Taufika Islam Anee

Exogenous Silicon Attenuates Cadmium-Induced Oxidative Stress in Brassica napus L. by Modulating AsA-GSH Pathway and Glyoxalase System

Cadmium (Cd) brings a devastating health hazard to human being as a serious consequence of agricultural and environmental contamination. We demonstrated the protective effect of silicon (Si) on cadmium (Cd)-stressed rapeseed (Brassica napus L. cv. BINA Sharisha 3) plants through regulation of antioxidant defense and glyoxalase systems. Twelve-day-old seedlings were exposed to Cd stress (0.5 and 1.0 mM CdCl2) separately and in combination with Si (SiO2, 1.0 mM) for 2 days. Cadmium toxicity was evident by an obvious oxidative stress through sharp increases in H2O2 content and lipid peroxidation (malondialdehyde, MDA content), and visible sign of superoxide and H2O2. Cadmium stress also decreased the content of ascorbate (AsA) and glutathione (GSH) as well as their redox pool. The activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and catalase (CAT) were decreased by Cd while ascorbate peroxidase (APX) and glutathione S-transferase (GST) activities were increased. The enzymes of glyoxalase system (glyoxalase I, Gly I and glyoxalase II, Gly II) were also inefficient under Cd stress. However, exogenous application of Si in Cd treated seedlings reduced H2O2 and MDA contents and improved antioxidant defense mechanism through increasing the AsA and GSH pools and activities of AsA-GSH cycle (APX, MDHAR, DHAR and GR) and glyoxalase system (Gly I and Gly II) enzymes and CAT. Thus Si reduced oxidative damage in plants to make more tolerant under Cd stress through augmentation of different antioxidant components and methylglyoxal detoxification system.

Glutathione in plants: biosynthesis and physiological role in environmental stress tolerance

Glutathione (GSH; γ-glutamyl-cysteinyl-glycine) is a small intracellular thiol molecule which is considered as a strong non-enzymatic antioxidant. Glutathione regulates multiple metabolic functions; for example, it protects membranes by maintaining the reduced state of both α-tocopherol and zeaxanthin, it prevents the oxidative denaturation of proteins under stress conditions by protecting their thiol groups, and it serves as a substrate for both glutathione peroxidase and glutathione S-transferase. By acting as a precursor of phytochelatins, GSH helps in the chelating of toxic metals/metalloids which are then transported and sequestered in the vacuole. The glyoxalase pathway (consisting of glyoxalase I and glyoxalase II enzymes) for detoxification of methylglyoxal, a cytotoxic molecule, also requires GSH in the first reaction step. For these reasons, much attention has recently been directed to elucidation of the role of this molecule in conferring tolerance to abiotic stress. Recently, this molecule has drawn much attention because of its interaction with other signaling molecules and phytohormones. In this review, we have discussed the recent progress in GSH biosynthesis, metabolism and its role in abiotic stress tolerance.

Nitric oxide pretreatment enhances antioxidant defense and glyoxalase systems to confer PEG-induced oxidative stress in rapeseed

ABSTRACT Nitric oxide (NO) is dynamic molecule implicated in diverse biological functions demonstrating its protective effect against damages provoked by abiotic stresses. The present study investigated that exogenous NO pretreatment (500 µM sodium nitroprusside, 24 h) prevented the adverse effect of drought stress [induced by 10% and 20% polyethylene glycol (PEG), 48 h] on rapeseed seedlings. Drought stress resulted in reduced relative water content with increased proline (Pro) level. Drought stress insisted high H2O2 generation and consequently increased membrane lipid peroxidation which are clear indications of oxidative damage. Drought stress disrupted the glyoxalase system too. Exogenous NO successfully alleviated oxidative damage effects on rapeseed seedlings through improving the levels of nonenzymatic antioxidant pool and upregulating antioxidant enzymes’ activities. Improvement of glyoxalase system (glyoxalase I and glyoxalase II activities) by exogenous NO was significant to improve plants’ tolerance. Nonetheless, regulation of Pro level and improvement of plant–water status were vital to confer drought stress tolerance.

Drought Stress Tolerance in Wheat: Omics Approaches in Understanding and Enhancing Antioxidant Defense

Plants face various kinds of stresses in the changing environment. Among the environmental stresses, drought is one of the most devastating stressors due to its diverse negative effects on crop plants. Drought stress in plants is very complex as it occurs due to varying environmental conditions such as soil water scarcity, soil salinity, and high temperature. The latter ones are termed as physiological drought. Bread wheat (Triticum aestivum L.) ranks first in the world’s grain production and is consumed as staple food by more than 36% of the world population. Wheat plant is highly sensitive to drought, especially at flowering and grain filling stages. Growth, photosynthesis, metabolic processes, nutrient assimilation, and yield of wheat plants remarkably decrease under drought. The responses of wheat to drought are varied at morphological, physiological, molecular, and biochemical levels. One of the most common consequences of drought is the disturbance of the balance between production of reactive oxygen species (ROS) and antioxidant defense causing overaccumulation of ROS which induces oxidative stress. This happens due to closure of the stomata, CO2 influx, and decrease of leaf internal CO2 which direct more electrons to form ROS and enhance photorespiration. These ROS can incur direct damage to protein, lipid, and nucleic acid which can ultimately cause plant cell death. Enhancing the antioxidant defense system to mitigate the oxidative stress is one of the effective strategies to make the wheat plants tolerant to drought. It appears that plants synthesize or activate several molecules like osmoprotectants, phytohormones, signaling molecules, and antioxidants to protect themselves from drought-induced oxidative damages. Novel approaches for enhancing the antioxidant defense system to minimize the impacts of drought-induced damage in plants are prime targets of plant biologists. Several genes and their overexpression were found to confer drought tolerance in plants. Application of plant probiotic bacteria also enhances tolerance of wheat plants to drought. Recent advances in genomic, transcriptomic, proteomic, and metabolomic studies on wheat under varying levels of drought generate useful information for designing drought-tolerant wheat. This chapter comprehensively reviews and updates our understanding on molecular mechanisms of adaptation of wheat plants to drought stress with special emphasis to antioxidant defense systems.

Responses, Adaptation, and ROS Metabolism in Plants Exposed to Waterlogging Stress

Waterlogging condition imposes serious threat to plant survival by disturbing normal growth and development by hampering different physiological and metabolic activities, which includes reduction in stomatal conductance, CO2 assimilation rate, photosynthesis rate, and nutritional imbalance resulting in crop yield loss. However, plant develops different morphological, anatomical, and physiological adaptive features, for instance, formation of adventitious roots and aerenchyma, enhances the production of ethylene, and increases ADH activities and proline content under flooding condition. Under flooding, plants show oxidative damage condition due to the excess ROS production. ROS interferes with normal metabolism through oxidation of protein, nucleic acid, and DNA and reduces membrane integrity. Under this condition, plants itself develop antioxidant defense system including both enzymatic and non-enzymatic antioxidants which scavenges excess ROS. In this chapter, we tried to focus on different types of strategies such as hormonal regulation, osmoprotectants, and mineral nutrients to cope up with excess ROS production and suggested the future need of research in hormonal interaction and significance of osmolytes in protecting crop plants under waterlogging environment.