Bilquees Gul

High Salt Tolerance in Germinating Dimorphic Seeds of Arthrocnemum indicum

Arthrocnemum indicum L. is a stem-succulent perennial in the family Chenopodiaceae and is widely distributed in the tidal marshes of Pakistan. Seeds were collected from a coastal salt marsh situated on the Arabian Sea coast at Sands Pit, Karachi, Pakistan. Arthrocnemum indicum produces dimorphic brown and black seeds, and brown seed was significantly (P < 0.05) heavier. Experiments were conducted to determine the effect of salinity and temperature on the germination of seeds. Results indicated that both seeds are highly salt tolerant, and 3% of the brown seeds germinated at 1000 mM NaCl. Germination was significantly higher at 15⚬-25⚬C thermoperiod at 600 and 800 mM NaCl. Rate of germination decreased with increase in salinity and there was no significant difference among various thermoperiods on the rate of germination in both seed types. When the seeds were transferred to distilled water after 20-d exposure to salinity, most recovered in 24 h, with recovery percentages at highest salinity varied from 72% to 86% at various thermoperiods.

Germination of dimorphic seeds of Suaeda moquinii under high salinity stress

Suaeda moquinii (Torrey) Greene (desert blite), a succulent shrub in the family Chenopodiaceae, is widely distributed in salt marshes of the western United States. Suaeda moquinii produces dimorphic seeds (soft brown and hard black). Both types of seeds were collected from a salt marsh in Faust, Utah. Experiments were conducted to determine the seed germination responses of the black and brown seeds to salinity and temperature. Brown seeds were found to be one of the most salt tolerant at the germination stage when compared to other halophytes. Brown seeds germinated (30%) at 1000 mM NaCl, but only a few black seeds germinated (8%) at 600 mM NaCl. Seed germination occurred in most saline treatments at the lowest thermoperiod (5–15˚C) tested. In some salinity treatments (600, 800, 1000 mM), further increases in temperature resulted in progressively decreased seed germination. Brown seeds germinated better and had a higher germination rate (germination velocity) than black seeds at all thermoperiods. The highest rate of germination of black seeds occurred at the lowest thermoperiod (5–15˚C). Recovery of germination for black seeds when transferred to distilled water after being in various salinity treatments for 20 days was nearly complete (82–100%) at the lowest thermoperiod (5–15˚C) but decreased with increase in the temperature. Brown seeds recovered substantially (59–97%) from salinity at all thermoperiods. Regression analyses indicated significant differences between the germination recovery of the black and brown seeds.

Seed Germination in Relation to Salinity and Temperature in Sarcobatus Vermiculatus

Sarcobatus vermiculatus (Hook) Torrey is a leaf succulent, sodium-accumulating shrub usually found in saline substrates of the Great Basin desert, Utah, USA. Laboratory experiments were conducted to determine the effect of salinity (0, 200, 400, 600, 800 and 1000 mM NaCl) and temperature (day/night: 5/15, 10/20, 15/25, 20/30, and 25/35°C) on seed germination. S. vermiculatus showed 100% germination in non-saline controls, at all thermoperiods. Percentage and rate of germination decreased with increases in salinity and few seeds germinated at even 1000 mM NaCl. High salinity exposure caused the loss of viability at higher temperature regimes, while some recovery was recorded in low salinity treatments.

Influence of salinity and temperature on the germination of Kochia scoparia

Kochia scoparia is one of the most common annual halophytes foundin the Great Basin. Seeds were collected from a population growing in asalt playa at Faust, Utah and were germinated at 5 temperature regimes(12 h night/12 h day, 5–15 °C, 10–20 °C, 15–25 °C,20–30 °C and 25–35 °C) and 6 salinities (0, 200, 400,600, 800 and 1000 mM NaCl) to determine optimal conditions forgermination and recovery of germination from saline conditions after beingtransferred to distilled water. Maximum germination occurred in distilledwater, and an increase in NaCl concentration progressively inhibited seedgermination. Few seeds germinated at 1000 mM NaCl. A temperatureregime of 25 °C night and 35 °C day yielded maximumgermination. Cooler temperature 5–15 °C significantly inhibited seedgermination. Rate of germination decreased with increase in salinity.Germination rate was highest at 25–35 °C and lowest at5–15 °C. Seeds were transferred from salt solutions to distilled waterafter 20 days and those from high salinities recovered quickly at warmertemperature regimes. Final recovery germination percentages in high salttreatments were high, indicating that exposure to high concentration ofNaCl did not inhibit germination permanently.

