Contents of volume 137 1991

The halophyte, Suaeda salsa, was grown in saline soil in pots and watered with a NaCl solution containing 0.2 g L^-1 Na-ions. S. salsa accumulated Na during a 120-day growing period and caused a net reduction in the Na content of the soil. S. salsa also decreased the Na content of saline soil in a field experiment. The Na content of the soil at depth 20–30 cm was reduced by 4.5% with S. salsa at a density of 15 plants m^-2 and by 6.7% with a density of 30 plants m^-2. In contrast, the Na content was decreased by only 1% with Medicago sativa at 15 plant m^-2 and increased by 3.8% with bare soil. The results confirm that S. salsa is an effective salt absorber in saline soils.     

Effects of salinity on photosynthesis,leaf anatomy,ion accumulation and photosynthetic nitrogen use efficiency in five Indian mangroves

Five species of mangroves (Bruguiera gymnorrhiza, Excoecaria agallocha, Heritiera fomes, Phoenix paludosa and Xylocarpus granatum) were investigated with respect to their photosynthesis rate, chlorophyll content, mesophyll conductance, specific leaf area, stomatal conductance and photosynthetic nitrogen use efficiency under saline (15–27 PPT) and non-saline (1.8–2 PPT) conditions. Some inorganic elements were estimated from the leaf samples to compare the concentrations with change in salinity. Elevated assimilation rate coupled with increased chlorophyll content, more mesophyll and stomatal conductance and higher specific leaf area in non-saline condition indicates that these mangroves can grow well even with minimal salinity in soil. In B. gymnorrhiza, E. agallocha and P. paludosa the optimum PAR acquisition for photosynthesis was higher under salt stress, while the maximal rate of assimilation was lower even with minimal salinity. H. fomes and X. granatum followed the opposite trend, where the peak photosynthesis rate was lower under non-saline conditions even at a higher irradiance than in the saline forest. This indicates less affinity of H. fomes and X. granatum to high substrate salinity. Accumulation of Na⁺ increased in plants in saline substrate, while in most of the species, salinity imposed reduction in Ca⁺ and Mg⁺ uptake. Increased K⁺ content can be attributed to high substrate level K⁺ in non-saline soil. Trace amount of salinity induced Cu⁺⁺ detected in leaves of H. fomes may impart some toxic effects. Photosynthetic nitrogen use efficiency increased in non-saline soil that can be attributed to higher photosynthetic peak in most of the species and/or lower nitrogen accumulation in plant samples.     

Nitrate‐dependent shoot sodium accumulation and osmotic functions of sodium in Arabidopsis under saline conditions

Improving crop plants to be productive in saline soils or under irrigation with saline water would be an important technological advance in overcoming the food and freshwater crises that threaten the world population. However, even if the transformation of a glycophyte into a plant that thrives under seawater irrigation was biologically feasible, current knowledge about Na⁺ effects would be insufficient to support this technical advance. Intriguingly, crucial details about Na⁺ uptake and its function in the plant have not yet been well established. We here propose that under saline conditions two nitrate‐dependent transport systems in series that take up and load Na⁺ into the xylem constitute the major pathway for the accumulation of Na⁺ in Arabidopsis shoots; this pathway can also function with chloride at high concentrations. In nrt1.1 nitrate transport mutants, plant Na⁺ accumulation was partially defective, which suggests that NRT1.1 either partially mediates or modulates the nitrate‐dependent Na⁺ transport. Arabidopsis plants exposed to an osmotic potential of ?1.0 MPa (400 mOsm) for 24 h showed high water loss and wilting in sorbitol or Na/MES, where Na⁺ could not be accumulated. In contrast, in NaCl the plants that accumulated Na⁺ lost a low amount of water, and only suffered transitory wilting. We discuss that in Arabidopsis plants exposed to high NaCl concentrations, root Na⁺ uptake and tissue accumulation fulfil the primary function of osmotic adjustment, even if these processes lead to long‐term toxicity.     

Effect of soil cadmium application and pH on growth and cadmium accumulation in roots, leaves and fruit of strawberry plants (Fragaria × ananassa Duch.)

