Showing papers in "New Phytologist in 1988"

Early events of vesicular-arbuscular mycorrhiza formation on Ri T-DNA transformed roots

Abstract: An in vitro system using Ri T-DXA transformed roots and the vesicular-arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall has been developed to study the initial events of mycorrhiza formation. Sucrose, sodium and phosphorus were found to be critical components of the medium used to establish the dual culture. Using a single spore as inoculum it was consistently possible to obtain colonization of a preselected point on the root and to time the colonization process (within 5 days). Abundant viable and aseptic spores can be obtained. The system is especially appropriate for studying the triggering of the fungal biotrophy towards the root.

Temperature and algal growth

Abstract: summary Genotypic variation in the temperature optimum for resource-saturated growth of microalgae has been used to provide envelopes of μm (maximum specific growth rate) as a function of temperature. The Q10 value for μm for batch-cultured algae with optimal growth temperatures in the range 5–40°C is 1.88; rather higher values (Q10= 2.08–2.19) are found, albeit with lower μ values at a given temperature, for continuous cultures. The envelope approach selects μ values for the smallest cells from the taxa (members of the Chlorophyta and Bacillariophyta) with the highest μ values at a given temperature. Larger cell size, or membership of the Dinophyta, gives a decreased μ at a given temperature. Phenotypic change in μ, within a given genotype grown at sub-optimal temperatures, has a Q10 in excess of 1.88. Analysis of constraints on the resource-saturated value of μ in the fastest-growing micro-algae suggest that, at their temperature optima, the cells are close (within a factor of 2) to their maximum potential growth rate, based on the known kinetic properties of their catalysts, the need for kinetic heterogenity in catalyses in metabolic pathways, and the need to allocate some cell resources to structural and storage components. Phenotypic and genotypic responses to lower temperatures for growth, in terms of reallocation of resources to increase the quantity per unit biomass of catalyst? as a means of offsetting lower catalytic capacity at lower temperatures, are limited. An exception is the light-harvesting and reaction centre apparatus which catalyses the temperature-insensitive processes of light absorption, excitation energy transfer and primary photochemistry, and which is present (as assayed by photosynthetic pigment per unit biomass) in smaller relative amounts during resource-saturated growth at lower temperatures. The involvement of other low-temperature ‘adaptations’ (e.g. homeoviscous behaviour of thylakoid membranes) in offsetting low temperature effects on catalytic rates is not clear. The scope for increasing the quantity of temperature-sensitive catalysts in the biomass as a means of offsetting the effects of low temperature on resource-saturated μ is potentially higher in the Dinophyta with their relatively low μ at their temperature optimum; however, this option does not appear to be taken up by the Dinophyta which have unexceptional Q10 values for μ. For resource-limited growth, the phenotypic effect of suboptimal temperatures on growth, when light is the limiting resource, is often less marked than when growth is light saturated. When a chemical nutrient is limiting, the temperature effect on growth of a given genotype is often, but not invariably, decreased. Cases in which the effect of temperature on growth rate is decreased under light-limiting conditions can be interpreted in terms of the intrinsically low Q10 of growth when temperature-insensitive reactions (light absorption, excitation energy transfer, primary photochemistry) are limiting and the acclimatory effects of changed temperature and light regimes for growth on resource allocation between pigment-protein complexes and downstream catalysts of temperature-sensitive reactions. Cases in which light-limited growth rate is quite temperature sensitive may be accounted for by a decrease in absorptance as a result of a lower pigment content per cell at low growth temperatures. For growth limited by chemical nutrients, the variable responses make analysis difficult. It is tempting to assign a low Q10 for μ under these conditions to a limitation by some transport process (diffusion through unstirred layers, or, less plausibly, the cell membrane) with a low Q10, although the evidence favouring this interpretation is not abundant.

Secretory tissues in vascular plants

Abstract: SUMMARY Secretory tissues occur in most vascular plants. Some of these tissues, such as hydathodes, salt glands and nectaries, secrete unmodified or only slightly modified substances supplied directly or indirectly by the vascular tissues. Other tissues secreting, for instance, polysaccharides, proteins and lipophilic material, produce these substances in their cells. The cells of secretory tissues usually contain numerous mitochondria. The frequency of other cell organelles varies according to the material secreted. In most glandular trichomes the side wall of the lowest stalk cell is completely cutinized. This prevents the secreted material from flowing back into the plant. The salt glands in Atriplex eliminate salt into the central vacuole of the bladder cell but, in other plants, the glands secrete salt to the outside. Different views exist as to the manner in which salt is eliminated from the cytoplasm. According to some authors, the mode of elimination is an eccrine one, while others suggest the involvement of membrane-bound vesicles. Nectar is of phloem origin. The pre-nectar moves to the secretory cells through numerous plasmodesmata present in the nectariferous tissue. Nectar is eliminated from the secretory cells by vesicles of either KR or dictyosomal origin. In some cases, both organelles may be involved but an eccrine mode of nectar secretion has also been suggested by some authors. Carbohydrate mucilages and gums are synthesized by dictyosomes but virtually every cell compartment has been suggested as having a role on the secretion of lipophilic substances. Most commonly, plastids are implicated in the synthesis of lipophilic materials but KR may also play a part. In some cases lipophilic materials may be transported towards the plasmalemma in the KR. Resin and gum ducts of some plants develop normally or in response to external stimuli, such as microorganisms or growth substances. Among the latter, ethylene is the most effective. During the course of evolution, secretory tissues seem to have developed from secretory idioblasts scattered among the cells of the ordinary tissues. Subsequently ducts and cavities developed and finally secretory trichomes.

