Drought strongly affects cereal yield in several regions of the world. Plant growth and plant water status in response to soil water deficit play an important role in tolerance to drought and in yield stability. In order to investigate the relationship between plant growth and water relations, 187 barley (Hordeum vulgare L.) recombinant inbred lines from a cross between two Mediterranean varieties, Tadmor and Er/Apm, were studied in a growth chamber for RWC, number of leaves on the main tiller (NL), number of tillers (NT) and total shoot fresh and dry biomass (TSFM and TSDM). Measurements were made at the beginning of tillering on well watered plants and at a soil moisture content of 14% of field capacity. A negative phenotypic correlation between RWC and growth parameters was obtained in both treatments. Under water stress, a negative genetic correlation was also found between the same characters. QTLs involved in RWC, NL and TSFM variation were positioned on a RFLP-RAPD genetic map. Different DNA regions involved in constitutive and water stress responses were detected. In the stress treatment, one region on chromosome 1 was involved in RWC and NL variation giving a genetic basis to the phenotypic correlations found. Separated map positions were also found for RWC and NL. Epistatic interactions between several QTLs and between QTLs and other markers were detected only in the water stress treatment, suggesting that some chromosomal regions might be involved in the regulation of the expression of the traits under water stress. This work suggested that even if some parameters are strongly correlated, finding QTLs for only one trait is not sufficient to detect all the candidate regions which might be involved in the control of the correlated traits. The results of localization and co-localization of QTLs are physiologically interpreted.

The 15N natural abundance and N concentrations of fruit bodies from 70 species (23 genera) of ectomycorrhizal fungi found in boreal forests are presented. Large intraspecific and intrageneric differences were found, e.g. 8·3‰ 15N in the species Dermocybe crocea and 12·6‰ in the genus Cortinarius. In addition, significant differences in both δ15N and %N were found between different parts of fruit bodies, with cap material giving consistently higher values. Proteins and amino acids were enriched by 9·7±0·4‰ (mean±1 SE) relative to chitin, irrespective of the part of the fruit body examined. Chitin had δ15N values similar to that of plant hosts. The higher δ15N and %N values of the caps than of the stipes probably reflect a higher portion of proteins and amino acids in the caps. The δ15N of mycorrhizal fungi can be a function of the N species used (organic N, NH4+, NO3−), the depth of soil at which the mycelium occurs, and metabolic fractionations. The metabolic fractionations, e.g. potential transaminations during the flux of N from the soil through the fungus to the plant, make it difficult, at present, to make inferences about sources of N based on δ15N values alone. No effect of sample drying temperature on δ15N values of fungal material was detected.

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.

The influence of three organic compounds and bakers' dry yeast on growth of external mycelium and phosphorus uptake of the arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith (BEG 87) was examined. Two experiments were carried out in compartmentalized growth systems with root-free sand or soil compartments. The sand and soil in the root-free compartments were left untreated or uniformly mixed with one of the following substrates (0.5 mg g−1 soil): bakers' dry yeast, bovine serum albumin, starch or cellulose. Effects of the organic substrates on biomass and hyphal length density of the arbuscular mycorrhizal fungus were examined by using specific fatty acid signatures in combination with direct microscopy. Micro-organisms other than the arbuscular mycorrhizal fungus were measured by fatty acid signatures, and radioactive 33P labelling of the root-free soil was used to determine arbuscular mycorrhizal hyphal phosphorus uptake. In general, hyphal growth of G. intraradices was enhanced by yeast and bovine serum albumin, whereas the carbon sources, starch and cellulose, depressed fungal growth. By analysing the fatty acid 16[ratio ]1ω5 from phospholipids (indicating mycelium) and neutral lipids (indicating storage structures) it was shown that increased fungal growth due to yeast was mainly in vegetative hyphae and less in storage structures. Arbuscular mycorrhizal hyphal phosphorus uptake was decreased by cellulose, but unaffected by the other substrates compared with the control. This means that both growth and phosphorus transport by the arbuscular mycorrhizal fungus were decreased under cellulose treatment. However, the composition of the microbial community varied under different substrate conditions indicating a possible interactive component with arbuscular mycorrhizal hyphal growth and phosphorus uptake.