Three strawberry (Fragaria × ananassa Duch.) cultivars Rainier, Totem and Selva were grown under greenhouse conditions in a Parkhill sandy loam soil with a background DTPA-extractable Cd concentration of 0.18 mg kg^-1 and a pH of 5.1. Experimental treatments included combinations of 4 Cd applications (0, 15, 30 and 60 mg Cd kg^-1 soil) applied as CdSO₄ and 2 soil pH values 5.1 and 6.8. Both the application of Cd and pH of the soil significantly affected plant growth, yield and Cd accumulation in plant tissue anf fruit. Although roots accumulated the highest concentrations of Cd of all plant parts investigated, increased soil Cd application reduced leaf weight more than root weight. In general, yield of strawberries was decreased by an increase in amount of soil-applied Cd, however the yield response varied among cultivars. At 60 mg Cd kg^-1 soil, yield of Rainier cultivar was reduced to 17.6% of control plants. Over 90% of total Cd taken up by plants grown in Cd-treated soil accumulated in roots, regardless of the Cd level in the soil. Root Cd concentrations ranged from 2.6 mg kg^-1 (control plants) to 505.7 mg kg^-1 (Totem plants grown in soil at highest Cd and a soil pH 5.1) and were directly related to soil Cd concentrations. Cd translocation from roots to leaves and fruit was very limited, resulting in a maximum Cd concentration in root leaf tissue of 10.2 mg kg^-1. Accumulation of Cd in fruit was found to correlate well with leaf Cd, although even at the highest amount of applied Cd, fruit Cd concentration did not exceed 700 g kg^-1 of fresh weight.Contribution no. 951     

NaCl enhances growth and morphogenesis potential of Alhagi graecorum

Summary The contamination of soils with excess salts is one of the greatest challenges to plant survival, but some unique species have evolved to thrive in highly saline environments. One such species, Alhagi graecorum Boiss., has been previously shown to accumulate high levels of sodium while growing in salt marshes. The aim of this research was to investigate the effects of saline conditions on the growth and the regeneration capacity of this species. Plantlets and explants of A. graecorum were cultured on a medium supplemented with various concentrations of NaCl, where A. graecorum tissues accumulated up to 8% Na⁺. The capacity for regeneration was enhanced by the excess sodium, indicating a requirement of salt for optimal growth and development in this species. Further study of this species may provide new concepts and understanding of the metabolism of sodium in higher plants.     

Alleviation of salt stress in Lotus glaber by Glomus intraradices

Lotus glaber is a glycophytic, perennial legume from Europe that occurs widely in saline habitats. We evaluated the effect of mycorrhizal fungus colonization on the response to salt stress of two genotypes of L. glaber differing in their tolerance to salinity. The experiment consisted of a randomized block design with two factors: (1) mycorrhizal fungus treatments (with or without AM fungus) and (2) two salinity levels of 0 and 200 mM NaCl. Our results indicated that Glomus intraradices established a more efficient symbiosis with the tolerant than with the sensitive genotype. G. intraradices improved growth of L. glaber plants under saline conditions. They showed higher values of net growth, shoot/root and K⁺/Na⁺ ratios, and protein concentrations than controls. Tolerant AM plants also showed higher chlorophyll levels than non-AM ones. Prevention of Na⁺ accumulation in the plant and enhancement of K⁺ concentrations in roots observed in this work could be part of the general mechanism of salt stress alleviation of L. glaber by G. intraradices.     