The iron and molybdenum use efficiencies of plant growth with different energy, carbon and nitrogen sources

Abstract: SUMMARY Iron has many catalytic roles in photosynthesis, respiration and nitrogen assimilation; molybdenum is involved in NO3 and (usually) N2 reduction. This paper concentrates on computing the efficiency of use of Fe and Mo in growth of organisms growing with different mixtures of the major resources photons, carbon and nitrogen. This computed efficiency is defined as mol C assimilated (mol catalytic metal in the organism)-1 s-1. The efficiency is computed from the known in vivo involvement of Fe- and Mo-containing enzymes, the specific reaction rate of these enzymes, the specific rate of these enzymes in vitro, and the growth requirements for the products of the reactions, for organisms using different energy, carbon and nitrogen sources. The predicted Fe use efficiency is greater for chemo-organotrophic than for photolithotrophic growth with a given nitrogen source, and increases in the order N2 NO3- NH4+ for growth with different nitrogen sources in the presence of constant photon and carbon availability. The predicted changes with variations in nitrogen source are greater than those with variations in photon and carbon source. These predicted values may be compared with observed metal use efficiencies, defined as mol C assimilated (mol total metal in the organism)-1 s-1. Relatively few such observed values are available From the literature. For Fe in photolithotrophically growing microalgae the observed values can be as low as 16–17% of the predicted values, i.e. 83–84% of the Fe in the organism is not accounted for by known catalytic uses of Fe if the catalysts are operating at their maximum specific reaction rates. One possibly discordant prediction relates to the Fe and Mo cost of N2 fixation; the computations suggest that in vitro estimates of nitrogenase activity may be less than those sometimes found in vivo. The predictions also have possible implications for resource availability interactions (photons, carbon, nitrogen, Fe, Mo) in natural conditions.

Phragmites australis– A preliminary study of soil‐oxidizing sites and internal gas transport pathways

Abstract: SUMMARY The possible pathways of oxygen transport within Phragmites australis and out into the soil were investigated by means of pressurized air flow, methylene-blue dye and by anatomical studies. In most cases, gas was easily forced through the plants, thus demonstrating gas-space connexion between aerial shoot, rhizomes and roots and a relatively low resistance to flow. Gas-space connexions between the pith cavity and cortical aerenchyma in the rhizomes were also detected and were investigated anatomically they are present only in nodal regions just above the insertion of the pith diaphragm and take the form of radial channels through the stelar cylinder. Similar pathways in the culm connect the pith cavity with nodal lines of stomata and it is suggested that these regions may often form the major oxygen entry point to the rhizome-root system. A failure to effect pressurized gas-flow through some rhizomes led to the detection of secondary barriers to longitudinal gas-flow. Seemingly a response to wounding, these are an impenetrable barrier to gases, to flooding, and probably also to microorganisms, and take the form of tylosoidal growths from and within regions of stellate-and/or circumvascular-parenchymas such as those of the nodal diaphragms. Stellate parenchymas of various sorts were found to be a common feature of the gas-path in Phragmites and evidently they form an important component of the gas-space system occurring within the nodal radial channels, the nodal diaghragms and, rather unusually, the root-shoot junctions where they must confer a porosity which is higher than for most plants. As measured by methylene-blue oxidation, oxygen release from underground parts was most rapid from young adventitious and secondary roots and particularly basal tufts of fine laterals. Zones of oxidation also occurred around the sprouting tips of horizontal and vertical rhizomes. Dormant tips showed very little oxidizing power, whilst the rhizomes themselves and the older parts of adventitious roots showed none. This was associated with cuticularization of the rhizome and hypodermal suberization and lignification; oxygen-impermeable regions of the roots were also hyperdermally suberized and lignified. The findings are discussed in relation to the use of Phragmites in sewage-treatment beds.

Different strategies of drought resistance in three Mediterranean sclerophyllous trees growing in the same environmental conditions

Abstract: SUMMARY Measurements have been made of leaf conductance to water vapour, relative water content and water potential in Olea oleaster Hoffmgg et Link, Ceratonia siliqua L. and Laurus nobilis L., three evergreen sclerophyllous trees growing in Sicily at sea level. Measurements were made hourly in May and September 1986. Although all the three species are regarded as components of a homogeneous group (sclerophylls) and they all showed a high degree of sclerophylly, the strategies they adopted to withstand drought were completely different. Olea oleaster behaved as a ‘drought-tolerating’ species. Drought was ‘avoided’ by Ceratonia siliqua by a ‘water-spending’ strategy and by Laurus nobilis by a ‘water-saving’ strategy combined with the capability of recovering even minimal water losses by dropping leaf water potential drastically. Such differences in drought resistance are discussed in terms of differences in the bulk elastic modulus of leaf cells and wood anatomy.

Non‐uniform stomatal closure induced by water stress causes putative non‐stomatal inhibition of photosynthesis

Abstract: summary The partial pressure of intercellular CO2 derived from gas exchange data for water-stressed grapevine (Vitis vinijera L.), oleander (Nerium oleander L.) and red-flowering gum (Eucalyptus ficifolia F. Muell.) does not indicate the actual average intercellular CO2 of the leaf. This can be determined from chlorophyll fluorescence signals and modelled from conventional gas exchange information. Water stress increases endogenous levels of abscisic acid and the leaves respond in a similar manner to that observed when exogenous abscisic acid is applied. Autoradiograms show that water stress results in non-uniform gas exchange over small areas of the leaf. Non-uniform stomatal closure can account for the apparent non-stomatal inhibition of photosynthesis in plants experiencing water stress.

