**About the Editors**

**Juan B. Barroso** who completed his Ph.D. in 1993 in Biochemistry and Molecular Biology, is now a Full Professor at the University of Jaen, Spain. In 2002, he established an independent research ´ group called Biochemistry and Cell Signaling in Nitric Oxide. He has written more than 160 scientific papers and reviews published in internationally renowned journals, in addition to book chapters, and edited a variety of journal topical issues on plant nitric oxide (NO) metabolism. He also serves as Editorial Board Member of several renowned journals in plant sciences. His pioneering work includes characterization of the generation of NO and its role in plants (1999). Since then, his research group is considered an international reference in the field of NO metabolism in plants, with extensive experience in study of the metabolism of reactive oxygen and nitrogen species (ROS and RNS) in the model plant Arabidopsis and plants of agronomic and biotechnological interest under physiological conditions as well as exposed to different biotic and abiotic stress situations. Since NO interacts with molecules such as ROS, RNS, and RSS and with biomolecules like proteins and lipids, the research group's interest is currently focused on the study of NO bioactivity. In fact, in recent years, they have studied the identification and characterization of post-translational modifications of NO-mediated proteins (NO-PTM) and the effect they have on biological activity in plant cells. As a result of these studies, this group has recently pioneered the characterization of electrophilic lipid derivatives resulting from the interaction of nitric oxide with unsaturated fatty acids, called nitrated fatty acids (NO2-FA), that trigger antioxidant defense mechanisms involved in the maintenance of redox homeostasis in situations of stress.

**Mounira Chaki** conducted her undergraduate studies at the University of Mohamed First, Morocco. Afterwards, she moved back to the University of Jaen, Spain, where she started her ´ research career. Here, she was awarded her PhD in Molecular and Cellular Biology in 2007 with the highest qualification. During her research career, she focused on the study of the nitro-oxidative stress generated in higher plants in response to different biotic and abiotic stress situations. She is a pioneer in the study of the role of post-translational modifications mediated by nitric oxide, for example, nitration and S-nitrosylation of proteins under stress conditions. She has been trained in recognized research institutions in Spain, France, and Germany, performing cutting-edge research in laboratories led by the most outstanding researchers in the nitric oxide field. She has been awarded with the Marie Curie fellowship, corresponding to a term of two years. She is currently studying the interaction of nitric oxide and derived molecules with lipids and their physiological consequences, which remain unknown in higher plants. This new topic constitutes an important advance in the generation of new knowledge about post-translational modifications mediated by nitrated lipids and their involvement in cellular defense mechanisms. Dr. Chaki has published 44 peer-reviewed papers, most of which are in the top journals in their specific area, in addition to 16 book chapters and 5 licensed patents, as well as contributing to 8 research projects. She has served as an expert for the evaluation of international projects, as well as reviewer of numerous JCR journals. She has also edited some Special Issues in the nitro-oxidative stress field. She teaches courses in the undergraduate and official Master degree in Biotechnology and Biomedicine at the University of Jaen. ´

**Juan C. Begara-Morales** completed his Ph.D. in Molecular and Cellular Biology in 2011 with cum laude qualification and received a special doctorate award from the University of Jaen´ (Spain). His main research line is related to the analysis of nitric oxide (NO) signaling events under physiological and stress conditions in plants. In this field, he has contributed positively to characterizing the functional modulation of key antioxidant systems by NO-related post-translational modifications, such as S-nitrosylation and tyrosine nitration, in response to abiotic and biotic stresses. He has participated in 8 research projects and he has published 38 scientific papers in international journals and 10 book chapters. Furthermore, he is co-author of 5 invention patents that are commercially licensed and exploited, demonstrating that the connection of his research activity to industry and its potential capacity to generate knowledge that can result in biotechnological applications. He has also edited numerous Special Issues of renowned international journals in the NO and oxidative stress field. Currently, he is a PI of a project whose main goal is to characterize the effect of the cellular oxidation status on the functional modulation of antioxidant systems during the time course of nitro-oxidative stress generated in crops subjected to different adverse environmental conditions.