Actinomycetes isolated from carrot rhizosphere were screened for their in vitro and in vivo antagonism to Pythium coloratum Vaartaja, a causal agent of cavity-spot disease of carrots (Daucus carota L.). Forty-five streptomycete and non-streptomycete actinomycete isolates were screened for in vitro antagonism in a carrot bioassay. Of these, seven which reduced or prevented lesion formation were identified using cultural, morphological, physiological, biochemical and cell wall characteristics as Streptomyces janthinus, S. cinerochromogenes, Streptoverticillium netropsis, Actinomadura rubra, Actinoplanes philippinensis, Micromonospora carbonaceae, and Streptosporangium albidum. All seven isolates tested produced non-volatile antifungal metabolites, but failed to produce inhibitory volatile compounds. Actinoplanes philippinensis and M. carbonacea grew epiphytically on the hyphae and oospores of P. coloratum. The external surface of the oospores of the pathogen was heavily colonized by both hyperparasites, their hyphae were found to coil tightly around the oospore wall, and frequently caused cytoplasmic collapse of oospores. Sporangia of A. philippinensis were often seen to emerge from the colonized hyphae and oospores of P. coloratum. None of the other actinomycete isolates showed hyperparasitism.

All seven isolates significantly reduced the incidence of cavity spot in soil artificially infested with the pathogen in the glasshouse. Streptomyces janthinus and Strepto. albidum were the most effective in reducing the disease in inoculated plants. In addition, all the actinomycetes species except Ac. rubra and M. carbonacea, in the presence or absence of the pathogen, significantly (P<0·05) increased mean fresh root weight compared to the treatment which included P. coloratum only. This study shows that these actinomycetes have considerable potential for future use as biocontrol agents of cavity spot under natural field conditions. This is the first report of cavity-spot disease of carrots being controlled by microbial antagonists, and is the first report of non-streptomycete actinomycetes to control a Pythium disease.

Roots of angiosperms differ in the behaviour of their apical meristems, and this diversity has been studied through the patterns of differentiation in a range of families. Except for three families of the Nymphaeales, all dicotyledons derive the epidermis wholly or partially with the root cap. In closed meristems the inner cell layer of the cap complex forms the epidermis; in open meristems, where cortex and cap are intermittently of common origin, linkages between the epidermis and the cap predominate. Roots of most monocotyledons derive the epidermis as the outer layer of the cortex. Nymphaeaceae, Cabombaceae and Barclayaceae resemble monocotyledons in this respect, and this applies even in the species with open meristems, in which a cleft forms between the cap and the rest of the apex. This feature fits with the close relationship between the Nymphaeales and monocotyledons revealed by other data. But none of the other Magnoliidae with close links to Liliidae has this type of epidermis. The Nymphaeales are also almost unique among dicotyledons in having trichoblasts in a vertical pattern. This results from transverse divisions of epidermal cells giving two conspicuously different daughters. The smaller and most densely staining one later bears a root hair. This is the way trichoblasts develop in many monocotyledons. The only other dicotyledons found with trichoblasts in vertical patterns are in the Piperaceae, though their closed meristems derive the epidermis in the normal dicotyledon pattern. All other dicotyledons that bear trichoblasts develop them in radial patterns probably related to the radial disposition of cells across the cortex. This pattern is more widespread than was previously known, though it can occur only in roots with closed meristems. In plants of both subclasses with vertical patterns of trichoblasts, it is usually the proximal daughter of the initiating mitosis which becomes the trichoblast. But it is the distal daughter in Juncaceae, Restionaceae, Cyperaceae and Poaceae. Vertical patterns differ further as to whether the atrichoblast daughters divide after initiation, thus changing the alternation of trichoblasts and atrichoblasts along a file of epidermal cells. Monocotyledons and the Nymphaeaceae can produce trichoblasts in open or closed meristems. In some embryos and root primordia the epidermis becomes discrete from cortex and cap and remains so in the meristems. This has now been found in six aquatic genera of the Liliidae, but reports of it occurring elsewhere are probably due to misinterpretation of sections. Discrete epidermises differentiate into trichoblasts and atrichoblasts in Hydrocharitaceae, but not in Araceae or Lemnaceae.

