bluuebunny/crossref_metadata_2025 huggingface dataset:
THE EFFECT OF WATERLOGGING ON SEEDLINGS OF EUCALYPTUS MARGINATA
Authors: DAVISON E. M. , TAY F. C. S.
Published: May 2006

Summary

Three‐ to four‐month‐old Eucalyptus marginata Donn ex Sm. (jarrah) were grown in the glasshouse in peat/sand at 20 °C root temperature, and either waterlogged continuously for up to 14 d, or waterlogged for a shorter time and then drained. During waterlogging, the O2 concentration of the soil solution declined to less than 1 mg l−1within 1 d. There was an increase in the resistance to water movement into or through the plant within 4 d of flooding the pots. The number of xylem vessels blocked by tyloses increased with the duration of flooding, and did not increase further when waterlogging ceased. The transpiration rate of plants continuously waterlogged and maintained in a dry atmosphere for 13d was closely correlated (r =− 0.98) with the proportion of occluded vessels in the tap‐root. The rate at which wilting developed depended on both the duration of waterlogging and the transpiration rate.
REQUIREMENT FOR A LONG LAG PERIOD FOR THE INDUCTION OF NITRATE REDUCTASE IN WHEAT (TRITICUM AESTIVUM) EMBRYOS DURING GERMINATION
Authors: DISA SUHAS , GUPTA ADITYA , GUHA‐MUKHERJEE SIPRA , SOPORY SUDHIR K.
Published: May 2006

Summary

The induction of nitrate reductase (NR) in the embryos of wheat required a period of 20 h of incubation in nitrate during the early stages of seed germination. The lag phase in the development of NR activity was not due to the non‐availability of nitrate in the embryos, the presence of a nitrate reductase inactivating factor, or the synthesis of inactive NR. At the onset of the inducible phase the enzyme was synthesized de novo, but was not dependent on the synthesis of fresh m‐RNA. Protein synthesis during the lag phase was essential for the subsequent induction of NR in the inducible phase.
ZINC TOLERANCE IN BETULA
Authors: BROWN M. T. , WILKINS D. A.
Published: May 2006

Summary

Seed samples of Betula spp. from Zn‐contaminated and control sites were cultured on agar with added Zn. The samples from contaminated soils were more Zn tolerant than the controls. Detailed work on clonal material showed differences of tolerance within samples.

Reducing the concentration of other ions, especially Ca, increased the toxicity of Zn. Chemical analyses of leaf material showed reduced uptake of Zn (a) in tolerant plants, and (b) in plants treated with high levels of Ca.
ZINC TOLERANCE OF MYCORRHIZAL BETULA
Authors: BROWN M. T. , WILKINS D. A.
Published: May 2006

Summary

Seedlings of Betula spp. were grown in conjunction with isolates of Amanita muscaria Hooker and Paxillus involutus Fr. under aseptic conditions. Mycorrhizas were established in sterilized peat and vermiculite to which nutrient media had been added. Zinc was supplied at various levels and growth of the host was assessed after eight weeks. The mycorrhizas increased the tolerance to Zn of both tolerant and non‐tolerant Betula. This was coupled with a reduction in the translocation of zinc to the shoots of Betula, but an accumulation of zinc in the mycorrhizas.
SALT STRESS DISTURBS THE CALCIUM NUTRITION OF BARLEY (HORDEUM VULGARE L.)
Authors: LYNCH JONATHAN , LÄUCHLI ANDRÉ
Published: May 2006

Summary

Soil salinity decreased the Ca contents of shoots of two cultivars of barley (Hordeum vulgare L.) grown under field conditions, particularly in younger leaves. Reduction in Ca content was more pronounced in cv. Arivat (the more salt‐sensitive cultivar) than in cv. Briggs. In seedlings grown in solution culture, relatively low concentrations of NaCl inhibited the transport of Ca to the shoot. This inhibition was not due to effects of NaCl on Ca influx into the root or on transpiration. We propose that NaCl inhibits Ca transport from root to shoot by interfering with the release of Ca into the root xylem, possibly via an effect on the active loading of Ca into xylem vessels.
IMPLICATION OF HYDROGEN PEROXIDE – ASCORBATE SYSTEM ON MEMBRANE PERMEABILITY OF WATER STRESSED VIGNA SEEDLINGS
Authors: MUKHERJEE S. P. , CHOUDHURI M. A.
Published: May 2006

Summary

When seedlings of Vigna catjang were subjected to increasing magnitudes of water stress (−0.5, −10 and −1.5 MPa) the induced changes in leaf water potential (LWP), were accompanied by increases in proline content, tissue permeability, H2O2 content and ascorbic acid oxidase activity, and decreases in catalase activity and ascorbic acid content.