Stomatal closure fully accounts for the inhibition of photosynthesis by abscisic acid

Abstract: SUMMARY The partial pressure of intercellular CO2 calculated from gas exchange data for abscisic acid-treated leaves of grapevine (Vitis vinifera L.) and sunflower (Helianthus annuus L.) does not indicate the average intercellular CO2 of the leaf. The latter can be determined from chlorophyll fluorescence quenching information and accurately modelled from gas exchange data. Stomatal closure can fully account for previously assumed non-stomatal inhibition of photosynthesis. Autoradiograms show that abscisic acid induces non-uniform gas exchange over small areas of the leaf.

Structural and ultrastructural disorders in cadmium‐treated bush bean plants (Phaseolus vulgaris L.)

Abstract: summary The effect of a growth reducing cadmium concentration (5 μg ml−1) on the structure and ultrastructure of leaves, stomata and plastids of bush bean plants (Phaseolus vulgaris L. cv. Contender) grown on perlite was studied using light, transmission electron and scanning electron microscopy. The structural and ultrastructural alterations observed were not directly related to the average Cd content of the whole organs. In roots, where the highest Cd concentration was found, plastid ultrastructure was hardly affected, while in the upper parts of the plant the chloroplasts showed severe alterations. Disruption of chlorophyll synthesis and plastid ultrastructure was greater in young trifoliate leaves than in primary leaves. The effects of Cd toxicity on the structure and ultrastructure and their physiological implications are discussed in relation to Cd uptake.

Vesicular–arbuscular mycorrhizas and the soil‐disturbance‐induced reduction of nutrient absorption in maize

Abstract: summary In previously reported studies, maize seedlings absorbed more phosphorus (P) from soil in a long-term zero-till system than from the same soil after disturbance. This partly resulted from greater vesicular-arbuscular (VA) mycorrhizal infection in the undisturbed soil. In the study reported herein, a growth room experiment was conducted to determine how long a soil must remain undisturbed before subsequent disturbance will reduce P absorption. Starting with disturbed soil, maize was grown for 3-week cycles. At the conclusion of each growth cycle, half of the pots were disturbed and replanted whereas the other half was replanted without disturbing. Over the three growth cycles, major increases in mycorrhizal infection in the plants in the undisturbed soil were observed concurrently with the increases in nutrient absorption. A significant increase in P absorption occurred in the first growth cycle on undisturbed soil and greater increases occurred after the second and third. At 21 d in the third growth cycle, plants grown in the undisturbed soil had almost twice the dry weight of plants grown in the disturbed and had higher concentrations of N, P, Mg, Cu and Zn in the shoots. Absorption of P between 14 and 21 d of the third growth cycle in the undisturbed soil was 10 times larger than that in the disturbed soil. Absorption of N, Mg, Cu and Zn was more than three times larger. In the third growth cycle, concentrations of N, P, Mg and Zn in the shoot and intensity of VA mycorrhizal infection were greater in the undisturbed soil as early as 14 d after planting. There was a concurrent and rapid increase in VA mycorrhizal infection and P absorption by maize over three growth cycles when an initially disturbed soil was left undisturbed. This rapid concurrent development, particularly starting from an initially disturbed soil, provides good evidence that soil disturbance reduces VA mycorrhizal infection and hence P absorption by maize.

Mycelial uptake, translocation and assimilation of nitrogen from 15N-labelled ammonium by Pinus sylvestris plants infected with four different ectomycorrhizal fungi

Abstract: The uptake and assimilation of 15N-labelled ammonium was followed in Pinus sylvestris L. plants infected with four different ectomycorrhizal fungi, Rhizopogon roseolus Fr. Suillus bovinus (Fr.) O. Kuntze, Pisolithus tinctorius (Fr.) Fr. and Paxillus involutus (Mich. ex Pers.) Cohen & Couch. Plants were grown in flat perspex observation chambers or in Petri dishes containing non-sterile peat; in each case the fungal mycelium growing from a host plant was allowed to cross a barrier and to colonize an area of peat from which roots had been excluded. Labelled ammonium was fed to the mycelium, and the shoot, root and mycelial tissues analysed for total and 15N-labelled free amino acid contents after a feeding period of 72 h. High proportions of 15N-labelled glutamate/glutamine, aspartate/asparagine, and alanine were found in the fungal mycelia of all species except Pax. involutus where labelled aspartate/asparagine was not found. Lower proportions of labelled serine, threonine, tyrosine, lysine, ornithine and arginine were also found in the mycelium. The degree of 15N enrichment declined throughout the transport pathway but between 5 and 50% of the amino acids were 15N-labelled in the plant shoots. In total, at least 2-3% of the nitrogen supplied was assimilated as labelled amino acid during the 3 day feeding period, the largest amounts of labelling occurred in glutamic acid/glutamine and aspartic acid/asparagine.

