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.

Multiple-marker techniques based on PCR are highly informative in genetic analysis. The bulk of many genomes is comprised of repeated sequences, and thus anonymous markers derived from genomic DNA are likely to correspond to repeated DNA sequences. Here we show that repeated-sequence-derived markers can provide information similar in quality to that of other PCR-based markers. Presumably this reflects the abundance of this repeat type in anonymous PCR markers such as RAPDs or AFLPs.

During the middle of the 1992 austral winter in the northern Windmill Islands, continental Antarctica, a highly unusual climatic event occurred in which the air temperature exceeded 0°C for some 60 h, at the end of which there was a significant rain shower before the ambient temperature returned to subzero conditions. This event caused most of the snow cover to melt and refreeze as clear ice. Lichens were thus rehydrated in the dark, in some places completely inundated, then frozen in ice. The effect that these conditions had on the distribution of K, Na, Mg and Ca within the thallus was estimated for two of the dominant macrolichen species, Umbilicaria decussata (Vill.) Zahlbr. and Usnea sphacelata R.Br, from three sites on a knoll on Clark Peninsula. One site acted as a natural control, owing to the very deep snow cover at the site, which protected lichens from the rewetting event. Despite persistent differences between species and the various sites, there was no overall effect of the climatic event on the membrane integrity of either lichen species. Only Usnea sphacelata from the most exposed site showed a significant leakage of K across the cell membrane, which indicated a loss of membrane integrity. Overall, both species were tolerant of the extreme conditions, although Umbilicaria decussata was the more tolerant.

We investigated the effect of elevated CO2 on the growth and mycorrhizal colonization of three tree species native to north-eastern American forests (Betula papyrifera Marsh., Pinus strobus L. and Tsuga canadensis L. Carr). Saplings of the tree species were collected from Harvard Forest, Massachusetts, and grown in forest soil under ambient (c. 375 ppm) and elevated (700 ppm) atmospheric CO2 concentrations for 27–35 wk.

In all three species there was a trend to increasing whole-plant, total-root and fine-root biomass in elevated CO2, and a significant increase in the degree of ectomycorrhizal colonization in B. papyrifera and P. strobus, but not in T. canadensis. However, in T. canadensis the degree of colonization with arbuscular mycorrhizas increased significantly. In both the ambient and elevated environments, on the roots of B. papyrifera and P. strobus 12 distinct ectomycorrhizal morphotypes were identified. Distinct changes in the ectomycorrhizal morphotype assemblage of B. papyrifera were observed under CO2 enrichment. This change resulted in an increase in the frequency of ectomycorrhizas with a higher incidence of emanating hyphae and rhizomorphs, and resulted in a higher density of fungal hyphae in a root exclusion chamber.

The concept of the ‘nucleotype’ embraces aspects of the nuclear DNA that affect the phenotype other than through the coding sequences. In this context, we consider one particular situation, namely DNA variation due to the presence of supernumerary B chromosomes (Bs); these Bs, which are additional to the basic complement of A chromosomes, generate a spectrum of DNA amounts, and thus nucleotypes, within many species. We consider the physiological consequences of carrying extra chromosomes that appear by and large to lack coding sequences, and focus on two species with contrasting case histories: rye (Secale cereale L.) and chives (Allium schoenoprasum L.), which illustrate ‘selfish’ and ‘adaptive’ explanations of the persistence of B chromosomes.

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.

In Nicotiana sylvestris Spegazzini and Comes (Solanaceae), we examined the relationships among wounding, endogenous leaf jasmonic acid (JA) pools, and whole-plant (WP) nicotine accumulation over a range of wounding intensities and spatial distributions, in order to explore optimal defence (OD) theory predictions. We quantitatively wounded one or four leaves and then quantified: (1) JA in damaged and undamaged leaves 90 min after wounding; (2) WP nicotine concentration after 5 d (the times when JA and nicotine attain the largest wound-induced concentrations). We find: (1) statistically significant, positive relationships on a leaf-by-leaf basis among the number of leaf punctures, endogenous leaf JA, and WP nicotine accumulation; (2) that young, undamaged leaves have a higher concentration of JA than do older, undamaged leaves, and produce a greater amount of JA per puncture than older leaves, but that all leaves have the same JA content (ng JA per leaf); and (3) that a damaged leaf produces less JA when other leaves in the canopy are wounded than when it is the only wounded leaf in the canopy, but that when it is the only wounded leaf, the phylotactically adjacent, undamaged leaves do not increase their JA concentrations. The observation that younger leaves produce more JA per puncture than do older leaves is consistent with OD theory predictions. The observation that a small amount of damage localized to a single leaf is as effective as a larger amount of damage dispersed across the canopy in increasing leaf JA and WP nicotine accumulation shows the plant's ability to differentiate between dispersed and localized damage. Because the quantity of JA in a wounded leaf 90 min after wounding is a reliable indicator of the WP nicotine response to wounding, this trait provides insight into how plants integrate information about environmental insults and tailor their defence responses.