Pretreatment with L‐cysteine (10−3 M), reduced glutathione (10 −3 M) and abscisic acid (ABA, 10−4 M) through the roots improved the water status of stressed seedlings maintained at – 10 MPa for 2 d, and decreased the tissue permeability, proline content, H2O2 content and ascorbic acid oxidase activity, but increased the ascorbic acid content and catalase activity. Stressed seedlings from seeds pretreated with CaCl2 (10−2 M) behaved like plants treated with the reducing agents and ABA, and not like untreated stressed seedlings. The studies suggest that the maintenance of membrane integrity is of paramount importance, and that the hardening treatments might modulate the endogenous levels of H2O2 and ascorbic acid in stressed seedlings which, in turn, might influence membrane integrity.
DIRECT FOLIAR EFFECTS OF SIMULATED ACID RAIN
Authors: HAINES B. L. , JERNSTEDT J. A. , NEUFELD H. S.
Published: May 2006

Summary

Surface characteristics and wettability of the leaves of six plant species have been examined in relation to their susceptibility to damage from simulated acid rain. The species examined differed in the type and extent of epicuticular wax deposits, surface topography of the cuticle, trichome type and distribution, and epidermal cell shape. Leaf wettability, as measured by either water‐holding capacity or droplet contact angle, was significantly different among species, and is highly correlated with previous reports of damage from simulated acid rain. The leaves of Platanus occidentalis L. were the most wettable of the species examined and are reported to be damaged the most by repeated applications of simulated acid rain. Mature leaves of hiriodendron tulipifera L., with high contact angles and very low water‐holding capacity, are the least damaged according to published reports. Leaf water‐holding capacity and surface‐droplet contact angle may be useful first indicators of resistance to acid rain, and should be included m future studies of foliar effects of acid rain.
VESICULAR‐ARBUSCULAR MYCORRHIZAS OF GINKGO BILOBA L. IN NATURAL AND CONTROLLED CONDITIONS
Authors: FONTANA ANNA
Published: May 2006

Summary

The morphology of Ginkgo biloba L. vesicular‐arbuscular mycorrhizas (VAM) was investigated in natural conditions and after innoculation with Glomus epigaeum Daniels and Trappe. Morphological features of the infections were similar. The most interesting morphological feature was the presence of abundant intracellular hyphae; intercellular hyphae were rare. Synthesis tests showed the complete Glomus epigaeum life cycle, with the production of sporocarps. Natural infection of Ginkgo biloba roots is considered to be a common phenomenon, and Glomus epigaeum inoculation in controlled conditions increased growth of seedlings.
THE NATURE OF GROWTH DEPRESSIONS IN SUNFLOWER CAUSED BY VESICULAR–ARBUSCULAR MYCORRHIZAL INFECTION
Authors: KOIDE ROGER
Published: May 2006

Summary

When mycorrhizal (M) and non‐mycorrhizal (NM) plants were grown in a soil of low phosphorus (P) availability (5 μg g−1), mycorrhizal infection caused a transient depression in leaf area relative to NM plants that lasted for seven to eight weeks. When plants were grown in this same soil with added P, leaf areas of M and NM plants were similar. When plants were grown in a soil of moderate P availability (15 μg g−1), infection decreased leaf area throughout the experiment.

High soil P levels were associated with lower degrees of infection. The degree of infection was positively correlated with the degree of depression of leaf area while the soil P level was negatively correlated with the ability to overcome the initial depression.