Mycorrhizal growth responses: interactions between photon irradiance and phosphorus nutrition

Abstract: SUMMARY The effects of photon irradiance, phosphorus (P) supply and mycorrhizal infection [Glomus mosseae (Nicol. and Gerd) Gerdemann and Trappe] on growth and P uptake by Allium cepa L. were measured. Two experiments were carried out, one in a naturally-lit glasshouse and the other in a growth cabinet. Shade cloth was used to provide 'high' irradiance (600 and 550 yamol m-2 s-' in glasshouse and growth cabinet respectively) and 'low' irradiance (250 yamol m-2 s-1). Growth at high irradiance was associated with increases in total dry weight, root: shoot dry weight ratio and total root length and with decreases in shoot fresh weight: dry weight ratio. Mycorrhizal growth responses were lower at low irradiance and depressions were observed at high P supply and high irradiance, as well as at low irradiance. Mycorrhizal plants generally had higher shoot fresh weight: dry weight ratios than those of equivalent non-mycorrhizal plants. Mycorrhizal infection was lower in the presence of additional P in both experiments. In the glasshouse there was an interaction between low irradiance and high P, leading to very low values of fractional infection. This effect was not apparent in the growth cabinet. At high irradiance mycorrhizal plants had higher inflows than those of equivalent non-mycorrhizal plants at all levels of P, regardless of the growth response. Low irradiance had little effect on inflow into non-mycorrhizal plants, but depressed inflow into mycorrhizal plants. This reduction in inflow can be attributed in part to lower levels of infection, but an effect on P uptake by hyphae or on transport between the symbionts is also likely.

Underground transfer of nitrogen between pasture plants infected with vesicular-arbuscular mycorrhizal fungi

Abstract: SUMMARY Experiments were carried out to investigate the possibility that vesicular-arbuscular (VA) mycorrhizal infection of grass (Lolium perenne L.) and clover (Trifolium repens L.) roots can enhance the exchange of nitrogen between the root systems of nitrogen-fixing pasture legumes and associated grasses. The results showed higher rates of transfer of 15N applied as (15NH4)2SO4 to the clover plants to companion grass plants when the roots were mycorrhizal. In some cases but not all the grass grew better in the mycorrhizal treatments. An experiment in which the clover and grass roots were separated by a 60 μm (mean pore size) nylon mesh screen showed that translocation of the nitrogen was probably along the mycorrhizal hyphae. It was not clear from the data whether transfer was mediated by a common hyphal net or some other less direct means.

Fungal colonization of attached beech branches

Abstract: summary Fungal colonization of healthy beech (Fogus sylvatica L.) branches was studied by sectioning branch lengths and drying the sections under controlled regimes. Maintaining water saturation prevented any fungal development in the wood, while active mycelium was isolated as soon as 14 days after the start of the drying period. Fungi developing in these sections were naturally established in healthy branches in the field and formed a floristically denned group, dominated by Hypoxylon fragiforme (Scop.) Kickx., H. nummularium Buill.: Fr., Nectria coccinea (Pers.: Fr.) Fr., and Coniophora putaena (Fr.) P. Karst., and also included coelomycete species. This group was obtained independently of position of the branch in the canopy, season of sampling over an 11 -month period, and site, sampling including four sites in south-west Britain and one in the French Pyrenees. Several species in this group are specific or show a preference for beech as a host. Direct observations and isolation from sections with time indicated that whereas most species developed inwards from the bark, H. fragiforme and H. nummularium grew out from pockets within the wood. Each pocket contained a genetically different individual, as revealed by colony morphology and vegetative incompatibility tests. It was established that water content of the wood is the major determinant for the initial development of fungi in the xylem of beech, and that these early colonizers derive from inoculum latent in the healthy, living branches.

Ectomycorrhizal rain-forest legumes and soil phosphorus in Korup National Park, Cameroon

Abstract: SUMMARY The mycorrhizal status of a group of caesalpinioid legumes in lowland rain-forest in Korup National Park, SW Cameroon, was examined. Species in ten genera, Anthonotha, Aphanocalyx, Berlinia, Didelotia, Gilbertiodendron, Julbernardia, Microberlinia, Monopetalanthus, Tetraberlinia(tribe Amherstieae) and Afzelia(tribe Detarieae) were ectomycorrhizal. These species were not uniformly distributed in the forest, and three large emergent species Microberlinia bisulcata A. Chev., Tetraberlinia bifoliolata(Harms) Hauman, and T. moreliana Aubr. in particular appear to form groves c. 600 m across. This type of distribution may be related to the ectomycorrhizal habit. A previous large scale enumeration and soil survey on four 5 km transects of plots in the forest, carried out during the wet season, had revealed an association between these ectomycorrhizal legumes and low concentrations ( 5 μg g-1) of extractable phosphorus in the mineral soil. In the current study part of one of the original transects in a low phosphorus area of the forest, where ectomycorrhizal trees comprise 29 % of the basal area, was resampled at the subplot level during the dry season. Whereas in the wet season soil phosphorus had been lower (2·8 μg g-1) within the ectomycorrhizal groves than without (3·8 μg g-1), in the dry season the situation was reversed and the overall concentrations were higher (12·3 and 7·9 μg g-1 respectively). Ordination analysis re-affirmed the association of the three Microberlina/Tetraberlinia species with relatively low concentrations of extractable phosphorus in the wet season but relatively high ones in the dry season. The groves are characterized by high inputs of leaf litter in the dry season, extensive colonization of surface organic matter by ectomycorrhizas and hyphal strands, and high carbon: extractable inorganic phosphorus ratios in the mineral soil in the wet season. These features are discussed in relation to the presumed ability of ectomycorrhizas to utilize organic phosphorus.

Cell-wall-bound peroxidase activity in roots of mycorrhizal Allium porrum

Abstract: summary The activity of cell-wall-bound peroxidase in Allium porrum L. roots was measured during root growth and development of vesicular–arbuscular mycorrhiza with Glomus versiforme (Karst.) Berch. The peak of activity in infected plants was higher than in non-infected ones and occurred during the initial stages of fungal penetration. When the infection was established and the roots highly colonized the activity decreased to the levels in non-mycorrhizal roots. Ultrastructural localization using diaminobenzidine revealed an increase in the electron-dense deposits in the middle lamella corresponding with fungal penetration. No activity was seen in the matrix deposited around the intracellular fungal structures. The overall distribution of peroxidase activity was the same in mycorrhizal and non-mycorrhizal roots.

