Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Summary Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg^–1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m^–1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low ( 0.2 mmol kg^–1 NaHCO₃-extractable P) at soil saturation extract salinities from 1.1 dS m^–1 to 8.8 dS m^–1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m^–1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.     

Use of an organic buffer for the selection of acid tolerantRhizobium meliloti strains

Summary Nine media used to grow rhizobia were examined for their ability to maintain a stable low pH during the growth ofR. meliloti Large fluctuations in the pH of all media were recorded within 72 h, indicating their unsuitability for use in the selection of acid tolerant rhizobia. Morpholino-ethanesulphonic acid (MES) was assessed for its ability to buffer the pH of the media whilst still permitting rapid growth ofR. meliloti, R. trifolii, andBr. lupini. With 30.7 mM MES, the pH of a defined medium containing galactose, arabinose, and glutamate did not change from the initial value of 5.5 even though rhizobial numbers increased from 10⁴ to 10⁹ cells.ml^–1. Even at a buffer concentration of 15.3 mM, pH only increased from 5.5 to 5.6. There was no effect of the buffer on rhizobial growth.     

Principles and strategies in breeding for higher salt tolerance

Summary Salinity is an environmental component that usually reduces yield. Recent advances in the understanding of salt effects on plants have not revealed a reliable physiological or biochemical marker that can be used to rapidly screen for salt tolerance. The necessity of measuring salt tolerance based upon growth in saline relative to non-saline environments makes salt tolerance measurements and selection for tolerance difficult. Additionally, high variability in soil salinity and environmental interactions makes it questionable whether breeding should be conducted for tolerance or for high yield. Genetic techniques can be used to identify the components of variation attributable to genotype and environment, and the extent of genetic variation in saline and nonsaline environments can be used to estimate the potential for improving salt tolerance. Absolute salt tolerance can be improved best by increasing both absolute yield and relative salt tolerance.     

Salinity tolerance of Mytilocypris henricae (Chapman) (Crustacea,Ostracoda)

Salinity tolerance, and the effects of temperature upon it, of the Australian ostracod Mytilocypris henricae (Chapman) was determined in direct transfer experiments using adults. Animals were subjected to a combination of 11 salinities (ranging between 0.0 g · 1^–1 and 45.0 g · 1^–1) and 4 temperatures (10, 15, 20 and 25 °C). Survival was analysed using two statistical techniques: the logit linear model and the proportional hazards model. Results show that both salinity and temperature have a significant effect on survival, but there is no significant interaction between temperature and salinity.     

Salt tolerance in the halophyte Suaeda maritima L. Dum.

Osmotic potentials and individual epidermal cell turgor pressures were measured in the leaves of seedlings of Suaeda maritima growing over a range of salinities. Leaf osmotic potentials were lower (more negative) the higher the salt concentration of the solution and were lowest in the youngest leaves and stem apices, producing a gradient of osmotic potential towards the apex of the plant. Epidermal cell turgor pressures were of the order of 0.25 to 0.3 MPa in the youngest leaves measured, decreasing to under 0.05 MPa for the oldest leaves. This pattern of turgor pressure was largely unaffected by external salinity. Calculation of leaf water potential indicated that the gradient between young leaves and the external medium was not altered by salinity, but with older leaves, however, this gradient diminished from being the same as that for young leaves in the absence of NaCl, to under 30% of this value at 400 mM NaCl. These results are discussed in relation to the growth response of S. maritima.     

Extension growth and cold hardening of young ‘Valencia’ orange trees sprayed with AMO-1618

Rate of extension growth, as measured by height, of 2-month-old Valencia orange trees (Citrus sinensis (L.) Osbeck) on rough lemon rootstock (C. limon Burm. f.) was reduced to 0.5 mm from 5.0 mm day^–1 with 0.1% (w/v) sprays of the growth retardant AMO-1618 (4 hydroxy-5-isopropyl-2-methyl phenyl trimethyl-ammonium chloride, 1 piperdine carboxylate) every 2 weeks during 11 weeks under natural daylight in a glasshouse. Trees sprayed with AMO-1618 were 10-fold shorter, more compact in appearance, and leaves were greener and more oval shaped than those on untreated trees. There was no chemical burn. AMO-1618-sprayed trees were more cold hardy than untreated trees during controlled-temperature, cold-hardening regimes. Alone, AMO-1618 had no effect on freeze tolerance at -5.5° C. AMO-1618 also was associated with greater tree tolerance to freeze injury determined by O₂ uptake in Valencia leaves to as low as -6.7° C.This paper reports the results of research only. Mention of a trademark of a proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable.     

