In a persistently changing environment, plants are constantly challenged by various abiotic stresses such as salinity, drought, temperature extremes, heavy metal toxicity, high-light intensity, nutrient deficiency, UV-B radiation, ozone, etc. which cause substantial losses in the yield and quality of a crop. A key sign of such stresses at the molecular level is the accelerated production of reactive oxygen species (ROS) such as singlet oxygen (1O2), superoxide (O2•−), hydrogen peroxide (H2O2) and hydroxyl radicals (OH•). ROS are extremely reactive in nature because they can interact with a number of cellular molecules and metabolites, thereby leading to irreparable metabolic dysfunction and death. Plants have well-developed enzymatic and non-enzymatic scavenging pathways or detoxification systems to counter the deleterious effects of ROS that include the enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), glutathione peroxidase (GPX) and peroxidases (POX) as well as non-enzymatic compounds such as ascorbate (AsA), glutathione (GSH), carotenoids and tocopherols. In plant cells, specific ROS-producing and scavenging systems are found in different organelles and the ROS-scavenging pathways from different cellular compartments are coordinated. Recent studies in plants have shown that relatively low levels of ROS act as signaling molecules that induce abiotic stress tolerance by regulating the expression of defense genes. Additionally, numerous results have shown that plants with higher levels of antioxidants, whether constitutive or induced, showed greater resistance to different types of environmental stresses. In this chapter we attempt to summarize recent researches on the mechanisms and possible regulatory roles of ROS in abiotic stress tolerance. Further, we discuss the progress made during the last few decades in improving the oxidative stress tolerance of plants through genetic engineering by different components of ROS detoxification systems in plants.

Plant Response and Tolerance to Abiotic Oxidative Stress: Antioxidant Defense Is a Key Factor

Gel electrophoresis of proteins: A practical approach

Drought is one of the major abiotic stresses affecting yield of dryland crops. Rhizobacterial populations of stressed soils are adapted and tolerant to stress and can be screened for isolation of efficient stress adaptive/tolerant, plant growth promoting rhizobacterial (PGPR) strains that can be used as inoculants for crops grown in stressed ecosystems. The effect of inoculation of five drought tolerant plant growth promoting Pseudomonas spp. strains namely P.entomophila strain BV-P13, P. stutzeri strain GRFHAP-P14, P. putida strain GAP-P45, P. syringae strain GRFHYTP52, and P. monteilli strain WAPP53 on growth, osmoregulation and antioxidant status of maize seedlings under drought stress conditions was investigated. Drought stress induced by withholding irrigation had drastic effects on growth of maize seedlings. However seed bacterization of maize with Pseudomonas spp. strains improved plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability and mean weight diameter and decreased leaf water loss. The inoculated plants showed higher levels of proline, sugars, free amino acids under drought stress. However protein and starch content was reduced under drought stress conditions. Inoculation decreased electrolyte leakage compared to uninoculated seedlings under drought stress. As compared to uninoculated seedlings, inoculated seedlings showed significantly lower activities of antioxidant enzymes, ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX) under drought stress, indicating that inoculated seedlings felt less stress as compared to uninoculated seedlings. The strain GAP-P45 was found to be the best in terms of influencing growth and biochemical and physiological status of the seedlings under drought stress. The study reports the potential of rhizobacteria in alleviating drought stress effects in maize.

Effect of plant growth promoting Pseudomonas spp. on compatible solutes, antioxidant status and plant growth of maize under drought stress

In present study Bacillus spp. screened for drought tolerance could tolerate minimal water potential (-0.73 MPa) were evaluated for plant growth promoting properties at –0.73 MPa. Drought stress affected growth of isolates as indicated by increased intracellular free amino acids, proline, total soluble sugars, and exopolysaccharides. Drought-tolerant Bacillus spp. HYD-B17, HYTAPB18, HYDGRFB19, BKB30, RMPB44 identified as Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus thuringiensis, Paenibacillus favisporus, Bacillus subtilis based on 16S rDNA gene sequence were used to study the effect of inoculation on growth, osmolytes, antioxidant status. Inoculation increased plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability, decreasing leaf water loss. Bacillus spp. effect on osmoregulation increased proline, sugars, free amino acids and decreased electrolyte leakage. Inoculation reduced the activity of antioxidant enzymes asc...