Under defined laboratory conditions it was shown that two glucosinolate-containing plant species, Tropaeolum majus and Carica papaya, were colonized by arbuscular mycorrhizal (AM) fungi, whereas it was not possible to detect AM fungal structures in other glucosinolate-containing plants (including several Brassicaceae). Benzylglucosinolate was present in all of the T. majus cultivars and in C. papaya it was the major glucosinolate. 2-Phenylethylglucosinolate was found in most of the non-host plants tested. Its absence in the AM host plants indicates a possible role for the isothiocyanate produced from its myrosinase-catalysed hydrolysis as a general AM inhibitory factor in non-host plants. The results suggest that some of the indole glucosinolates might also be involved in preventing AM formation in some of the species. In all plants tested, both AM hosts and non-hosts, the glucosinolate pattern was altered after inoculation with one of three different AM fungi (Glomus mosseae, Glomus intraradices and Gigaspora rosea), indicating signals between AM fungi and plants even before root colonization. The glucosinolate induction was not specifically dependent on the AM fungus. A time-course study in T. majus showed that glucosinolate induction was present during all stages of mycorrhizal colonization.

The present understanding of the genetic control of flowering in wheat is reviewed. Although this information will continue to be of value in breeding and in recognizing the role such genes have had in adapting the wheat crop to global agriculture, its use in defining the processes responsible for flowering will be limited. Progress here will depend on developments in model plant systems such as Arabidopsis, where methods for isolating genes are much more advanced than in wheat. These developments, which have already started, will probably be used to establish homologies between the genes for flowering within the cereals, as well as more widely. An understanding of the flowering process in wheat is likely to emerge from this approach. In the meantime, there are some unknowns in the genetics of flowering in wheat which need to be resolved. These include the identification of a gene(s) on the group 4 chromosomes of wheat which is homoeoallelic with the gene Sh in barley. Also, the proposed gene(s) delaying flowering and located on the group 6 chromosomes needs to be recognized and mapped. Similar needs occur for the group 1 chromosomes as well as the resolution of whether or not Vrn5 is correctly positioned on chromosome 7BS.

Earlier work has shown that rice plants growing in reduced soil are able to solubilize P and thereby increase their P uptake by inducing an acidification in the rhizosphere; the acidification is caused by H+ produced in Fe2+ oxidation by root-released O2, and by the direct release of H+ from the roots to balance cation–anion intake. Here, we report rates of release of O2 and H+ from P-stressed and P-sufficient rice plants into sand cultures continuously perfused with deoxygenated nutrient solution. The P stress was sufficient to reduce plant dry mass by roughly half, but root dry mass increased roughly twofold and root surface area 2·5-fold. The proportion of fine roots increased from 11 to 21% of root length under P deficiency; root porosity, averaged over the whole root system, increased from 0·25 to 0·40. Apparent rates of O2 release were 0·8–3·3 μmol per plant d−1, or 22–87 μmol g−1 (root dry mass) d−1. Assuming that the bulk of the O2 was released from medium and fine roots, the fluxes of O2 were 0·02–0·13 nmol dm−2 (root surface) s−1, which is in the range found for soil-grown plants. The release per plant was twofold greater in the low P treatment, although rates of release per unit root mass were slightly lower. The increased release under P deficiency is consistent with the increased length of fine roots and increased porosity. Rates of H+ release were 0·7–1·2 mmol per plant−1 d−1, or 1·4–6·1 mmol g−1 (root dry mass) d−1. The H+ release per unit plant dry mass was 60% greater in the low P treatment, but the release per unit root mass was 2·5-fold lower. The increased H+ release under P deficiency was associated with increased NH4+ intake and decreased NO3− intake, and a tenfold increase in plant NO3-N. This suggests that P deficiency reduced NO3− assimilation, causing reduced NO3− influx and/or increased efflux.