### *Editorial* **Oxidative Stress in Plants**

#### **Mounira Chaki, Juan C. Begara-Morales and Juan B. Barroso \***

Group of Biochemistry and Cell Signaling in Nitric Oxide, Department of Experimental Biology, Center for Advanced Studies in Olive Grove and Olive Oils, Faculty of Experimental Sciences, University of Jaén, Campus Las Lagunillas, s/n, E-23071 Jaén, Spain; mounira@ujaen.es (M.C.); jbegara@ujaen.es (J.C.B.-M.) **\*** Correspondence: jbarroso@ujaen.es

Received: 27 May 2020; Accepted: 1 June 2020; Published: 3 June 2020

Environmental stresses negatively affect plant growth, development and crop productivity. These adverse conditions alter the metabolism of reactive oxygen and nitrogen species (ROS and RNS, respectively). The high concentrations of these reactive species that exceed the capacity of antioxidant defence enzymes, disturb redox homeostasis, which could trigger damage to macromolecules, such as membrane lipids, proteins and nucleic acids, and ultimately result in nitro-oxidative stress and plant cell death. Significant progress has been made to understand how plants persist in these stressful environments that could be vital to improve plant crop yield. In this special issue "*Oxidative Stress in Plants*", both original articles and detailed reviews have been published with the aim to provide an up-date view in this research area in higher plants.

In the natural environment, plants are constantly exposed to abiotic stresses, such as extreme temperatures, salt stress, drought and heavy metals that have a huge impact on agriculture worldwide and consequently, lead to massive economic losses. In this sense, three research papers have analysed the effect of abiotic stress on plant growth and development. Dr. Wani's group [1] studied the role of *Serratia marcescens* BM1 in response to cadmium (Cd) stress in soybean plants by different physiological, biochemical and molecular assays. They found that, in Cd-stressed plants, the *Serratia marcescens* BM1 treatment not only down-regulated Cd levels and oxidative stress markers, but also up-regulated levels of osmolytes, stress-related gene expression and activities of antioxidant enzymes. These authors suggested that inoculation with the *Serratia marcescens* BM1 would promotes Cd stress tolerance and phytoremediation potential. The impact of abiotic stress was also reported by Dr. Barroso's group [2] as they demonstrated the effect of short-term low temperature stress on the metabolism of reactive oxygen and nitrogen species in *Arabidopsis* plants. These authors showed that the low temperature produces nitro-oxidative stress, and reduces cytosolic NADP-malic enzyme activity, which was negatively modulated by the protein tyrosine nitration process. In addition, they proposed that Tyr73 would be a possible residue to be involved in reducing this enzymatic activity. Moreover, Dr. Rivero's group [3] investigated the response of tomato plants to the effects of calcium and potassium on plant tolerance to combined high-temperature and salinity stress conditions. They showed the positive effect of a rise in calcium and potassium in the nutrient medium on the improvement of oxidative stress produced under these environmental stress injuries. The authors underlined the importance of the correctly administering of nutrient solution and fertilisation to face the damaging effects of adverse conditions in plant cells.

On the other hand, plant cells develop an antioxidant defence mechanism, which includes the non-enzymatic and enzymatic antioxidants for the detoxification of ROS. However, if the ROS production is higher than the ability of the antioxidant systems to scavenge them, it can lead to oxidative stress, and finally to cell death. In this context, Dr. De Maio's group [4] used citrus plants to investigate the modulation of poly (ADP-ribose) polymerase and antioxidant enzymes, using leaves in different developmental stages, including young, mature and senescent. Their work addressed the physiological, biochemical and molecular changes that occur in plant cells during leaf ageing. In young leaves, photochemical and glutathione-S-transferase activities increased. However, while the ageing process advanced, the non-enzymatic antioxidant systems reduced and reached the lowest levels in senescent leaves, while poly (ADP-ribose) polymerase activity increased. In the same way, Hasanuzzaman et al. [5] discussed in an extensive review, the available and up-to-date knowledge on the Ascorbate-Glutathione pathway concerning the oxidative stress tolerance, as well as plant defence mechanisms. Furthermore, the review by Laxa et al. [6] provided up-to-date information about the response and function of ROS and RNS, mainly with regard to superoxide radicals, hydrogen peroxide and nitric oxide under drought stress conditions, and their scavenging by the antioxidant defence enzymes in several plant species. To better understand the interaction between chitosan and *Vitis vinifera* L. plants, the original article by Singh et al. [7] analysed the antioxidant potential, the total phenolic content and the expression of ROS detoxification genes in two red grapevine varieties treated by chitosan. They concluded that chitosan induced the phenolic compounds, as well as acted as the organiser for the transfer of polyphenols from the *Vitis vinifera* leaves to the berries.

