Chamaegigas intrepidus Dinter (syn. Lindernia intrepidus (Dinter) Oberm.) is a poikilohydric aquatic plant that lives in rock pools on granitic outcrops in Central Namibia. The pools are only filled intermittently during the summer rains, and the plants can pass through 15–20 rehydration/dehydration cycles during a single wet season. Rehydrated plants also have to cope with substantial diurnal fluctuations in the pool pH as a result of photosynthetic CO2 uptake. We have used in vivo31P NMR spectroscopy to investigate the effect of external pH and dehydration (low water potential) on intracellular pH in the roots and submerged leaves of C. intrepidus. Increasing the external pH from 6 to 10 had no effect on the steady state cytoplasmic and vacuolar pH values of submerged leaves, but caused a slight alkalinization of the root cytoplasm. Similarly dehydration with PEG-600 at either pH 6 or pH 10 had no effect on the cytoplasmic pH of the leaves, but it did cause a small alkalinization of the leaf vacuoles at pH 10. These results imply an unusually effective regulation of intracellular pH, consistent with the adaptation of C. intrepidus to the extreme environmental conditions of its habitat. The NMR analysis also showed that dehydration had no effect on the inorganic phosphate and phosphocholine pools, and this was taken to indicate that the cell membranes were well protected from the effects of the low water potential.

Littorella uniflora (L.) Ascherson is a small, perennial, amphibious rhizophyte of rosette life-form which is common along the margins of lakes, tarns and reservoirs where water-level fluctuations are often rapid and unpredictable. The majority of plants are continuously submersed and reproduce vegetatively, but a small proportion become completely emersed for variable lengths of time, when flowering and seed set occur. To find out how L. uniflora adjusts to sudden emersion we studied the plants at a reservoir where water level falls each spring and remains low throughout the summer; L. uniflora adjusted very quickly showing a degree of phenotypic plasticity not expected in a ‘stress tolerator’, including the production of a new set of terrestrial leaves with reduced lacunal volume and increased stomatal density, a rapid increase in leaf growth rate, and flowering within 3–4 wk. Comparison of terrestrial L. uniflora with aquatic plants growing permanently submersed in lake and tarn habitats showed that three to fourfold more carbon (C) and nitrogen (N) was incorporated into above-ground biomass by emersed plants. However, ramet production in the aquatic environment appeared to be more costly, in terms of C and N invested, than terrestrial flower and seed production. The combination of continuous, submersed vegetative spread with the capacity for a high degree of phenotypic plasticity allowing some flower and seed production to occur during brief periods of emersion seems to account for the success of this plant in the amphibious niche.

Quasi-steady-state measurements of root hydraulic conductance (KR) of Olea oleaster Hoffmgg. et Link potted seedlings were performed using a pressure chamber with the aim of: (a) measuring the impact of different water-stress levels on a KR; (b) measuring the kinetics of KR recovery several days after soil rewetting; (c) relating changes in KR to changes in root anatomy and morphology. Increasing water-stress was applied in terms of ratio of leaf water potential (ΨL) measured at midday to that at zero turgor (ΨTLP), i.e. ΨL/ΨTLP=0·5, 1·0, 1·2, 1·6; KR was measured initially and at 24, 48, 72, 96 h after irrigation.

Values of KR in seedlings stressed to ΨL/ΨTLP=1·2 increased for 48 h after irrigation from 0·23 to 0·97×10−5 kg s−1 m−2 MPa−1 i.e. from 16% to 66% of that measured in unstressed seedlings. A marked shift of the x-axis intercept of the straight line relating flow to pressure (zero flow at non-zero pressure) was recorded initially after irrigation and persisted up to 48 h. Recovery of KR occurred within 24 h after irrigation in seedlings at ΨL/ΨTLP=0·5 and 48 h later in those at ΨL/ΨTLP=1·0.