Monoliths of two contrasting vegetation types, a species-rich grassland on a brown earth soil over limestone and a species-poor community on a peaty gley, were transferred to solardomes and grown under ambient (350 μl l−1) and elevated (600 μl l−1) CO2 for 2 yr. Shoot biomass was unaltered but root biomass increased by 40–50% under elevated CO2. Root production was increased by elevated CO2 in the peat soil, measured both as instantaneous and cumulative rates, but only the latter measure was increased in the limestone soil. Root growth was stimulated more at 6 cm depth than at 10 cm in the limestone soil. Turnover was faster under elevated CO2 in the peat soil, but there was only a small effect on turnover in the limestone soil. Elevated CO2 reduced nitrogen concentration in roots and might have increased mycorrhizal colonization. Respiration rate was correlated with N concentration, and was therefore lower in roots grown at elevated CO2. Estimates of the C budget of the two communities, based upon root production and on net C uptake, suggest that C sequestration in the peat soil increases by c. 0·2 kg C m−2 yr−1 (=2 t ha yr−1) under elevated CO2.

Carbodioxide uptake, oxygen evolution and chlorophyll fluorescence of leaves of Lobelia rhynchopetalum Hemsl., a giant rosette plant of the tropical alpine regions of Ethiopia, were studied under field conditions at 4000 m above sea level. Our objective was to investigate the photosynthetic adaptation to the combination of wide fluctuation in diurnal temperature, high photon flux densities (PFD) and low CO2 partial pressure encountered in these regions. At an ambient CO2 partial pressure of c. 17 Pa, maximal rates of CO2 uptake were low, ranging between 4 and 6 μmol m−2 s−1. Such rates, however, required high PFDs and were observed only at levels of 1500 μmol photons m−2 s−1. Carbon dioxide uptake was significantly inhibited when PFD was >2000 μmol photons m−2 s−1. On the other hand, at saturating CO2 levels, maximal photosynthetic oxygen evolution was higher (30 μmol O2 m−2 s−1), saturating at the same PFD as CO2 uptake. Quantum efficiency of CO2 uptake (0·006 mol CO2 mol photons−1, at high altitude and a low CO2 partial pressure of 17 Pa) and even of oxygen evolution under CO2-saturating conditions in the leaf O2 electrode (0·05 mol O2 mol photons−1) indicated reduced photosynthetic efficiency. Electron transport rate (ETR) was strongly correlated with the leaf temperature. Non-photochemical quenching (NPQ) responded inversely to leaf temperature and stomatal conductance.

The results indicated that in the morning, when the sun irradiates the partly frozen leaves with closed stomata, NPQ is the principal mechanism by which Lobelia leaves protect their photosynthetic apparatus. However, during the day, the predominant upright inclination of the leaves significantly contributes to protecting the leaves from excess light absorption. A comparison of the chlorophyll fluorescence of young and old leaves revealed that the former had high ETR and quantum efficiency of photosynthetic electron transport but a lower capacity for NPQ. Extremely high NPQ values but low ETR and low quantum efficiency were recorded for the old leaves. Thus, in the course of maturation the leaves apparently lose photosynthetic efficiency but increase their capability for protective non-photochemical quenching.

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.

