Deciphering the redox metabolism of the maize-Azospirillum brasilense interaction exposed to arsenic-affected groundwater

PERALTA JUAN MANUEL; FURLAN ANA; BIANUCCI, ELIANA; CASTRO STELLA; ROMERO-PUERTAS, MARÍA C.; TRAVAGLIA CLAUDIA N.

On-line

Congreso; SAIB-SAMIGE Joint Meeting 2020 on line; 2020

SAIB-SAMIGE

The presence of arsenic (As) in groundwater constitutes a serious agronomic problem since its closeness to the rhizosphere allows the roots to absorb the metalloid and distributes into the edible parts. The aim of this work was to elucidate the redox metabolism changes and the antioxidant system response of As-exposed maize (Zea mays L.) in order to recognize tolerance mechanisms and contribute to the mitigation of potential risks to human health. Thirty-days old maize plants inoculated with Azospirillum brasilense strains (Az39 or CD) were exposed to a realistic arsenate (3 µM AsV) dose. The assays involved root anatomy, reactive oxygen species (ROS) detection in leaves and roots, along with the NADPH oxidase activity. Photosynthetic pigments and damage to lipids and proteins were determined as oxidative stress markers. Basides, enzymatic and nonenzymatic components of the antioxidant system were determined in plant roots, together with the gene expression analysis by qRT-PCR. Results showed that AsV caused notable phenotypic changes in root epidermal cells. ROS were accumulated in the evaluated tissues, compared to control conditions, regardless the tested strain. Regarding it, the partial participation of the NADPH oxidase complex was particularly intriguing. Likewise, an increase in the lipid peroxidation and protein carbonyls was also observed throughout the plant, while chlorophylls and carotenes decreased and were independently of the assayed strain. The antioxidant response was strain-differential since, in the maize-A brasilense Az39 interaction the enzymatic activities remained unchanged, with the particular exception of the decrease in activities of ascorbate peroxidase (APX) and monodeshidroascorbate reductase (MDHAR). On the other hand, plants inoculated with the strain CD showed an increase in the activities of superoxide dismutase (SOD), glutathione S-transferase (GST) and glutathione reductase (GR), while APX and MDHAR were reduced. Interestingly, the transcript level of GST23 was upregulated by AsV stress, whereas GR and APX remained unaltered, regardless of the inoculated strain. According to the analysis of glutathione, while AsV reduced the GSH content of roots of maize plants inoculated with A. brasilense Az39, those inoculated with A. brasilense CD showed a decrease in 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 inoculated strain. Particularly, GSH plays a central role acting mainly as a substrate for the GST, essential enzyme to the maintenance of cell viability, under metalloid stress. These findings provide a sustainable response by generating knowledge for a suitable selection of Plant Growth-Promoting Bacteria, and its scaling to an effective bioinoculants that can be applied in maize crops exposed to adverse environmental conditions.