Severe drought stress (ΨL/ΨTLP=1·6) caused anatomical changes to roots which formed a two-layered exodermis with thicker suberized walls and a three- to four-layered endodermis with completely suberized tangential walls. Recovery of KR in these roots required resumed growth of root tips and emergence of new lateral roots.

Arbuscular mycorrhizal (AM) fungi extensively colonize the root cortex under low-soil-phosphate (P) conditions, whereas infection is limited under high-P conditions. Fungal growth under both P conditions might be influenced by plant defence-related gene expression. In this study, we used in situ hybridization methods to compare the cellular localization of three defence-related mRNAs in non-infected bean roots and in relation to fungal infection units. In non-infected and infected roots, mRNAs encoding acidic and basic endochitinases were generally most abundant in the vascular cylinder. High-P-grown mycorrhizal roots showed localized accumulation of the acidic endochitinase mRNA in cortical cells containing arbuscules and in their immediate vicinity (one to five cell layers). The pattern of accumulation of the basic endochitinase mRNA was not affected by P or AM fungal infection. At the low P concentration, the β-1,3-glucanase mRNA accumulated predominantly in the vascular cylinder of non-infected roots. Suppression of β-1,3-glucanase mRNA accumulation in these tissues was observed in non-infected roots at the high-P and in mycorrhizal roots at both P concentrations. The observed suppression extends at least several mm from fungal infection units, characterizing a systemic effect. Beta-1,3-glucanase mRNA accumulated also around a number of cortical cells containing arbuscules only at the low P concentration. The localized accumulations of the endochitinase and β-1,3-glucanase mRNAs suggest that the encoded proteins might be involved in the control of intraradical fungal growth.

Calluna vulgaris L. (Hull) is not one of the usual hosts of the winter moth, Operophtera brumata L., but outbreaks have caused extensive damage to heather moorland in Scotland in recent years. This study investigated the potential role of environmental change in such outbreaks by rearing O. brumata larvae on C. vulgaris plants grown in open-top chambers for 20 months with enriched CO2 (600 ppm) and nitrogen supply (average 52·5 kg N ha−1 yr−1) in factorial combination. This prolonged exposure to elevated CO2 caused no change in shoot growth, photosynthesis or foliar C[ratio ]N ratio of C. vulgaris, even with increased N supply, indicating that the absence of response was not due to N limitation. Increased N supply itself resulted in increased shoot growth and a decrease in tissue C[ratio ]N ratio. Phenolic content did not change in response to either CO2 or N enrichment, contrary to the predictions of the carbon/nutrient balance hypothesis. In line with the absence of plant response, there was no effect of CO2 on the development of Operophtera brumata on C. vulgaris, and so continued increase in atmospheric CO2 concentration is unlikely to affect directly O. brumata outbreaks on heather moorland. Operophtera brumata showed increased larval development, growth rate and pupal weight on N-treated plants, correlated both to the decrease in foliar C[ratio ]N ratio, and to the increase in shoot extension which was predictive of survivorship. Thus, increased atmospheric N deposition, or increased rates of mineralization in a warmer environment, might increase the severity of O. brumata outbreaks on C. vulgaris. Since the combination of high N availability and disturbance of heather canopy by herbivory is known to result in increased dominance of grasses, it is suggested that this could lead to further degradation of moorland in upland Britain.

