A critical review on halophytes: Salt tolerant plants (original) (raw)
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Salt Adaptation Mechanisms of Halophytes: Improvement of Salt Tolerance in Crop Plants
Elucidation of Abiotic Stress Signaling in Plants, 2015
Soil salinity is one of the most serious environmental factors that affect crop productivity worldwide. Inevitable global climate change leading to rise in sea water level would exacerbate degradation of irrigation systems and contamination of ground water resources, which render conventional agricultural practices impossible due to the sensitivity of most crops to salinity. Breeding for development of salt-tolerant crop plants has been a major challenge due to the complexity and multigenic control of salt tolerance traits. Halophytes are capable of surviving and thriving under salt at concentrations as high as 5 g/L, by maintaining negative water potential. Physiological and molecular studies have suggested that halophytes, unlike glycophytes, have evolved mechanisms, such as ion homeostasis through ion extrusion and compartmentalization, osmotic adjustments, and antioxidant production for adaptation to salinity. Employment of integrated approaches involving different omics tools would amplify our understanding of the biology of stress response networks in the halophytes. Translation of the knowledge and resources generated from halophyte relatives of crop plants through functional genomics will lead to the development of new breeds of crops that are suitable for saline agriculture.
Salt Tolerance and Crop Potential of Halophytes
Critical Reviews in Plant Sciences, 1999
Although they represent only 2% of terrestrial plant species, halophytes are present in about half the higher plant families and represent a wide diversity of plant forms. Despite their polyphyletic origins, halophytes appear to have evolved the same basic method of osmotic adjustment: accumulation of inorganic salts, mainly NaCl, in the vacuole and accumulation of organic solutes in the cytoplasm. Differences between halophyte and glycophyte ion transport systems are becoming apparent. The pathways by which Na + and Clenters halophyte cells are not well understood but may involve ion channels and pinocytosis, in addition to Na + and Cltransporters. Na + uptake into vacuoles requires Na + /H + antiporters in the tonoplast and H + ATPases and perhaps PP i ases to provide the proton motive force. Tonoplast antiporters are constitutive in halophytes, whereas they must be activated by NaCl in salt-tolerant glycophytes, and they may be absent from salt-sensitive glycophytes. Halophyte vacuoles may have a modified lipid composition to prevent leakage of Na + back to the cytoplasm. Becuase of their diversity, halophytes have been regarded as a rich source of potential new crops. Halophytes have been tested as vegetable, forage, and oilseed crops in agronomic field trials. The most productive species yield 10 to 20 ton/ha of biomass on seawater irrigation, equivalent to conventional crops. The oilseed halophyte, Salicornia bigelovii , yields 2 t/ha of seed containing 28% oil and 31% protein, similar to soybean yield and seed quality. Halophytes grown on seawater require a leaching fraction to control soil salts, but at lower salinities they outperform conventional crops in yield and water use efficiency. Halophyte forage and seed products can replace conventional ingredients in animal feeding systems, with some restrictions on their use due to high salt content and antinutritional compounds present in some species. Halophytes have applications in recycling saline agricultural wastewater and reclaiming salt-affected soil in arid-zone irrigation districts.
Adaptive Mechanisms of Halophytes and Their Potential in Improving Salinity Tolerance in Plants
International Journal of Molecular Sciences
Soil salinization, which is aggravated by climate change and inappropriate anthropogenic activities, has emerged as a serious environmental problem, threatening sustainable agriculture and future food security. Although there has been considerable progress in developing crop varieties by introducing salt tolerance-associated traits, most crop cultivars grown in saline soils still exhibit a decline in yield, necessitating the search for alternatives. Halophytes, with their intrinsic salt tolerance characteristics, are known to have great potential in rehabilitating salt-contaminated soils to support plant growth in saline soils by employing various strategies, including phytoremediation. In addition, the recent identification and characterization of salt tolerance-related genes encoding signaling components from halophytes, which are naturally grown under high salinity, have paved the way for the development of transgenic crops with improved salt tolerance. In this review, we aim to ...
Responses of Halophytes to Salt Stress
Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca: Horticulture, 2007
Halophytes. plants naturally adapted to conditions of high salinity in the soil. have been the subject of many different studies but. paradoxically. not so much to investigate the mechanisms of salt tolerance at the biochemical and molecular level. Halophytes can be considered important. but underutilised. genetic resources for the identification of salt tolerance determinants. We present here a brief summary of the initial results of our ongoing. multidisciplinary studies on the general responses to salt stress in halophytes of the genera Plantago and Juncus. focusing on the effect of NaCl on seed germination. vegetative growth. reproductive development. and on the accumulation of mono and divalent cations and putative osmolytes in the aerial part of the plants
Crop diversification through halophyte production on salt-prone land resources
CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2006
Rapid population growth in the less developed countries of arid and semiarid regions and concomitant decline in productivity of agricultural lands due to shortage of good-quality irrigation water and increasing soil salinity, are exerting enormous pressure on the dwindling supplies of human consumption for food. Equally or even more affected in some cases are other resources, such as fodder for animals and fuel wood for the rural poor. There is growing evidence that this trend is unlikely to reverse at least in the near future. The last quarter of the 20th century has seen an explosion of information leading to a better understanding of the biology of salt tolerance in plants. Most conventional crops have marginal salt tolerance and there is a need to explore alternate options for utilization of salt-affected lands and saline water resources. Research has indicated the potential of many halophytes to withstand high soil salinity and saline water irrigation, some even with seawater. This tolerance is achieved through a number of adaptations such as selective uptake and transport of ions, localization of ions in vacuoles, synthesis of compatible organic solutes for cytoplasmic balancing and protection of enzyme systems. As a consequence, these plants are able to reduce damage and exhibit sustained growth by establishing homeostatic conditions. A wealth of halophytic flora exists which can be exploited for an array of uses like food, fodder, fuel wood, oilseed, medicines, chemicals, landscaping, ornamentals, and environment conservation through carbon sequestration.
