects.