Effect of oxygen availability and salinity on EARLY LIFE HISTORY STAGES OF SALT MARSH PLANTS. I. Different germination strategies of Spartina alterniflora and Phragmites australis (Poaceae)

Gradients in oxygen availability and salinity are among the most important environmental parameters influencing zonation in salt marsh communities. The combined effects of oxygen and salinity on the germination of two salt marsh grasses, Spartina alterniflora and Phragmites australis, were studied in growth chamber experiments. Germination of both species was initiated by emergence of the shoot and completed by root emergence. Percentage S. alterniflora germination was reduced at high salinity (40 g NaCl/L) and in decreased oxygen (5 and 2.5%). In 0% oxygen shoots emerged, but roots did not. P. australis germination was reduced at a lower salinity (25 g NaCl/L) than S. alterniflora, and inhibited at 40 g NaCl/L and in anoxia. However, a combination of hypoxia (10 and 5% O2) and moderate salinity (5 and 10 g NaCl/L) increased P. australis germination. When bare areas in the salt marsh are colonized, the different germination responses of these two species to combinations of oxygen and salt concentrations are important in establishing their initial zonation. In high salinity wetlands S. alterniflora populates the lower marsh and P. australis occupies the high marsh at the upland boundary.     

Effect of 5-Aminolevulinic Acid on Development and Salt Tolerance of Potato (Solanum tuberosum L.) Microtubers in vitro

The effects of 5-aminolevulinic acid (ALA), a key precursor in the biosynthesis of porphyrins such as chlorophyll and heme, on development and salt tolerance of microtubers of two potato (Solanum tuberosum L.) cultivars Jingshi-2 and Zihuabai were examined under in vitro conditions. ALA at 0.3–3 mg/l promoted microtuber formation by increasing the average number, diameter, and fresh weight of microtubers especially under 0.5% NaCl stress conditions, but further increase in ALA concentration resulted in a reduction of microtuber yield irrespective of NaCl stress. Under 1.0% NaCl stress conditions, microtuberization was seriously repressed and could not be restored by the addition of ALA. The accumulation of malondialdehyde in the microtubers treated with 30 mg/l ALA increased by 22% compared to the controls (no salinity), while only a 7% increase was observed when the microtubers were exposed to 0.5% NaCl, indicating that ALA functions as a protectant against oxidative damages of membranes. Under 0.5% NaCl stress conditions, the highest activities of peroxidase and polyphenoloxidase were detected in microtubers treated with ALA at 0.3 and 3 mg/l, being by 73% and by 28% greater than those in the untreated controls, respectively. These results demonstrate that ALA at lower concentrations of 0.3–3 mg/l promotes development and growth of potato microtubers in vitro and enhances protective functions against oxidative stresses, but ALA at 30 mg/l and higher concentrations seems to induce oxidative damage probably through formation and accumulation of photooxidative porphyrins.     

Factors influencing bud break and rooting and mass-scale micropropagation of three Phragmites species: P. karka, P. communis and P. australis

A procedure has been described for the large-scale micropropagation of three Phragmites species, P. karka, P. communis and P. australis, from axillary buds excised from the main and side branches. Position of the buds on the branches had an effect on the bud break and establishment of the cultures under in vitro conditions. Lower buds of P. australis and middle buds of P. karka and P. communis were the most suitable. The presence of yeast extract as one of the ingredients of the sprouting medium helped in the early detection of systemic contamination. Multiple shoot formation and root initiation were obtained on Murashige and Skoog's basal medium supplemented with different concentrations of BA – 0.5 mg/l for P. karka, 0.25 mg/l for P. communis and 0.1 mg/l for P. australis– 0.5 mg/l Kn and 2% sucrose (w/v). Shoots and roots elongated on half-strength MS basal medium with 2% sucrose but without any plant growth regulators. A zone of root hair was observed in the case of P. australis. Hardening occurred on 95% of the plantlets within 30 days of transfer to the polyhouse. Over 10,000 plants were produced from three buds of each species within 9 months. The plants were supplied to a private company for their industrial waste treatment. Received: 1 June 1998 / Revision received: 28 August 1998 / Accepted: 10 October 1998     

Effect of salinity on seed germination and seedling growth of the halophyte Suaeda japonica Makino

Seed germination and seedling growth of the annual halophyte species Suaeda japonica Makino were investigated in response to variable salinity of sediment pore water. The germination percentage of S. japonica’s soft brown seeds, which are dominant among dimorphic seeds, decreased with an increase in salinity, although germination was still observed at 1200‐mM NaCl concentration. The germination percentage and germination speed observed in April were higher than those observed in December when treated with sediment water with 400–1200 mM of NaCl concentrations. These data suggest that S. japonica seedlings could be established on sediments that experience high temperatures. Germination recovery of S. japonica seeds transferred from 600‐mM NaCl containing sediment (seawater equivalent) was lowest among 0–1200‐mM NaCl treatments, implying the low tolerance of seawater conditions of S. japonica seeds. Seeds germinated in 900‐ to 1200‐mM NaCl medium showed poor growth, but survived, in hypersaline conditions, and exhibited improvement in growth upon transfer to lower salinity.     

Ameliorating effect of triacontanol on salt stressederythrina variegata seedlings. Changes in growth,biomass, pigments and solute accumulation

Erythrina variegata Lam. seedlings were grown under low (100 mM NaCl) and high (250 mM NaCl) salinity. Seedlings exposed to high salinity for 10 d showed significant reduction in growth rate and biomass production while the root/shoot ratio increased. In contrast to pigment and protein contents, starch and saccharide contents increased in salt stressed seedlings. When the seedlings were subsequently sprayed with triacontanol (1 mg kg^-1) the salinity effect was partially ameliorated and growth, biomass, chlorophyll and carotenoid contents increased.     

Photosynthetic Gas Exchange and Chlorophyll a Fluorescence in Salicornia brachiata (Roxb.) Under Osmotic Stress

Osmotic stress negatively affects the photosynthetic efficiency and cause a significant loss of crop productivity. Salicornia brachiata (Roxb.) is a eu-halophyte. We hereby report on photosynthetic gas exchange and chlorophyll fluorescence in S. brachiata under sodium chloride (NaCl), seawater and polyethylene glycol (PEG) induced osmotic stress. It grows luxuriantly and exhibited a higher tolerance index and better accumulation of organic solutes under 100% strength of seawater (32.5 ppt) and 0.5 M NaCl salinity. It exhibited comparatively better gas exchange, stomatal conductance, PSII photochemistry and electron transfer under 100% strength of seawater salinity. Higher chlorophyll a/b ratio under stress conditions indicated a lower ratio of PSII to PSI and balanced excitation of PSI and PSII in S. brachiata resulting in efficient photosynthetic processes. The lower total chlorophyll/carotenoids ratio and higher non-photochemical quenching indicated the photo-protection and safer dissipation of heat energy in S. brachiata under stress. The 100% strength of seawater and 0.5 M NaCl salinity in S. brachiata did not cause significant changes in antenna size, connectivity between PSII reaction centres (RCs) and reduction of electrons on PSII donor side. The 20% PEG induced the inactivation of RCs and cause damage to PSII RCs in S. brachiata thus reduced the electron transfer from QA^– to QB pool-sized and activity of water-splitting complex. Higher φ(P₀) and F_V/F_M in S. brachiata under seawater salinity indicated a comparatively better quantum yield of primary photochemistry. The higher PI_Total in S. brachiata under 100% strength of seawater and 0.5 M NaCl stress indicated a better energy flux reaching to PSII RCs, electron transport and performance of RCs. The higher strengths of osmotic stress cause reduction in the quantum yield of PSII electron transport and capturing efficiency of excitation energy by open PSII RCs in S. brachiata.

Graphic Abstract

     

Effects of environmental calcium deprivation on the egg masses of Physa marmorata Guilding (Gastropoda: Physidae) and Biomphalaria glabrata Say (Gastropoda: Planorbidae)

Eggs of the basommatophoran snails Physa marmorata and Biomphalaria glabrata were cultured in low concentrations of calcium to determine effects on growth and development. In both species there was some development in media with 0.12 mg/l Ca²⁺ but embryos were unable to hatch. 61.04% of embryos of P. marmorata could develop to hatching in 0.22 mg/l Ca²⁺ but those of B. glabrata required a level of 0.42 mg/l Ca²⁺, to attain even a 31.07% hatch. Marked effects on growth rate, embryo size and on time taken to achieve hatching were noted in both species at very low calcium levels. The possibility of cation-controlling mechanisms in the egg membrane is discussed.     

Maintenance of photosynthesis and the antioxidant defence systems have key roles for survival of Halopeplis perfoliata (Amaranthaceae) in a saline environment

• Coastal salt marsh plants employ various combinations of morphological and physiological adaptations to survive under saline conditions. Little information is available on salinity tolerance mechanisms of Halopeplis perfoliata, a C3 stem succulent halophyte.
• We investigated the growth, photosynthesis and antioxidant defence mechanisms of H. perfoliata under saline conditions (0, 150, 300 and 600 mM NaCl) in an open greenhouse.
• Optimal shoot succulence, projected shoot area and relative growth rate were obtained in the low (150 mm NaCl) salinity treatment, while growth was inhibited at the highest salinity (600 mm NaCl). The CO₂ compensation point and carbon isotope composition of biomass confirmed C₃ photosynthesis. Increases in salinity did not affect the photosynthetic pigment content or maximum quantum efficiency of PSII of H. perfoliata. Assimilation of CO₂ (A) also remained unaffected by salinity. A modest effect on some gas exchange and photochemistry parameters was observed at 600 mm NaCl. With increasing salinity, there was a continual increase in respiration, suggesting utilisation of energy to cope with saline conditions. Under 300 and 600 mm NaCl, there was an increase in H₂O₂ and MDA with a concomitant rise in AsA, GR content and CAT activity.
• Hence, H. perfoliata appears to be an obligate halophyte that can grow up to seawater salinities by modulating photosynthetic gas exchange, photochemistry and the antioxidant defence systems.

     

Salt stress effects on growth,pigments, proteins and lipid peroxidation in <Emphasis Type="Italic">Salicornia persica</Emphasis> and <Emphasis Type="Italic">S. europaea</Emphasis>

The effects of NaCl stress on growth, water status, contents of protein, proline, malondialdehyde (MDA), various sugars and photosynthetic pigments were investigated in seedlings of Salicornia persica and S. europaea grown in vitro. Seeds were germinated under NaCl (0, 100, 200, 300, 400, 500 and 600 mM) on Murashige and Skoog medium for 45 d. The shoot growth of both species increased under low NaCl concentration (100 mM) and then decreased with increasing NaCl concentrations. In contrast to S. persica, root length in S. europaea reduced steadily with an increase in salinity. Proline content in S. persica was higher than in S. europaea at most NaCl concentrations. Proline, reducing saccharide, oligosaccharide and soluble saccharide contents increased under salinity in both species. In contrast, contents of proteins and polysaccharides reduced in both species under salt stress. MDA content remained close to control at moderate NaCl concentrations (100 and 200 mM) and increased at higher salinities. MDA content in S. europaea was significantly higher than S. persica at higher salinities. Salt treatments decreased K⁺ and P contents in seedlings of both species. Significant reduction in contents of chlorophylls and carotenoids due to NaCl stress was also observed in seedlings of both species. Some differences appeared between S. persica and S. europaea concerning proteins profile. On the basis of the data obtained, S. persica is more salt-tolerant than S. europaea.     

Cellular responses of two rapid-cycling Brassica species, B. napus and B. carinata, to seawater salinity

Cellular responses of two rapid-cycling Brassica species. B. napus and B. carinata , to seawater salinity were characterized to determine whether callus showed a tolerance similar to that of whole plants. Callus was initiated from the leaves of 7-day-old seedlings of B. napus and B . carinata and then subcultured with two different levels of seawater salinity (2.3 and 5.2 g l⁻¹ Instant Ocean. Aquarium Systems, Inc. Mentor. OH, USA) for 14 days. Callus growth of both species was reduced by seawater salinity. Based on the percentage of the reduction in the relative fresh weight gain. B. napus was more salt-tolerant than B. carinata . consistent with the response of whole plants of the same species to seawater salinity. Seawater salinity caused changes in the concentrations of Na, K. Ca, Mg and Cl in both B. napus and B. carinata . The growth expressed as the percentage of control was significantly (P = 0.05) positively correlated with the concentration of Ca. and K/Na and Ca/Na ratios. It was also negatively correlated ( P = 0.01) with the concentrations of Na. Cl and Mg. In comparison with B. carinala . the salt-tolerant species, B . napus , showed a small reduction in the concentrations of Ca and K in the salt-stressed plants relative to the control.     

Comparative Study of the Interactive Effects of Salinity and Phosphorus Availability in Wild (Hordeum maritimum) and Cultivated Barley (H. vulgare)

The present study aimed to compare the effects of phosphorus (P) deficiency applied only or combined with salinity on root response, P partitioning, acid phosphatase activity, and phenolic compounds in wild (Hordeum maritimum) and cultivated (H. vulgare) barley species. Seedlings were grown hydroponically under low or sufficient P supply, with or without 100 mM NaCl for 55 days. Results showed that, when individually applied, P deficiency and salinity restricted the whole plant relative growth rate in both species of barley, with a more pronounced impact of the former stress. These depressive effects were more pronounced in H. vulgare than in H. maritimum. The combined effects of P deficiency and salinity were not additive neither on whole plant RGR nor on root response parameters in both species. The root area, root/shoot P content, root and leaf acid phosphatase activities, and shoot flavonoids contents increased under P deficiency conditions with and without salt in both species. Overall, the relatively better tolerance of H. maritimum plants to P deficiency applied only or combined with salinity could be explained by the capacity of this species to maintain higher P acquisition efficiency in concomitance with a larger root system, a higher root/shoot DW ratio, a higher root/shoot P content, a greater root and leaf acid phosphatase activities, and a higher flavonoid content and antioxidant capacity under combined effects of both stresses. Thus, H. maritimum constitutes a promising model to ameliorate the tolerance of the cultivated barley species under low-P soils and/or saline regions.     

盐分对河口淡水、微咸水沼泽湿地土壤甲烷产生潜力的影响

海平面上升导致河口区盐水入侵现象日益明显,深刻影响着河口潮汐淡水、微咸水湿地生物地球化学循环。采集闽江河口区淡水、微咸水短叶茳芏潮汐沼泽湿地表层土样,室内添加盐度为5,10,15,21 g/L的人造海水、Na Cl溶液及盐度为0的去离子水,通过室内泥浆厌氧培养试验,对比研究海水和Na Cl溶液对淡水、微咸水沼泽湿地土壤甲烷产生潜力的影响。与对照相比,1—12 d培养期内4个盐度的海水处理均显著抑制河口淡水、微咸水沼泽湿地甲烷产生潜力,抑制率在93%以上,盐度10—21 g/L的3个海水处理对于河口淡水、微咸水沼泽湿地甲烷产生潜力的抑制效应无显著差异。Na Cl溶液只有在盐度达到15和21 g/L才显著抑制淡水、微咸水沼泽湿地甲烷产生潜力,且抑制率最多为80.9%,盐度为5、10 g/L的Na Cl溶液对淡水、微咸水沼泽湿地甲烷产生潜力的抑制作用不显著,抑制率多小于30%。伴随着盐水入侵而发生的硫酸盐还原作用及离子胁迫作用对河口淡水、微咸水沼泽湿地甲烷产生具有显著的抑制效应。     

The effect of light, salinity, and nitrogen availability on lipid production by Nannochloropsis sp

We examined responses of batch cultures of the marine microalga Nannochloropsis sp. to combined alterations in salinity (13, 27, and 40 g/l NaCl) and light intensity (170 and 700 μmol photons/m²·s). Major growth parameters and lipid productivity (based on total fatty acid determination) were determined in nitrogen-replete and nitrogen-depleted cultures of an initial biomass of 0.8 and 1.4 g/l, respectively. On the nitrogen-replete medium, increases in light intensity and salinity increased the cellular content of dry weight and lipids due to enhanced formation of triacylglycerols (TAG). Maximum average productivity of ca. 410 mg TFA/l/d were obtained at 700 μmol photons/m²·s and 40 g/l NaCl within 7 days. Under stressful conditions, content of the major LC-PUFA, eicosapentaenoic acid (EPA), was significantly reduced while TAG reached 25% of biomass. In contrast, lower salinity tended to improve major growth parameters, consistent with less variation in EPA contents. Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca. 200 mg TFA/l/day, respectively. The highest biomass TFA content (ca. 47% DW) and average lipid productivity of ca. 360 mg TFA/l/day were achieved at 13 g/l NaCl and 700 μmol photons/m²·s. Our data further support selecting Nannochloropsis as promising microalgae for biodiesel production. Moreover, appropriate cultivation regimes may render Nannochloropsis microalgae to produce simultaneously major valuable components, EPA, and TAG, while sustaining relatively high biomass growth rates.     

Germination and growth responses of hybridizing Carpobrotus species (Aizoaceae) from coastal California to soil salinity

Germination, growth, and physiological responses of hybridizing Carpobrotus from coastal California to soil salinity were studied. Hybrids are presumably the result of hybridization and introgression between the exotic Carpobrotus edulis, a succulent perennial invading coastal habitats, and the native or long-naturalized C. chilensis. Germination responses were investigated at 0, 10, 20, and 50% seawater. Seedling growth and physiology were compared by irrigating seedlings with solutions of the same seawater concentrations and in low and high nutrients. Germination was inhibited in the presence of salt, but recovered after transferring the seeds to fresh water. Seeds exposed to salt had higher final germination rates than control. Growth of Carpobrotus was slightly enhanced by low seawater concentrations but reduced at high salinity at both nutrient regimes. Leaf cell sap osmolarity increased with increasing soil salinity, and taxa did not differ significantly in this physiological adjustment. Leaf carbon isotope ratios (∂¹³C) ranged from −28 to −22‰ and became less negative at higher salinities, indicating an improved water use efficiency in the seedlings at high salt concentrations. In addition, ∂¹³C values were generally less negative at high than at low nutrients. Differences among taxa were generally small. The results show that salinity affects both establishment and growth of hybridizing Carpobrotus. The overall weak species differences in salt tolerance indicate that the exotic C. edulis can occupy the same sites as C. chilensis in terms of salinity. The similarity of hybrids in their response to salinity suggests that they may contribute to the invasion by Carpobrotus.     

