Sulfite reductase protects plants against sulfite toxicity.

Dmitry Yarmolinsky,Galina Brychkova,Moshe Sagi,Robert Fluhr

doi:10.1104/pp.112.207712

Dmitry Yarmolinsky, Galina Brychkova + Show 2 more

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https://doi.org/10.1104/pp.112.207712

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Abstract

Plant sulfite reductase (SiR; Enzyme Commission 1.8.7.1) catalyzes the reduction of sulfite to sulfide in the reductive sulfate assimilation pathway. Comparison of SiR expression in tomato (Solanum lycopersicum 'Rheinlands Ruhm') and Arabidopsis (Arabidopsis thaliana) plants revealed that SiR is expressed in a different tissue-dependent manner that likely reflects dissimilarity in sulfur metabolism between the plant species. Using Arabidopsis and tomato SiR mutants with modified SiR expression, we show here that resistance to ectopically applied sulfur dioxide/sulfite is a function of SiR expression levels and that plants with reduced SiR expression exhibit higher sensitivity than the wild type, as manifested in pronounced leaf necrosis and chlorophyll bleaching. The sulfite-sensitive mutants accumulate applied sulfite and show a decline in glutathione levels. In contrast, mutants that overexpress SiR are more tolerant to sulfite toxicity, exhibiting little or no damage. Resistance to high sulfite application is manifested by fast sulfite disappearance and an increase in glutathione levels. The notion that SiR plays a role in the protection of plants against sulfite is supported by the rapid up-regulation of SiR transcript and activity within 30 min of sulfite injection into Arabidopsis and tomato leaves. Peroxisomal sulfite oxidase transcripts and activity levels are likewise promoted by sulfite application as compared with water injection controls. These results indicate that, in addition to participating in the sulfate assimilation reductive pathway, SiR also plays a role in protecting leaves against the toxicity of sulfite accumulation.

Highlights

Plant sulfite reductase (SiR; Enzyme Commission 1.8.7.1) catalyzes the reduction of sulfite to sulfide in the reductive sulfate assimilation pathway
The enhancement of SiR activity in response to sulfite injection in the wild-type tomato leaves was observed later than in Arabidopsis, being evident 3 h post injection with 8 mM sulfite and 8 h after the injection with 0.5 and 4 mM sulfite (Supplemental Fig. S8). These results show that SiR transcript and activity levels rose within minutes (30– 180 min), and this rise extended over a period of a few hours in both plant species, demonstrating the inducible nature of SiR in response to sulfite application
In Arabidopsis, relatively high SiR promoter expression was observed in the vascular system in the vicinity of S-cells (Fig. 1), which are regarded as the storage site of sulfur metabolites, mainly glucosinolates (Koroleva et al, 2000, 2010)

Summary

Introduction

Plant sulfite reductase (SiR; Enzyme Commission 1.8.7.1) catalyzes the reduction of sulfite to sulfide in the reductive sulfate assimilation pathway. Peroxisomal sulfite oxidase transcripts and activity levels are likewise promoted by sulfite application as compared with water injection controls. These results indicate that, in addition to participating in the sulfate assimilation reductive pathway, SiR plays a role in protecting leaves against the toxicity of sulfite accumulation. The toxic intermediate sulfite generated by APR enzymes is further reduced by sulfite reductase (SiR; EC 1.8.7.1) to sulfide, which is incorporated into Cys by O-acetylserine(thiol)lyase (EC 2.5.1.47; Leustek and Saito, 1999; Nakayama et al, 2000). SO activity has recently been shown to play an essential part in protecting plants against SO2/sulfite toxicity (Brychkova et al, 2007; Lang et al, 2007)

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