High temperature effects on photosynthesis and water relations of grain legumes

Effects of high temperature on photosynthesis, and its interaction with water relations in common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), faba bean (Vicia faba), and five cultivars of field pea (Pisum sativum) were investigated. Responses of all species were compared at 20/15, 30/15, or 30/25 °C day/night, and cowpea and pea were compared at 20/15 and 30/25 °C under well-watered and limited-water conditions. Response of pea to 20/15 and 30/25 °C during flowering was ascertained, and sensitivity of the photosystem of pea and faba bean to 40 °C was determined.High temperature decreased chlorophyll variable fluorescence (F_v), a measure of injury to photosynthesis, in all species except cowpea, which was highly tolerant. Leaf chlorophyll and most measures of growth were favored by high day temperature but not by high night temperature, and photosynthetic rates were enhanced by high temperatures that increased leaf chlorophyll and nitrogen (N) contents. High temperature diminished growth less than water deficiency and increased water use of all three species but only lowered the water potential in faba bean. Water deficiency generally decreased growth, water use, and water potential more at 30/25 °C than at 20/15 °C. Stress from high temperature during flowering of pea decreased all components of yield at maturity, particularly at nodes that flowered latest. Whole-chain photosynthetic activity in thylakoids of pea, faba bean, and wheat (Triticum aestivum) were equally sensitive to high temperature, suggesting that Photosystem Il was the most labile component. The results show that high temperature affects photosynthesis, growth, and water relations of grain legumes, and sensitivity to the stress differs among species and genotypes.     

Nickel tolerance and copper - nickel co - tolerance in Mimulus guttatus from copper mine and serpentine habitats

Previous work on M. guttatus suggested that nickel tolerance in copper mine populations may also be given by the genes for copper tolerance. It has been shown that copper tolerance in M. guttatus is controlled by a single major gene, plus a number of minor genes (or modifiers) which elevate copper tolerance. Crosses between nickel tolerant individuals from three families and non - tolerants showed that nickel tolerance in M. guttatus is heritable. In order to study the effects of the major copper tolerance gene on copper - nickel co - tolerance in M. guttatus, homozygous copper tolerant and non - tolerant lines were screened against nickel. Significant differences occur between these lines for copper, but were not found when analysed for nickel, indicating that copper - nickel tolerance is not governed by the major gene for copper tolerance. To test whether the minor genes for copper have a pleiotropic effect on nickel tolerance, five selection lines derived from three copper mines (Copperopolis, Penn and Quail) in Calaveras county, California, which vary in degree of tolerance to copper, by the presence or absence of minor copper genes, were also screened against nickel. Two out of three of the lines from Copperopolis showed elevated tolerance to nickel, but two further selection lines derived from Penn and Quail copper mines gave no indication of increased nickel tolerance. These results suggest that the minor genes for copper do not give tolerance to nickel. This was confirmed by the screening of modifier lines, in which modifiers for differing degrees of copper tolerance were inserted into a non - tolerant background. Genotypes possessing fewer copper modifiers yielded higher nickel tolerance than those genotypes which have a greater number of modifiers. Thus nickel tolerance in this species is heritable and under the control of different genes to those producing copper tolerance.     

Do ectomycorrhizal fungi exhibit adaptive tolerance to potentially toxic metals in the environment ?

The effects of potentially toxic metals on ectomycorrhizal (ECM) fungi and their higher plant hosts are examined in this review. Investigations at a species and community level have revealed wide inter- and intraspecific variation in sensitivity to metals. Adaptive and constitutive mechanisms of ECM tolerance are proposed and discussed in relation to proven tolerance mechanisms in bacteria, yeasts and plants. Problems with methodology and research priorities are highlighted. These include the need for a detailed understanding of the genetic basis of tolerance in the ECM symbiosis, and for studies of ECM community dynamics in polluted sites.     

