Polyamines (PAs) and the cell wall have important roles in plant morphogenesis. An interaction between cell wall components (pectic substances) and polyamines is known and inhibition of polyamine biosynthesis induces inhibition of some morphogenic processes. This is the case of rhizogenesis in tobacco (Nicotiana tabacum L.) thin layers. This paper investigates whether inhibition of polyamine biosynthesis induces modifications in the structure, shape and size of the primary cell walls in tobacco thin layers cultured on a rhizogenic medium, and whether polyamines (putrescine and spermidine) administered in combination with their corresponding inhibitors DL-α-difluoromethylornithine +DL-α-difluoromethylarginine (DFMO+DFMA), cyclohexylamine (CHA), methylglyoxal-bis(guanylhydrazone) (MGBG) restore cell wall characteristics. In treatments with polyamine inhibitors, cell hypertrophy occurred in the lowermost layer of the explant in contact with the medium. Many unusual features were observed in the walls of the hypertrophic cells: an amorphous structure, loosening of the fibrillar component; detachment between contiguous cells, lysis of wall components and an uneven thickness often giving a wavy appearance (in transverse walls). The inhibitors reduced cell wall thickness, and caused a weak positive PATAg reaction for polysaccharides. Polyamines restored cell wall thickness and, in general, the other wall features. Our results show that polyamines are necessary for maintaining cell wall characteristics by strengthening the links between cell-wall components.

We have used a pulsed u.v. laser to ablate the cell wall of the filamentous fungus Aspergillus niger van Tiegh., and expose the plasma membrane at defined points along the hypha. Using the patch clamp technique, giga ohm seals (up to 20 GΩ) and recordings of plasma membrane ion channels were obtained. We describe, for the first time in fungi, a 43 pS plasma membrane anion efflux channel. Its potential role in cell signalling and pH homeostasis is discussed.

Two parameters were applied to estimate the degree of stress induced by exposure of the lichen Ramalina duriaei (De Not.) Bagl. to air pollution in urban-industrial sites in Israel. Changes in the spectral reflectance response of the thallus and in the production of stress-ethylene, were compared with the concentration of sulphate-S, V, Ni, K, Pb, P, Cu, Cr, Fe, Mn and Mg in either in situ or in transplanted thalli of the lichen.

The concentrations of Cu, Mg, Fe, Ni, Pb, V, Cr, Mn and sulphate-S in in situ thalli collected in a nature reserve in an industrial town (Ashdod, SW Israel) were higher than those detected in in situ thalli collected in a forest (HaZorea Forest) in the north-east of Israel. The high concentrations of these mineral elements in R. duriaei from the nature reserve coincided with a high rate of production of stress-ethylene and with a low normalized difference vegetation index (NDVI) indicating that changes in the spectral reflectance response relate to damage to the chlorophyll.

Lichens collected in the unpolluted forest in February 1994, either resuspended in the same site or transplanted in nine sites in the Ashdod region, and retrieved in November of the same year, contained a higher concentration of sulphate-S, Pb, Cu, Ni, V and Cr in the urban-industrial sites than in most of the rural localities. Statistical analysis revealed a positive correlation between the amount of ethylene produced by R. duriaei and the concentration of V and Ni in the same thalli.

To test the integrity of the ethylene-producing system, lichens were soaked in either 5 mM or 10 mM FeCl2 at pH 3·7. Thalli exposed to a very polluted environment produced less ethylene after this treatment. The NDVI correlated positively with the concentration of K in the thallus but negatively with the concentration of Mn, Ni, Pb and sulphate-S in the same material.

It may be concluded that the in situ thalli of R. duriaei in the nature reserve are severely stressed and possibly endangered by the pollution produced by the combustion of heavy fuel oil in the local power plant and oil refineries and by acid rain.