Recent advances in the cytogenetics of the Lolium–Festuca complex provide new opportunities for understanding and manipulating complex physiological mechanisms such as drought and cold resistance. This paper describes breeding programmes involving hybrids between two species: L. multiflorum, which offers good early growth and high nutritive value, and F. arundinacea, which is more stress tolerant. The programmes are designed to allow a rapid recovery of the Lolium genome and to restrict numbers of recombinants derived from Festuca. Use of genomic in situ hybridization (GISH) and an isozyme marker demonstrates how gene complexes from any part of the Festuca genome can be introgressed into Lolium. This enables us to construct genotypes combining desirable traits of both Lolium and Festuca species. By introgressing different Festuca genes into Lolium, quantitative traits such as tolerance to drought and cold can be ‘dissected’ into their different components, to clarify their function. Festuca genes for stress tolerance can be located by genomic in situ hybridization (GISH) and assigned to regions of chromosome arms in Lolium. Two Lolium genotypes are described, in which genes for drought resistance transferred from the F. pratensis sub-genome of F. arundinacea onto chromosome 2 of Lolium. The two drought-resistant lines have the high water conductance of Festuca on their adaxial leaf surface and the low abaxial conductance of Lolium. The paper also describes how androgenesis of L. multiflorum × F. arundinacea hybrids has led to the selection and characterization of genotypes with coacclimation to drought and freezing stress, in some cases exceeding that in the Festuca parent.

A split-root growth system was used to study photosynthate partitioning to developing nodules and roots of soybean (Glycine max L., Merr.). Opposite sides of the root systems were inoculated with Bradyrhizobium japonicum at 8 and 12 d after planting (early/delayed inoculation treatment) or, alternatively, only one side was inoculated 8 d after planting (early/uninoculated treatment). Plants were incubated with 14CO2 at 24-h intervals from early inoculation until the onset of N2 fixation (acetylene reduction). After staining with Eriochrome black, root and nodule meristematic structures were excised under a dissecting microscope and their radioactivity determined by scintillation counting. The specific radioactivity of nodule structures increased with nodule development, and was as much as 4 times higher in early nodules than in roots and nodules on half-roots receiving delayed inoculation. By the time that N2 fixation could be measured in the first mature nodules, the early inoculated half-root contained over 70% of the radioactivity recovered from the entire root systems of both early/delayed and early/uninoculated treatments. These results suggest that developing nodules create a strong sink for photosynthate, and that nodules and roots compete for current photosynthate. Early initiated nodules might develop at the expense of late initiated nodules, as well as at the expense of the roots themselves.

The photosynthetic and respiratory activities of the leaves of a tropical tree, cacao, Theobroma cacao L., grown under shading, were determined in relation to leaf age and light conditions within the canopy, in order to gain a deeper insight into characteristics of the leaf population composing a canopy.

The specific leaf weight and leaf water content varied with the height of leaves from the ground and/or the irradiance. The net photosynthetic rate also varied markedly depending on leaf age and irradiance. The leaves in full or nearly full irradiance (<70% full daylight) attained the maximum rate c. 60 d after the leaves emerged, and the rate decreased to nearly zero at a leaf age of c. 270 d.

The nocturnal leaf respiratory activity was proportional to the photosynthetic activity during the day, but the proportional ratio was not constant throughout the survival period of leaves. Within the closed canopy, the upper leaves, which much higher ratios of respiratory to photosynthetic activity, under full or nearly full irradiance, tended to have much shorter mean longevities (c. 160 d) than the lower leaves under a lower irradiance (c. 310 d).

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.

Dehydrin proteins (late embryogenesis abundant (LEA) D11 family) are produced in a wide variety of plant species in response to environmental stimuli with a dehydrative component, including drought, low temperature, salinity, and developmental stages such as seed and pollen maturation. Despite their widespread occurrence and abundance in cells under dehydrative conditions, the biochemical role of dehydrins remains elusive. The subcellular location of dehydrins is consistent with a biochemical role as an intracellular stabilizer, possibly with surfactant characteristics, acting upon targets in both the nucleus and cytoplasm. In some species, dehydrin loci are located within quantitative trait loci (QTL) intervals for important phenotypic traits including winter hardiness in barley (Hordeum vulgare L.) and anthesis-silking interval in maize (Zea mays L.). Dehydrin loci tend to be multigenic and occur in clusters on more than one chromosome. Investigations are currently under way in our laboratory and others' to move beyond protein accumulation studies and correlations with QTL to uncover direct cause-and-effect relationships between dehydrin (dhn) genes and phenotypes associated with physiological responses to stress.

