Salt tolerance and salinity effects on plants: a review.

https://www.researchgate.net/profile/Rupam_Kapoor/publication/26881549_Arbuscular_mycorrhizal_fungi_in_alleviation_of_salt_stress_A_review/links/0c960523fd2cc5ec7f000000.pdf

Arbuscular mycorrhizal fungi in alleviation of salt stress: a review.

The extraordinary contemporary species richness and ecological predominance of flowering plants (angiosperms) are even more remarkable when considering the relatively recent onset of their evolutionary diversification. We examine the evolutionary diversification of angiosperms and the observed differential distribution of species in angiosperm clades by estimating the rate of diversification for angiosperms as a whole and for a large set of angiosperm clades. We also identify angiosperm clades with a standing diversity that is either much higher or lower than expected, given the estimated background diversification rate. Recognition of angiosperm clades, the phylogenetic relationships among them, and their taxonomic composition are based on an empirical compilation of primary phylogenetic studies. By making an integrative and critical use of the paleobotanical record, we obtain reasonably secure approximations for the age of a large set of angiosperm clades. Diversification was modeled as a stochastic, time-homogeneous birth-and-death process that depends on the diversification rate (r) and the relative extinction rate (epsilon). A statistical analysis of the birth and death process was then used to obtain 95% confidence intervals for the expected number of species through time in a clade that diversifies at a rate equal to that of angiosperms as a whole. Confidence intervals were obtained for stem group and for crown group ages in the absence of extinction (e = 0.0) and under a high relative extinction rate (epsilon = 0.9). The standing diversity of angiosperm clades was then compared to expected species diversity according to the background rate of diversification, and, depending on their placement with respect to the calculated confidence intervals, exceedingly species-rich or exceedingly species-poor clades were identified. The rate of diversification for angiosperms as a whole ranges from 0.077 (epsilon = 0.9) to 0.089 (epsilon = 0.0) net speciation events per million years. Ten clades fall above the confidence intervals of expected species diversity, and 13 clades were found to be unexpectedly species poor. The phylogenetic distribution of clades with an exceedingly high number of species suggests that traits that confer high rates of diversification evolved independently in different instances and do not characterize the angiosperms as a whole.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0014-3820.2001.tb00826.x

Absolute diversification rates in angiosperm clades

Rapid seed germination and stand establishment are critical factors to crop production under salt‐stress conditions. In many crop species, seed germination and early seedling growth are the most sensitive stages to salinity stress. Salinity may delay the onset, reduce the rate, and increase the dispersion of germination events, leading to reductions in plant growth and final crop yield. The adverse effects of salt‐stress can be alleviated by various measures, including seed priming (a.k.a. pre‐sowing seed treatment). The general purpose of seed priming is to partially hydrate the seed to a point where germination processes are begun but not completed. Most priming treatments involve imbibing seed with restricted amounts of water to allow sufficient hydration and advancement of metabolic processes but preventing germination or loss of desiccation tolerance. Treated seeds are usually redried before use, but they would exhibit rapid germination when re‐imbibed under normal or stress conditions. Various seed priming techniques have been developed, including hydropriming (soaking in water), halopriming (soaking in inorganic salt solutions), osmopriming (soaking in solutions of different organic osmotica), thermopriming (treatment of seed with low or high temperatures), solid matrix priming (treatment of seed with solid matrices), and biopriming (hydration using biological compounds). Each treatment has advantages and disadvantages and may have varying effects depending upon plant species, stage of plant development, concentration/dose of priming agent, and incubation period. In this article, we review, evaluate, and compare effects of various methods of seed priming in improving germination of different plant species under saline and non‐saline conditions. We also discuss the known metabolic and ultra‐structural changes that occur during seed priming and subsequent germination. To maximize the utility of various seed priming techniques, factors affecting their efficiency must be examined and potential benefits and drawbacks determined. For example, quality of the seed before treatment, concentration/dose of priming agent, time period for priming, and storage quality of the seed following priming treatment must be carefully determined. Furthermore, such assessments must be based on large‐scale experiments if seed priming is to be used for large‐scale field planting. A better understanding of the metabolic events that take place in the seed during priming and subsequent germination will improve the effective application of this technology. The incorporation of advanced molecular biology techniques in seed research is vital to the understanding and integration of multiple metabolic processes that can lead to enhanced seed germination, and consequently to improved stand establishment and crop yield under saline and non‐saline conditions.

