Shade avoidance and the regulation of leaf inclination in Arabidopsis

Abstract

As a rosette plant, Arabidopsis thaliana forms leaves near to the ground, which causes the plant to be vulnerable to shading by neighbours. One mechanism to avoid such shading is the regulation of leaf inclination, such that leaves can be raised to more vertical orientations to prevent neighbouring leaves from overtopping them. Throughout Arabidopsis rosette development, rosette leaves move to more vertical orientations when shaded by neighbouring leaves, exposed to low light levels or placed in the dark. After darkinduced reorientation of leaves, returning them to white light causes the leaves to reorient to more horizontal inclinations. These light-dependent leaf movements are more robust than, and distinct from, the diurnal movements of rosette leaves. However, the movements are gated by the circadian clock. The light-dependent leaf orientation response is mediated primarily through phytochromes A, B and E, with the orientation varying with the ratio of red light to far-red light, consistent with other shade-avoidance responses. However, even plants lacking these phytochromes were able to alter leaf inclination in response to white light, suggesting a role for other photoreceptors. In particular, we found significant changes in leaf inclination for plants exposed to green light. This green light response may be caused, in part, by light-dependent regulation of abscisic acid (ABA) biosynthesis.

Green Light Induces Shade Avoidance Symptoms

“…These findings support an interpretation that green light signals adjust plant form through a mechanism that is distinct from that which imparts far-red effects. This finding is consistent with the report from Mullen et al (2006) indicating another signaling pathway involved in the control of leaf position aside from phytochromes. Mullen et al (2006) demonstrated that leaf inclination in phyB as well as the triple mutants phyAphyBphyD and phyAphyBphyE is lower than that in darkness.…”

“…This finding is consistent with the report from Mullen et al (2006) indicating another signaling pathway involved in the control of leaf position aside from phytochromes. Mullen et al (2006) demonstrated that leaf inclination in phyB as well as the triple mutants phyAphyBphyD and phyAphyBphyE is lower than that in darkness. They also observed that monochromatic green light induces changes in leaf position, a finding consistent with the results herein.…”

“…The goal of this work is to test if the relative enrichment of green light also affects the development of shade symptoms. Previous reports have shown a role for green light in leaf position changes (Mullen et al, 2006). In this work, green light was added to a constant background of red and blue light.…”

Contributions of green light to plant growth and development

“…Another interesting observation from Hangarter's group suggested that green light alone could lead to signifi cantly lower inclination angles of Arabidopsis rosette leaves than those positioned in darkness. This phenomenon was not observed in npq2 / aba1 mutant plants, indicating that the greenlight-induced leaf inclination changes might be partially mediated by the regulation of ABA biosynthesis ( Mullen et al, 2006 ). [Vol.…”

Ethylene-Mediated Regulation of A2-Type CYCLINs Modulates Hyponastic Growth in Arabidopsis

“…Arabidopsis (Arabidopsis thaliana) exhibits hyponasty upon several environmental signals (e.g. submergence, waterlogging, proximity of neighboring vegetation, low red:far-red light ratios, reduced blue light fluence rates, low light intensities, and high temperatures; Millenaar et al, 2005Millenaar et al, , 2009Mullen et al, 2006;Koini et al, 2009;Moreno et al, 2009;Van Zanten et al, 2009;Keuskamp et al, 2010;Keller et al, 2011;Vasseur et al, 2011;De Wit et al, 2012;Rauf et al, 2013;Dornbusch et al, 2014). Hyponasty alleviates the impact of environmental stresses (Van Zanten et al, 2010b).…”