We tested how nitrogen availability affects suitability of ectomycorrhizal (ECM) and non-mycorrhizal Pinus sylvestris (L.) for a polyphagous insect herbivore. Seedlings grown on sterile agar at two N levels, were infected or not with the ECM fungus Cenococcum geophilum (Sow.) Ferd. & Winge. Ultrastructural observations showed that C. geophilum formed well-developed ectomycorrhizas in pine roots. After mycorrhizal establishment, oviposition preference of the polyphagous tarnished plant bug (Lygus rugulipennis Popp.) was determined in three different experiments. The duration of these experiments and the amount of irradiance were different. Nitrogen level or mycorrhizal treatment did not have significant effects on oviposition preference. However, mycorrhizal seedlings were favoured as an oviposition site at the lower N level, but only in expt 1. Total or individual terpene, total resin acid and total or individual sugar concentrations in pine shoots were not altered by treatment. Total phenolics concentration in pine shoots and roots was also the same in different treatments. Of individual resin acids, the concentration of dehydroabietic acid was increased after mycorrhizal treatment. Total resin acid, abietic acid and sandaraco pimaric acid concentrations correlated negatively with the number of Lygus eggs, but the correlations were only marginally significant. Of individual terpenes, β-pinene and bornylacetate concentrations had a significant positive correlation with the number of Lygus eggs. Greater amounts of N predictably increased total N concentration in pine seedlings in expts 1 and 2, but mycorrhizal infection increased total nitrogen concentration only in expt 3. Total N concentration did not correlate with the number of Lygus eggs in expts 1 and 2. An early stage of mycorrhizal development did not provide mycorrhizal benefits to the host plant as a higher nutrient concentration or as increased growth. These results suggest that host–plant quality might be involved in selection of oviposition site by L. rugulipennis, but ectomycorrhizal infection at this level does not seem to be an important mediator.

The influence of the root holoparasitic angiosperm Orobanche minor Sm. on the biomass, photosynthesis, carbohydrate and nitrogen content of Trifolium repens L. was determined for plants grown at two CO2 concentrations (350 and 550 μmol mol−1). Infected plants accumulated less biomass than their uninfected counterparts, although early in the association there was a transient stimulation of growth. Infection also influenced biomass allocation both between tissues (infected plants had lower root[ratio ]shoot ratios) and within tissues[ratio ]infected roots were considerably thicker before the point of parasite attachment and thinner below. Higher concentrations of starch were also found in roots above the point of attachment, particularly for plants grown in elevated CO2. Elevated CO2 stimulated the growth of T. repens only during the early stages of development. There was a significant interaction between infection and CO2 on growth, with infected plants showing a greater response, such that elevated CO2 partly alleviated the effects of the parasite on host growth. Elevated CO2 did not affect total O. minor biomass per host, the number of individual parasites supported by each host, or their time of attachment to the host root system. Photosynthesis was stimulated by elevated CO2 but was unaffected by O. minor. There was no evidence of down-regulation of photosynthesis in T. repens grown at elevated CO2 in either infected or uninfected plants. The data are discussed with regard to the influence of elevated CO2 on other parasitic angiosperm-host associations and factors which control plant responses to elevated CO2.

Differences between individuals collected from sun and shade populations could result from either somatic or genetic differences, particularly in populations of perennial plants. Our objective in this study was to separate somatic from genetic differences. We collected Anthoxanthum odoratum and Plantago lanceolata from sun and shade populations and made measurements on both vegetatively propagated clones and seed progeny from each clone. The parental populations differed in a wide range of physiological and morphological traits. However, only photosynthetic capacity was significantly different between both the original sun and shade populations and their seed progeny. In both species, plants from the sun population had higher photosynthetic capacities than those from the shade population when grown in a common environment. This demonstrates that there was genetic differentiation between the sun and shade populations. Photosynthetic capacity of parents and offspring also differed, suggesting a somatic effect. Since many of the original clones were virus-infected, but all but one of the offspring were virus-free, this might have been a result of virus infection. However, in spite of the fact that the parents and offspring clones were propagated vegetatively so that the plants were at the same developmental stage at the time of measurement, we cannot rule out the possibility that differences in age of cell lines could also have been a factor.