Seedlings of Pseudotsuga menziesii (Mirb.) Franco were grown for six–16 months in untrenched and trenched treatments in three 90–120-yr-old mixed forests dominated by Betula papyrifera Marsh. and P. menziesii in the southern interior of British Columbia. Each forest was characterized by mesic conditions and low light intensity (PAR<200 μmol m−2 s−1) in the understorey. The objective of the study was to evaluate the influence of overstorey tree roots on (i) ectomycorrhizal fungal composition, richness and diversity, and (ii) photosynthesis and growth of understorey P. menziesii seedlings. Seventeen ectomycorrhizal morphotypes were recognized on seedlings in the untrenched treatment, and nine in the trenched treatment over the three sites. Six types occurred in both treatments, of which on average Rhizopogon vinicolor Smith type was 20 times more abundant and Thelephora type six times less abundant in the untrenched as in the trenched treatment. Of types that formed strands or rhizomorphs, eight occurred in the untrenched treatment, where they occupied on average 23% of root tips, and only four occurred in the trenched treatment over 4% of the root tips. Mean richness, diversity, and evenness of ectomycorrhizal associates per seedling were approx. twice as great in the untrenched as in the trenched treatment.

Net photosynthetic rate of P. menziesii seedlings was greater in the untrenched than in the trenched treatment in July and August, but not in September 1994. Height, diameter and biomass of seedlings did not differ between treatments, but height[ratio ]diameter ratio was greater in the untrenched treatment at time of harvest. The effect of trenching on seedling performance was attributed mainly to differences in ectomycorrhizal colonization patterns because trenching had no significant effect on soil nutrient concentrations (total C, total N, NH4-N, available N, exchangeable Ca, exchangeable Mg, exchangeable K), C[ratio ]N ratio, soil pH or light availability. Nor was there a significant difference in soil water in August, when seedlings in untrenched plots had higher net photosynthetic rates than those in trenched plots. Results suggest that influence of overstorey trees and pattern of ectomycorrhizal formation are important to P. menziesii seedling performance in deeply shaded forest environments.

Improving the drought resistance of high yielding rice (Oryza sativa L.) varieties for upland areas is a goal of rice breeders since upland rice relies exclusively on rainfall for water and is generally low yielding. Identifying quantitative trait loci (QTLs) which confer drought resistance promises to speed this goal. We have previously described the use of 82 restriction fragment length polymorphism (RFLP) markers in the genetic mapping of root growth characteristics that are potentially involved in drought resistance in a population of 178 F2 plants derived from a cross of two drought resistant upland varieties, Azucena and Bala. Here we report the characterization and QTL mapping of three other mechanisms of drought resistance, leaf rolling, stomatal behaviour and early flowering, in this population. When the youngest fully expanded leaf was excised from 12 rice varieties, ‘IR20’ and ‘Bala’ were identified as slow at rolling. Although ‘Azucena’ rolled its leaves much faster than ‘Bala’ upon excision, stomatal resistance rose more rapidly in ‘Bala’, resulting in a lower rate of water loss. By assessing leaf rolling and stomatal resistance in the F2 population, it was possible to identify QTLs for these traits. A QTL for slow leaf rolling from ‘Bala’ was found on chromosome 1. Two QTLs associated with resting stomatal conductance were found on chromosomes 3 and 12. QTLs for the rate of stomatal closure were found on chromosomes 3 and 7. In addition, it was possible to map QTLs associated with the days to heading which were found on chromosomes 3, 8 and 10. These results identify markers of potential value to breeders and are discussed in the context of previously reported data for heading date QTLs in rice and for stomatal conductance QTLs in maize.