Agronomical and physiological characterization of salinity tolerance in a commercial tomato hybrid

The salt tolerance of the commercial F1 tomato hybrid (Lycopersicon esculentum Mill) Radja (GC-793) has been agronomically and physiologically evaluated under greenhouse conditions, using a control (nutrient solution), a moderate (70 mM NaCl added to the nutrient solution) and a high salt level (140 mM NaCl), applied for 130 days. The results show that Radja is a Na⁺-excluder genotype, tolerant to moderate salinity. Fruit yield was reduced by 16% and 60% and the shoot biomass by 30% and more than 75% under moderate and high salinities, respectively. At 90 days of salt treatment (DST), the mature leaves feeding the 4th truss at fruiting accumulated little Na⁺ (178 mmol kg^-1 DW). At this time, the sucrose concentration in these leaves even increased with moderate salinity and the amino acid proline was not accumulated under salt conditions as compared to control. At 130 DST, Na⁺ was accumulated mainly by the roots in proportion to the salt level applied, while in leaves appreciable amounts were found only at high salinity (452 mmol kg^-1 DW). In the leaves, Cl^- was always accumulated in proportion to the salt level and in a very much greater amounts than Na⁺ (until 1640 mmol kg^-1 DW). The sucrose content was reduced in all plants by salinity, and was distributed preferentially toward the distal stem and peduncle of a truss at fruiting under moderate salinity, and toward the basal stem and root at high salinity. Moreover, proline was accumulated in different organs of the plant only at high salinity, coinciding with Na⁺ accumulation in leaves. Attempts are made to find a clear relationship between physiological behaviour triggered by stress and the agronomical behaviour, in order to assess the validity of physiological traits used for salt-tolerance selection and breeding in tomato.     

WGA reduces the level of oxidative stress in wheat seedlings under salinity

Protective effect of exogenous wheat germ agglutinin (WGA) on wheat seedling (Triticum aestivum L.) during salinity stress was studied. In particular, we examined the state of pro- and antioxidant systems as well as the level of peroxide oxidation of lipids and electrolyte leakage under control conditions and when stressed with NaCl. Generation of superoxide anions and activity of both superoxide dismutase (SOD) and peroxidase increased during saline stress. Accumulation of O₂ ^·− resulted in peroxide oxidation of lipids and electrolyte leakage in response to stress. The injurious effect of salinity on root growth of seedlings was manifested by a decreased mitotic index (MI) in apical root meristem. This study show that WGA pretreatment decreased salt-induced superoxide anion generation, SOD and peroxidase activities, levels of lipid peroxidation and electrolytes leakage as well as correlating with a reduction in the inhibition of root apical meristem mitotic activity in salt-treated plants. This suggests that exogenous WGA reduced the detrimental effects of salinity-induced oxidative stress in wheat seedlings. Thus WGA effects on a balance of reactive oxygen species (ROS) and activities of antioxidant enzymes may provide an important contribution to a range of the defense reactions induced by this lectin in wheat plants.     

Development of callus and suspension cultures of potato resistant to NaCl and mannitol and their response to stress

Callus and suspension cultures adapted to various concentrations of NaCl or mannitol were developed from the cultivated potato Solanum tuberosum cv. Desire. Growth of the calli was less inhibited by mannitol than by iso-osmotic concentrations of NaCl. Reduction of growth by both NaCl and mannitol was considerably lower in osmotically adapted calli than in non-adapted ones. Salt-adapted suspension cultures that grew in the medium to which they had been originally adapted had a shorter lag in growth as well as a shorter time required to achieve the maximum growth, as compared with non-adapted cells. Suspension cultures adapted to NaCl concentrations higher than 150 mM were obtained only after preadaptation to osmotic stress. Adaptation of these cells was found to be stable. Accumulation of Na⁺ was lower and level of K⁺ was more stable in osmotically adapted than in non-adapted calli, when both were exposed to salt. Potassium level in NaCl-adapted calli exposed to saline medium was lower than that in non-adapted calli in standard medium. The maximum of Cl^– and Na⁺ accumulation was reached at higher external salt concentration in salt-adapted than in non-adapted suspension cultures. In both callus and suspension cultures, Cl^– accumulated more than Na⁺. Potassium level decreased more in non-adapted than in NaCl-adapted suspension cultures. The decrease of osmotic potential in osmotically adapted calli exposed to mannitol and in salt-adapted calli and suspension cultures exposed to salt was correlated to the increase of the external concentration. Such a correlation was not found in osmotically adapted calli exposed to salt. Non-electrolytes were found to be the main contributors to the decrease is osmotic potential in both callus and suspension cultures.     