Resistance to photoinhibition of photosystem II and catalase and antioxidative protection in high mountain plants

In leaves of three alpine high mountain plants, Homogyne alpina, Ranunculus glacialis and Soldanella alpina, both photosystem II (PSII) and the enzyme catalase appeared to he highly resistant to photoinactivation under natural field conditions. While the Dl protein of PSII and catalase have a rapid turnover in light and require continuous new protein synthesis in non-adapted plants, little apparent photoinactivation of PSII or catalase was induced in the alpine plants by translation inhibitors or at low temperature, suggesting that turnover of the Dl protein and catalase was slow in these leaves. In vitro PSII was rapidly inactivated in light in isolated thylakoids from H. alpina and R. glacialis. In isolated intact chloroplasts from R. glacialis, photoinactivation of PSII was slower than in thylakoids. Partially purified catalase from R. glacialis and S. alpina was as sensitive to photoinactivation in vitro as catalases from other sources. Catalase from H. alpina had, however, a 10-fold higher stability in light. The levels of xanthophyll cycle carotenoids, of the antioxidants ascorbate and glulathione, and of the activities of catalase, superoxide dismutase and glutathione reductase were very high in S. alpina, intermediate in H. alpina, but very low in R. glacialis. However, isolated chloroplasts from all three alpine species contained much higher concentrations of ascorbate and glutathione than chloroplasts from lowland plants.     

A model for the impact of herbicide tolerance on the performance of oilseed rape as a volunteer weed

The introduction of genetically modified, herbicide-tolerant, oilseed rape into the agricultural environment will have ramifications beyond weed control of the crop. Herbicide-tolerant rape will undoubtedly become part of established volunteer weed populations that occur in many cereal rotations, but its longevity in these populations and its impact as a weed and contaminant of future oilseed rape crops is uncertain. A life cycle model of volunteer oilseed rape was therefore constructed, incorporating existing information on physiological processes such as emergence pattern, longevity of buried seed, death rates of various structures and flowering and seeding as functions of density. The model was designed to allow interaction with control factors such as harvesting efficiency, herbicide treatment, ploughing and the sequence of crops in the rotation. Many of the physiological parameters (including seed decay rates, fecundity at high density) are uncertain, simply through lack of information in the appropriate context. Other parameters such as harvesting efficiency and herbicide kill rates, are inherently variable in farming. Accordingly, a Monte-Carlo approach, in which the model was run many times with different random realisations of parameter sets, was used to expose factors to which the seedbank was sensitive. Sets of 1250 realisations were compared for each of two extreme conditions: where herbicide could be used according to current intensive farming practice and where it was not an option (representing total herbicide tolerance). Modelled seedbank numbers after 5 yr ranged from 10^-3to 10⁴m^-2, realistic values found in arable soils. The use of herbicide, together with efficient harvesting of seed, clearly has an important suppressive effect on the oilseed rape seedbank, keeping it lower than 10²m^-2(a typical sowing rate) after 5 yr in more than 80% of realisations. In the absence of herbicide, seedbanks were invariably greater, but their absolute value depended strongly on harvesting efficiency and the extent to which high density of plants suppressed fecundity. Analysis of the time series from the simulations showed that the seedbank levels fluctuated by orders in magnitude from year to year in the absence of herbicide use. The sensitivity analysis of the life-cycle model led to the development of a simplified model for the seedbank dynamics. The model shows that the essential features of the dynamics result from an interaction between density-dependent fecundity and the perturbations due to management. Therefore predictions of the effect of herbicide tolerance on seedbank dynamics are highly uncertain without knowledge of the density dependence of fecundity. Furthermore, the sensitivity to management practices suggests that seedbank levels will be substantially more difficult to control if the efficacy of herbicide is compromised. It is concluded that the model and Monte-Carlo approach have many potential uses in exploring the effects of management, cultivar physiology and the nature of the transgenes.     