Roots of bluebell (Hyacinthoides non-scripta (L.) Chouard ex Rothm.) are colonized by a range of fungal symbionts from several genera of the order Glomales. Using the identification scheme described in Merryweather & Fitter (1998), arbuscular mycorrhizal (AM) fungi in bluebell roots were quantified throughout the single growing season of 1994–5 and compared with populations of spores found in the soil around the roots.

In the early part of the growing season, when its activity is entirely subterranean (autumn and winter), bluebell habitually associates with a Scutellospora morphotype which is almost certainly S. dipurpurescens Morton & Koske (emend. Walker, 1993) whose spores occur in the root zone. This is the time of maximum phosphorus inflow and bulb-stored carbohydrate utilization by this mycorrhiza. A diverse flora of other AM fungal morphotypes (Acaulospora and Glomus), which might also form mycorrhizas with other plants in the vicinity of bluebells, invade the roots later in the season (spring), when P inflow is reduced and carbohydrate is available as fresh photosynthate. Their contribution to the mycorrhiza might be less than that of Scutellospora, particularly in terms of P assimilation.

Both AM fungi in roots and glomalean spores recovered from soil around bluebell roots showed a significant degree of correlation with the vegetation within which the test plants grew. In the case of AM fungi in roots, Scutellospora showed no special preference for either, but Glomus correlated with a canopy of sycamore (Acer pseudoplatanus L.) and Acaulospora with oak (Quercus petraea (Mattuschka) Liebl.). Spores which most closely resembled S. dipurpurescens and Acaulospora gerdemannii Schenck & Nicolson were significantly more numerous under sycamore, but a spore like Acaulospora koskei Blaskowski, the most numerous and frequently encountered glomalean spore in the system, showed no preference for areas dominated by either tree. There was no significant relationship between AM fungal populations in bluebell roots and glomalean spores recovered from associated soil.

The two spore taxa most frequently found in the vicinity of bluebell roots (A. koskei and S. dipurpurescens) were also found in lower numbers in soil from a region of the field site in which bluebell was absent, indicating that the main bluebell AM fungi do not exclusively associate with that host.

Numerous authors have attempted to quantify the physical properties of leaves in relation to aspects of leaf ecology, including decomposition, sclerophylly, herbivory, and leaf function and longevity. This paper examines the relative merits of the punch-and-die, tearing and shearing tests for assessing leaf physical properties. We conducted a series of these three mechanical tests on leaves of Solanum laciniatum, and determined the effect of various test parameters on the measurement of fracture properties. For the punch-and-die test, the parameters considered were machine speed, clearance between the punch and the die, edge definition of the punch, and area of the punch. Aspects of the tearing test examined were notch length, end effects, and length-to-width requirements of test strips, and for shearing tests the effects of blade proximity, angle and sharpness were investigated. All the test parameters investigated were found significantly to affect the assessment of leaf-fracture properties. In addition, fracture properties were found to vary significantly within leaves. Some general principles for designing and implementing tests are outlined. This study suggests that while punching and shearing tests are useful means of quantifying leaf fracture properties, the value of the tearing test may be reduced as it is most constrained by the biological nature of the test material.