Long‐term effect of salinity on plant quality,water relations,photosynthetic parameters and ion distribution in Callistemon citrinus

The effect of saline stress on physiological and morphological parameters in Callistemon citrinus plants was studied to evaluate their adaptability to irrigation with saline water. C. citrinus plants, grown under greenhouse conditions, were subjected to two irrigation treatments lasting 56 weeks: control (0.8 dS·m^?1) and saline (4 dS·m^?1). The use of saline water in C. citrinus plants decreased aerial growth, increased the root/shoot ratio and improved the root system (increased root diameter and root density), but flowering and leaf colour were not affected. Salinity caused a decrease in stomatal conductance and evapotranspiration, which may prevent toxic levels being reached in the shoot. Net photosynthesis was reduced in plants subjected to salinity, although this response was evident much later than the decrease in stomatal conductance. Stem water potential was a good indicator of salt stress in C. citrinus. The relative salt tolerance of Callistemon was related to storage of higher levels of Na⁺ and Cl^? in the roots compared with the leaves, especially in the case of Na⁺, which could have helped to maintain the quality of plants. The results show that saline water (around 4 dS·m^?1) could be used for growing C. citrinus commercially. However, the cumulative effect of irrigating with saline water for 11 months was a decrease in photosynthesis and intrinsic water use efficiency, meaning that the interaction of the salinity level and the time of exposure to the salt stress should be considered important in this species.     

Salt tolerance conferred by overexpression of Arabidopsis vacuolar Na+/H+ antiporter gene AtNHX1 in common buckwheat (Fagopyrum esculentum)

Agriculture productivity is severely affected by soil salinity. One possible mechanism by which plants could survive salt stress is to compartmentalize sodium ions away from the cytosol. In the present work, transgenic buckwheat plants overexpressing AtNHX1, a vacuolar Na⁺/H⁺ antiporter gene from Arabidopsis thaliana, were regenerated after transformation with Agrobacterium tumefaciens. These plants were able to grow, flower and accumulate more rutin in the presence of 200 mmol/l sodium chloride. Moreover, the content of important nutrients in buckwheat was not affected by the high salinity of the soil. These results demonstrated the potential value of these transgenic plants for agriculture use in saline soil.     

Comparative analysis of trehalose production by Debaryomyces hansenii and Saccharomyces cerevisiae under saline stress

The comparative analysis of growth, intracellular content of Na⁺ and K⁺, and the production of trehalose in the halophilic Debaryomyces hansenii and Saccharomyces cerevisiae were determined under saline stress. The yeast species were studied based on their ability to grow in the absence or presence of 0.6 or 1.0 M NaCl and KCl. D. hansenii strains grew better and accumulated more Na⁺ than S. cerevisiae under saline stress (0.6 and 1.0 M of NaCl), compared to S. cerevisiae strains under similar conditions. By two methods, we found that D. hansenii showed a higher production of trehalose, compared to S. cerevisiae; S. cerevisiae active dry yeast contained more trehalose than a regular commercial strain (S. cerevisiae La Azteca) under all conditions, except when the cells were grown in the presence of 1.0 M NaCl. In our experiments, it was found that D. hansenii accumulates more glycerol than trehalose under saline stress (2.0 and 3.0 M salts). However, under moderate NaCl stress, the cells accumulated more trehalose than glycerol. We suggest that the elevated production of trehalose in D. hansenii plays a role as reserve carbohydrate, as reported for other microorganisms.     

Generation and analysis of expressed sequence tags from the mangrove plant, Acanthus ebracteatus Vahl

Salinity is a major abiotic stress that greatly affects plant growth and crop production. Sodium ions in saline soil are toxic to plants because of their adverse effects on potassium nutrition, cytosolic enzyme activities, photosynthesis, and metabolism. It is important to identify genes involved in salinity tolerance from mangrove plants that survive under saline conditions. In this study, a total of 864 randomly selected cDNA clones were isolated and sequenced from the primary cDNA library of Acanthus ebracteatus. Among the 521 readable sequences, 138 of them were assembled into 43 contigs, whereas 383 were singletons. Sequence analyses demonstrated that 349 of these expressed sequence tags showed significant homology to functional proteins, of which 18% are particularly interesting as they correspond to genes involved in stress response. Some of these clones, including putative mannitol dehydrogenase, plastidic aldolase, secretory peroxidase, ascorbate peroxidase, and vacuolar H⁺-ATPase, may be related to osmotic homeostasis, ionic homeostasis, and detoxification.     

