Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants

Reactive oxygen species (ROS) are produced as a normal product of plant cellular metabolism. Various environmental stresses lead to excessive production of ROS causing progressive oxidative damage and ultimately cell death. Despite their destructive activity, they are well-described second messengers in a variety of cellular processes, including conferment of tolerance to various environmental stresses. Whether ROS would serve as signaling molecules or could cause oxidative damage to the tissues depends on the delicate equilibrium between ROS production, and their scavenging. Efficient scavenging of ROS produced during various environmental stresses requires the action of several nonenzymatic as well as enzymatic antioxidants present in the tissues. In this paper, we describe the generation, sites of production and role of ROS as messenger molecules as well as inducers of oxidative damage. Further, the antioxidative defense mechanisms operating in the cells for scavenging of ROS overproduced under various stressful conditions of the environment have been discussed in detail.

https://downloads.hindawi.com/archive/2012/217037.pdf

Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

Water deficit and salinity, especially under high light intensity or in combination with other stresses, disrupt photosynthesis and increase photorespiration, altering the normal homeostasis of cells and cause an increased production of reactive oxygen species (ROS). ROS play a dual role in the response of plants to abiotic stresses functioning as toxic by-products of stress metabolism, as well as important signal transduction molecules. In this review, we provide an overview of ROS homeostasis and signalling in response to drought and salt stresses and discuss the current understanding of ROS involvement in stress sensing, stress signalling and regulation of acclimation responses.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2009.02041.x

Reactive oxygen species homeostasis and signalling during drought and salinity stresses

Adaptation to environmental changes is crucial for plant growth and survival. However, the molecular and biochemical mechanisms of adaptation are still poorly understood and the signaling pathways involved remain elusive. Active oxygen species (AOS) have been proposed as a central component of plant adaptation to both biotic and abiotic stresses. Under such conditions, AOS may play two very different roles: exacerbating damage or signaling the activation of defense responses. Such a dual function was first described in pathogenesis but has also recently been demonstrated during several abiotic stress responses. To allow for these different roles, cellular levels of AOS must be tightly controlled. The numerous AOS sources and a complex system of oxidant scavengers provide the flexibility necessary for these functions. This review discusses the dual action of AOS during plant stress responses.

Dual action of the active oxygen species during plant stress responses.

Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects – A review

Changes in antioxidant metabolism because of the effect of salinity stress (0, 80, 160 or 240 mM NaCl) on protective enzyme activities under ambient (350 micromol mol(-1)) and elevated (700 micromol mol(-1)) CO(2) concentrations were investigated in two barley cultivars (Hordeum vulgare L., cvs Alpha and Iranis). Electrolyte leakage, peroxidation, antioxidant enzyme activities [superoxide dismutase (SOD), EC 1.15.1.1; ascorbate peroxidase (APX), EC 1.11.1.11; catalase (CAT), EC 1.11.1.6; dehydroascorbate reductase (DHAR), EC 1.8.5.1; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; glutathione reductase (GR), EC 1.6.4.2] and their isoenzymatic profiles were determined. Under salinity and ambient CO(2), upregulation of antioxidant enzymes such as SOD, APX, CAT, DHAR and GR occurred. However, this upregulation was not enough to counteract all ROS formation as both ion leakage and lipid peroxidation came into play. The higher constitutive SOD and CAT activities together with a higher contribution of Cu,Zn-SOD 1 detected in Iranis might possibly contribute and make this cultivar more salt-tolerant than Alpha. Elevated CO(2) alone had no effect on the constitutive levels of antioxidant enzymes in Iranis, whereas in Alpha it induced an increase in SOD, CAT and MDHAR together with a decrease of DHAR and GR. Under combined conditions of elevated CO(2) and salinity the oxidative damage recorded was lower, above all in Alpha, together with a lower upregulation of the antioxidant system. So it can be concluded that elevated CO(2) mitigates the oxidative stress caused by salinity, involving lower ROS generation and a better maintenance of redox homeostasis as a consequence of higher assimilation rates and lower photorespiration, being the response dependent on the cultivar analysed.

The oxidative stress caused by salinity in two barley cultivars is mitigated by elevated CO2.

Sunflower seedlings (Helianthus annuus cv. Licia Stella) reached a mild, moderate and severe level of water deficit stress after 5, 8 and 11 days of soil water depletion, respectively. At a moderate level of water deficit stress, an elastic adjustment occurred. At the same time, in response to a minor osmotic potential (Ψπ) and an intermediate rate of water potential (Ψw) decrease, glutathione level increased and enzyme activities related to the ascorbate/glutathione cycle were induced. At severe water deficit stress, the efficiency of this defence mechanism fell, oxidative processes intensified and soluble protein content decreased further. The results of the present experiments suggest that during water deficit stress the water status of the plants plays a key role in the activation of defence mechanisms.

Sunflower seedlings subjected to increasing water deficit stress: oxidative stress and defence mechanisms

Antioxidative responses of wheat treated with realistic concentration of cadmium

Antioxidant system in sporobolus stapfianus: changes in response to desiccation and rehydration

Raphanus sativus L. cv. Rimbo was grown for 10 days after emergence in hydroponic culture containing 0.12 (control), 5, 10 and 15 micro M copper. The seeds were germinated in the presence of the copper solution. The Cu contents increased with the treatment in both shoots and roots, maintaining in the roots a value eight- to ten-fold higher than in the shoots. With the treatment both shoots and roots underwent growth inhibition and an increase in the percentage of dry weight. Membrane damage and lipid peroxidation increased and glutathione was oxidized as the copper concentration increased, indicating an acceleration of oxidative processes. Control shoots had high contents of reduced glutathione and low contents of phytochelatin-SH whereas roots showed an opposite pattern, suggesting an utilization of reduced glutathione for phytochelatin synthesis. In both parts phytochelatin-SH content reached the maximum at 5 micro M copper and then decreased, reaching at 15 micro M copper the control value in the roots and a value five-fold higher than the control value in the shoots. The main phenolic acids represented in R. sativus were chlorogenic, vanillic, caffeic, siringic, p-coumaric and ferulic acids whereas the least represented were gallic, protocatechuic and p-hydroxybenzoic acids. The phenolic acids as well as the total and reduced ascorbate contents increased with the intensification of copper treatment. Notwithstanding these changes, total ascorbate remained 35% higher in the shoots than in the roots. The reduced ascorbate was thus able to replenish reducing equivalents to phenoxyl radicals thus explaining the increase in the phenolic compounds.

Cristina Sgherri

Papers

The oxidative stress caused by salinity in two barley cultivars is mitigated by elevated CO2.

Sunflower seedlings subjected to increasing water deficit stress: oxidative stress and defence mechanisms

Antioxidative responses of wheat treated with realistic concentration of cadmium

Antioxidant system in sporobolus stapfianus: changes in response to desiccation and rehydration

Phenols and antioxidative status of Raphanus sativus grown in copper excess