When M and NM plants were grown in the soils of either low or moderate P availability, the relationship between relative leaf expansion rate (RLER) and tissue P concentration was the same for M and NM plants. Also, mycorrhizal infection did not affect plant N concentration to the same degree as it did P concentration. When grown in the soil of low P availability, dry matter in the shoot was shown to be partitioned differently for M and NM plants. M plants in vested mo re dry matter in leaves relative to stems compared to NM plants. Phosphorus‐amended NM plants also invested more dry matter in leaves relative to stems compared to unamended NM plants. Because of the possible difference in leaf dry weight: stem dry weight ratio between M and NM plants, final harvest shoot dry weights were not an adequate measure of the physiological status of the plants. Leaf expansion was shown to be a good indicator of M effects on plant growth.
RELATIONSHIP BETWEEN DOSE OF SO2 AND NO2 MIXTURES AND GROWTH OF POA PRATENSIS
Authors: WHITMORE MARY E.
Published: May 2006

Summary

A series of experiments was conducted in controlled environment chambers to investigate the relationship between the concentration of mixtures of SO2 and NO2, length of exposure and growth of the amenity grass Poa pratensis L. cv. Monopoly. Plants were exposed to concentrations of 40, 70 and 100 nl 1−1 SO2 and NO2, in one to one ratio, for periods of 20, 34 and 38 d and compared with controls grown in partially filtered air. The effects of the pollutants on plant dry weight were related to the product of exposure concentration and duration within the limits of the experimental conditions. A dose‐response curve was therefore constructed which illustrated that although small doses may have no effect or may even stimulate growth, slightly larger doses may be severely inhibitory. In order to clarify the effects of small doses a further experiment was performed in which the response was observed at intervals during a 50 d exposure to 40 nl 1−1 SO2 plus 40 nl 1−1 NO2. The results confirmed that low doses could cause small growth stimulations and that the transition from beneficial to inhibitory effects occurs over a narrow range of doses.

A subsequent exploratory experiment provided an example of how the environmental conditions during exposure may affect this relationship, and illustrated that each dose‐response curve is only applicable to a given set of conditions.
A HOXNIAN INTERGLACIAL SITE AT ATHELINGTON, SUFFOLK
Authors: COXON P.
Published: May 2006

Summary

Interglacial deposits lying in a basin in till of Anglian age 7.5 km south east of Hoxne are shown to be of Hoxnian age. The sedimentary record suggests deposition in quiet and flowing water with occasional periods of drying out as the basin filled with sediment. The palaeobotanical record indicates the basin was surrounded by mixed oak forest during the earlier period of deposition and later by a forest dominated by Abies. The depositional environment and the palaeobotanical record at Athelington are similar to those at neighbouring Hoxnian sites.
GLUTAMINE SYNTHETASE ISOFORMS IN ALGAE
Authors: CASSELTON P. J. , CHANDLER G. , SHAH N. , STEWART G. R. , SUMAR N.
Published: May 2006

The occurrence of glutamine synthetase isoforms in algae, from seven different phyla, has been investigated, using ion‐exchange chromatography. The algae have been classified into three groups according to their glutamine synthetase isoform content. The first group is characterized by having only the cytosolic glutamine synthetase, whereas the second group is distinguished by having only the chloroplastic glutamine synthetase. The third group is characterized by having both the isoenzymes. Stability studies were used along with the elution profiles from ion‐exchange chromatography to designate the isoforms to the cytosolic or the chloroplastic isoform. Immunoprecipitation studies, for specific identification of the cytosolic and chloroplastic isoforms showed varied results and indicated that the two forms from the lower algae have very similar antigenic sites.
THE DEVELOPMENT OF ENDOMYCORRHIZAL ROOT SYSTEMS VI. THE RELATIONSHIP BETWEEN DEVELOPMENT OF INFECTION, AND INTENSITY OF INFECTION IN YOUNG LEEK ROOTS
Authors: AMIJEE F. , STRIBLEY D. P. , TINKER P. B.
Published: May 2006

Leek plants (Allium porrum L.) were grown on gamma‐irradiated soil in tall pots with two layers of inoculum of the vesicular‐arbuscular mycorrhizal fungus Glomus mosseae (Nicolson and Gerdemann) Gerdemann and Trappe, at depths of 6 and 9 cm respectively. The main axes of primary and adventitious roots extended linearly with time. However, the total root length and infected root length both increased exponentially, as did total root numbers. The fractional infection had a lag phase, a phase of rapid increase, and then a steady value.

The density of internal hyphae rapidly increased in the main axis of infected primary roots while the infected segments extended at a constant rate, with sharply demarcated fronts each progressing at approx. 0.2 cm d−1. Where internal hyphae from the two infected segments met there was no resulting increase in hyphal density. This coalescence formed a single infection segment of uniform hyphal density. On these main axes, the total number of entry points increased exponentially with time after initial infection, but after 20 d the rate of increase declined sharply. At sites of initial infection there were high concentrations of unusually small entry points, but away from these the numbers per unit length of root diminished.

