Soil Chemical Analysis

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

Antioxidants, Oxidative Damage and Oxygen Deprivation Stress: a Review

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

https://hal.archives-ouvertes.fr/hal-00886451/document

Plant drought stress: effects, mechanisms and management

Heat tolerance in plants: An overview

Differential response of wheat genotypes to long term salinity stress in relation to oxidative stress, antioxidant activity and osmolyte concentration

ions and to some extent Cl and SO 4 2 of Mg 2+ and nutrient imbalance caused by excess of Na + and Cl ions. Salinity stress response is multigenic, as a number of processes i n- volved in the tolerance mechanism are affected, such as var ious compatible solutes/osmolytes, polyamines, reactive oxygen species and antioxidant defence mecha- nism, ion transport and compartmentalization of inj u- rious ions. Various genes/cDNAs encoding proteins involved in the above-mentioned processes have been identified and isolated. The role of genes/cDNAs e n- coding proteins involved in regulating other genes/ pro- teins, signal transduction process involving hormones like ABA, JA and polyamines, and strategies to i mprove salinity stress tolerance have also been di scussed. EXCESS amount of salt in the soil adversely affects plant growth and development. Nearly 20% of the world's cul- tivated area and nearly half of the world's i rrigated lands are affected by salinity 1

Physiology and molecular biology of salinity stress tolerance in plants

Free radicals and other active derivatives of oxygen are inevitable by-products of biological redox reactions. Reactive oxygen species inactivate enzymes and damage important cellular components. The increased production of toxic oxygen derivatives is considered to be a universal or common feature of stress conditions. Plant and other organisms have evolved a wide range of mechanisms to contend with this problem. The antioxidant defence system of the plant comprises a variety of antioxidant molecules and enzymes. The effects of the action of free radicals on membranes include the induction of lipid peroxidation and fatty acid de-esterification. Both ethylene biosynthesis and membrane breakdown, which appear to be closely linked, seem to involve free radicals, although the sequence of events generating these free radicals is still poorly understood. It is clear that the capacity and activity of the antioxidative defence system are important in limiting oxidative damage and in destroying active oxygen species that are produced in excess of those normally required for metabolism. Transgenic plants offered us a means by which to achieve complete understanding of the roles of the enzymes involved in protection against stress of many types, environmental and induced. Studies on transformed plants expressing increased activities of single enzymes of the antioxidative defence system indicate that it is possible to confer a degree of tolerance to stress by these means. The advent of plant transformation has placed within our grasp the possibility of engineering greater stress tolerance in plants by enhancements of the antioxidative defence system.

Raj Kumar Sairam

Papers

Differential response of wheat genotypes to long term salinity stress in relation to oxidative stress, antioxidant activity and osmolyte concentration

Physiology and molecular biology of salinity stress tolerance in plants

Oxidative stress and antioxidative system in plants

Oxidative stress and antioxidant activity as the basis of senescence in maize leaves

Protective role of antioxidant enzymes under high temperature stress.