Chromium Phytoaccumulation from Solution by Selected Hydrophytes

There is increasing interest in the role of wetland plants in the aquatic phytoremediation of toxic metals. In this experiment, we evaluate the Cr removal capacity of four hydrophyte species (Nasturtium officinale L., Veronica beccabunga L., Mentha longifolia L., R.Br., Cardamine uliginosa L.) under varying nutritional conditions (full-strength and half-strength solution cultures), and over a range of Cr concentration (0, 2, 4, 6, and 8 mg L^-1). The results indicate that Cr accumulation is affected by both initial Cr concentration and strength of the nutrient solution. Phytoaccumulation increased with initial Cr concentration and plants grown in the full-strength solution accumulated more Cr at the higher initial solution concentration. Cr was predominantly accumulated in the roots, with minimal shoot translocation, which limits the hazard of Cr entering the food chain through ingestion by animals. Accumulation was large and reached up to 6700 mg Cr Kg^-1 in the roots of Veronica beccabunga.     

Dynamics of the phycotoxin domoic acid: accumulation and excretion in two commercially important bivalves

Batch cultures of the toxigenic diatomNitzschia pungens Grunow f.multiseries Hasle were fed to blue mussels (Mytilus edulis) and deep sea Atlantic scallops (Placopecten magellanicus) to elucidate conditions under which domoic acid (DA) was accumulated and excreted (depurated). Mussels accumulated the toxin to a maximum level of 13 g g^-1, at rates of 0.21 to 3.7 g h^-1 g^-1, dry weight. Accumulation efficiency (the proportion of accumulated DA to estimated net uptake) ranged from 1–5%. The highest filtration rate of 1.71 h^-1 occurred at concentrations of 4–8 × 10⁶ Nitzschia cells 1^-1 with no formation of pseudofeces. Depuration rates between fed and starved mussels over a 2 h test period were the same. The depuration rate of domoic acid was about 17% d^-1 and did not account for the low uptake efficiencies, so it is suggested that most of the DA is lost from mussels in the solution during the feeding process. Domoic acid accumulation in mussels was dependent on the amount of toxin available, which in turn was a function of the density and growth phase of theNitzschia population. Changes in filtration rate withNitzschia concentration and depuration rate with time can account for the DA levels of mussels collected during toxic episodes in Cardigan Bay, Prince Edward Island, Canada in 1988 and 1989.Scallops accumulated DA (0.39–1.3 g h^-1 g^-1, more slowly than mussels, however, accumulation efficiencies ranged from 5–100%. Filtration rates remained relatively low and constant at 0.081 h^-1. Scallops retained domoic acid longer than mussels, a fact which must be considered in the marketing of whole scallops for human consumption.     

Increased glycine betaine synthesis and salinity tolerance in AhCMO transgenic cotton lines

Glycine betaine is an osmoprotectant that plays an important role and accumulates rapidly in many plants during salinity or drought stress. Choline monooxygenase (CMO) is a major catalyst in the synthesis of glycine betaine. In our previous study, a CMO gene (AhCMO) cloned from Atriplex hortensis was introduced into cotton (Gossypium hirsutum L.) via Agrobacterium mediation to enhance resistance to salinity stress. However, there is little or no knowledge of the salinity tolerance of the transgenic plants, particularly under saline-field conditions. In the present study, two transgenic AhCMO cotton lines of the T₃ generation were used to study the AhCMO gene expression, and to determine their salinity tolerance in both greenhouse and field under salinity stress. Molecular analysis confirmed that the transgenic plants expressed the AhCMO gene. Greenhouse study showed that on average, seedlings of the transgenic lines accumulated 26 and 131% more glycine betaine than those of non-transgenic plants (SM3) under normal and salt-stress (150 mmol l⁻¹ NaCl) conditions, respectively. The osmotic potential, electrolyte leakage and malondialdehyde (MDA) accumulation were significantly lower in leaves of the transgenic lines than in those of SM3 after salt stress. The net photosynthesis rate and Fv/Fm in transgenic cotton leaves were less affected by salinity than in non-transgenic cotton leaves. Therefore, transgenic cotton over-expressing AhCMO was more tolerant to salt stress due to elevated accumulation of glycine betaine, which provided greater protection of the cell membrane and photosynthetic capacity than in non-transgenic cotton. The seed cotton yield of the transgenic plants was lower under normal conditions, but was significantly higher than that of non-transgenic plants under salt-stressed field conditions. The results indicate that over-expression of AhCMO in cotton enhanced salt stress tolerance, which is of great value in cotton production in the saline fields.     