Effect of salinity on the growth and ion content of Salicornia rubra

Salicornia rubra is a stem succulent annual halophyte, which is widely distributed in the saltpans of Northern Utah playas. This study reports the effect of salinity (0, 200, 400, 600, 800, and 1000 mM NaCl) on the growth, succulence, osmotic and water relations of the species under greenhouse conditions. Fresh and dry weight of plants increased with an increase in salinity. Optimal growth of S. rubra plants were recorded at 200 mM NaCl and the growth declined with a further increase in salinity. Both sodium (Na) and chloride (Cl) contents of plants increased with an increase in salinity, while Ca2+, Mg2+, and K+ content decreased. Succulence of shoots increased at low salinity and decreased at high salinity. Water potential of plants become more negative with an increase in salinity. The Fv/Fm ratio was more affected by higher salinity and irradiation stress during growth.

Action of Compatible Osmotica and Growth Regulators in Alleviating the Effect of Salinity on the Germination of Dimorphic Seeds of Arthrocnemum indicum L.

Arthrocnemum indicum Willd., a stem succulent perennial in the family Chenopodiaceae, is widely distributed along the coastal areas of Pakistan and forms an important component of the vegetation of salt marshes in the vicinity of mangrove swamps. Seed germination of halophytes is often inhibited by hypersaline conditions at these sites, which prevents the establishment of new populations (Ungar 1991). We studied the affect of growth regulators and compatible osmotica in alleviating the innate and salinity-induced dormancy in dimorphic (brown and black) seeds of A. indicum. Germination of both types of seeds decreased with an increase in salinity. Brown seeds germinated at the highest salinity concentration (1000 mM), whereas only a few black seeds germinated at 800 mM NaCl, and no germination was recorded at 1000 mM NaCl. The osmotica, proline and betaine, did not relieve salinity-induced dormancy in either black or brown seeds. Plant growth regulators, gibberellic acid (GA) and kinetin, significantly (P < 0.05) alleviated the salinity-induced germination inhibition of both seed types but over different salinity ranges and to different degrees. Both growth regulators significantly increased (P < 0.05) the rate of germination over most salinities, but the effect of GA was more pronounced than kinetin.

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

BackgroundImprovement 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.ResultsTwelve 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.ConclusionsThis 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.

The place of halophytes in Pakistan’s biofuel industry

An unsustainable supply of fossil fuel necessitates the need to look for suitable alternatives. One solution lies in using plant biomass, which can be converted into a wide range of biofuels. To avoid conflict between feed and fuel, the crops available for human consumption being used presently as biofuel feedstock may be replaced with halophytes, which have the potential to thrive in saline lands and can be irrigated with brackish water; some can even tolerate seawater salinity. This approach will help in producing sustainable fuel without encroaching on the good quality land and water resources needed for food crops. A candidate species should preferably be perennial, having high yield in saline lands with minimum inputs. Other attributes include cellulose/hemicellulose >25–30%, lignin <10%, low salt load in foliage and a non-invasive nature. The unexplored aspects of agronomy of these wild plants need careful study, especially with regards to land degradation and ecological consequences, before large-scale cultivation.

The influence of genes regulating transmembrane transport of Na+ on the salt resistance of Aeluropus lagopoides

Plantlets of Aeluropus lagopoides (Linn.) Trin. Ex Thw. were grown at different NaCl concentrations (26, 167, 373 and 747mM) for 3, 7 and 15 days; their growth, osmotic adjustment, gas exchange, ion compartmentalisation and expression of various genes related to Na+ flux was studied. Plantlets showed optimal growth in non-saline (control; 26mM NaCl) solutions, whereas CO2/H2O gas exchange, leaf water concentration and water use efficiency decreased under all salinity treatments, accompanied by increased leaf senescence, root ash, sodium content and leaf osmolality. A decrease in malondialdehyde (MDA) content with time was correlated with Na+ accumulation in the leaf apoplast and a concomitant increase in Na+ secretion rate. A. lagopoides accumulated a higher concentration of Na+ in root than in leaf vacuoles, corresponding with higher expression of V-NHX and lower expression of PM-NHX in root than leaf tissue. It appears that V-ATPase plays a vital role during Na+ transport by producing an electromotive force, driving ion transport. Leaf calcium increased with increasing salinity, with more rapid accumulation at high salinity than at low salinity, indicating a possible involvement of Ca2+ in maintaining K+:Na+ ratio. Our results suggest that A. lagopoides successfully compartmentalised Na+ at salinities up to 373mM NaCl by upregulating the gene expression of membrane linked transport proteins (V-NHX and PM-NHX). At higher salinity (747mM NaCl), a reduction in the expression of V-NHX and PM-NHX in leaves without any change in the rate of salt secretion, is a possible cause of the toxicity of NaCl.

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

Limonium stocksii is a potential commercial cut-flower crop for saline areas using brackish water. We therefore were interested to learn about the mechanism of its salinity tolerance. Plants grew well under lower saline conditions (300 mM NaCl) but higher salinities reduced growth. An increase in leaf osmolality and the management of salinity-induced oxidative stress are the key strategies employed. Exogenous AsA application improved the functioning of the AsA-dependent antioxidant system, leading to better growth.