Halophytes: Potential Resources for Salt Stress Tolerance Genes and Promoters
Halophytes have demonstrated their capability to thrive under extremely saline conditions and thus considered as one of the best germplasm for saline agriculture. Salinity is a worldwide problem, and the salt-affected areas are increasing day-by-day because of scanty rainfall, poor irrigation system, salt ingression, water contamination, and other environmental factors. The salinity stress tolerance mechanism is a very complex phenomenon, and some pathways are coordinately linked for imparting salinity tolerance. Though a number of salt responsive genes have been reported from the halophytes, there is always a quest for promising stress-responsive genes that can modulate plant physiology according to the salt stress. Halophytes such as Aeluropus, Mesembryanthemum, Suaeda, Atriplex, Thellungiella, Cakile, and Salicornia serve as a potential candidate for the salt-responsive genes and promoters. Several known genes like antiporters (NHX, SOS, HKT, VTPase), ion channels (Cl − , Ca 2+ , aquaporins), antioxidant encoding genes (APX, CAT, GST, BADH, SOD) and some novel genes such as USP, SDR1, SRP etc. were isolated from halophytes and explored for developing stress tolerance in the crop plants (glycophytes). It is evidenced that stress triggers salt sensors that lead to the activation of stress tolerance mechanisms which involve multiple signaling proteins, up-or down-regulation of several genes, and finally the distinctive or collective effects of stress-responsive genes. In this review, halophytes are discussed as an excellent platform for salt responsive genes which can be utilized for developing salinity tolerance in crop plants through genetic engineering.
Salt-tolerant genes from halophytes are potential key players of salt tolerance in glycophytes
Environmental and Experimental Botany, 2016
Crop productivity strongly depends on several biotic and abiotic factors. Salinity is one of the most important abiotic factors, besides drought, extreme temperatures, light and metal stress. The enhanced burden of secondary salinization induced through anthropogenic activities increases pressure on glycophytic crop plants. The recent isolation and characterization of salt tolerance genes encoding signaling components from halophytes, which naturally grow in high salinity, has provided tools for the development of transgenic crop plants with improved salt tolerance and economically beneficial traits. In addition understanding of the differences between glycophytes and halophytes with respect to levels of salinity tolerance is also one of the prerequisite to achieve this goal. Based on the recent developments in mechanisms of salt tolerance in halophytes, we will explore the potential of introducing salt tolerance by choosing the available genes from both dicotyledonous and monocotyledonous halophytes, including the salt overly sensitive system (SOS)-related cation/proton antiporters of plasma (NHX/SOS1) and vacuolar membranes (NHX), energy-related pumps, such as plasma membrane and vacuolar H + adenosine triphosphatase (PM & V-H + ATPase), vacuolar H + pyrophosphatases (V-H + PPase) and potassium transporter genes. Various halophyte genes responsible for other processes, such as crosstalk signaling, osmotic solutes production and reactive oxygen species (ROS) suppression, which also enhance salt tolerance will be described. In addition, the transgenic overexpression of halophytic genes in crops (rice, peanut, finger millet, soybean, tomato, alfalfa, jatropha, etc.) will be discussed as a successful mechanism for the induction of salt tolerance. Moreover, the advances in genetic engineering technology for the production of genetically modified crops to achieve the improved salinity tolerance under field conditions will also be discussed. 2015 Elsevier B.V. All rights reserved.
† Background Freshwater comprises about a mere 2. 5 % of total global water, of which approximately two-thirds is locked into glaciers at the polar ice caps and on mountains. In conjunction with this, in many instances irrigation with freshwater causes an increase in soil salinity due to overirrigation of agricultural land, inefficient water use and poor drainage of unsuitable soils. The problem of salinity was recognized a long time ago and, due to the importance of irrigated agriculture, numerous efforts have been devoted towards improving crop species for better utilization of saline soils and water. Irrigating plants with saline water is a challenge for practitioners and researchers throughout the world. † Scope Recruiting wild halophytes with economic potential was suggested several decades ago as a way to reduce the damage caused by salinization of soil and water. A range of cultivation systems for the utilization of halophytes have been developed, for the production of biofuel, purification of saline effluent in constructed wetlands, landscaping , cultivation of gourmet vegetables, and more. This review critically analyses past and present halophyte-based production systems in the context of genetics, physiology, agrotechnical issues and product value. There are still difficulties that need to be overcome, such as direct germination in saline conditions or genotype selection. However, more and more research is being directed not only towards determining salt tolerance of halophytes, but also to the improvement of agricultural traits for long-term progress.
In arid and semi-arid regions, irrigation water contributes to salinisation of the upper layer of the soil, where most root activity takes place. Along the path of plant domestication, many crop species have lost resistance mechanisms to various stress conditions [1], including salt stress [2]. Thus, most crop plants do not fully express their original genetic potential for growth, development and yield under salt stress, and their economic value declines as salinity levels increase [3, 4]. Improving salt resistance of crop plants is, therefore, of major concern in agricultural research. A potential genetic resource for the improvement of salt resistance in crop plants resides among wild populations of halophytes [5, 6]. These can be either domesticated into new, salt-resistant crops, or used as a source of genes to be introduced into crop species by classical breeding or molecular methods.