Accumulation of organic and inorganic solutes in the subantarctic cruciferous species Pringlea antiscorbutica in response to saline and cold stresses

Pringlea antiscorbutica R. Br., a subantarctic endemic cruciferous species, is endangered in its natural sites by several ecological changes. This species is tolerant to salinity and a permanent cold temperature on Kerguelen and Crozet Islands. We attempted the investigation of regulating mechanisms of osmotic adjustment in this species. ¹³C NMR analyses of water-soluble compounds from leaves collected from the field revealed glucose and proline to be the main accumulated organic solutes. Colorimetric determinations in these samples showed that proline and soluble carbohydrates were present at remarkably high levels. When young plants were cultivated in growth chambers they showed a good resistance to cold and medium resistance to saline conditions. High levels of soluble carbohydrates were present in all situations. Proline was accumulated in response to a saline and a cold treatment. The quantitative variations of the pool of proline in response to saline treatments were rapid and important. The adaptive value of these responses of organic solutes in the tolerance of Pringlea antiscorbutica to various stresses is discussed. Received: 16 June 1997 / Accepted: 5 May 1998     

The endophyte Serendipita indica reduces the sodium content of Arabidopsis plants exposed to salt stress: fungal ENA ATPases are expressed and regulated at high pH and during plant co-cultivation in salinity

Serendipita indica (formerly Piriformospora indica) is an endophytic fungus that colonizes plant roots producing a beneficial effect on plant growth and development under optimal and suboptimal conditions provoked by any biotic or abiotic stress, such as salt stress. Salinity induces osmotic and ionic imbalances in plants, mainly by altering the Na⁺ and K⁺ contents. However, the mechanism by which Serendipita improves plant growth has yet to be elucidated. Previous works suggest that this fungus improves the plant osmotic state but not much is known about whether it participates in readjustment of the ionic imbalance in plants. Here, we report that co-cultivation with Serendipita reduces the Na⁺ content of Arabidopsis plants under saline conditions. Additionally, we describe the functional characterization of the two Serendipita ENA ATPases, which are homologous to the main proteins involved in the salt tolerance of other fungi. Their heterologous expression in salt-sensitive yeast mutants shows that SiENA1 is involved in Na⁺ and K⁺ efflux, while SiENA5 seems to only be involved in Na⁺ detoxification. Both are induced and might have a relevant function at alkaline pH, condition in which there are few chlamydospores in the mycelium, as well as during co-cultivation with plants exposed to saline conditions.     

Generation of Mercury-Hyperaccumulating Plants through Transgenic Expression of the Bacterial Mercury Membrane Transport Protein MerC

The merC gene from Acidithiobacillus ferrooxidans functions as a mercury uptake pump. MerC protein localizes in the cytoplasmic membrane of plant cells. When Arabidopsis thaliana and tobacco plants were transformed with the merC gene under the control of the Cauliflower mosaic virus 35S promoter, the resulting overexpression of merC rendered the host plants hypersensitive to Hg²⁺ and they accumulated approximately twice as much Hg²⁺ ion as the wild type plants. Thus, bacterial mercuric ion transporters such as MerC may be useful molecular tools for producing transgenic plants that hyperaccumulate Hg²⁺ ion.