Acquisition of nitrogen by the shoots of land plants: its occurrence and implications for acid-base regulation

Abstract: summary The typical N source for terrestial vascular plants is the soil in which they are rooted. N exchange between the aerial shoot and its environment, as gaseous, dissolved or particulate N, can involve either net loss or net gain of N by the plant. Net gain of N by the plant shoot at the expense of its aerial environment can be significant, under natural or agricultural conditions, for all three forms of aerial N (NH3,N2,NO3), Gaseous N gain can be substantial, as NH3, for plants growing on soils receiving large inputs of animal excreta and faeces. Soluble N uptake by shoots is the major N source for ‘atmospheric’ epiphytes. Particulate N supply to shoots is a major N source for carnivorous plants. Experimentally, several plants which normally grow with N supply mainly via their roots can be grown with a predominant, or sole, supply via their shoots. Plant growth with CO2, as C source, SO42− as S source and H2PO4, as P source generates excess OH (∼ 0.78 OH−/N assimilated) in the synthesis of core metabolites when the N source is NO3− supplied to roots or shoots. All other N sources (except dicarboxylic amino-acids) yield excess H+during synthesis of core metabolites. NH4+ (in solution) supplied to roots or shoots yields some 1.22 H+/N assimilated, while NH3, N2 or NO2 supplied to shoots as gases, dissolved urea supplied to shoots or roots, and animal protein supplied to shoots of carnivorous plants, yields some 0.22 H+/N assimilated. These biochemically caused acid-base perturbations may be exacerbated (NO2) or partially or, occasionally, completely offset (NH3) by effects related to solution and dissociation of the gas in growing shoots. Assimilation of the shoot-acquired N in the shoots leads to somewhat different constraints on acid-base homoiostasis relative to those found with assimilation of root-acquired N. The shoot cannot generally excrete excess H+ or OH− to its environment (as is so for root-assimilation of N), nor can it dispose of H+ biochemically without co-operation of root metabolism and root–shoot and root-rhizosphere transport processes. Excess OH− from shoot-acquired and shoot-assimilated NO3− can, by contrast, be disposed of biochemically after the fashion of root-acquired, shoot-assimilated NO3−. Tentative conclusions as to the disposal of excess H+ generated in shoot acquisition and assimilation of N-sources other than NO3− and NO2− are different for rhizophytes and for haptophytes. Rhizophytes probably carry out a net synthesis of organic acid in the roots, with subsequent cation-H+ exchange at the root plasmalemma, transport of cation salt of the organic acid to the shoot in the xylem, and metabolism of the organic acid anion in the shoot to yield OH−. Haptophytes probably have an excess of liquid water supply over their needs for growth and transpiration due to the very low N concentration in this water; they thus have the potential for H+ (as strong acid) excretion to the excess surface water which is lost, at least in part, as liquid water.

The use of benomyl to control infection by vesicular–arbuscular mycorrhizal fungi

Abstract: SUMMARY The effect of the fungicide, benomyl, on vesicular arbuscular (VA) mycorrhizal infection and phosphorus uptake was studied in two pot experiments, using pea Pisum sativum L., mustard Sinapis alba L. and red clover Trifolium pratense L. Benomyl was either incorporated into the soil or sprayed on to the surface of the pot. Benomyl had no effect on concentrations of water-soluble P in soil but reduced VA mycorrhizal infection and P inflow in pea. Mustard plants were uninfected even in untreated pots and benomyl had no effect on P inflow in mustard. In clover, there was a positive correlation between shoot P concentration and percentage of root length infected with VA mycorrhizal fungi. Copper, zinc and manganese concentrations in clover shoots were affected by benomyl but this may not have been related to mycorrhizal infection. Benomyl is recommended as a treatment to control VA mycorrhizal infection, with many fewer undesirable consquences than result from soil sterilization.

Ascorbic acid-induced progression of quiescent centre cells from G1 to S phase

Abstract: summary Quiescent centre cells, which are known to have their cycle extended mostly in G, and to divide rarely, art-stimulated to undergo DNA synthesis in root meristems of Allium cepa L. by treatment with ascorbic acid. The effect of ascorbic acid is dramatic: 21% of all the cells in the quiescent centre remain in the G, phase while 79% enter S phase. From a mean value of 2204 × 103μ3 in water-grown roots, the volume of the quiescent centre drops to a mean value of 167 × 103μ3 following treatment with ascorbic acid. These results indicate that ascorbic-acid stimulates not only the activity of the quiescent centre cells but also cell proliferation in the entire root meristem. The rate of cell progression through the cycle may be related to cellular ascorbic acid content.

Iron-deficiency specifically limits nodule development in peanut inoculated with Bradyrhizobium sp

Abstract: Severely iron-deficient peanuts (Arachis hypogaaea L.) grown on calcareous soils in central Thailand failed to nodulate until given foliar iron applications. Glasshouse experiments were conducted on two cultivars (Tainan 9 and Robut 33-1) to identify which stage of the nodule symbiosis was most sensitive to iron-deficiency. Iron-deficiency did not limit growth of soil or rhizosphere populations of peanut liradyrhizobium. Similar numbers of root nodule initials formed in the roots of both control and iron-sprayed plants, showing that iron-deficiency did not directly affect root infection and nodule initiation. Plants sprayed with iron produced greater numbers of excisable nodules and carried a greater nodule mass than untreated plants. Five days after iron application, nodules on sprayed plants of CV. Tainan 9 contained 200-fold higher bacteroid numbers per unit weight and 14-fold higher concentrations of leghaemoglobain. The onset of nitrogenase activity was also delayed by iron deficiency in both cultivars. Tainan 9 appeared more sensitive to iron-deficiency than Robut 33-1 in terms of nodule mass produced, but both cultivars showed the same effect of iron-deficiency on nitrogenase activity per plant. It is concluded that the failure of the infecting rhizobia to obtain adequate amounts of iron from the plant results in arrested nodule development and a failure of nitrogen fixation.

