M.M. Azooz

Ecophysiology and responses of plants under salt stress

Preface.- Role of Ca2+ in alleviating salt stress.- An overview on the role of plant volatile organic compounds (VOCs) in salt stress.- Adaptive Plasticity of salt stressed root systems.- Salt-stressed plants and their responses to cadmium.- Soil and water management for sustained agriculture in alluvial plains and floodplains exposed to salinity: A case study of Neretva river estuary.- In vitro culture and salt stress in plants.- Role of Arbuscular mycorrhiza in inducing resistance to salinity.- The role of NO in alleviating salt stress in plants.- Plant growth regulators and biomass partitioning in crops under salinity.- Salt stress and Photosynthesis.- Role of Jasmonates in Plant Adaptation to Stress.- Salt stress and nitrogen and phosphorus metabolism in plants.- Proline and glycinebetaine: chemistry, synthesis and role in plants.- Non-enzymatic antioxidants and ROS as signaling molecules in plants under salt stress.- Role of polyamines in alleviating salt stress.- Salt stress: Causes, Types and Physiological Responses of Plants.- Role of Phytochrome in Stress Tolerance.- Sulfur: Metabolism and role in plants under salt stress.- Breeding citrus.- Index.

Evaluation of salicylic acid (SA) application on growth, osmotic solutes and antioxidant enzyme activities on broad bean seedlings grown under diluted seawater

Exogenously applied salicylic acid has been shown to be an essential signal molecule involved in both local defense reactions and induction of systemic resistance response of plants after salt stress. Our study was aimed at evaluating the foliar spray with different levels (0.0, 0.5 and 1.0 mM) of salicylic acid (SA) on broad bean (Vicia faba L) seedlings grown under diluted seawater on growth and some related physiological responses. Seawater irrigation negatively affected growth parameters, free amino acids and K + , while the contents of soluble sugars and protein, proline, Cl , Na + , ion leakage, lipid peroxidation and antioxidant enzyme activities were significantly increased. Foliar spray with SA improved all growth parameters and increases the activities of antioxidant enzymes. On the other hand, plants treated with SA had lower Cl and Na + , while K + had a reverse pattern. Based on our findings, the effectiveness of SA in inducing seawater stress tolerance depends upon the concentration of SA applied. The inducer effect of SA was greater with 1 than 0.5 mM treatment. This effect includes the stimulation of antioxidant enzyme activities and regulation of osmotic adjustment through accumulation of osmotic solutes and regulation of absorption and distribution of inorganic ions.

Salt Stress: Causes, Types and Responses of Plants

Salt stress is one of the major abiotic stresses limiting crop production especially in arid and semi-arid regions. It is reported that about 7 % of the total earths land and 20 % of the total arable area are affected by high salt contents. Reclamation of salt affected soils is necessary as the salt is engulfing the cultivable land day by day. The earliest response of plants to salt stress is reduction in the rate of leaf surface expansion followed by cessation of expansion as the stress intensifies but growth resumes when the stress is relieved. Metabolic processes like photosynthesis, protein synthesis and lipid metabolisms are affected due to salt stress. Salinity is responsible for different types of stresses like, osmotic stress, ionic stress, oxidative stress and hormonal imbalances. The osmotic stress is caused by the excess of Na+ and Cl− ions in the soil that decrease the osmotic potential and hampers the water uptake and nutrients. Low molecular mass compounds known as compatible solutes is accumulated under salt stress. These compatible solutes include proline, glycinebetaine, sugars, proteins, polyols, etc. They do not interfere with the normal biochemical reactions and helps the plants in building the resistance against the stress.

Polyamines: Role in Plants Under Abiotic Stress

Environmental changes, irrespective of source, cause a variety of stresses in plants. These stresses affect the growth and development and trigger a series of morphological, physiological, biochemical and molecular changes in plants. Abiotic stress is the primary cause of crop loss worldwide. The most challenging job before the plant biologists is the development of stress tolerant plants and maintenance of sufficient yield of crops in this changing environment. Polyamines can be of great use to enhance stress tolerance in such crop plants. Polyamines are small organic polycations present in all organisms and have a leading role in cell cycle, expression of genes, signaling, plant growth and development and tolerance to a variety of abiotic stresses. High accumulation of polyamines (putrescine, spermidine and spermine) in plants during abiotic stress has been well documented and is correlated with increased tolerance to abiotic stress. Genetic engineering of PA biosynthetic genes in crop plants is the way to create tolerance against different stresses. The present review throws light on the role of polyamines in plants.

Effect of physical desiccation on plant regeneration efficiency in rice (Oryza sativa L.) variety super basmati

This experiment assessed the effect of partial physical desiccation on plant regeneration efficiency in scutellum-derived embryogenic calluses of rice (Oryza sativa L.) variety Super basmati. A number of callusing cultures were developed, and efficient callus induction was observed on MS (Murashige and Skoog) basal medium supplemented with 2.0mg/L 2,4-dichlorophenoxy acetic acid. The calluses were proliferated on the same medium for 3 weeks and then shifted to dehydration desiccation treatment for 72h. The desiccated calluses were cultured on different media for somatic embryogenesis and plant regeneration. A medium with 2.0mg/L alpha-napthaleneacetic acid, 10.0mg/L abscisic acid , 2.0mg/L kinetin was best for somatic embryogenesis only, but not for further plant development. After 10d, differentiated calluses were sub-cultured on medium with various concentrations and types of carbohydrates (carbon source) in (1)MS(2j) medium. A large number of plantlets (14.51+/-2.81 and 8.56+/-2.90 plants/callus) were regenerated via chemical desiccation, on MS with 3% maltose+3% sorbitol and 6% sucrose, respectively. Under dehydration on only simple MS (3% sucrose), 11.23+/-3.22 plants/callus were developed. Under conditions of dehydration and chemical desiccation, plant regeneration rates were higher than the calluses cultured on simple MS medium in the presence of plant growth regulator. After somatic embryogenesis, >25% plants were sterile. The protocol used here may allow maximum regeneration of normal and fertile plantlets of super basmati rice within 3 months.