This study examines interrelationships between eight leaf attributes (specific leaf mass, area, dry mass, lamina thickness, mesophyll cell number per cm2, mesophyll cell volume, chloroplast volume, and number of chloroplasts per mesophyll cell) in field-grown plants of 94 species from the Eastern Pamir Mountains, at elevations between 3800 and 4750 m. Unlike most other mountain areas, the Eastern Pamirs, Karakorum system, Tadjikistan provide localities where low temperatures and radiation combine with moisture stress at high altitudes. For all the attributes measured, significant differences were found between plants with different mesophyll types. Leaves with dorsiventral palisade structure (dorsal palisade, ventral spongy mesophyll cells) had thicker leaves with larger but fewer mesophyll cells, containing more and larger chloroplasts. These differences in mesophyll type are reflected in differences in the total surface of mesophyll cells per unit leaf area (Ames/A) or volume (Ames/V). Plants with isopalisade leaf structure (palisade cells under both dorsal and ventral surfaces) are more commonly xerophytes and their increased values of Ames/A and Ames/V decrease CO2 mesophyll resistance, which is an important adaptation to drought. Path analysis shows the critical importance of mesophyll cell volume in leading to the covariance between the different leaf attributes and hence to specific leaf mass (SLM), even though mesophyll cell volume is not itself strongly correlated with SLM. This is because mesophyll cell volume increases SLM through its effects on leaf thickness and chloroplast number per cell, but decreases SLM through its negative effect on mesophyll cell density.

A mechanistic model was developed, to simulate the main facets of photoinhibition in phytoplankton. Photoinhibition is modelled as a time dependent decrease in the initial slope of a photosynthesis versus irradiance curve, related to D1 (photosystem II reaction centre protein) damage and non-photochemical quenching. The photoinhibition model was incorporated into an existing ammonium-nitrate nutrition interaction model capable of simulating photoacclimation and aspects of nitrogen uptake and utilization. Hence the current model can simulate the effects of irradiance on photosynthesis from sub-saturating to inhibitory photon flux densities, during growth on different nitrogen sources and under nutrient stress. Model output conforms well to experimental data, allowing the extent of photoinhibition to be predicted under a range of nutrient and light regimes. The ability of the model to recreate the afternoon depression of photosynthesis and the enhancement of photosynthesis during fluctuating light suggests that these two processes are related to photoinhibition. The model may be used to predict changes in biomass and/or carbon fixation under a wide range of oceanographic situations, and it may also help to explain the progression to dominance of certain algal species, and bloom formation under defined irradiance and nutrient conditions.

The effects of partial defoliation on photosynthesis, whole-seedling carbon allocation, partitioning and growth were studied for two species with contrasting foliar traits. Field-grown seedlings of deciduous Japanese larch (Larix leptolepis) and evergreen red pine (Pinus resinosa) were defoliated by hand in early summer for 2 consecutive years. In the first year (1990), seedlings were defoliated by removing the distal 0, 25, 50 or 75% of each needle. In the second year (1991), seedlings were defoliated either 0 or 50%, regardless of previous defoliation treatments. Defoliation had little effect on photosynthesis and starch concentration in whole seedlings of either species in the first year. In the second year, photosynthesis increased in both species in response to the 1991 defoliation treatment, and in red pine also increased in response to the 1990 defoliation treatment. Further, in 1991 both larch and pine had decreased whole-seedling total non-structural carbohydrate concentrations in all seedlings that were defoliated at least once over the 2-yr period. This decrease was noted mostly in the starch component of the non-structural carbohydrates, and was similar in both species. In 1991, biomass was similarly decreased in both species in response to 1991 defoliation. Both species showed overcompensation in total and component biomass in seedlings defoliated by 25% in 1990. Overall, the results do not support the widely held belief that evergreen trees are substantially more affected than deciduous trees by defoliation.

It is generally accepted that larger seeds give rise to seedlings with better performance. On the other hand, the size that a seed reaches is genetically determined by at least two different traits ; the genetic variability of the developing embryo and the genetic variability of the maternal plant. Thus, the relative contributions of these two traits affect seedling performance by influencing seed size. In this paper, I investigate the effect of seed size on seedling performance in the Scots pine (Pinus sylvestris). From eight maternal plants, 50 seeds were planted in each of two soil types (800 seeds in total), and seedling performance was monitored for 1 yr. Seed mass proved to be highly constant within maternal plants. Soil type influenced emergence and survival; however, the effect of soil type differed depending on maternal origin. Seed mass was positively correlated with seedling emergence, although this relationship was not found for seedling survival or date of emergence. The initial growth of the shoot was also positively correlated with seed mass. However, after one growing season, seed mass had no effect on seedling performance, which depended exclusively on maternal origin. Nevertheless, the mean mass of seeds produced by plants was positively correlated with mean values of growth parameters. Thus, first-year seedling performance seems to be a maternal trait indirectly associated with seed size.