OPTIMIZATION OF SALT CONCENTRATIONS FOR A HIGHER CAROTENOID PRODUCTION IN DUNALIELLA SALINA (CHLOROPHYCEAE)1

Dunaliella salina (Dunal) Teodor, when treated over 25 d with a wide range of NaCl salinities (0.6–4.5 M), showed its maximal growth potentialities at 1.5–3.0 M NaCl and was able to survive even at 4.5 M NaCl. Sodium concentrations increased significantly at the supraoptimal salinities, reaching up to 5 mmol · g^?1 dry weight (dwt) at 4.5 M NaCl. Interestingly, ability of D. salina to take up essential mineral nutrients was not impaired by increased salinity. As for growth, chl concentrations were maximal in the 1.5–3.0 M NaCl range. Interestingly, carotenoid concentrations increased with the increasing salinity. The highest values of total antioxidant activity (5.2–6.9 mg gallic acid equivalents [GAE] · g^?1 dwt), antiradical activity, and reducing power were measured at 1.5–3.0 M NaCl. As a whole, these results showed that at 1.5–3.0 M NaCl, D. salina produce appreciable antioxidant level. But, once it reaches its growth maximum, a salt addition up to 4.5 M could enhance its carotenoid yield.     

Thermal ecotypes of amphi-Atlantic algae. II. Cold-temperate species (Furcellaria lumbricalis andPolyides rotundus)

Two species of cold-temperate algae from the North Atlantic Ocean,Polyides rotundus andFurcellaria lumbricalis, were tested for growth and survival over a temperature range of −5 to 30 °C. In comparisons of eastern and western isolates, bothF. lumbricalis, a North Atlantic endemic, andP. rotundus, a species having related populations in the North Pacific, were quite homogeneous.F. lumbricalis tolerated −5 to 25°C and grew well from 0 to 25°C, with optimal growth at 10–15 °C.P. rotundus tolerated −5 to 27°C, grew well from 5 to 25°C, and had a broad optimal range of 10–25°C. Both species tolerated 3 months in darkness at 0°C. In neither case could any geographic boundary be explained in terms of lethal seasonal temperatures, suggesting that these species are restricted in distribution by strict thermal and/or daylength requirements for reproduction. The hypothesis that northern species are more homogeneous than southern taxa in terms of thermal tolerance was supported. A second hypothesis, that disjunct cold-temperate species should be more variable than pan-Arctic species, was not supported.     

GROWTH AND ORGANIC OSMOLYTES OF GEOGRAPHICALLY DIFFERENT ISOLATES OF MICROCOLEUS CHTHONOPLASTES (CYANOBACTERIA) FROM BENTHIC MICROBIAL MATS:RESPONSE TO SALINITY CHANGE1

The comparative growth and osmotic acclimation often culture strains of the marine benthic cyanobacterium Microcoleus chthonoplastes Thuret isolated from microbial mats in Germany, Spain, Egypt, the United States, Mexico, Chile, and Australia were investigated in salinities ranging from freshwater to twice seawater. All isolates showed a broad growth versus salinity response consistent with the dominance of this species in intertidal and hypersaline microbial communities. Growth optima, salinity preferences, and maximum growth rates differed for each isolate and could be related to the habitat from which they were isolated. This is most obvious when comparing strains from brackish habitats with those from a hypersaline lake. While the former isolates exhibited sharply pronounced growth optima under hyposaline conditions, cultures from the hypersaline environment grew best in salinity more than double seawater. The major low-molecular weight organic compounds present in all M. chthonoplastes strains were the carbohydrates glycosylglycerol and trehalose. This was proven by using ¹³C-nuclear magnetic resonance spectroscopy. Glycosylglycerol was synthesized and accumulated with increasing salinities, indicating its role as an osmolyte. In contrast, trehalose was present in relatively high concentrations under hyposaline conditions only. Differences in the patterns of growth versus salinity, as well as in those of osmotic acclimation among the M. chthonoplastes isolates, point to the development of different physiological ecotypes within the species.     

