Fold-change Response of Photosynthesis to Step Increases of Light Level

Avichai Tendler,Avihai Danon,Bat Chen Wolf,Uri Alon,Vivekanand Tiwari

doi:10.1016/j.isci.2018.09.019

Abstract

SummaryPlants experience light intensity over several orders of magnitude. High light is stressful, and plants have several protective feedback mechanisms against this stress. Here we asked how plants respond to sudden rises at low ambient light, far below stressful levels. For this, we studied the fluorescence of excited chlorophyll a of photosystem II in Arabidopsis thaliana plants in response to step increases in light level at different background illuminations. We found a response at low-medium light with characteristics of a sensory system: fold-change detection (FCD), Weber law, and exact adaptation, in which the response depends only on relative, and not absolute, light changes. We tested various FCD circuits and provide evidence for an incoherent feedforward mechanism upstream of known stress response feedback loops. These findings suggest that plant photosynthesis may have a sensory modality for low light background that responds early to small light increases, to prepare for damaging high light levels.

Highlights

Photosynthesis converts sunlight into chemical energy that feeds the food chain
PSII Chl a Fluorescence Shows Fold-change Response in the Low to Medium Light Intensity Range To study the response of PSII Chl a fluorescence to small abrupt increases of light level, we presented A. thaliana plants with a series of uniform step increases of light level ð35 mE=m2sÞ that spanned the low to medium light intensity range ð10 À 185 mE=m2sÞ (Figure 1A, input light)
A decreasing type of response is consistent more with regulation of optical cross-sectional absorption of PSII rather than regulation by availability of electron acceptors of PSII, which is expected to result in a similar response to similar absolute steps in light

Summary

Introduction

Photosynthesis converts sunlight into chemical energy that feeds the food chain. Photosynthesis must operate under several orders of magnitude of light input. Sunlight energy is captured by the light-harvesting reactions and excites sequentially the photosystem (PS) II (PSII) and PSI chlorophyll (Chl)-containing reaction centers. These centers together generate electron transport that reduces NADP+ to form a transmembrane proton gradient that produces ATP. Plants evolved a complex set of short- and long-term photoprotective mechanisms that protect the PSII reaction center by dissipating excessive light energy (Albanese et al, 2016; Allen et al, 1981; DemmigAdams et al, 2012; Horton et al, 2008; Li et al, 2009; Minagawa, 2013; Muller et al, 2001; Niyogi and Truong, 2013; Pinnola and Bassi, 2018; Puthiyaveetil et al, 2017; Rochaix, 2014; Ruban, 2016; Schottler and Toth, 2014). The feedback regulation of the fast photoprotective mechanisms is thought to be mediated posttranslationally by structural or activity changes of existing regulatory proteins (Bassi and Caffarri, 2000; Brooks et al, 2014; Demmig-Adams, 1990; Horton et al, 1996)

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Conclusion