The influence of ozone on the winter hardiness of Norway spruce [Picea abies (L.) Karst.]

Abstract: SUMMARY Three-year-old clonal saplings of Picea abies (L) Karst were exposed in chambers to 240μg O3 m-3 for 70 d, 6hd-1 and then hardened for 14 d at 4°C day/night The winter hardiness of trees was tested by subjecting excised shoots, bearing previous and current year's needles, to night temperatures of –6, –9, –12, –15 and – 18°C in a computer-controlled freezer No visible injury was observed during the fumigation, hardening period or on the current year's needles of any of the clones However, during post-freezing recovery in a mist spray unit four of the clones exposed to ozone developed extensive visible injury on the previous year's needles, in the form of severe, uniform necrosis The affected needles began to fall prematurely Induced chlorophyll fluorescence was significantly reduced by O3 in two of the clones that showed post-freezing injury This suggested that O3-induced membrane injury increased the sensitivity of needles to freezing One clone (no 4076), which exhibited no effect of ozone on fluorescence kinetics, showed severe ozone-induced injury of the previous year's needles, developing about 40 d after fumigation independent of temperature Previous year's needles of O3-treated plants of this clone showed significantly greater rates of euticular transpiration, so the O3 may have induced gradual desiccation of the needles The restriction of damage to the older needles of certain clones of Norway spruce is consistent with symptoms of forest decline affecting high-altitude forests on acid soils Results indicate that O3 predisposes trees to freezing injury, winter desiccation and drought, and it is proposed that such interactions are important factors contributing to the decline of high-altitude forests of Norway spruce in Europe

Competition between three species of Glomus used as spatially separated introduced and indigenous mycorrhizal inocula for leek (Allium porrum L.)

Abstract: SUMMARY The ability of three vesicular-arbuscular (VA) mycorrhizal fungi - Glomus caledonium (Nicol. and Gerd.) Trappe and Gerd., Glomus sp. type E3 and Glomus mosseae (Nicol. and Schenck) Gerd. and Trappe - to infect leek (Allium porrum L.), when used as spatially separated pairs of inocula was assessed by analysing the roots for the presence of diagnostic fungal enzymes after separation of root proteins by gel electrophoresis. A difference in competitiveness was observed, such that Glomus sp. E3 was unable to infect a root system if either G. caledonium or G. mosseae were also present. When the latter two fungi were used as a pair of inocula, the one which had been placed to simulate an indigenous strain predominated in the root to the almost total exclusion of the one placed as an introduced inoculum. These results suggest that the successful establishment of VA mycorrhizal inocula in field soils will depend on the indigenous species present, the species being introduced and its placement in the soil. The use of diagnostic fungal isozyme analysis offers a method of monitoring the outcome of an inoculation programme by detecting the presence of the introduced species in the host roots.

Dynamics of arbuscule development and degeneration in mycorrhizas of Triticum aestivum L. and Avena sativa L. with reference to Zea mays L

Abstract: SUMMARY A quantitative light and electron microscope study of developing and degenerating arbuscules of the mycorrhizal fungus Glomus fasciculatum (Thax. sensu Gerd.) Gerd. & Trappe in Triticum aestivum L. (wheat) and Avena sativa L. (oats) was carried out in order to estimate three parameters during the colonization cycle and to compare these parameters to those in Zea mays L. The parameters are: (1) Vv (f,c), the fraction of the host cell volume (c) occupied by a volume of fungus (f); (2) Vv,(cy, c), the fraction of the host cell volume occupied by host cytoplasm (cy); (3) Sv(p,c) the surface area-to-volume ratio of the host protoplast (p) to the whole host cell. Uninfected cortical cells of wheat had an Sv,(p,c) of 0.11 μm2μm −3 and those of oats 0.10 μm2μm −3. As the fungus penetrates the cell wall, the protoplast invaginates, causing a decrease in protoplast volume and an increase in St. In wheat this increase reached 1.17 μm2μm−3 and in oats, 1.04 μm2μm−3. When the arbuscule is mature, the fungus occupies 35% of the cell in wheat with 20% as branches and 15% as trunk. In oats, the fungus occupies 36% of the cell, with 23 % as branches and 13 % as trunk. In wheat, host cell cytoplasm was initially 39 % and increased to 21.6% and in oats, from 3.6 to 28.8%. These values are similar to those observed in Zea mays. The rates at which the parameters Vv(f,c) and Sv(p,c) changed during arbuscule development and degeneration were similar. The amount of encasement and host cell cytoplasm showed the greatest variation among host species.

