Transcriptome assembly, profiling and differential gene expression analysis of the halophyte Suaeda fruticosa provides insights into salt tolerance

Background Improvement of crop production is needed to feed the growing world population as the amount and quality of agricultural land decreases and soil salinity increases. This has stimulated research on salt tolerance in plants. Most crops tolerate a limited amount of salt to survive and produce biomass, while halophytes (salt-tolerant plants) have the ability to grow with saline water utilizing specific biochemical mechanisms. However, little is known about the genes involved in salt tolerance. We have characterized the transcriptome of Suaeda fruticosa, a halophyte that has the ability to sequester salts in its leaves. Suaeda fruticosa is an annual shrub in the family Chenopodiaceae found in coastal and inland regions of Pakistan and Mediterranean shores. This plant is an obligate halophyte that grows optimally from 200–400 mM NaCl and can grow at up to 1000 mM NaCl. High throughput sequencing technology was performed to provide understanding of genes involved in the salt tolerance mechanism. De novo assembly of the transcriptome and analysis has allowed identification of differentially expressed and unique genes present in this non-conventional crop. Results Twelve sequencing libraries prepared from control (0 mM NaCl treated) and optimum (300 mM NaCl treated) plants were sequenced using Illumina Hiseq 2000 to investigate differential gene expression between shoots and roots of Suaeda fruticosa. The transcriptome was assembled de novo using Velvet and Oases k-45 and clustered using CDHIT-EST. There are 54,526 unigenes; among these 475 genes are downregulated and 44 are upregulated when samples from plants grown under optimal salt are compared with those grown without salt. BLAST analysis identified the differentially expressed genes, which were categorized in gene ontology terms and their pathways. Conclusions This work has identified potential genes involved in salt tolerance in Suaeda fruticosa, and has provided an outline of tools to use for de novo transcriptome analysis. The assemblies that were used provide coverage of a considerable proportion of the transcriptome, which allows analysis of differential gene expression and identification of genes that may be involved in salt tolerance. The transcriptome may serve as a reference sequence for study of other succulent halophytes.Pakistan-U.S. Science and Technology Cooperation Program, U.S. Dept. of State and Higher Education Commission of Pakistan, and by the Department of Microbiology and Molecular Biology at Brigham Young University

Effects of salinity and ascorbic acid on growth, water status and antioxidant system in a perennial halophyte

Salinity causes oxidative stress in plants by enhancing production of reactive oxygen species, so that an efficient antioxidant system, of which ascorbic acid (AsA) is a key component, is an essential requirement of tolerance. However, antioxidant responses of plants to salinity vary considerably among species. Limonium stocksii is a sub-tropical halophyte found in the coastal marshes from Gujarat (India) to Karachi (Pakistan) but little information exists on its salt resistance. In order to investigate the role of AsA in tolerance, 2-month-old plants were treated with 0 (control), 300 (moderate) and 600 (high) mM NaCl for 30 days with or without exogenous application of AsA (20 mM) or distilled water. Shoot growth of unsprayed plants at moderate salinity was similar to that of controls while at high salinity growth was inhibited substantially. Sap osmolality, AsA concentrations and activities of AsA-dependant antioxidant enzymes increased with increasing salinity. Water spray resulted in some improvement in growth, indicating that the growth promotion by exogenous treatments could partly be attributed to water. However, exogenous application of AsA on plants grown under saline conditions improved growth and AsA dependent antioxidant enzymes more than the water control treatment. Our data show that AsA-dependent antioxidant enzymes play an important role in salinity tolerance of L. stocksii.Higher Education Commission of Pakistan for provision of funds under a research grant entitled ‘Salt-induced Oxidative Stress: Consequences and Possible Management’

Seed priming with melatonin improved salinity tolerance of halophytes during early life-cycle stages

Melatonin (MT) is a tryptophan derivative with multiple functions in both animals and plants. Exogenously-provided MT such as through seed priming has emerged as an effective way to improve stress tolerance of plants. However, little is known about MT priming in improving salinity tolerance of halophytes particularly during their early life-cycle stages. We therefore examined roles of MT priming in enhancing salinity tolerance of seeds and nascent seedlings of five warm subtropical halophytes. Priming with different MT concentrations alleviated primary dormancy of the seeds of annual halophytes Z. simplex and P. oleracea. Seed priming with MT also reduced the inhibitory effects of salinity on germination of halophytes by improving mean final and rate of germination under saline conditions. MT priming also improved germination recovery, when un-germinated seeds were transferred from saline solutions to water. Furthermore, MT priming also improved growth parameters such as total length, leaf area and photosynthetic pigments of the seedlings of test species under both non-saline and saline conditions. In general, low (5 and 100 µM) concentrations of MT were found most effective in improving seed dormancy, germination and early seedling growth of halophytes particularly under saline condition

Salinity inhibits seed germination of perennial halophytes Limonium stocksii and Suaeda fruticosa by reducing water uptake and ascorbate dependent antioxidant system