Pre‐Sowing Seed Treatment—A Shotgun Approach to Improve Germination, Plant Growth, and Crop Yield Under Saline and Non‐Saline Conditions

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 gly-cophyte ion transport systems are becoming apparent. The pathways by which Na+ and Cl− enters halophyte cells are not well understood but may involve ion channels and pinocytosis, in addition to Na+ and Cl− transporters. Na+ uptake into vacuoles requires Na+/H+ antiporters in the tonoplast and H+ ATPases and perhaps PPi 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...

Salt Tolerance and Crop Potential of Halophytes

Kosteletzkya virginica (L.) Presl. (Malvaceae) is a perennial that grows in saline or brackish water, and is salt-tolerant in its mature state, but less tolerant during germination. The seeds show a very low permeability to water that increases during storage. The permeability to water differs in seeds harvested in different years. Optimal temperature for germination is 2830 C. The effect of salinity on imbibition is largely osmotic, but germination is inhibited, apparently, by the combined osmotic and "ionic" effects, especially at high NaCl concentrations. Inhibition of germination by high NaCl concentrations is relatively more severe in scarified than in intact seeds, indicating that the seed coat acts as a partial barrier to Na+ influx. External application of proline or betaine did not improve germination under saline conditions. Dry seeds contain a significant amount of betaine and 1ow levels of proline, but during germination and in the presence of NaCl the betaine content decreased while the proline content increased. Thus, the likely compatible solute in the germinating seed seems to be proline. Kosteletzkya virginia (L.) Presl. (Malvaceae) is a perennial that grows in salt or brackish marshes along the warmer part of the Atlantic and Gulf shores of the United States where it flowers during the months of July to October (Radford, Ahles, and Bell, 1968). It is a C3 plant inhabiting ecologically stable habitats such as the high marsh or areas flooded with brackish water (Rumer, 1982). Somers (1982) has reported that K. virginica is more

Seeds of Kosteletzkya virginica (Malvaceae): their structure, germination, and salt tolerance. II. Germination and salt tolerance

Summary 1 Genetic differences among populations of a keystone species may affect ecosystem functional properties. We tested this by planting Spartina alterniflora from different geographical regions in a newly created salt marsh in Delaware, USA. 2 Spartina alterniflora plants from morphologically distinct short-form (back marsh) populations were originally collected from Massachusetts (41 ° 34 ' N ), Delaware (38 ° 47 ' N ), and Georgia (31 ° 25 ' N ) in the USA and vegetatively propagated for 6 years in a salt water-irrigated common garden in Delaware before transfer to a newly created salt marsh. 3 The magnitude of the expression of marsh functions in the created marsh, measured over 5 years, remained distinct in patches of each ecotype. End of season aerial biomass, below-ground biomass, root and rhizome distribution, canopy height, stem density, and carbohydrate reserves were closer to values reported for the plants' native sites than to those typical of Delaware. Thus, many of the plant features characteristic of particular latitudes appear to be under genetic control. Such ecotypic differentiation influences ecosystem function through keystone resource and keystone modifier activities. 4 Respiration of the microbial community associated with either dead shoots or the soil varied with plant ecotype in the created wetland and the patterns reflected those reported for their native sites. High edaphic respiration under the Massachusetts ecotype was correlated with the high percentage of sugar in the rhizomes. Edaphic chlorophyll was greater under the canopies of the Massachusetts and Delaware ecotypes than under the Georgia canopy and exhibited a relationship similar to that of algal production rates reported for the native sites. Larval fish were most abundant in pit traps in the Massachusetts ecotype.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.0022-0477.2001.00632.x

The regulation of ecosystem functions by ecotypic variation in the dominant plant: a Spartina alterniflora salt‐marsh case study

Phragmites australis is considered the most invasive plant in marsh and wetland communities in the eastern United States. Although allelopathy has been considered as a possible displacing mechanism in P. australis, there has been minimal success in characterizing the responsible allelochemical. We tested the occurrence of root-derived allelopathy in the invasiveness of P. australis. To this end, root exudates of two P. australis genotypes, BB (native) and P38 (an exotic) were tested for phytotoxicity on different plant species. The treatment of the susceptible plants with P. australis root exudates resulted in acute rhizotoxicity. It is interesting to note that the root exudates of P38 were more effective in causing root death in susceptible plants compared to the native BB exudates. The active ingredient in the P. australis exudates was identified as 3,4,5-trihydroxybenzoic acid (gallic acid). We tested the phytotoxic efficacy of gallic acid on various plant systems, including the model plant Arabidopsis thaliana. Most tested plants succumbed to the gallic acid treatment with the exception of P. australis itself. Mechanistically, gallic acid treatment generated elevated levels of reactive oxygen species (ROS) in the treated plant roots. Furthermore, the triggered ROS mediated the disruption of the root architecture of the susceptible plants by damaging the microtubule assembly. The study also highlights the persistence of the exuded gallic acid in P. australis's rhizosphere and its inhibitory effects against A. thaliana in the soil. In addition, gallic acid demonstrated an inhibitory effect on Spartina alterniflora, one of the salt marsh species it successfully invades.