Growth and nutrition of guayule (Parthenium argentatum) in a saline soil as influenced by vesicular–arbuscular mycorrhiza and phosphorus fertilization*

Abstract: SUMMARY Growth of guayule (Parthenium argentatum A. Gray) in a moderate and a highly saline-sodie soil was increased by inoculation with Glomus intraradices Schenck & Smith. The growth of guayule plants was stimulated equally by the addition to the soil of either 100 μg g1 of phosphorus (P) or inoculum of G. intraradices. Mycorrhizal plants had increased concentrations of PO4 and decreased concentrations of Na in shoot tissues compared to non inoculated control plants. Addition of 100/μgg 1 of P to the soil increased the accumulation of PO4 in the shoot tissues and in most instances decrease accumulation of Cu, Zn, Na, K, and SO4. Concentrations of Na, K, and Cl and frequently Mn in the shoot tissues were increased while the concentrations of PO4 and SO4 in shoot tissues were generally decreased by the addition of NaCl to the soil. Addition of 100μgg 1 of P to the soil did not markedly affect the colonization of guayule roots by G. intraradices. The roots of mycorrhizal guayule grown in soil with NaCl added contained decreased numbers of arbuscules and vesicles. Addition of both P and NaCl to the soil reduced the formation of arbuscules and vesicles and reduced the occurrence of moderate and heavy levels of root colonization.

Efficacy of native vesicular-arbuscular mycorrhizal fungi after severe soil disturbance

Abstract: SUMMARY Field and greenhouse experiments were conducted to determine whether the VA mycorrhizal fungi present on a site before surface coal mining could form effective mycorrhizas in the disturbed soil on the site after mining. The disturbed soil had different physical, chemical and morphological characteristics than the soil on the site prior to perturbation. Artemisia tridentata subsp. Wyomingensis Beetle and Young (Wyoming big sagebrush), inoculated or not with VA mycorrhizal fungi, was planted on the field site both as seed and as container-grown seedlings. The native VA mycorrhizal endophytes produced only limited amounts of mycorrhizal infection in the disturbed soil (approximately 20% of total root length) and after 2 years were found to have no significant effect on the establishment, growth or survival of sagebrush plants. In the greenhouse study, mycorrhiza development and efficacy was compared in native sagebrush-grassland soil and disturbed soil from the reclamation site with identical concentrations of mycorrhizal inoculum (19 propagules g−1). Mycorrhiza development in native soil greatly exceeded that in disturbed soil after 45 d growth (50 vs. 10% of total root length). Also, native mycorrhizal fungi effected significant increases in biomass production (+ 70%) and tissue phosphorus content (+ 70%) in sagebrush-grassland soil but not in reclamation soil. The ecological implications of these results are discussed.

Mycorrhizal associations of isolates of Sebacina vermifera

Abstract: SUMMARY Isolates of Sebacina vermifera Oberwinkler (Tremellaceae), identified by their teleomorphs, from orchid and non-orchid hosts have been examined for their mycorrhizal associations. All isolates stimulated germination of seed of species of Microtis (Orchidaceae). Three isolates from ectomycorrhizal hosts formed ectomycorrhizas on Melaleuca uneinata R. Br. ex Alton I. and other ectomycorrhizal plants. None of the orchid isolates nor an isolate which was endophytic in Phyllanthus formed ectomycorrhizas but in addition to species of Micron's they stimulated germination of one or more species of Caladenia, Cyrtostylis or Glossodia but not other terrestrial orchids. Protocorms of Microtis developed at depth in soil in the presence but not the absence of ectomycorrhizal S. vermifera on M. uneinata. Young albino plants of Microtis rara R. Br. grew for 4 months in the presence of ectomycorrhizal S. vermifera with M. uneinata but mycorrhizal albino plants on their own all died, suggesting a possible tripartite mycorrhizal association.

The role of co2 uptake by roots and cam in acquisition of inorganic c by plants of the isoetid life-form - a review, with new data on eriocaulon-decangulare l

Abstract: SUMMARY The isoetid life-form was originally defined on morphological grounds; subsequent physiological investigations showed that all of the isoetids examined took up a large fraction of the inorganic C fixed in their leaves from the root medium under natural conditions, and that some of them carried out much of their assimilation of inorganic C via a CAM-like mechanism. Root-dominated uptake of inorganic C appeared to be unique to, and ubiquitous in, the isoetids. I However, a large capacity for CAM-like metabolism in submerged vascular plants is not universal in isoetids, nor is it restricted to this life-form, being also found in Crassulaa aquatica. The work described here shows that submerged specimens of the North American Eriocaulon decangulare have a high fraction of their dry weight in the root system, a trait characteristic of isoetids but uncommon in other submerged vascular plants. E. decangulare has vesicular-arbuscular mycorrhizas, as do other flowering plant isoetids hut not, generally, submerged Isoetes spp. Under conditions of natural supply of inorganic C, E. decangulare, like other isoetids, takes up most of its inorganic C through its roots. Uptake of inorganic C by both roots and shoots involves CO2 rather than HCO3: photosynthesis at high external pH values does not exceed the rate of uncatalysed HCO3- to CO2 conversion in the medium and there is no detectable extracellular carbonic anhydrase activity. Measurements of titratable acidity and of malate content of leaves sampled at dawn and at dusk showed that E. decangulare, growing and tested under either emersed or submersed conditions, did not exhibit CAM-like behaviour. CAM was also absent from three non-isoetid aquatic macrophytes (Amphibolic antarctica, Eeklonia radiata and Vallisneria spiralis) which were examined. E. decangulare thus resembles all other isoetids tested in acquiring much of its inorganic C via the root system. E. decangulare also resembles most of the isoetids which are not members of the Isoetaceae (e.g.) E. septangulare, Lobelia dortmanna and Subularia aquatica) but differs from submerged Isoetaceae and Littorella uniflora in lacking CAM. The ecological significance of uptake of CO2 via the roots and, where it occurs, of CAM in isoetids may be related to either inorganic C or, via improved N use efficiency, inorganic C as a limiting resource. The isoetid life-forms has evolved independently in at last five different families of vascular plants; it probably derived fairly immediately from terrestrial or amphibious ancestors with a similar rosette form. Emergent Isoetaceae with acquisition of CO2 via roots and CAM probably evolved from submerged isoetids.