Sulphide tolerance in coastal halophytes

The effect of sulphide on the growth of several species of salt-marsh plants was investigated. Relative growth rates were significantly reduced in two upper-marsh species, Festuca rubra and Atriplex patula, and in the lower-marsh species Puccinellia maritima. However the growth of Salicornia europaea, a species frequently associated with sulphide-containing sediments, was unaffected. In a separate experiment the wide ranging halophyte Aster tripolium, also appeared to be tolerant of sulphide at a concentration frequently encountered in salt marshes. Sulphide pretreatment inhibited the activity of two metallo-enzymes, polyphenol oxidase and external phosphatase, in plants from the upper marsh, but had no effect on enzymes from P. maritima or S. europaea. The rate of respiration by root tissue was significantly reduced in all of the species investigated but whereas the uptake of ⁸⁶rubidium was markedly inhibited in the other three species, uptake by S. europaea showed a significant stimulation. Similarly, whereas sulphide-grown plants of F. rubra, A. patula and P. maritima had a considerably reduced tissue iron content, the total iron concentration in S. europaea tissues was comparable to that of the controls. When the sulphide-tolerant species A. tripolium was grown in sulphide-containing media there was no significant effect on the tissue concentration of any of the elements investigated. These results are discussed in relation to possible mechanisms of sulphide toxicity and resistance.     

Adaptive respiratory significance of organophosphates (ATP & GTP) in air-breathing fishes

The ATP and GTP contents of erythrocytes of Protopterus annectens, Polypterus senegalus and Clarias lazera were assessed in relation to maturation and hypoxia. The steady state normal concentrations of ATP were: 446, 316 and 475 µM/100 ml and those of GTP were 286, 93 and 85 µM/100 ml in Protopterus, Polypterus and Clarias, respectively. The level of ATP decreased and that of GTP increased with increments in body growth, especially during development of the pulmonary organs. The concentration of GTP also increased progressively with hypoxia (O₂: 7.4 to 3.6 mg/l); the level ATP remained almost unaltered. The ratio of GTP increased markedly with increased hypoxia particularly in the adaptive respiratory range of aquatic oxygen concentrations (6.5–4.8 mg/l) when the fish were forced to depart from branchial respiration and became reliant on air-breathing.     

Toxicity oft-butylhydroperoxide in hepatocyte monolayers exposed to hypoxia and reoxygenation

Summary Inasmuch as it is known that the toxicity of anesthetic agents is potentiated by hypoxia and that the reductive metabolism of these agents results in the formation of lipid hydroperoxides, we investigated the toxicity of hydroperoxides under low-oxygen concentrations. We found that hypoxia exacerbates the toxicity oft-butyl hydroperoxide, shifting the dose-response curve oft-butyl hydroperoxide vs. lysis of hepatocytes approximately an order of magnitude to the left. Furthermore, although at the end of a 4-h exposure to 0.5% O₂ hepatocyte monolayers seemed normal by three indices (release of⁵¹Cr and serum glutamate transaminase or exclusion of trypan blue), they were completely lysed after an additional 20 h reoxygenation at 20%. O₂. In contrast, monolayers exposed to 2% O₂ for 4 h seemed normal after 20 h reoxygenation. However, cells exposed to both a subtoxic dose of hydroperoxide and 4 h of 2% O₂, although seeming healthy at the end of the hypoxic period, were completely lysed within 20 h after reoxygenation. The study was supported by grant OH 00978 from the National Institutes for Occupational Safety and Health, Atlanta, Georgia.     

Density fluctuations in populations (1982–1986) and biological observations ofPotamopyrgus Jenkinsi in two trophically differing lakes

The hydrobiid snailPotamopyrgus jenkinsi (E.A. Smith), characterized by parthenogenesis and ovovivipary, was quantitatively sampled monthly between June, 1982, and December, 1986, on sandy bottoms in the shallow zones of the meso-oligotrophic Lake Maarsseveen I and the eutrophic Lake Maarsseveen II. The snail demonstrated a very clumped distribution in both lakes. The mean numbers of juveniles and adults taken together fluctuated strongly. Organisms in Lake I showed relatively high densities (up to 25,000 per m²) in 1982, followed by a sudden drop to values approaching zero in December, 1982, with a subsequent rapid increase in densities, fluctuating between 2,000 and 200 per m². In Lake II, densities of snails fluctuated between 13,000 and 300 per m² with decreases in the spring of 1985 and 1986. The various types of decreases in the lakes are extensively discussed, but no explanation is presently available. The reduction in Lake I was of catastrophic proportions, but the speed of recovery of the population was remarkable.Floating was observed only in Lake I, and only during the occurrence of the highest densities on the sediment. Burrowing behaviour was very common, but strongly suppressed under an uninterrupted dark regime. A shift of temperature from 15 to 22°C had the same effect. A number of submerged macrophyte species from Lake I proved to attractP. jenkinsi in the absence of sandy substrate, though these plants were only covered by the snail during the period of the highest densities in 1982. Temperatures of 20°C or lower were well tolerated, unlike temperatures of 25 and 30°C. Growth was distinct at 10, 15 and 20°C. Keeled individuals were encountered in much higher numbers in Lake I than in Lake II.