Relationship Between Effect of Ethanol on Proton Flux Across Plasma Membrane and Ethanol Tolerance, inPichia stipitis

Pichia stipitisefficiently converts glucose or xylose into ethanol but is inhibited by ethanol concentrations exceeding 30 g/L. InSaccharomyces cerevisiae, ethanol has been shown to alter the movement of protons into and out of the cell. InP. stipitisthe passive entry of protons into either glucose- or xylose-grown cells is unaffected at physiological ethanol concentrations. In contrast, active proton extrusion is affected differentially by ethanol, depending on the carbon source catabolized. In fact, in glucose-grown cells, the H⁺-extrusion rate is reduced by low ethanol concentrations, whereas, in xylose-grown cells, the H⁺-extrusion rate is reduced only at non-physiological ethanol concentrations. Thus, the ethanol inhibitory effect on growth and ethanol production, in glucose-grown cells, is probably caused by a reduction in H⁺-extrusion. Comparison of the rates of H⁺-flux with the relatedin vitroH⁺-ATPase activity suggests a new mechanism for the regulation of the proton pumping plasma membrane ATPase (EC 3.6.1.3) ofP. stipitis, by both glucose and ethanol. Glucose activates both the ATP hydrolysis and the proton-pumping activities of the H⁺-ATPase, whereas ethanol causes an uncoupling between the ATP hydrolysis and the proton-pumping activities. This uncoupling may well be the cause of ethanol induced growth inhibition of glucose grownP. stipitiscells.     

Stress co-tolerance and trehalose content in baking strains of Saccharomyces cerevisiae

Fourteen wild-type baking strains of Saccharomyces cerevisiae were grown in batch culture to true stationary phase (exogenous carbon source exhausted) and tested for their trehalose content and their tolerance to heat (52°C for 4.5 min), ethanol (20% v/v for 30 min), H₂O₂ (0.3 M for 60 min), rapid freezing (−196°C for 20 min, cooling rate 200°C min⁻¹), slow freezing (−20°C for 24 h, cooling rate 3°C min⁻¹), salt (growth in 1.5 M NaCl agar) or acetic acid (growth in 0.4% w/v acetic acid agar) stresses. Stress tolerance among the strains was highly variable and up to 1000-fold differences existed between strains for some types of stress. Compared with previously published reports, all strains were tolerant to H₂O₂ stress. Correlation analysis of stress tolerance results demonstrated relationships between tolerance to H₂O₂ and tolerance to all stresses except ethanol. This may imply that oxidative processes are associated with a wide variety of cellular stresses and also indicate that the general robustness associated with industrial yeast may be a result of their oxidative stress tolerance. In addition, H₂O₂ tolerance might be a suitable marker for the general assessment of stress tolerance in yeast strains. Trehalose content failed to correlate with tolerance to any stress except acetic acid. This may indicate that the contribution of trehalose to tolerance to other stresses is either small or inconsistent and that trehalose may not be used as a general predictor of stress tolerance in true stationary phase yeast. Received 10 October 1995/ Accepted in revised form 10 September 1996     

Seed Size,Seed Germination,and Seedling Survival of Brazilian Tropical Tree Species Differing in Successional Status1

Seed germination and seedling establishment patterns have been used to classify species as shade tolerant or intolerant. The main objective of this research was to investigate, under controlled conditions, seed germination of species from different successional positions as well as to follow seed germination and seedling survival under natural shade in the field. The species studied were Solarium granuloso‐leprosum, Trema micrantha, Cecropia pachystachya, Croton piptocalyx, Bauhinia forficata subsp. pruinosa. Senna macranthera, Schizolobium parahyba, Piptadenia gonoacantha, Chorisia speciosa, Pseudobombax grandiflorum, Ficus guaranitica, Esenbeckia leiocarpa, Pachystroma longifolium, Myroxylon peruiferum, and Hymenaea courbaril. Field trials were carried out at Santa Genebra Municipal Reserve, Campinas, SP, Brazil, at the forest edge and in the understory. No significant correlations were detected between successional status and seed size or seed water content. Light‐regulated germination was present only in small‐seeded species. In field experiments, most species, including the light‐sensitive ones, were able to germinate under the canopy, where a low red/far‐red ratio predominates. Most species, mainly those of early‐ and intermediate successional positions, presented low seedling survival rates under shade. Myroxylon peruiferum was the most shade tolerant species, while 5. granuloso‐leprosum, C. speciosa, P. gonoacantha, F. guaranitica, T. micrantha, and 5. parahyba were the most shade intolerant. These latter species showed little or no survival under the shade conditions.