Compensation Mechanism of the Photosynthetic Apparatus in Arabidopsis thaliana ch1 Mutants.

Joanna Wójtowicz,Adam K Jagielski,Agnieszka Mostowska,Katarzyna B Gieczewska

doi:10.3390/ijms22010221

Joanna Wójtowicz, Adam K Jagielski + Show 2 more

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https://doi.org/10.3390/ijms22010221

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Abstract

The origin of chlorophyll b deficiency is a mutation (ch1) in chlorophyllide a oxygenase (CAO), the enzyme responsible for Chl b synthesis. Regulation of Chl b synthesis is essential for understanding the mechanism of plant acclimation to various conditions. Therefore, the main aim of this study was to find the strategy in plants for compensation of low chlorophyll content by characterizing and comparing the performance and spectral properties of the photosynthetic apparatus related to the lipid and protein composition in four selected Arabidopsis ch1 mutants and two Arabidopsis ecotypes. Mutation in different loci of the CAO gene, viz., NW41, ch1.1, ch1.2 and ch1.3, manifested itself in a distinct chlorina phenotype, pigment and photosynthetic protein composition. Changes in the CAO mRNA levels and chlorophyllide a (Chlide a) content in ecotypes and ch1 mutants indicated their significant role in the adjustment mechanism of the photosynthetic apparatus to low-light conditions. Exposure of mutants with a lower chlorophyll b content to short-term (1LL) and long-term low-light stress (10LL) enabled showing a shift in the structure of the PSI and PSII complexes via spectral analysis and the thylakoid composition studies. We demonstrated that both ecotypes, Col-1 and Ler-0, reacted to high-light (HL) conditions in a way remarkably resembling the response of ch1 mutants to normal (NL) conditions. We also presented possible ways of regulating the conversion of chlorophyll a to b depending on the type of light stress conditions.

Highlights

Plants require light to live, notably to conduct photosynthesis
Our study was performed on four selected Arabidopsis ch1 mutants and two Arabidopsis ecotypes
The maximum quantum yield of photosystemII dimer (PSII) (Fv /Fm ) reduced in the ch1 mutants (Table 1), implying an altered function of the photosynthetic apparatus, which is consistent with previous reports [21,25,26]

Summary

Introduction

Plants require light to live, notably to conduct photosynthesis. This process takes place in chloroplasts and converts light energy into chemical energy, which fuels multiple metabolic processes and sustains plant growth. Chloroplasts’ internal membranes, called thylakoids, provide a platform for the light reactions during photosynthesis. The major chlorophyll a/b light-harvesting complexes (LHCII) and minor light-harvesting complexes (Lhcb, Lhcb, Lhcb6) form the LHCII-PSII supercomplex with the photosystem. The LHCII-PSII and mobile LHCII trimers build up a less stable macrodomain structure [1]. In intact grana, these complexes have been shown to form densely packed aggregates. The photosystem I (PSI), composed of twelve subunits and associated with external antenna (Lhca1-4), constitutes the LHCI-PSI supercomplexes [2,3]

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