https://www.tandfonline.com/doi/pdf/10.1080/17429145.2010.535178

Drought-tolerant plant growth promoting Bacillus spp.: effect on growth, osmolytes, and antioxidant status of maize under drought stress

Water deficiency compromises plant performance and yield in many habitats and in agriculture. In addition to survival of the acute drought stress period which depends on plant-genotype-specific characteristics, stress intensity and duration, also the speed and efficiency of recovery determine plant performance. Drought-induced deregulation of metabolism enhances generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which in turn affect the redox regulatory state of the cell. Strong correlative and analytical evidence assigns a major role in drought tolerance to the redox regulatory and antioxidant system. This review compiles current knowledge on the response and function of superoxide, hydrogen peroxide and nitric oxide under drought stress in various species and drought stress regimes. The meta-analysis of reported changes in transcript and protein amounts, and activities of components of the antioxidant and redox network support the tentative conclusion that drought tolerance is more tightly linked to up-regulated ascorbate-dependent antioxidant activity than to the response of the thiol-redox regulatory network. The significance of the antioxidant system in surviving severe phases of dehydration is further supported by the strong antioxidant system usually encountered in resurrection plants.

https://www.mdpi.com/2076-3921/8/4/94/pdf

The Role of the Plant Antioxidant System in Drought Tolerance.

Drought stress is a major factor in reduce growth, development and production of plants. Stress was applied with polyethylene glycol (PEG) 6000 and water potentials were: zero (control), -0.15 (PEG 10%), -0.49 (PEG 20%), -1.03 (PEG 30%) and -1.76 (PEG40%) MPa. The solutes accumulation of two maize (Zea mays L.) cultivars -704 and 301- were determined after drought stress. In our experiments, a higher amount of soluble sugars and a lower amount of starch were found under stress. Soluble sugars concentration increased (from 1.18 to 1.90 times) in roots and shoots of both varieties when the studied varieties were subjected to drought stress, but starch content were significantly (p<0.05) decreased (from 16 to 84%) in both varieties. This suggests that sugars play an important role in Osmotic Adjustment (OA) in maize. The free proline level also increased (from 1.56 to 3.13 times) in response to drought stress and the increase in 704 var. was higher than 301 var. It seems to proline may play a role in minimizing the damage caused by dehydration. Increase of proline content in shoots was higher than roots, but increase of soluble sugar content and decrease of starch content in roots was higher than shoots.

/pdf/drought-induced-accumulation-of-soluble-sugars-and-proline-4etjzbgmxm.pdf

Drought-induced Accumulation of Soluble Sugars and Proline in Two Maize Varieties

Drought stress was generated by PEG 6000. Water potentials were: zero as the control, and -0.15, -0.49, -1.03, and -1.76 MPa as treatments. After 24-h treatment the total soluble protein content of 2 maize (Zea mays L.) cultivars (704 and 301) was determined and SDS-PAGE gel electrophoresis in the first dimension was performed. By decreasing water potentials, total soluble protein content first increased, and then decreased in the roots and leaves of both varieties. The decrease in total soluble protein content in the roots of both varieties was equal, but in the leaves of cv. 301 it was greater than in cv. 704. In drought conditions the decrease in root and shoot fresh weight in cv. 704 was greater than in cv. 301. With water potential -1.76 MPa, the accumulation of dehydrin-like 38, 50, 57, and 65 KDa M.W. root proteins and 15, 17, 20, 27, 30, 37, 54, and 59 KDa M.W. leaf proteins increased. However, the expression of 15, 19, and 27 KDa M.W. root proteins, and 22 KDa M.W. leaf protein was induced in both varieties. The accumulation of dehydrin-like proteins in the roots and leaves of cv. 704 was higher than in cv. 301. There was no relationship between protein changes and drought tolerance.

