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The roles of cytosolic O-acetylserine-(thiol)-lyase A (OASTLA), chloroplastic OASTLB, and mitochondrial OASTLC in plant selenate resistance were studied in Arabidopsis. Impairment in OASTLA and OASTLB resulted in reduced biomass, chlorophyll and soluble protein content compared with selenate-treated OASTLC-impaired and wild-type plants. The generally lower total selenium (Se), protein-Se, organic-sulfur and protein-sulfur (S) content in oastlA and oastlB compared with wild-type and oastlC leaves indicated that Se accumulation was not the main cause for the stress symptoms in these mutants. Notably, the application of selenate positively induced S-starvation markers and the OASTLs, followed by increased sulfite reductase, sulfite oxidase activities, and increased sulfite and sulfide concentrations. Taken together, our results indicate a futile anabolic S-starvation response that resulted in lower glutathione and increased oxidative stress symptoms in oastlA and oastlB mutants. In-gel assays of l -cysteine and l -seleno-cysteine, desulfhydrase activities revealed that two of the three OASTL activity bands in each of the oastl single mutants were enhanced in response to selenate, whereas the impaired proteins exhibited a missing activity band. The absence of differently migrated activity bands in each of the three oastl mutants indicates that these OASTLs are major components of desulfhydrase activity, degrading l -cysteine and l -seleno-cysteine in Arabidopsis. [ABSTRACT FROM AUTHOR]

Purine degradation products have been shown to play roles in plant response to stresses such as drought, salinity, extended dark, nitrogen deficiency, and pathogen infection. In this study, we used Arabidopsis wild-type (WT) and an Atxdh1 -knockout mutant defective in xanthine dehydrogenase1 (XDH1) to examine the role of degraded purine metabolites in the responses to wounding or UV-C stress applied to the middle leaves of the plant. Wounding or UV-C stress in the mutant resulted in lower fresh-weight, increased senescence symptoms, and increased cell death compared to WT plants. In addition, WT plants exhibited lower levels of oxidative stress indicators, reactive oxygen species, and malondialdehyde in their leaves than the mutant. Notably, transcripts and proteins functioning in the purine degradation pathway were regulated in such a way that it led to enhanced ureide levels in WT leaves 24h after applying the UV-C or wound stress. However, different remobilization of the accumulated ureides was observed after 72h of stress. In plants treated with UV-C, the concentration of allantoin was highest in young leaves, whereas in wounded plants it was lowest in these leaves and instead accumulated mainly in the middle leaves that had been wounded. These results indicated that in WT plants treated with UV-C, ureides were remobilized from the lower older and damaged leaves to support young leaf growth during the recovery period from stress. After wounding, however, whilst some ureides were remobilized to the young leaves, more remained in the wounded middle leaves to function as antioxidants and/or healing agents. [ABSTRACT FROM AUTHOR]

Chloroplast-localized adenosine-5'-phosphosulphate reductase (APR) generates sulfite and plays a pivotal role in reduction of sulfate to cysteine. The peroxisome-localized sulfite oxidase (SO) oxidizes excess sulfite to sulfate. Arabidopsis wild type, SO RNA-interference (SO Ri) and SO overexpression (SO OE) transgenic lines infiltrated with sulfite showed increased water loss in SO Ri plants, and smaller stomatal apertures in SO OE plants compared with wild-type plants. Sulfite application also limited sulfate and abscisic acid-induced stomatal closure in wild type and SO Ri. The increases in APR activity in response to sulfite infiltration into wild type and SO Ri leaves resulted in an increase in endogenous sulfite, indicating that APR has an important role in sulfite-induced increases in stomatal aperture. Sulfite-induced H2O2 generation by NADPH oxidase led to enhanced APR expression and sulfite production. Suppression of APR by inhibiting NADPH oxidase and glutathione reductase2 (GR2), or mutation in APR2 or GR2 , resulted in a decrease in sulfite production and stomatal apertures. The importance of APR and SO and the significance of sulfite concentrations in water loss were further demonstrated during rapid, harsh drought stress in root-detached wild-type, gr2 and SO transgenic plants. Our results demonstrate the role of SO in sulfite homeostasis in relation to water consumption in well-watered plants. [ABSTRACT FROM AUTHOR]