Another interesting feature of this special issue focuses on investigating the other H2O2 targets involved in programmed cell death. Dr. Mano's group [8] studied the mechanism that increased the reactive carbonyl species in the H2O2-produced programmed cell death in tobacco Bright Yellow-2 cells. They suggested that H2O2 initially inactivates a carbonyl reductase(s), which increases the reactive carbonyl species content, leading to the activation of the caspase-3-like protease of the 20S proteasome. The authors proposed that carbonyl reductase acted as a ROS sensor for inducing programmed cell death.

In plant cells, the ROS metabolism has been widely studied in different compartments, including mitochondria, cytosol, chloroplast, cell wall, plasma membrane, apoplast, glyoxysomes and peroxisomes [9]. The review by Dr. Petˇrivalský's group [10] provided the present knowledge about the compartment-specific pathways of reactive oxygen species generation and decomposition in plant cells, and the mechanisms that controlling their homeostasis in cell compartments. Likewise, with a particular example at the chloroplastic level, in an in-depth review Miyake [11] summarised the current research concerning the molecular mechanisms of ROS formation and suppression in photosystem I. He established a novel molecular mechanism for the oxidation of the P700 oxidation system in photosystem I and the elimination of ROS formation from the strong relationship between the light and dark reactions of photosynthesis. Furthermore, in an original article, Lewandowska et al. [12] investigated the effect of H2O2 on the structure and function of Arabidopsis chloroplastic DJ-1B. They found that AtDJ-1B has double functions, namely holdase and glyoxalase activity, which responded differently to H2O2. Glyoxalase activity was reduced by H2O2, however the holdase chaperone function did not change. They also analysed the phenotype of T-DNA lines that lacked the protein, and showed that AtDJ-1B was not necessary for plant growth under stress stimuli.

In summary, to better understand the nitro-oxidative stress networks in higher plants (Figure 1), the subjects addressed in this special issue provide an update and new knowledge about ROS and RNS metabolisms in plant responses to adverse environmental stimuli and the modulation of antioxidant systems to control ROS production and accumulation.

**Figure 1.** Schematic model of cross-talk between reactive oxygen species (ROS) and reactive nitrogen species (RNS) in plant responses to abiotic stress. Different abiotic stress situations can generate an uncontrolled production of ROS and RNS that oxidatively modify different biomolecules (proteins, lipids and nucleic acids). These modifications can lead to a gain of function of the antioxidant systems to control the production of ROS or generate a situation of cellular damage supported by a process of nitro-oxidative stress. The numbers indicate the relationship of each article in the Special Issue to the subject matter covered. (1) El-Esawi et al., 2020 [1]. (2) Begara-Morales et al., 2019 [2]. (3) García-Martí et al., 2019 [3]. (4) Biswas et al., 2020 [8]. (5) Jank ˚u et al., 2019 [10]. (6) Miyake, 2020 [11]. (7) Lewandowska et al., 2019 [12]. (8) Arena et al., 2019 [4]. (9) Hasanuzzaman et al., 2019 [5]. (10) Laxa et al., 2019 [6]. (11) Singh et al., 2019 [7].

**Funding:** This research was funded by ERDF grants co-financed by the Ministry of Economy and Competitiveness (project PGC2018-096405-B-I00), the Junta de Andalucía (group BIO286), the action 6 of the Research Support Plan of the University of Jaén for (2017-2019) R08/06/2019 and the R + D + I project within the framework Program of FEDER Andalucía 2014-2020 (Reference: 1263509).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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