Changes in various cell functions were examined during a shift of the cyanobacterium Anabaena sp. strain PCC7120 to acidic external pH (pHex) in the presence and absence of added calcium. In the presence of 0·25 mM Ca (the standard Ca concentration of the growth medium), growth and O2 evolution were inhibited at pH values lower than 6. The cyanobacterium was unable to maintain a relatively constant internal pH (pHi) at pH 6 and below, which led to acidification of the cytoplasm. In the absence of Ca, the acidification found at acid pH values was even more pronounced. The elimination of Ca did not affect pHi at pHex of 6·5 and above. Increased acidification of the internal cell contents correlated well with a general impairment of growth in Ca-deficient cells exposed to external acid pH values. On the other hand, Ca enrichment of cells grown under acidic conditions resulted in a significant improvement of several physiological processes. The protein pattern of cell extracts of Anabaena sp. strain PCC7120 was altered by acidity. The most significant modifications of the protein profiles induced at low pH were not evident in the presence of high concentrations of Ca. Increasing concentrations of Ca allowed Anabaena sp. strain PCC7120 to perform better at lower pH.

The aim of this study was to quantify the long-term effects of Al in solution on mineral ion uptake and associated H+ release by the roots of maize cultivated in conditions compatible with field data. Two maize (Zea mays L.) cvs of differing sensitivity to Al were compared. The culture was conducted in hydroponic conditions for culture periods of 2–5 d in the presence of 0–30 μM Al. Proton fluxes were localized along the roots using a videodensitometry method with bromocresol green on agarose gel.

Aluminium reduced the uptake of anions, particularly NO3−, whereas the uptake of K+ and NH4+ was unaffected. These effects were accompanied by an increase in net H+ release which was quantitatively comparable with the reduction in NO3− uptake. The reduction in NO3− uptake and the concomitant increase in H+ release increased with the quantity of Al accumulated in the roots, which was itself dependent on the concentration of Al in solution. The Al-sensitive cultivar bound more Al to its roots than the Al-tolerant one; the reduction in NO3− uptake and the increase in H+ release were also greater in the Al-sensitive cv. Dye indicator videodensitometry showed that the increased H+ release was general all along the roots.

These results led us to specify the relation between the Al deposition in roots, the reduction in NO3− uptake and the stimulation in rhizosphere acidification by the plants. They show that, with maize, Al induces an inhibition in NO3− uptake and an increase in net H+ release in a 1[ratio ]1 ratio. These concomitant effects suggest that inhibition in NO3−/OH− exchange unmasks active H+ excretion which is otherwise insensitive to Al. Both these effects are closely related to the Al content in roots expressed per unit root length.

Birch (Betula pendula Roth) seedlings were grown under enhanced u.v.-B radiation and simulated forest-soil conditions, after which individual secondary metabolites were determined in the leaves. It was found that not all of the u.v.-absorbing secondary metabolites of the seedlings responded to supplementary u.v.-B radiation. Under increased u.v.-B radiation, significant increases in concentration were observed only for the major flavonoid, quercitrin, the minor flavonoid, myricetin-3-galactoside, and for chlorogenic acid. On the other hand, 3,4′dihydroxypropiophenone-3-β-D-glucopyranoside decreased under u.v.-B irradiation. The concentration of phenolic compounds in the leaves changed during the growing season (between two harvests) but this change was not related to u.v.-B enhancement. A low availability of mineral nutrients did not impair the capacity of the seedlings to accumulate u.v.-protecting phenolic compounds under increased u.v.-B radiation. The growth conditions used might have affected the intracellular concentrations of secondary metabolites, and thus furnished the birch seedlings with an increased tolerance of u.v.-B radiation. These findings point to the significance of certain phenolic components in the protection of deciduous trees against u.v.-B radiation.

