Polyunsaturated fatty acids present in plant membranes react with reactive oxygen species through so-called lipid oxidation events. They generate great diversity of highly-reactive lipid-derived chemical species, which may be further degraded enzymatically or non-enzymatically originating new components like Reactive Carbonyl Species (RCS). Such RCS are able to selectively react with proteins frequently producing loss of function through lipoxidation reactions. Although a basal concentration of lipoxidation products exists in plants (likely involved in signaling), their concentration and variability growth exponentially when plants are subjected to biotic/abiotic stresses. Such conditions typically increase the presence of ROS and the expression of antioxidant enzymes, together with RCS and also metabolites resulting from their reaction with proteins (advanced lipoxidation endproducts, ALE), in those plants susceptible to stress. On the contrary, plants designed as resistant may or may not display enhanced levels of ROS and antioxidant enzymes, whereas levels of lipid oxidation markers as malondialdehyde (MDA) are typically reduced. Great efforts have been made in order to develop methods to identify and quantify RCS, ALE, and other adducts with high sensitivity. Many of these methods are applied to the analysis of plant physiology and stress resistance, although their use has been extended to the control of the processing and conservation parameters of foodstuffs derived from plants. These foods may accumulate either lipid oxidation/lipoxidation products, or antioxidants like polyphenols, which are sometimes critical for their organoleptic properties, nutritional value, and health-promoting or detrimental characteristics. Future directions of research on different topics involving these chemical changes are also discussed.

https://digital.csic.es/bitstream/10261/181214/1/2019_Alche.pdf

A concise appraisal of lipid oxidation and lipoxidation in higher plants.

Lipid peroxidation-derived reactive carbonyl species (RCS): Their interaction with ROS and cellular redox during environmental stresses

Salinity stress is one of the major abiotic stresses that result in significant losses in agricultural crop production across the globe. Salinity stress results in osmotic stress, ionic stress, and oxidative stress; among these, oxidative stress is considered to be the most detrimental. Oxidative stress induces the production of different reactive oxygen species (ROS) at both intracellular and extracellular locations. Plants possess redox regulatory mechanisms by employing different enzymatic and nonenzymatic antioxidants to scavenge ROS. Different antioxidants have different tissue- and organelle-specific ROS-scavenging effects. However, the causal link between the amount of antioxidants and plant salinity stress tolerance is not as straightforward as one may assume, with controversial reports available in the literature. This chapter addresses those controversies and argues that there is a need for better understanding and development of tools for targeted regulation of plant redox systems in specific cellular compartments and tissues.

Targeting Redox Regulatory Mechanisms for Salinity Stress Tolerance in Crops

Membrane damage is a hallmark of both biotic and abiotic stress responses. The membrane determines the ability of a cell to sustain altered environmental conditions and hence can be used as a biomarker to assess stress-induced cell damage or death. We present an easy, quick, cost-effective, staining and spectrophotometric method to assess membrane stability of plant cells. In this method, Evan's blue, an azo dye, is used to assay for cell viability. More specifically, Evan's blue dye can penetrate through ruptured or destabilized membranes and stain cells. Thus, when plant cells are subjected to stress that compromises membrane integrity, the number of cells that are permeated by Evan's blue dye will be increased compared to control cells that are not stressed. In contrast, live, healthy cells that are capable of maintaining membrane integrity do not take up Evan's blue dye. Cells that have taken up Evan's blue dye will have an accumulation of a blue protoplasmic stain and these stained cells can be qualitatively documented under bright field microscopy with or without the use of a camera. Furthermore, the dye can be extracted from cells that are stained by Evan's blue dye and can be quantified spectrophotometrically. Using this analysis, the accumulation of dye in positively-stained cells correlates with the extent of cell membrane damage and thus the amount of cells that are stained with Evan's blue dye under various conditions can be used as an indicator of cellular stress.

https://bio-protocol.org/pdf/Bio-protocol2519.pdf

Quantification of Membrane Damage/Cell Death Using Evan's Blue Staining Technique.

Plant growth-promoting rhizobacteria (PGPR) not only enhance plant growth but also control phytopathogens and mitigate abiotic stresses, including water-deficit stress. In this study, 21 (26.9%) rhizobacterial strains isolated from drought-prone ecosystems of Bangladesh were able to form air-liquid (AL) biofilms in the glass test tubes containing salt-optimized broth plus glycerol (SOBG) medium. Based on 16S rRNA gene sequencing, Pseudomonas chlororaphis (ESR3 and ESR15), P. azotoformans ESR4, P. poae ESR6, P. fluorescens (ESR7 and ESR25), P. gessardii ESR9, P. cedrina (ESR12, ESR16, and ESR23), P. veronii (ESR13 and ESR21), P. parafulva ESB18, Stenotrophomonas maltophilia ESR20, Bacillus cereus (ESD3, ESD21, and ESB22), B. horikoshii ESD16, B. aryabhattai ESB6, B. megaterium ESB9, and Staphylococcus saprophyticus ESD8 were identified. Fourier transform infrared spectroscopy studies showed that the biofilm matrices contain proteins, polysaccharides, nucleic acids, and lipids. Congo red binding results indicated that these bacteria produced curli fimbriae and nanocellulose-rich polysaccharides. Expression of nanocellulose was also confirmed by Calcofluor binding assays and scanning electron microscopy. In vitro studies revealed that all these rhizobacterial strains expressed multiple plant growth-promoting traits including N2 fixation, production of indole-3-acetic acid, solubilization of nutrients (P, K, and Zn), and production of ammonia, siderophores, ACC deaminase, catalases, lipases, cellulases, and proteases. Several bacteria were also tolerant to multifarious stresses such as drought, high temperature, extreme pH, and salinity. Among these rhizobacteria, P. cedrina ESR12, P. chlororaphis ESR15, and B. cereus ESD3 impeded the growth of Xanthomonas campestris pv. campestris ATCC 33913, while P. chlororaphis ESR15 and B. cereus ESD21 prevented the progression of Ralstonia solanacearum ATCC® 11696TM. In a pot experiment, tomato plants inoculated with P. azotoformans ESR4, P. poae ESR6, P. gessardii ESR9, P. cedrina ESR12, P. chlororaphis ESR15, S. maltophilia ESR20, P. veronii ESR21, and B. aryabhattai ESB6 exhibited an increased plant growth compared to the non-inoculated plants under water deficit-stressed conditions. Accordingly, the bacterial-treated plants showed a higher antioxidant defense system and a fewer tissue damages than non-inoculated plants under water-limiting conditions. Therefore, biofilm-producing PGPR can be utilized as plant growth promoters, suppressors of plant pathogens, and alleviators of water-deficit stress.

/pdf/biofilm-producing-rhizobacteria-with-multiple-plant-growth-3xyitswyn4.pdf

Jayant K. Solanki

Papers

Aldo-keto reductase-1 (AKR1) protect cellular enzymes from salt stress by detoxifying reactive cytotoxic compounds.