During the growing session of 1995, the total soluble non-protein nitrogen (TSNN) composition and contents of mycorrhizal fine roots, xylem sap and phloem exudates of roots from a coniferous (Picea abies L.(Karst)) and a deciduous (Fagus sylvatica L.) tree species were analysed at a field site (‘Höglwald’, Germany) exposed to high loads of N. In April, TSNN in fine roots of spruce and beech trees amounted to 16 μmol N g−1 f. wt and 23·3 μmol N g−1 f. wt, respectively. It decreased to 9·2 μmol N g−1 f. wt and 18·1 μmol N g−1 f. wt, respectively, after bud break in June. The seasonal maximum of TSNN in fine roots of spruce was observed in July (32·7 μmol N g−1 f. wt) followed by a decline of c. 30% until the end of the growing season in September. TSNN in fine roots of beech trees showed a further decline between June and July, when its seasonal minimum was determined (15·6 μmol N g−1 f. wt), and increased to c. 29 μmol N g−1 f. wt until September. In spruce roots Gln and Arg were the most abundant TSNN compounds during the entire growing season. In roots of beech Asn played an important role alongside Gln and Arg, especially in April, when it was the most abundant TSNN compound. Other proteinogenic and non-proteinogenic N compounds comprised c. 20–30% of TSNN. Nitrate made up <1%, and ammonium <7% of TSNN in the fine roots of both species.

In April, TSNN in the xylem sap of roots of spruce and beech trees amounted to 3·4 and 8·6 μmol N ml−1, respectively. In roots of spruce trees xylem sap TSNN increased after bud break up to 12·7 μmol N ml−1 in July. At the end of the growing season TSNN had declined again to 3·9 μmol N ml−1. TSNN in the root xylem sap of beech trees decreased after bud break until July (2·4 μmol N ml−1 in July) followed by a slight increase until September (2·9 μmol N ml−1). Arg, Gln and Asp were the most abundant TSNN compounds in the xylem sap of spruce trees contributing together c. 90% to TSNN. The same TSNN compounds prevailed in the root xylem sap of beech trees in April and July, whereas in June and September Asp was replaced by Asn comprising 57% of TSNN in June. In addition to the N compounds mentioned above, a number of other proteinogenic and non-proteinogenic amino compounds were found in root xylem sap of both species. In either species, nitrate and ammonium were present in small amounts, contributing <1% and <4% to TSNN, respectively. Apparently, inorganic N taken up by the mycorrhizal roots is mainly assimilated in root tissues or by the mycorrhiza and N uptake by the roots is largely adapted to the assimilatory capacity of this organ.

In phloem exudates of spruce roots, TSNN amounted to 10·7 μmol N g−1 f. wt in April, increased in June to 23·4 μmol N g−1 f. wt and decreased again until September to a seasonal minimum of 4·8 μmol N g−1 f. wt. In contrast to spruce, TSNN content in phloem exudates of beech roots showed a seasonal maximum (c. 20 μmol N g−1 f. wt) in April with a subsequent decrease in June after bud break (c. 2 μmol N g−1 f. wt). A fourfold increase in July was followed by a decrease in September, when TSNN in phloem exudates of beech roots amounted to 4·3 μmol N g−1 f. wt. Arg was the most abundant N compound in the phloem of roots from spruce trees and made up c. 60–85% of TSNN during the entire growing season. In beech trees the seasonal course of TSNN correlated with the relative abundance of Arg. Arg comprised 69 and 57% of TSNN in April and July, respectively, but contributed <20% in June and September. Besides Arg, other proteinogenic and non-proteinogenic amino compounds could be detected in the phloem of both species. In addition, nitrate and ammonium were present in considerable amounts.