The role of water level and salinity in the regulation of Juncus gerardi populations in former ricefields in southern France

Abstract. In the Rhône delta (southern France) Juncus gerardi is a dominant, strongly aggregating species in artificially flooded former rice fields. In order to explain this pattern, the effects of water depth, salinity and their interaction were measured on (1) seed germination and seedling development and (2) vegetative growth of J. gerardi in a controlled-environment experiment. The germination pattern of J. gerardi was affected by salinity. Low salinity (2 g/l NaCl) delayed germination while moderate salinity (12 g/l NaCl) reduced germination rate. In contrast, the germination of J. gerardi was not affected in the range of water depths tested (i.e. 0–10cm). Salinity negatively affected the development of below-ground parts, shoots and inflorescences. This negative effect of salinity on the vegetative growth of J. gerardi was amplified when combined with flooding. Flooding with fresh water (0–20 cm depth) did not limit biomass production during the experiment. However, a decrease in the ratio of below-ground/above-ground dry weight at deeper water depths suggests a limitation of the vegetative propagation of J. gerardi under prolonged flooding conditions. This hypothesis is supported by the negative correlation between the cover of J. gerardi and water depth found in an abandoned rice field. The limitation on seedling recruitment imposed by salinity and the depression of vegetative growth of J. gerardi due to a combination of salinity and water depth could explain the aggregate distribution of J. gerardi in former rice fields.     

Variation in response of accessions of minor millets,Pennisetum americanum (L.) Leeke (pearl millet) and Eleusine coracana (L.) Gaertn (finger millet), and Eragrostis tef (Zucc.) Trotter (tef) to salinity in early seedling growth

The response to increasing NaCl concentration of seedlings of 25 accessions of Ethiopian land races of each of Pennisetum americanum (L.) Leeke (pearl millet) and Eleusine coracana (L.) Gaertn (finger millet), and 15 accessions of Eragrostis tef (Zucc.) Trotter (tef), was examined after two week's growth in NaCl solution culture. Although increasing NaCl concentration significantly reduced seedling root lengths, there was considerable variation within, and between accessions within each species.Analysis based upon a non-linear least square inversion method, using root length data, revealed significant differences in accessions of P. americanum and E. tef on the basis of the estimated salinity threshold, C _t , the NaCl concentrations at which root length begins to decrease. C _t did not differ significantly between E. coracana accessions. Estimates of C₅₀ and C₀, mininum concentrations causing a 50% decrease in root length, and zero root growth respectively, revealed differences between and within accessions for all three species. Overall, finger millet was more tolerant than tef, which was more tolerant than pearl millet. There is clear evidence that differences in tolerance are genetically based from broad sense heritability estimates.     

Studies on toxigenic fungi in roasted foodstuff (Salted seed) and halotolerant activity of emodin-producingAspergillus wentii

Commercial roasted salted peanuts (3% NaCl), popcorn (1% NaCl), summer-squash (9% NaCl), sunflower (3% NaCl) and wild-melon (3% NaCl) seeds are polluted with fungi, mostlyAspergillus flavus, A. niger, Penicillium chrysogenum, P. corylophilum andRhizopus stolonifer. Contamination of popcorn with the fungi is about 10 times higher than in the other foods. These fungi, common also on unsalted seeds, are significantly inhibited in seeds (30% moisture content) treated with 9–21% NaCl. The halotolerantA. wentii represents the main fungus recovered from seeds treated by 15–21% NaCl. 9% NaCl stimulated emodin production byA. wentii on peanut and citrinin production byP. chrysogenum on popcorn and sunflower. Aflatoxin, citrinin and emodin production on popcorn persisted up to 15% NaCl. Popcorn is thus strongly susceptible to fungal invasion and toxin pollution. The halotolerance ofA. wentii was confirmed by its strong permanent growth in liquid medium at up to 15% NaCl. At 3% NaCl the mycelial growth and nitrogen content increased while the level of emodin and lipid production decreased. CO₂ evolution strongly increased at 9–15% NaCl as a characteristic ofA. wentii salt tolerance. Emodin inhibited seed viability and the inhibition dose for 50% reduction (LD₅₀) was 65 mg/L for popcorn and 45 mg/L for sunflower.