Root-secreted Allelochemical in the Noxious Weed Phragmites Australis Deploys a Reactive Oxygen Species Response and Microtubule Assembly Disruption to Execute Rhizotoxicity

Several hundred halophytes from salt marshes and salt deserts of the world have been evaluated in our laboratory at various degrees of intensity, and a few have been selected for development as crops. The development of the cultivars and the basic biology of the plants is being studied in Delaware in the United States. Agronomic testing, feeding trials, and development of the best agronomic practices are taking place in the saline desert at the American University in Cairo research station in Sadat City. Our present efforts focus primarily on three forages, one grain, and one vegetable. Sporobolus virginicus cultivars for both hay and pasture are being tested. A Distichlis spicata cultivar for hay has been identified, and Spartina patens is being evaluated as a hay as well. Although we do not yet have the data for a full year’s growth in Egypt, forage yields of these various cultivars, when harvested as hay crops, range to 6.9 or more tons per acre, depending on the salinity and other environmental conditions, and the crude protein content as indicated by the nitrogen content ranges from 6 to 10%. Cultivars having the most useful agronomic qualities have been identified and are being increased in quantity. The grain crop Kosteletzkya virginica is a perennial, producing a seed which resembles millet; its whole seeds contain approximately 25% protein and 15% oil. The yields of one of our better cultivars are about 1460 kg/ha (1300 lb/acre) when grown under 25‰ salinity. The vegetable Atriplex triangularis (similar to spinach) has been under mass selection for four years; a cultivar has been identified and seed is now being increased for this species.

Halophytic crops for cultivation at seawater salinity

The C-4 salt marsh grass, Spartina patens, thrives in the upper portion of the marsh where soil salinities may be equal to coastal seawater. Spartina patens was grown in hydroponic culture in a greenhouse at 0, 340, and 510 mM NaCl, and measured for growth, tissue cation content, and root plasma membrane (PM) lipid composition. From 0 to 340 and 510 mM, the shoot growth decreased, but root growth was not affected. The Na + content increased in both shoots and roots when plants were grown in salt, while the shoots had a decreased K + content and the roots had a decreased Ca 2+ content. Spartina patens root plasma membrane was isolated with an aqueous polymer two-phase system. The purity of the plasma membrane was verified with cytochemical tests on membrane enzyme markers. Plasma membrane lipids were stable relative to the membrane protein content. Molar percentages of sterols (including free sterols) and phospholipid decreased with increasing salinity. However, glycolipid showed a statistically significant increase in the total lipid as salinity in the medium was increased from 0 to 510 mM. Even at a salinity of 510 mM, the plasma membrane sterol/phospholipid ratio was unaffected by NaCI. When the plants were grown in NaCI media, the plasma membrane had a decreased phosphatidylcholine (PC) and phosphatidylethanolamine (PE) content, but the PC/PE ratios were not affected. The plasma membrane molar percentage of sitosterol in total free sterol increased when plants were grown in salt media. The predominant membrane fatty acids were C11 and C14, and the major unsaturated one was C14:1. An increase in growth medium salinity resulted in a decreased root plasma membrane fluidity.

John L. Gallagher

Papers

Seeds of Kosteletzkya virginica (Malvaceae): their structure, germination, and salt tolerance. II. Germination and salt tolerance

The regulation of ecosystem functions by ecotypic variation in the dominant plant: a Spartina alterniflora salt‐marsh case study

Root-secreted Allelochemical in the Noxious Weed Phragmites Australis Deploys a Reactive Oxygen Species Response and Microtubule Assembly Disruption to Execute Rhizotoxicity

Halophytic crops for cultivation at seawater salinity

Stress tolerance in the marsh plant Spartina patens: Impact of NaCl on growth and root plasma membrane lipid composition