Drought Stress Induced Oxidative Damage and Antioxidants in Plants

Crop production is affected by a number of abiotic factors including temperature, salinity, drought, pesticides, pH of the soil, and heavy metals as they affect all metabolic activities of the plant. When the plant is unable to grow normally, it is said to be affected by water deficit. The mechanism involved in combating water stress is not clear in spite of the various research programs and practices. Therefore, it is of great importance to understand the molecular mechanism of water deficit in order to significantly enhance the production of crop plants and quality of the environment. As transcript profiling data are available, the genetic approaches are necessary to determine the changes in gene expression. In this chapter, we tried to describe the mechanism of drought resistance in plants on an antioxidant, physiological, enzymatic and proteomic basis.

Recent Advances of Metabolomics to Reveal Plant Response During Salt Stress

Salt stress is the major limiting factor in agriculture and portraits a major challenge to food security. The adverse effect of salt stress is expressed on whole plant levels. Plants have acquired various processes that functions to balance cellular hyperosmolarity and ion disequilibrium in an effort to combat salt stress. These processes occur due to significant changes in the gene expression that in turn bring about changes in plant metabolism. These metabolic changes help the plant to adapt to disorganized metabolic homeostasis. It has been observed that adverse growth conditions have impact on the synthesis of secondary plant products or metabolites that help in plant defence. The diverse nature of these metabolites has lead to the development of ‘Metabolomics’. The metabolite fingerprinting and profiling approaches provides accurate identification and quantification of stressed sample even before they can bring about change(s) in the transcriptome or proteome. Using metabolic profile changes as a marker for stress physiology, metabolic movements and factors can be analysed in combination with other ‘omic’ techniques, such as transcriptomics. Revealed analyses of salt acclimation effects and related stress factors to salinity stress may provide help in crop breeding programs to develop salt tolerance varieties. In this review, we will focus on recent advancements and application of metabolomics in plants under salinity stress.

Transgenic plants as green factories for vaccine production

Edible vaccine technology represents an alternative to fermentation based vaccine production system. Transgenic plants are used for the production of plant derived specific vaccines with native immunogenic properties stimulating both humoral and mucosal immune responses. Keeping in view the practical need of new technology for production and delivery of inexpensive vaccines, especially in developing world, plant derived edible vaccines is the best option in hand to combat infectious diseases. Plant derived vaccine is easy to administer, cost effective, readily acceptable, have increased safety, stability, versatility and efficacy. Several plant derived vaccines are under research, some are under clinical trials for commercial use. Like most biotechnology products, the IP situation for edible vaccines is complex as IP rights influence every stage of vaccine development. n n xa0 n n Keywords: Transgenic plants, edible vaccines, chimeric viruses, bacterial diseases, viral diseases.

Jasmonate-induced tolerance of Hassawi okra seedlings to salinity in brackish water

Jasmonic acid (JA) critically participates in modulating plant responses to salt stress. Here, the protective role of JA against dilute seawater stress was investigated for Hassawi okra seedlings in pot experiments under controlled growth conditions. Seeds were soaked in 50xa0µM JA. The seedlings were irrigated with different dilutions of seawater (0–40xa0%) for 3xa0weeks. Okra seedlings pretreated with JA tolerated brackish water up to the level of 10xa0%, and survived up to 40xa0%, while they exhibited damage and finally death if untreated. On the other hand, the level of 5xa0% seawater favorably affected the growth parameters compared to the fresh water control. The beneficial effect of JA was manifested by higher biomass, photosynthetic pigment and osmoprotectant levels, and decreased general stress markers such as ion leakage and lipid peroxidation. In addition, mineral composition was altered and the activity of some antioxidant enzymes improved. In conclusion, our results indicate that JA affects plant acclimation to sublethal salinity stress by brackish water. Since seed germination and seedling establishment are critical steps in plant growth, it is recommended to consider priming with JA as measure to ameliorate the detrimental effects of seawater stress and to improve Hassawi okra seedlings tolerance when irrigating with brackish water.

Genetic Approaches to Improve Salinity Tolerance in Plants

Abiotic stress tolerance in plants is gaining importance day by day. Different techniques are being employed to develop salt tolerant plants that directly or indirectly combat global food problems. Advanced comprehension of stress signal perception and transduction of associated molecular networks is now possible with the development in functional genomics and high throughput sequencing. In plant stress tolerance various genes, proteins, transcription factors, DNA histone-modifying enzymes, and several metabolites are playing very important role in stress tolerance. Determination of genomes of Arabidopsis, Oryza sativa spp. japonica cv. Nipponbare and integration of omics approach has augmented our knowledge pertaining to salt tolerance mechanisms of plants in natural environments. Application of transcriptomics, metabolomics, bioinformatics, and high-through-put DNA sequencing has enabled active analyses of regulatory networks that control abiotic stress responses. To unravel and exploit the function of genes is a major challenge of the post genomic era. This chapter therefore reviews the effect of salt stress on plants and the mechanism of salinity tolerance along with contributory roles of QTL, microRNA, microarray and proteomics.