The ultramafic sites at Meikle Kilrannoch, Scotland, have small sparsely colonized patches with soils which have highly toxic (to many non-indigenous plants) concentrations of Mg and Ni. These toxic metals are unlikely to be the main cause of the open vegetation as the indigenous plants are at least partially tolerant of them. The hypothesis that low soil nutrients were a likely cause of the open vegetation was tested by a fertilization experiment in which major nutrients and Ca were added in August 1991 and July 1992 to replicated quadrats which initially had 5·3–6·6% plant cover. There was a large increase in plant cover on major nutrient addition. The increase in rosette size, flowering, seed production, and recruitment of the dominant semelparous Cochlearia pyrenaica DC. ssp. alpina (Bab.) Dalby was studied in detail. The increased growth of Cochlearia (and some other native species at the site) on nutrient addition strengthens the argument that a major nutrient deficiency rather than a metal toxicity limits plant growth at Meikle Kilrannoch and shows that at least some stress tolerators respond with rapid growth and reproduction when nutrient limitation is removed. A small-scale experiment set up in June 1993, in which the major nutrients were added separately, suggested that P and not N, or K was the limiting element. The effects of P seem to be unrelated to any possible reduction in the availability of the toxic ions Mg 2+ and Ni2+.

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.

Elevated [CO2] has been shown to protect photosynthesis and growth of wheat against moderately elevated [O3]. To investigate the role of ozone exclusion and detoxification in this protection, spring wheat (Triticum aestivum L. cv. Wembley) was grown from seed, in controlled-environment chambers, under reciprocal combinations of [CO2] at 350 or 700 μmol mol−1 and [O3] peaking at <5 or 60 nmol mol−1, respectively. Cumulative ozone dose to the mesophyll and antioxidant status were determined throughout flag leaf development. Catalase activity correlated with rates of photorespiration and declined in response to elevated [CO2] and/or [O3]. Superoxide dismutase activity was not significantly affected by either condition. Neither ascorbate nor glutathione content was enhanced by elevated [CO2]. In wheat, at moderately elevated [O3], our results show that stomatal exclusion plays a major role in the protective effect of elevated [CO2] against O3 damage.

Cuticular water permeance was manipulated in Corylus avellana L., Hypericum androsaemum L. and Populus tremula L. by (1) long-term application of low doses of various systemic herbicides inhibiting biosynthesis of cuticular waxes, (2) very short-term application of organic solvents to the leaf surface, and (3) exposure to natural strong winds. Treatment effects were very variable, but increased the natural range of permeances by a factor of 10 or so in undamaged leaves. All species had hypostomatous leaves. Relative change of leaf conductance (g) in response to stepwise increases of leaf-to-air water vapour pressure difference (VPD) was measured for individual leaves (Corylus) or groups of leaves at the shoot or branch tip. Adaxial cuticular water permeance (P) was determined for the same leaves after measurement of the VPD-response. A proportional measure of relative change of g with VPD, d(logeg)/dVPD, was then plotted against P. No increase in the strength of the closing response to increasing VPD was found with increasing P, as would have been expected if water loss through the cuticle was involved in stomatal response to changes in VPD via a direct effect on guard cell turgor. By contrast, high P coincided, most clearly in Corylus, with a reduced strength of the stomatal closing response to increasing VPD, i.e. less negative d(logeg)/dVPD. As the responses were non-linear, the value of d(logeg)/dVPD changed with VPD. With rising VPD, all three species and a fourth one previously studied showed a decline in the value of d[d(logeg)/dVPD]/d(log P), reaching negative values in one species. This is interpreted in terms of two independent and antagonistic effects of increased cuticular water permeance on guard cell response to VPD, one acting by reducing the backpressure exerted on guard cells by the epidermis, and the other one possibly causing greater depression of guard cell turgor through delivery of more chemical messengers (such as abscisic acid) to the guard cells with the cuticular transpiration stream.

Salt-affected soil is a major problem and has led to large areas of the earth's surface being unable to support agriculture. Wheat is not tolerant to high levels of salt; however, a number of its wild relatives, in particular Thinopyrum bessarabicum Savul. and Rayss, which grows on the Black Sea shore in the Crimea, are tolerant to high levels of NaCl. Thus the introgression of genes conferring salt tolerance from Th. bessarabicum into Triticum aestivum is one way in which salt-tolerant wheat varieties can be produced. This paper reviews the progress made in developing salt-tolerant wheat carrying Th. bessarabicum genes and salt-tolerant wheat/Th. bessarabicum amphiploids.