From these results and a previous report on TSNN in above-ground parts of spruce and beech at the same site, a whole-plant model for the cycling of TSNN in both species is proposed. Differences in the location of storage pools are assumed to be responsible for the differences in the seasonal course of TSNN composition and contents observed between the two tree species.

Variation for K+ and Na+ accumulation at low salinities in hydroponic (water) culture were observed in shoots of different wheat species. Greater discrimination (in favour of K+ and against Na+ accumulation) was shown by hexaploid bread wheat (Triticum aestivum L.) than by tetraploid durum wheat (T. turgidum L.). Since Aegilops tauschii Cosson (A. squarrosa L.), the source of the D genome in bread wheat, also exhibited high discrimination between K+ and Na+, it was concluded that the character resided in the D genome. Studies of aneuploid bread wheat lines and disomic substitution lines of D genome chromosomes for their A and B genome homoeologues in durum wheat cv. Langdon revealed that the trait was controlled by the long arm of chromosome 4D. Since the aneuploid and disomic substitution lines showed better relative salt tolerance than durum wheat, but had lower yield potentials, we recombined chromosome 4D with chromosome 4B in a tetraploid wheat background using a homoeologous pairing mutant. This produced families of 4D/4B recombinant lines, some of which exhibited the enhanced K+/Na+ discrimination trait. RFLP analysis confirmed that the trait was controlled by a single gene (Kna1) which was completely linked to five markers on the distal third of the long arm of 4D. A second cycle of homoeologous recombination was employed to remove the distal 4D genetic material from the recombined Kna1 4B/4D chromosome and to map Kna1 in greater detail. By this strategy, Kna1 was mapped within a short 2 cM region. Genetic analysis of K+[ratio ]Na+ ratios showed very high LOD scores in this region for plants grown in solution culture, but lower values for plants grown in the field.

In general, recombinant lines which exhibited the enhanced K+/Na+ trait were slightly more tolerant of salinity in the field and in sand culture than recombinants lacking the trait. There was, however, considerable variation between individual lines. Ion discrimination and relative tolerance were also higher in a Kna1 recombinant (line no. R3) than in a kna1 recombinant (line no. R165) in sodic conditions. In these two lines the enhanced K+/Na+ discrimination trait did not alter responses to low potassium or calcium supply.

We tested if fumigation with exogenous monoterpenes might induce thermotolerance in leaves of an oak species (Quercus suber) which does not form and emit isoprenoids. To understand if exogenous monoterpene fumigation results in internal accumulation of monoterpenes, a physical method of monoterpene extraction was used. The internal content of monoterpenes increased in concert with increasing fumigation doses. This unambiguously demonstrated acquisition of exogenous monoterpenes. We exposed fumigated Q. suber leaves to two cycles of increasing temperatures from 35 to 55°C at 5°C steps. When leaves were exposed to a low dose of exogenous monoterpenes, yielding an internal content similar to that endogenously formed in the leaves of the monoterpene-emitter Q. ilex, no clear improvement in thermotolerance was found. When leaves were exposed to a high dose of exogenous monoterpenes, yielding an internal content of about five fold the endogenous pool of Q. ilex, but comparable with the expected content following stress-induced stomatal closure, photosynthesis inhibition at high temperatures was attenuated. This effect was observed only at temperatures <45°C during the first cycle, but at all temperatures between 35 and 55°C when plants were exposed to two cycles of high temperatures. Monoterpenes were still found in the leaves of Q. suber 12 h after ending the fumigation. Monoterpenes were also found in non-fumigated leaves distant up to 45 cm from the fumigated leaves. If monoterpenes make the photosynthetic apparatus more resistant to high temperatures, the effect might not be limited to the fumigated leaves and might be persistent after fumigation.