In many plants, mucilage permeates the interface between root and soil, yet little is known about its physical properties or its influence on the physical properties of the rhizosphere. Mucilage was collected from 3–4-d-old, axenically-grown maize (Zea mays L. cv. Freya) and lupin (Lupinus angustifolius L. cv. Merrit) seedlings. Surface tension and viscosity were measured over a range of mucilage hydration, and neutral sugar analyses of the hydrolysed mucilages were obtained by gas chromatography. Surface tension of both maize and lupin mucilage was reduced to ∼48 mN m−1 at total solute concentrations >0·7 mg ml−1, indicating the presence of powerful surfactants. Mucilage viscosity increased with increasing solute concentration and decreasing temperature. At a total solute concentration of 0·7 mg ml−1, the viscosity of maize mucilage at 20°C was 2·1 mPa s (approx. double that of pure water), increasing to 3·3 mPa s at 5°C. Both maize and lupin mucilage showed viscoelastic behaviour. The major component of maize mucilage was found to be glucose, but in lupin it was fucose.

The surface tension and viscosity results support the idea that mucilage plays a major role in the maintenance of root–soil contact in drying soils. As surface tension decreases, the ability of the mucilage to wet the surrounding soil particles becomes greater. Also, as viscosity and elasticity increase, the resistance to movement of any soil particles in contact with the mucilage increases, a degree of stabilization of the rhizosphere structure is achieved and hydraulic continuity is maintained. It is unclear whether the surfactant is actively secreted by the root or is present simply as a result of leakage from root cells.

Environmental effects on the concentration of photosynthetic pigments in micro-algae can be explained by dynamics of photosystem synthesis and deactivation. A model that couples photosystem losses to the relative cellular rates of energy harvesting (light absorption) and assimilation predicts optimal concentrations of light-harvesting pigments and balanced energy flow under environmental conditions that affect light availability and metabolic rates. Effects of light intensity, nutrient supply and temperature on growth rate and pigment levels were similar to general patterns observed across diverse micro-algal taxa. Results imply that dynamic behaviour associated with photophysical stress, and independent of gene regulation, might constitute one mechanism for photo-acclimation of photosynthesis.

Pollen counting is an important element of research in pollination, and the majority of current methods involve manual counting. An image-processing technique has been developed for accurate counting and sizing of small particles, and this was tested on almond pollen grains. Our automatic process was found to be several times faster than manual counting and more accurate, with an average error of only 3%. Because of its simplicity, it is an attractive tool for research on such topics as pollen viability or germination. It was found that in the methods using vials there were ‘residues’ of c. 17% on the vial walls and on the handling tools. In addition, the first drop from each vial contained, on average, 1·65 times more grains than the average number of grains in all drops, whereas the last drop from each vial contained fewer grains than the average. This phenomenon was correlated with the non-uniform pollen distribution in the suspension. An automatic counting system is therefore, recommended, to avoid the problem, otherwise a calibration procedure should be used that accounts for both the residues on the tools and the non-uniformity of contents of sample drops.

Geographically separated populations of Plantago major L. differ in ozone resistance, and this is correlated with the exposure to ozone at the location of each population. In addition, two populations of P. major have been demonstrated to show an increase in ozone resistance after summers when ozone concentrations were high. However, if evolution of ozone resistance has occurred in the field there must be appropriate heritable genetic variation and this must be demonstrated.

In the present study, artificial selection for ozone resistance and sensitivity was imposed on a resistant (‘Lullington Heath’) and sensitive (‘Bush’) population of P. major. Artificial selection is an efficient means of demonstrating additive genetic variance for a character. Selection was based on 2 wk growth in ozone (70 nl O3 l−1 for 7 h d−1), and selected lines were tested for ozone resistance under both short and long term ozone exposures. Changes in ozone resistance were demonstrated for each population. On the basis of a 2-wk screening test, selection from the initially sensitive Bush population led to a line that was significantly more resistant to ozone, but it was not possible to select a line with greater sensitivity than the original population. Conversely, selection from the initially resistant Lullington Heath population led to a line with increased sensitivity but not to a line with increased resistance. Differences in ozone resistance between the selected lines were maintained over the long term and were reflected in growth and seed production at the final harvest. Net assimilation rate, stomatal conductance and leaf pigments were measured. In both populations the lines selected for sensitivity showed a greater effect of ozone on net assimilation rate. Ozone had a minor effect on chlorophyll content in the Lullington Heath sensitive line but tended to increase carotenoid concentrations. However, this effect on carotenoids was not related to ozone resistance.