Impacts of defoliation on the growth and physiology of sugar maple (Acer saccharum Marsh.) and trembling aspen (Populus tremuloides Michx.) were examined in ambient and CO2-enriched atmospheres. Saplings were grown for 70 d in controlled environments, wherein CO2 mole fractions averaged either 356 μmol mol−1 or 645 μmol mol−1, under a PPF of 500 μmol m−2 s−1. On day 49 of the study, 50% of the leaf area was removed from a subset of each species in both CO2 environments. Relative growth rate (rgr) and its physiological and morphological determinants were monitored before and after defoliation. For non-defoliated saplings of both species, a slight stimulation of rgr (c. 5%) in elevated CO2 led to a modest increase (9–11%) in final sapling weight. In the case of maple, the minimal growth response corresponded with minor CO2 effects on specific leaf area (sla) and leaf weight ratio (lwr), and an apparent CO2-induced down-regulation of photosynthetic metabolism. For aspen, the CO2 stimulation of photosynthesis was largely offset by a decrease in sla. Responses to defoliation differed markedly between species and CO2 environments. Defoliation decreased maple rgr in ambient CO2, whereas the opposite occurred in elevated CO2. The latter led to complete recovery of plant weight (compensation), and was attributed to a defoliation-induced increase in carbon allocation to new leaves, along with a reversal of photosynthetic CO2 acclimation in that foliage. In both environments, aspen rgr increased after defoliation, facilitating almost full compensation. Defoliation increased light penetration into the aspen canopy, and it was estimated that the resultant stimulation of photosynthesis in lower leaves would have more than offset the concomitant decrease in lwr. CO2 enrichment might substantially enhance the ability of certain tree species to recover from herbivory. Moreover, responses to elevated CO2 might be largest in the presence of stresses, such as herbivory, that decrease plant source[ratio ]sink ratios.

Phytosiderophore (PS) release occurs under both iron and zinc deficiencies in representative Poaceae and has been speculated to be a general adaptive response to enhance the acquisition of micronutrient metals. We tested this hypothesis within an on-going study of the role of micronutrient metal nutrition for patterns of spontaneous vegetation in relation to soil pH and carbonate content. Hordelymus europaeus (L.) Harz, a negative grass species commonly found on soils rich in CaCO3 in Western Central Europe, was subjected to deficiencies of Fe, Zn, Mn and Cu using chelator-buffered nutrient solutions. PS release rates were determined at 3–5 d intervals during onset and development of deficiency symptoms. Plant dry matter yields and nutrient concentrations, measured at three time points were used to construct growth curves for calculation of PS release per unit root mass. In comparison with trace metal-sufficient control plants, dry matter production was markedly reduced in the Fe, Zn, Mn and Cu-deficiency treatments, with final relative yields of 6, 11, 15 and 31%, respectively. The phytosiderophore produced under Fe- and Cu-deficiency treatments was identified, using HPLC, as desoxymugineic acid. The highest rate of PS release (18 μmol g−1 root d. wt in 2 h) was measured in the Fe-deficiency treatment, and there was substantial release in the Cu-deficiency treatment (7·25 μmol g−1 root d. wt in 2 h). No PS release above control levels (2·6 μmol g−1 root d. wt in 2 h) was observed in the Zn- or Mn-deficiency treatments (1·5 and 2·6 μmol g−1 root d. wt in 2 h, respectively). It remains to be clarified whether PS release in response to Cu deficiency is a primary reaction to the deficiency, or is caused by a chain of events similar to that observed in Zn-deficient wheat, which involves internal Fe deficiency. Our results suggest that PS release in the native plant species H. europaeus is a specific response to Fe and Cu deficiency and is not significantly induced in response to deficiencies of Zn and Mn. Induction of the PS mechanism in different plant species might be more diverse than previously thought.

