The Involvement of Nitric Oxide in Integration of Plant Physiological and Ultrastructural Adjustments in Response to Arsenic.

Fernanda S Farnese,Juraci A Oliveira,Fernanda V Campos,Paulo E Menezes-Silva,Adinan A Da Silva,Elder A S Paiva,Cléberson Ribeiro

doi:10.3389/fpls.2017.00516

Abstract

High arsenic (As) concentrations are toxic to all the living organisms and the cellular response to this metalloid requires the involvement of cell signaling agents, such as nitric oxide (NO). The As toxicity and NO signaling were analyzed in Pistia stratiotes leaves. Plants were exposed to four treatments, for 24 h: control; SNP [sodium nitroprusside (NO donor); 0.1 mg L-1]; As (1.5 mg L-1) and As + SNP (1.5 and 0.1 mg L-1, respectively). The absorption of As increased the concentration of reactive oxygen species and triggered changes in the primary metabolism of the plants. While photosynthesis and photorespiration showed sharp decrease, the respiration process increased, probably due to chemical similarity between arsenate and phosphate, which compromised the energy status of the cell. These harmful effects were reflected in the cellular structure of P. stratiotes, leading to the disruption of the cells and a possible programmed cell death. The damages were attenuated by NO, which was able to integrate central plant physiological processes, with increases in non-photochemical quenching and respiration rates, while the photorespiration level decreased. The increase in respiratory rates was essential to achieve cellular homeostasis by the generation of carbon skeletons and metabolic energy to support processes involved in responses to stress, as well to maintaining the structure of organelles and prevent cell death. Overall, our results provide an integrated view of plant metabolism in response to As, focusing on the central role of NO as a signaling agent able to change the whole plant physiology.

Highlights

Arsenic is a toxic metalloid naturally occurring in the environment and that originates primarily from the dissolution of certain types of rocks
The presence of sodium nitroprusside (SNP) did not alter the pattern of As accumulation compared with the treatment containing only the metalloid, the pattern of reactive oxygen species (ROS) generation was modified
The addition of SNP, in turn, decreased the production of ROS and, the damages triggered by the metalloid were reduced, as has been observed for several other plants exposed to As (Farnese et al, 2013; Fan et al, 2014; Saeid et al, 2014)

Summary

Introduction

Arsenic is a toxic metalloid naturally occurring in the environment and that originates primarily from the dissolution of certain types of rocks. High As concentrations, are toxic to all the living organisms and occur worldwide, especially as a result of human activities (Gomes et al, 2014; Kumar et al, 2015). Arsenate is the most common form of As in oxygenated environments such as Abbreviations: As, arsenic; NO, nitric oxide; ROS, reactive oxygen species; SNP, sodium nitroprusside. As a chemical analog of phosphate, arsenate is absorbed by the plant through highaffinity phosphate transporters located in the roots (Castrillo et al, 2013). The pollutant triggers serious changes in the plant metabolism, affecting both the physiological and the biochemical processes, which may reveal alterations in morphology and in the plant cell organization (de Freitas-Silva et al, 2016)

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