Swiss vegetation history during the last 18 000 years

Abstract: summary This paper gives a detailed outline of Swiss vegetation history during the last 18 000 years. For each pollen zone, a map is given showing vegetation development from the late Wurmian to the present. A concise historical review of the Swiss pollen analytical research during the last 60 years is presented is followed by some discussion of the central European glacial refugia. Based on a selection of over 100 pollen-analytically investigated sites, the development of Swiss vegetation since the late Wurmian can be presented as follows: 1 Oldest Dryas. After the Wurm maximum the ice network melted back quickly to small mountain glaciers. At some localities, several types of an Artemisia-Chenopodiaceae-Jitniperus-Ephedra-Helianthemim Poaceae steppe/tundra have been recorded, representing an apparent uniformity over the whole Swiss area. 2 Boiling Interstadial. This first, late Wurmian, warm phase is characterized by the occurrence of Betula, Hippophae, Juniperus, Ephedra and Salix. 3 Older Dryas, Little evidence for this period has yet been found in Switzerland. 4 Allerod Interstadial. This marked warm phase led to a typical late Wiirmian reforestation, with both Betula and Pinus up to about 1200–1600 m above sea level. 5 Younger Dryas. In the whole alpine area there is good evidence for this last, late Wurmian climate deterioration, which led to renewed glacier activity and to an alpine timber-line depression of 200–300 m. 6 Preboreal. For the central Alps and the Prealps a wide occurrence of Pinus sylvestris/mugo, P. cembra, Larix and Betula has been recorded, whereas in southern Switzerland the first mixed oak forest developed. 7 Boreal. Corytus and mixed oak forest spread in some cases rapidly over a wide area, chiefly in the Prealps, the Plateau, the Jura and in southern Switzerland. In the high mountains Pinus sylvestris/mugo, P. cembra and Larix still dominated. 8 Older Atlantic. In both the Plateau and the Prealps, Corylus and mixed oak forest dominated, whereas in the continental Alps Pinus sylvestris/mugo, P. cembra and Betula grew with some elements of mixed oak forest. In the Orisons the immigration of Picea from east to west has been identified; in the eastern Prealps Abies spread. 9 Younger Atlantic. This period is characterized by a first maximum of the timber-line extension to an altitude of about 2300 m. The spread ot Fagus from west to east is seen. On both the montane and subalpine belt, first Abies and later Picea dominated. Picea immigration to the west continued. 10 Subboreal. Until 3000 yr B. P. forest achieved its optimum development with a distribution up lo 2000 m above sea level. In both the Plateau and the Jura the major spread of Fagus took place in this period. Picea now reached southwestern Jura and even the Lake Geneva region. 11 Subatlantic. This period is characterized by man's influence on the vegetation. According to the evidence of both pollen analysis and archaeology, the first anthropogenic influences on Swiss vegetation took place between 6000 and 4500 yr B.P. In the anthropogenic timber-line belt secondary forests of Belula, Alnus and Pinus formed. On the southern alpine border, the Romans introduced Castanea, whereas on the Plateau Picea, Abies and Pinus have been planted.

Seasonal accumulation of mineral nutrients by kiwifruit 2. Fruit

Abstract: SUMMARY Changes in the concentration, distribution and quantity of macro- and micronutrients in the skin and flesh of fruit from 30 mature kiwifruit vines (Actinidia deliciosa var. deliciosa cv. Hayward) were recorded over a growing season in two high-producing orchards. The concentration of copper, iron, nitrogen, phosphorus, potassium, sulphur and zinc in the flesh (seeds inclusive) declined sharply during the first 8 weeks of growth, reaching values which remained relatively constant, or declined only gradually, until harvest. For boron, calcium, magnesium and manganese flesh concentrations declined steadily throughout the season. Concentrations of nitrogen, phosphorus and potassium in the flesh were generally higher, and those of calcium manganese and zinc consistently lower, than corresponding concentrations in skin over the entire maturation period (23 weeks). Flesh concentrations of copper, iron, magnesium and sulphur exceeded those in the skin but only during the early stages of fruit development (up to 11 weeks after pollination). Boron concentrations in flesh and skin were similar during the season. The quantity of all nutrients increased throughout the season to be at a maximum by harvest The rate of accumulation of each element was greatest during the first 8 weeks of growth corresponding to the cell division phase of fruit development. There was 61–75% of the total calcium, manganese and zinc content taken up during this time, compared with 37–54% of the content of other nutrients. In the subsequent 15 weeks of development rates for nutrient accumulation declined. In the case of boron, calcium, magnesium, manganese, potassium and zinc there was minimal accumulation in the final 6 weeks prior to harvest. A mass How-vascular transport model based on carbon and water influxes was used to predict the relative importance of phloem and xylem supply, and to partition nutrient accumulated by fruit over two time intervals; 2–8, and 8–17 weeks of growth. The model implies that where transpiration rates and phloem carbon concentrations are both high (i.e. approx. 6 ml water fruit−1 day−1 early in the season or 2 ml water mid season, and > l00 mg C ml−1), transport of nutrients occurs primarily via phloem. The only exceptions under these conditions are calcium, manganese and zinc which are translocated preferentially in xylem.