Information about production and detoxification of reactive oxygen species during seed germination of halophytes under saline conditions is scanty. We therefore studied levels of common oxidative stress markers, antioxidant substances and antioxidant enzyme activities in germinating seeds of two subtropical coastal halophytes Limonium stocksii and Suaeda fruticosa under various NaCl (0, 200 and 400. mM) treatments. Mature seeds of both species lacked reduced ascorbate (AsA) in dry state. However, glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX) and glutathione reductase (GR) were detected in dry seeds of both species. Higher and rapid germination was noted in L. stocksii seeds compared to S. fruticosa in distilled water. Ascorbate (AsA) was detected in water imbibed seeds of both species, along with increase in GSH levels and SOD, APX and GR activities during germination in distilled water. Germination and hydration of the seeds of both species decreased with increases in NaCl concentration. CAT and GPX activities were higher while APX, AsA and GSH decreased in salt stressed seeds compared to water-imbibed seeds. Thus, it appears that the salinity inhibits seed germination of L. stocksii and S. fruticosa by reducing water uptake and compromising ascorbate dependent antioxidant system.Higher Education Commission of PakistanScopu

Sabkha Ecosystems: Volume IV: Cash Crop Halophyte and Biodiversity Conservation

XXIII, 339 p. 121 illus.online resource

Germination strategies of halophyte seeds under salinity

Halophytes are plants of saline habitats that grow under conditions that may vary in extremes of temperatures (freezing to very hot), water availability (drought to water logging) and salinity (mild to almost saturation). Halophytes may also face sudden micro-environmental variations within their habitats. In this review we examine some of the factors that determine the ability of seeds of halophytes to germinate when conditions are optimal for seedling growth and survival. Seed dormancy (innate, induced or acquired) is an important means of initiating growth under appropriate conditions. Saline environments are often wet and so the seeds of halophytes may remain un-germinated over extended periods even after imbibition if the external environment does not favour germination and seedling survival. Many perennial halophytes, however, do not possess elaborate dormancy systems because they propagate largely through ramets and have no ecological compulsions for seed germination. The seeds of halophytes also have the capacity to recover from a salinity shock and start germination once salinity is reduced, which may happen following rain. In some cases, imbibition in a low-salt solution may help in osmo-priming and improve germination. Seed heteromorphism is yet another strategy adopted by some halophytes, whereby seeds of different size and colour are produced that germinate consecutively at suitable intervals. Light-dependent germination may also help if the seed is under a dense canopy or buried in debris; germination only occurs once these restraints are removed thus increasing the chances of seedling survival. (C) 2012 Elsevier B.V. All rights reserved

Polarity directed optimization of phytochemical and in vitro biological potential of an indigenous folklore: Quercus dilatata Lindl. ex Royle

Abstract Background Plants have served either as a natural templates for the development of new chemicals or a phytomedicine since antiquity. Therefore, the present study was aimed to appraise the polarity directed antioxidant, cytotoxic, protein kinase inhibitory, antileishmanial and glucose modulatory attributes of a Himalayan medicinal plant- Quercus dilatata. Methods Total phenolic and flavonoid contents were determined colorimetrically and various polyphenols were identified by RP-HPLC analysis. Brine shrimp lethality, SRB and MTT assays were employed to test cytotoxicity against Artemia salina and human cancer cell lines respectively. Antileishmanial activity was determined using standard MTT protocol. Glucose modulation was assessed by α-amylase inhibition assay while disc diffusion assay was used to establish protein kinase inhibitory and antifungal spectrum. Results Among 14 extracts of aerial parts, distilled water-acetone extract demonstrated maximum extract recovery (10.52% w/w), phenolic content (21.37 ± 0.21 μg GAE/mg dry weight (DW)), total antioxidant capacity (4.81 ± 0.98 μg AAE/mg DW) and reducing power potential (20.03 ± 2.4 μg/mg DW). On the other hand, Distilled water extract proficiently extracted flavonoid content (4.78 ± 0.51 μg QE/mg DW). RP-HPLC analysis revealed the presence of significant amounts of phenolic metabolites (0.049 to 15.336 μg/mg extract) including, pyrocatechol, gallic acid, catechin, chlorogenic acid, p-coumaric acid, ferulic acid and quercetin. Highest free radical scavenging capacity was found in Methanol-Ethyl acetate extract (IC50 8.1 ± 0.5 μg/ml). In the brine shrimp toxicity assay, most of the tested extracts (57%) showed high cytotoxicity. Among these, Chloroform-Methanol extract had highest cytotoxicity against THP-1 cell line (IC50 3.88 ± 0.53 μg/ml). About 50% of the extracts were found to be moderately antiproliferative against Hep G2 cell line. Methanol extract exhibited considerable protein kinase inhibitory activity against Streptomyces 85E strain (28 ± 0.35 mm bald phenotype at 100 μg/disc; MIC = 12.5 μg/ disc) while, Chloroform extract displayed maximum antidiabetic activity (α-amylase inhibition of 21.61 ± 1.53% at 200 μg/ml concentration). The highest antileishmanial potential was found in Ethyl acetate-Acetone extract (12.91 ± 0.02% at 100 μg/ml concentration), while, Q. dilatata extracts also showed a moderate antifungal activity. Conclusion This study proposes that multiple-solvent system is a crucial variable to elucidate pharmacological potential of Q. dilatata and the results of the present findings prospects its potential as a resource for the discovery of novel anticancer, antidiabetic, antileishmanial and antioxidant agents