The experiment demonstrated that ozone resistance in P. major is heritable. The response to selection reported here supports previous evidence from field collections of a rapid evolution of ozone resistance.

Anti-transpiration and anti-growth activities of xylem sap were studied for maize, sunflower, cotton and castor bean, which were subjected to several stress treatments: soil drying, flooding and salinity. All samples of xylem sap showed an increased concentration of proteins when plants were either soil-dried, salt-treated or flooded. The protein transportation flux in xylem sap, i.e. the product of protein concentration and volume flux, was also increased as a result. Electrophoresis using SDS–PAGE analysis showed that xylem proteins were of variable size. When samples of xylem sap were used to feed detached leaves or shoots in a bioassay system for their anti-transpiration and anti-growth activities, such xylem proteins in their original concentrations apparently showed neither direct inhibition nor enhanced effects of ABA. All samples of xylem sap from plants subjected to different stresses showed anti-transpiration and anti-growth activities that could be fully accounted for by their ABA concentration. In cases where such activities were more than could be explained by the ABA concentrations, filtration with a 0·20 μm microfilter removed the discrepancies.

We examined the importance of seed size in the early establishment of seedlings of four cotyledonous species restricted to nutrient-impoverished soils in south-western Australia. Experimentally removing cotyledons from seedlings increased mortality and reduced root-penetration, growth rate and final weight of plants after 12 wk, in proportion to seed size. The impact of removal of the cotyledons was least in the smallest-seeded, Eucalyptus loxophleba Benth., grown in the more fertile of two soils, and greatest in the largest-seeded, Hakea psilorrhyncha R. M. Barker, whose growth was otherwise unaffected by soil type. In the smallest-seeded species, cotyledon content of most mineral nutrients increased over time, especially in the more fertile soil, while chlorophyll content showed some decrease by the end of the experiment. In the other species, most nutrients (especially N, P, K and Cu in the less fertile soil) were translocated from the cotyledons to the growing plant, and chlorophyll content declined markedly. The translocated N, P, K, Mg and Cu in these species made up a substantial part of the total plant content by 12 wk after germination, while total Ca and Fe tended to increase in the cotyledons via substantial soil uptake. The results indicate, contrary to reports for some other species, that the cotyledons have an important nutritional function in the early establishment of seedlings in these species. The results also show that, in the larger-seeded species, young seedlings rely to a greater extent on nutrient support from the cotyledons than from the soil. We propose that large seeds might be an adaptation for enhancing establishment in nutrient-poor soils.

Birch cuttings (Betula pendula Roth) were grown in a sand-culture system with two concentrations (0·05, HF and 0·005%, LF) of fertilizer containing macronutrients and micronutrients, and were exposed to 90/40 nl l−1 O3 (day/night) and <3 nl l−1 O3 (control) for one growing season in the field fumigation chambers at Birmensdorf (Switzerland). Leaves of different ages were analysed for gas exchange, contents of chlorophyll, protein, and for metabolites as well as enzyme activities of carbohydrate metabolism.

Ozone reduced net photosynthesis and chlorophyll contents in mature leaves of both fertilization treatments, whereas that of protein was only reduced in high-fertilized plants (HF). However, net photosynthesis, chlorophyll, and protein increased in young leaves of low-fertilized plants (LF). The effects of ozone on enzyme activities of carbohydrate metabolism were most pronounced in leaves of LF plants. Specific activities of the sucrose-cleaving enzymes, sucrose synthase and alkaline invertase, were induced, whereas acid invertase was unchanged. Extractable activity of sucrose phosphate synthase, which is a key enzyme of sucrose synthesis, was reduced. Levels of fructose 2,6-bisphosphate, an inhibitor of sucrose synthesis, were increased in leaves of O3/LF plants, but reduced in O3/HF plants. In addition, activities of enzymes involved in starch metabolism, ADP-glucose pyrophosphorylase and starch phosphorylase, were lowered in ozone-treated samples and the ratio of ATP[ratio ]ADP was increased.