Mycorrhizas can produce negative crop responses when phosphorus availability is sufficient in agricultural soils because the fungi are of no benefit in nutrient acquisition yet continue to colonize roots and invoke parasitic costs. Benomyl fungicide was used to test this prediction in the field by limiting mycorrhizal colonization of 2-yr-old Valencia orange trees (Citrus sinensis (L.) Osbeck) on four rootstocks of varying mycorrhizal dependency in P-deficient soil fertilized with and without phosphate. No known fungal pathogens of citrus roots controlled by benomyl were present on the trees or in the field soil. Young trees with or without P fertilization and benomyl treatment remained sufficient in P ([ges ]0·10% leaf P) throughout the 27-month study. Root zone drenches of benomyl reduced mycorrhizal colonization and leaf P status of Valencia orange trees on the three slower-growing rootstocks, trifoliate orange (Poncirus trifoliata (L. ) Raf.), Swingle citrumelo (Citrus paradisi Macf.×P. trifoliata) and sour orange (Citrus aurantium L.), for the duration of three growing seasons. Benomyl affected root colonization and P status of trees on the faster-growing rootstock, Volkamer lemon (Citrus volkameriana Tan. and Pasq.), less than for trees on the slower-growing rootstocks and the effects were sustained for only two seasons. The shorter duration of benomyl effect for trees on Volkamer lemon rootstock compared with the slower-growing rootstocks was explained by the loss of inhibition of mycorrhizal activity when roots grew out of the drench zone and mycorrhizas were no longer in direct contact with the fungicide. Benomyl treatment increased growth rate of Valencia orange on the slow-growing rootstocks from 5 to 17% after three seasons, and from 2 to 9% on Volkamer lemon rootstock after two seasons compared with the non-benomyl treated trees. The benomyl effect was attributed to reduction of costs of root colonization over time, and consequently, a greater availability of carbon assimilate for shoot growth of trees. Since mycorrhizal fungi are ubiquitous in fertilized agricultural soils and obligate biotrophs on the roots of most crop species, these results indicate a need to further investigate whether negative growth responses of P-sufficient plants in the field occur because mycorrhizal fungi are no longer behaving as mutualists.

The purpose of this work was to establish how the distribution of local curvatures changed during the mushroom stem gravitropic reaction and to suggest a suitable mathematical model based on these new data.

The gravitropic bending of base- and apex-pinned Coprinus cinereus (Fries) S. F. Gray stems was recorded on videotapes. The images were captured from the tapes after each 10 min, rotated by 45° and transformed into tables of changing co-ordinates of points for each stem. The non-linear regression of these points was performed using Legendre polynomials. From the resulting equations the patterns of changing local curvature for 50 subsections per stem during 400 min of gravitropic reaction were calculated.

It was observed that base-pinned stems first bent from the apex, but later the curvature of this part decreased, and in the late stages the apex became nearly completely straight again. Subsections, located about one third of stem length from the base determined the main part of the final curvature. The free basal part of the apex-pinned stems bent upward and after a certain bending time also began to straighten. However, this process started significantly later and was weaker. Bending of the subsections close to the pinned apex did not stop when they reached the vertical position, and the final angle of gravitropic curvature could exceed 180°.

Plotting various functions of local bending speed and its derivatives against each other and against local angle indicated that, if the hypothetical signal about reorientation arises in the apex, its propagation towards the base did not follow simple wave or simple diffusion laws. The importance of the local angle of all subsections both for signal origin and transmission was established and a signal transmission equation, involving local angle of each subsection, was derived. After creating a suitable program this partial differential equation was solved numerically. The generated shapes of the bending stem coincided in high degree with experimentally observed images.

Eucalyptus coccifera Hook., a plant capable of forming both arbuscular mycorrhizas and ectomycorrhizas, was used to compare the effects of the two mycorrhizal types on phosphorus uptake and C allocation. Seedlings were grown in a P-deficient soil/sand mixture inoculated with peat/vermiculite spawn of Laccaria bicolor (Maire) Orton or Thelephora terrestris (Ehrh.) Fr.; or with 250-μm sievings from leek colonized by Glomus caledonium (Nicol. & Gerd.) Trappe & Gerde., Glomus sp. type E3 or Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or with autoclaved spawn (non-mycorrhizal control). Before the 89-d harvest, a subset of the harvested plants was labelled with 14C (45–60-min pulse, 202-h chase). Growth promotion and the increase in seedling P content was largest in the two ectomycorrhizal treatments. Production of fluorescein diacetate-stained external hyphae was three to seven times higher by ectomycorrhizal (ECM) fungi compared with arbuscular mycorrhizal (AM) fungi and was highly correlated with P uptake and shoot weight. Phosphorus inflow rates of ECM and AM seedlings were 3·8 times, and 2·0–2·7 times those of non-mycorrhizal seedlings. Phosphorus acquisition efficiencies were similar (11·2 and 10·0 μmol P mmol−1C for T. terrestris and Glomus E3 plants, respectively) for the two mycorrhizal types, and appeared to be greater than in uninoculated plants (7.2 μmol P mmol−1C) grown at the same P level.

