The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na + or Cl − exclusion, and the tolerance of tissue to accumulated Na + or Cl − . Our understanding of the role of the HKT gene family in Na + exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na + accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability.

https://rodas5.us.es/file/c2a700e9-8b4a-1970-d343-4a269c302970/1/estres_salino_bibliografia_scorm.zip/files/estres_salino_bibliografia.pdf

Mechanisms of salinity tolerance

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

Salinity tolerance comes from genes that limit the rate of salt uptake from the soil and the transport of salt throughout the plant, adjust the ionic and osmotic balance of cells in roots and shoots, and regulate leaf development and the onset of senescence. This review lists some candidate genes for salinity tolerance, and draws together hypotheses about the functions of these genes and the specific tissues in which they might operate. Little has been revealed by gene expression studies so far, perhaps because the studies are not tissue-specific, and because the treatments are often traumatic and unnatural. Suggestions are made to increase the value of molecular studies in identifying genes that are important for salinity tolerance.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2005.01487.x

Genes and salt tolerance: bringing them together.

Salinity is a major abiotic stress limiting growth and productivity of plants in many areas of the world due to increasing use of poor quality of water for irrigation and soil salinization. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, and molecular or gene networks. A comprehensive understanding on how plants respond to salinity stress at different levels and an integrated approach of combining molecular tools with physiological and biochemical techniques are imperative for the development of salt-tolerant varieties of plants in salt-affected areas. Recent research has identified various adaptive responses to salinity stress at molecular, cellular, metabolic, and physiological levels, although mechanisms underlying salinity tolerance are far from being completely understood. This paper provides a comprehensive review of major research advances on biochemical, physiological, and molecular mechanisms regulating plant adaptation and tolerance to salinity stress.

/pdf/mechanism-of-salinity-tolerance-in-plants-physiological-3ixvqhezre.pdf

Mechanism of Salinity Tolerance in Plants: Physiological, Biochemical, and Molecular Characterization

An ordered draft sequence of the 17-gigabase hexaploid bread wheat (Triticum aestivum) genome has been produced by sequencing isolated chromosome arms. We have annotated 124,201 gene loci distributed nearly evenly across the homeologous chromosomes and subgenomes. Comparative gene analysis of wheat subgenomes and extant diploid and tetraploid wheat relatives showed that high sequence similarity and structural conservation are retained, with limited gene loss, after polyploidization. However, across the genomes there was evidence of dynamic gene gain, loss, and duplication since the divergence of the wheat lineages. A high degree of transcriptional autonomy and no global dominance was found for the subgenomes. These insights into the genome biology of a polyploid crop provide a springboard for faster gene isolation, rapid genetic marker development, and precise breeding to meet the needs of increasing food demand worldwide.

A chromosome-based draft sequence of the hexaploid bread wheat (Triticum aestivum) genome

Enhanced salt tolerance of transgenic wheat (Tritivum aestivum L.) expressing a vacuolar Na+/H+ antiporter gene with improved grain yields in saline soils in the field and a reduced level of leaf Na+

A Proteomic Study of the Response to Salinity and Drought Stress in an Introgression Strain of Bread Wheat

Soil salinity is a major abiotic constraint to agricultural productivity. We successfully bred a new common wheat (Triticum aestivum L.) introgression variety (Shanrong No. 3) with high salt-tolerance via asymmetric somatic hybridization between common wheat cultivar (Jinan 177) and UV-irradiated Agropyron elongatum (Thinopyrum ponticum Podp). We report here a comparative proteomic analysis to investigate variety-specific and salt-responsive proteins between seedling-roots of Shanrong No. 3 and Jinan 177. In total, 114 spots reproducibly presented differential expression patterns on 2-DE maps. Of them, 34 were variety-specific and 49 were salt-responsive. We identified 110 spots by MALDI-TOF MS and partially confirmed by MALDI-TOF-TOF MS, and functionally classified them into signal transduction, transcription and translation, transporting, chaperones, proteolysis and detoxification, etc. Meanwhile, we also found the alteration of protein expression of Shanrong No. 3 through inhibition of old proteins and production of novel ones, change in abundance and sensitivity of some nonsalt-responsive and salt-responsive proteins, as well as PTMs. Furthermore, comparison between proteome and transcripteome using cDNA microarray showed that there were only 20 proteins with abundances correlative to signal densities of corresponding EST probes. This study gives us a global insight into proteomic difference between Shanrong No. 3 and Jinan 177 in constitute and to salt-response.

Proteomic analysis on a high salt tolerance introgression strain of Triticum aestivum/Thinopyrum ponticum

One of the two branches of the α-linolenic acid metabolism pathway is catalyzed by 12-oxo-phytodienoic acid reductase I, and the other is involved in jasmonic acid (JA) synthesis. The former is known to be active in the response to salinity tolerance in wheat (Triticum aestivum), but the participation of the latter in this response has not been established as yet. Here, the salinity-responsive bread wheat gene TaAOC1, which encodes an allene oxide cyclase involved in the α-linolenic acid metabolism pathway, was constitutively expressed in both bread wheat and Arabidopsis (Arabidopsis thaliana). In both species, transgenic lines exhibited an enhanced level of tolerance to salinity. The transgenic plants accumulated a higher content of JA and developed shorter roots. Both the shortened roots and the salinity tolerance were abolished in a background lacking a functional AtMYC2, a key component of the JA and abscisic acid signaling pathway, but were still expressed in a background deficient with respect to abscisic acid synthesis. We provide the first evidence, to our knowledge, suggesting that JA is also involved in the plant salinity response and that the α-linolenic acid metabolism pathway has a regulatory role over this response.

A Wheat Allene Oxide Cyclase Gene Enhances Salinity Tolerance via Jasmonate Signaling

Summary

The vast majority of angiosperms are (or were once) polyploid, and as hexaploid bread wheat has undergone two ploidy events separated by approximately 0.5 million years, it represents an elegant model to study gene silencing over time in polyploids. Using an SSCP platform, we have analysed patterns of transcriptional silencing (frequency, genome identity and organ specificity) within 236 single-copy genes, each mapping to one locus on one of the three homoeologous chromosomes within groups 1, 2, 3 and 7 of wheat. In about 27% of unigenes expressed in leaf, and about 26% of those in root, one (rarely two) members of a gene set (homoeoalleles) were not present in the cDNA template. Organ-specific regulation is commonplace, with many homoeoalleles transcribed in leaf but not root (and vice versa). There was little indication of extensive bias towards selective silencing of a particular genome copy. Expression of some of the silenced homoeoalleles was restored in certain aneuploid lines and varieties, and these displayed a significant degree of genetic variation for the silencing of a given homoeoallele. We propose that a substantial proportion of this phenomenon is effected by an epigenetic mechanism, and suggest that this form of genetic variation may be a significant player in the determination of phenotypic diversity in breeding populations.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2006.02841.x

Guangmin Xia

Papers

Enhanced salt tolerance of transgenic wheat (Tritivum aestivum L.) expressing a vacuolar Na+/H+ antiporter gene with improved grain yields in saline soils in the field and a reduced level of leaf Na+

A Proteomic Study of the Response to Salinity and Drought Stress in an Introgression Strain of Bread Wheat

Proteomic analysis on a high salt tolerance introgression strain of Triticum aestivum/Thinopyrum ponticum

A Wheat Allene Oxide Cyclase Gene Enhances Salinity Tolerance via Jasmonate Signaling

Homoeologous gene silencing in hexaploid wheat