CONICET | Buscador de Institutos y Recursos Humanos

The presence of arsenic (As) in groundwater constitutes a serious agronomic problem since its closeness to the rhizosphereallows the roots to absorb the metalloid and distribute it into the edible parts. The aim of this work was to elucidate the redoxmetabolism changes and the antioxidant system response of As-exposed maize (Zea mays L.) in order to recognize tolerancemechanisms and contribute to the mitigation of potential risks to human health. Thirty-days old maize plants inoculated withAzospirillum brasilense strains (Az39 or CD) were exposed to a realistic arsenate (3 µM AsV) dose. The assays involved rootanatomy, reactive oxygen species (ROS) detection in leaves and roots, along with the NADPH oxidase activity. Photosyntheticpigments and damage to lipids and proteins were determined as oxidative stress markers. Besides, enzymatic and nonenzymatic components of the antioxidant system were determined in plant roots, together with the gene expression analysisby qRT-PCR. Results showed that AsV caused notable phenotypic changes in root epidermal cells. ROS were accumulated inthe evaluated tissues, compared to control conditions, regardless of the tested strain. Regarding it, the partial participation ofthe NADPH oxidase complex was particularly intriguing. Likewise, an increase in the lipid peroxidation and protein carbonylswas also observed throughout the plant, while chlorophylls and carotenes decreased and were independent of the assayedstrain. The antioxidant response was strain-differential since, in the maize-A brasilense Az39 interaction the enzymaticactivities remained unchanged, with the particular exception of the decrease in activities of ascorbate peroxidase (APX) andmonodeshidroascorbate reductase (MDHAR). On the other hand, plants inoculated with the strain CD showed an increase inthe activities of superoxide dismutase (SOD), glutathione S-transferase (GST) and glutathione reductase (GR), while APX andMDHAR were reduced. Interestingly, the transcript level of GST23 was upregulated by AsV stress, whereas GR and APXremained unaltered, regardless of the inoculated strain. According to the analysis of glutathione, while AsV reduced the GSHcontent of roots of maize plants inoculated with A. brasilense Az39, those inoculated with A. brasilense CD showed a decreasein the GSSG level. However, the GSH/(GSH+GSSG) ratio showed no changes in either interaction evaluated. We suggest amodel in which it is highlighted that the antioxidant response of the maize-diazotrophs system is modulated by the inoculatedstrain. Particularly, GSH plays a central role, acting mainly as a substrate for the GST, an essential enzyme to the maintenanceof cell viability, under metalloid stress. These findings provide a sustainable response by generating knowledge for a suitableselection of Plant Growth-Promoting Bacteria, and its scaling to an effective bioinoculant that can be applied in maize cropsexposed to adverse environmental conditions