To analyse the effect of arbuscular mycorrhizal (AM) colonization on tomato gene expression, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) patterns of crude extracts, soluble and membrane proteins of tomato roots, either mycorrhizal and the AM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or non-mycorrhizal, have been compared. In the three fractions analysed, AM colonization induced up-regulation with down-regulation of the synthesis of polypeptides already present in tomato roots and induction of some new polypeptides. Separation of root extracts into soluble and membrane fractions allowed us to identify two soluble, and five membrane-bound, newly induced polypeptides in AM roots. Comparison of the protein patterns of AM roots with those of the external mycelium of G. mosseae showed that one of the newly induced polypeptides might correspond to a fungal polypeptide. By using this experimental approach, we have been able to detect 44 polypeptides that are differentially displayed in tomato roots as a consequence of the establishment of the AM symbiosis.

One hundred and sixty-eight sterile endophytic mycelia were isolated from roots of four Woollsia pungens (Cav.) F. Muell. (Epacridaceae) plants collected from a field site in New South Wales, Australia. All isolates formed typical ericoid mycorrhizal structures when inoculated onto roots of Vaccinium macrocarpon Ait. (Ericaceae). Microsatellite-primed PCR fingerprints generated using the primers (GTG)5 and (GACA)4 indicated that considerable genetic diversity exists within the endophyte population. It was estimated that a minimum of 43 genetically distinct mycelial genets were present in the root systems of the sampled W. pungens population, with most genets confined to individual plants. Two genets, however, were present within the root systems of two adjacent plants. While most genets were represented by less than eight isolates, three genets contained up to 41 isolates, suggesting that root system colonization by some endophytic mycelia might be extensive.

The ability of four species of vesicular–arbuscular mycorrhizal (VAM) fungi to increase phosphorus uptake and growth of clover plants (Trifolium subterraneum L.) at different levels of soil compaction and P application was studied in a pot experiment. Dry matter in the shoots and roots of clover plants decreased with increasing soil compaction. Colonization by Glomus intraradices Schenck & Smith and Glomus sp. City Beach WUM16 increased plant growth and P uptake up to a bulk density of 1·60 Mg m−3, although the response was smaller as soil compaction was increased. Glomus etunicatum Becker & Gerdeman and Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe had no effect on the shoot d. wt and P uptake when the bulk density of the soil was [ges ]1·40 and [ges ]1·60 Mg m−3, respectively. Soil compaction to a bulk density of 1·60 Mg m−3 had no effect on the percentage of root length colonized by G. intraradices and Glomus sp. City Beach, but total root length colonized decreased as soil compaction was increased. Decreased P uptake and growth of clover plants colonized by G. intraradices and Glomus sp. City Beach, with increasing soil compaction up to a bulk density of 1·60 Mg m−3, was mainly attributed to a significant reduction in total root length colonized and in the hyphal biomass. Soil compaction, which increased bulk density from 1·20 to 1·75 Mg m−3, reduced the O2 content of the soil atmosphere from 0·16 to 0·05 m3 m−3. The absence of any observable mycorrhizal growth response to any of the four species of VAM fungi in highly compacted soil (bulk density = 1·75 Mg m−3) was attributed to the significant decrease in the O2 content of the soil atmosphere, change in soil pore size distribution and, presumably, to ethylene production.