It is concluded that chronic ozone exposure leads to an inhibition of sucrose synthesis and favours sucrose degradation. This effect is modulated by the nutrient status of the plants, indicating higher O3 tolerance in HF plants. Furthermore, as the metabolic responses in the ozone-treated samples resemble very closely those observed under end-product inhibition of photosynthesis, we assume that the O3 effect is mainly due to reduced photosynthate export.

Longleaf pine (Pinus palustris Mill.) seedlings were exposed to two concentrations of atmospheric CO2 (365 or 720 μmol mol−1) and two levels of N (0·02 or 0·20 mg N g−1 soil yr−1) within open-top chambers for 20 months. Seedlings were adequately watered for 19 wk to ensure seedling establishment, after which two water-stress treatments (target values −0·5 or −1·5 MPa xylem pressure potential) were implemented. Fine-root samples were collected in July and November 1993, and in March and November 1994. Ectomycorrhizal and non-mycorrhizal short roots per unit length of fine root were quantified. The percentage of ectomycorrhizal short roots and numbers of ectomycorrhizas per unit root length were higher for seedlings grown with elevated CO2, low N and adequate water. Interactions among main treatment variables demonstrated higher percentages of ectomycorrhizal short roots, fine root length per seedling, and total numbers of ectomycorrhizas per seedling for plants grown with high CO2 (compared with ambient) or adequate water (compared with water stress) only under high N conditions. Increased fine-root length and ectomycorrhizal colonization under elevated CO2 resulted in higher (almost double) numbers of ectomycorrhizas per seedling at each sampling.

The identity of individual ectomycorrhizas, root colonization patterns and early growth responses of interconnected Scots pine (Pinus sylvestris L.) seedlings were investigated following interactions between local genets of Suillus bovinus (L. ex Fr.) O. Kuntze (SBK4b and SBK5b) and S. variegatus (Swartz ex Fr.) O. Kuntze (SVK3b) and different host–genotype combinations. Three equidistant 39-d-old seedlings, in pots that contained sterile N-limited nursery soil, were each inoculated with one of the three genets in the multiple inoculation treatment (MIT). Single inoculation treatments (SITs), involving inoculation of only one seedling in the triad with one of the three genets, and a similarly configured uninoculated treatment (UIT), were also prepared for comparative analysis. All seedling roots in the inoculated treatments, except for one SIT/SBK4b combination, hosted large numbers (>150) of Suillus-type ectomycorrhizas after 23–25 wk growth without additional fertilization. Esterase (EST) isozyme analysis of individual ectomycorrhizas from all SIT and MIT combinations enabled efficient interspecific and intraspecific typing of fungal (genet) colonization (89 and 72%, respectively) and identification of host genotype variation (Z locus polymorphism) at a lower rate (51%). Species, but not S. bovinus genet, typing within randomly sampled individual ectomycorrhizas from selected SITs was successful (50–70%) following PCR/RFLP analysis of diagnostic sequences of fungal rRNA genes. In the SITs, only the inoculated fungal genet was detected in ectomycorrhizas on all three seedlings. Roots were predominantly colonized by SBK4b in one, and SBK5b in three, of the MIT combinations, although ectomycorrhizas of the former genet were detected at low frequencies on nearly all seedlings. In the remaining MIT combination, both SBK4b and SVK3b were found to co-dominate as ectomycorrhizas on the seedling roots. Small numbers of the latter genet were detected in ectomycorrhizas of two SBK5b-dominated MIT combinations. However, no significant trends in host-mycorrhiza interactions were detected using a log–linear analysis. Compared with the UIT, significant positive mycorrhizal plant growth responses, particularly increased needle length, were recorded in all the heavily colonized seedlings in most SIT and all MIT combinations. Intermediate seedling growth was restricted to the one SIT/SBK4b combination where seedlings supported limited numbers of ectomycorrhizas. The general host-fungal colonization patterns observed provide further below-ground evidence supporting genet interactions previously detected through sporocarp population analyses in young Scots pine reforestation sites.