Phototropin 1 and dim-blue light modulate the red light de-etiolation response

Yihai Wang,Kevin M Folta

doi:10.4161/15592324.2014.976158

Abstract

Light signals regulate seedling morphological changes during de-etiolation through the coordinated actions of multiple light-sensing pathways. Previously we have shown that red-light-induced hypocotyl growth inhibition can be reversed by addition of dim blue light through the action of phototropin 1 (phot1). Here we further examine the fluence-rate relationships of this blue light effect in short-term (hours) and long-term (days) hypocotyl growth assays. The red stem-growth inhibition and blue promotion is a low-fluence rate response, and blue light delays or attenuates both the red light and far-red light responses. These de-etiolation responses include blue light reversal of red or far-red induced apical hook opening. This response also requires phot1. Cryptochromes (cry1 and cry2) are activated by higher blue light fluence-rates and override phot1's influence on hypocotyl growth promotion. Exogenous application of auxin transport inhibitor naphthylphthalamic acid abolished the blue light stem growth promotion in both hypocotyl growth and hook opening. Results from the genetic tests of this blue light effect in auxin transporter mutants, as well as phytochrome kinase substrate mutants indicated that aux1 may play a role in blue light reversal of red light response. Together, the phot1-mediated adjustment of phytochrome-regulated photomorphogenic events is most robust in dim blue light conditions and is likely modulated by auxin transport through its transporters.

Highlights

In the developing seedling the transition from a dark growth program to a light growth program includes a well described set of physiological changes
The same effect on the apical hook opening was observed when B light was delivered with FR light (Fig. 1C)
While the kinetics of hypocotyl growth inhibition were affected in abcb[19] mutants, a B light effect was still observed Phytochrome is a classic example of how two wavelengths of (Fig. S3D)

Summary

Introduction

In the developing seedling the transition from a dark growth program to a light growth program includes a well described set of physiological changes. The process of photomorphogenesis is typified by hypocotyl/stem growth inhibition, apical hook opening, chloroplast development, cotyledon expansion and other responses that are finely tuned to match the ambient light environment. Quantity, direction, and duration are all the key parameters in guiding this transition. Blue (B), red (R), and far-red (FR) light induce the most conspicuous changes. These alterations begin with photons activating specific photoreceptors, the cryptochromes (crys) and phototropins (phots) sensing B and UV-A light, and the phytochromes (phys), responsive to R and FR light. The different light signals initiate specific transduction events that work independently, cooperatively, or even counteractively to modulate photomorphogenic events.[1,2,3]

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