/pdf/effects-of-drought-stress-on-soluble-proteins-in-two-maize-49ar2ipwvc.pdf

Effects of Drought Stress on Soluble Proteins in two Maize Varieties

Tomatoes, originally a tropical fruit, cannot easily be stored at low temperatures, due to the risk of chilling injury (CI). To develop an effective technique to reduce CI, the effects of treatment with 0, 3, and 6 μM brassinolide (BR) on chilling injury, electrolyte leakage (EL), contents of malondialdehyde (MDA) and proline, and activities of phospholipase D (PLD) and lipoxygenase (LOX) were investigated in tomato fruit stored at 1 °C for 21 days. Treatment with BR, especially at 6 μM, significantly alleviated chilling injury, reduced EL and MDA content, and increased proline content. Also, fruit treated with BR exhibited significantly lower PLD and LOX activities as compared with the control fruit. These results suggest that PLD and LOX are associated with the induction of CI in tomato fruit. BR might reduce CI by inhibiting PLD and LOX activities and by enhancing membrane integrity.

Enhancement of Chilling Stress Tolerance of Tomato Fruit by Postharvest Brassinolide Treatment

Responses of growth and germination to water stress induced by PEG 6000 and NaCl in two maize (Zea mays L.) cultivars 704 and 301 were studied. Water stress was generated by additions of PEG 6000 or sodium chloride to the root medium. Water potentials were: zero as control and -0.15, -0.49, -1.03 and -1.76 MPa as treatments. After 24 h treatment, the roots and shoots length and dry weight were of plants determined. In water stress, roots and shoots length and dry weight decreased at both treatments in both varieties. The germination is inversely proportional to the NaCl and PEG concentrations, it means that 704 and 301 cultivars of maize showed a reduction in germination with an increasing in NaCl or PEG concentrations induced water deficit, but this reduction in NaCl treatment were higher than PEG treatment. At treatment by PEG, the germination was severely decreased at -1.03 MPa. At treatment by NaCl no germination occurred at -1.03 in 301 var. and germination was very low at -1.03 MPa in 704 var., no germination occurred at -1.76 MPa in both varieties at both treatments. Decrease of germination in 704 variety was higher than 301 variety.

Water stress induced by polyethylene glycol 6000 and sodium chloride in two maize cultivars.

Water stress is one of the most important environmental factors that reduce growth, development and production of plants. Stress was applied with polyethyleneglycol (PEG) 6000 and water potentials were: zero (control), -0.15 (PEG 10%), -0.49 (PEG 20%), -1.03 (PEG 30%) and -1.76 (PEG 40%) MPa. The roots and leaves respiration of two maize (Zea mays L.) cultivars -704 and 301- were determined in various concentrations of PEG 6000. Oxygen uptake declined in leaves and roots with increasing PEG concentrations. Decrease of oxygen uptake in roots and leaves of 704 variety were higher than 301 variety. Chlorophyll a, b and total chlorophyll content were significantly decreased (p < 0.05), but carotenoids content increased (p < 0.05) under water stress. Decrease of chlorophyll content in 704 var. was higher than 301 var., but carotenoids content in 301 var. was higher than 704 var. Relative Water Content (RWC) was used to indicate the degree of stress. RWC decreased with increasing PEG concentrations. Lowering of RWC reduced growth and increased shoot/root ratio. Decrease of water content in 704 plants was higher than 301 plants. Shoot/root ratio in 704 var. was higher than 301 var.

Nayer Mohammadkhani

Papers

Drought-induced Accumulation of Soluble Sugars and Proline in Two Maize Varieties

Effects of Drought Stress on Soluble Proteins in two Maize Varieties

Enhancement of Chilling Stress Tolerance of Tomato Fruit by Postharvest Brassinolide Treatment

Water stress induced by polyethylene glycol 6000 and sodium chloride in two maize cultivars.

Effects of water stress on respiration, photosynthetic pigments and water content in two maize cultivars.