At a higher concentration of soil phosphorus, results were similar for hyphal density and numbers of entry points, but fractional infection was less, because of increased root growth. We conclude that the length of infected root closely reflects hyphal biomass at moderate levels of soil phosphorus.
GROWTH, NUTRITION AND GAS EXCHANGE OF BROMUS INERMIS INOCULATED WITH GLOMUS FASCICULA TUM
Authors: BILDUSAS I. J. , DIXON R. K. , PFLEGER F. L. , STEWART E. L.
Published: May 2006

Plants of Bromus inermis Leyss. inoculated or not with the mycorrhizal fungus Glomus fasciculatum (Thaxter sensu. Gerd.) Gerd. and Trappe, were pre‐conditioned at two soil moisture levels (Φs− 0.03 or − 0.8 MPa) for 17 weeks, then subjected to a drying cycle. Stomatal conductance (g1), soil‐plant liquid flow resistance (Rs−p), and photosynthesis rates (Ps) were measured before, during, and after the drying cycle. Soil water stress and mycorrhizal inoculation significantly reduced plant top dry weight during the 18 week study. Chlamydospore production by the mycorrhizal symbiont G. fasciculatum was significantly increased by soil water stress of −0.8 MPa. Foliar Ca and Mg concentrations were significantly greater in mycorrhizal plants. Foliar concentrations of P, K, N, Mn, Zn and Cu were significantly greater in drought stressed plants whereas Ca and Mg concentrations were significantly greater in well‐watered plants.

Mycorrhizal plants pre‐conditioned at Φs−0.8 MPa had 36 and 34% lower Rs−p values than nonmycorrhizal plants at pre and peak drought sampling times, respectively. Following re‐irrigation, g1 was 64% greater in mycorrhizal plants when compared to nonmycorrhizal plants. Inoculation with G. fasciculatum increased photosynthesis rates by 20, 52, and 22 % over the noninoculated plants before, during, and after the drying cycle respectively. Despite increased rates of photosynthesis, top dry weight of mycorrhizal plants was 15 % less than that of noninoculated plants.

Regardless of inoculation treatment, plants pre‐conditioned at ΦS−0.8 MPa exhibited greater g1 and Ps values during and after the drying cycle. Bromus inermis demonstrated the ability to adapt to water deficits. Mycorrhizal symbiosis may play a role in the adaptation of B. inermis to dry sites.
THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA
Authors: SCOTT MARTHA G. , LARSON DOUGLAS W.
Published: May 2006

Umbilicaria vellea (L.) Ach. and U. deusta (L.) Baum. have distribution patterns that are mutually exclusive. U. vellea occurs in vertically inclined microsites that are permanently snow‐free. In contrast, U. deusta occurs on flat or gently sloping surfaces that receive a substantial snow cover. Earlier field work had suggested that this distribution pattern was maintained, at least in part, by the inability of U. vellea to store photosynthetic products and thereby maintain a positive carbon balance when growing in areas receiving a significant snow‐cover. We report controlled laboratory experiments conducted in order to determine which aspect of the subnivean environment interfered with U. vellea, but not with U. deusta. The four experiments investigated effects of long‐term continuous subzero temperatures, alternating periods of freeze and thaw, exposure to slightly above‐zero conditions (in the dark), and lastly, a combination of freezethaw and slightly‐above‐zero treatments.

Only the slightly above‐zero treatment in the dark interfered significantly with CO2 exchange in U. vellea. None of the treatments reduced significantly CO2 exchange in U. deusta. The decline in productivity of U. vellea in the current experiments was identical to that found in material reciprocally transplanted in the field.

We conclude that U. vellea is excluded from snow‐covered habitats because of an inability to store or mobilize stored respiratory substrate in the subnivean environment. In contrast, U. deusta which stores such products in great number, is able to survive long periods of time without a flux of photosynthates. It would appear that one of the costs of such an ability, is the allocation of very few reserves to growth.
PATHWAYS OF AMMONIUM ASSIMILATION IN THE SOIL ALGA STICHOCOCCUS BACILLARIS NAEG.
Authors: AHMAD IFTIKHAR , HELLEBUST JOHAN A.
Published: May 2006

Glutamine synthetase (GS) and NADPH‐glutamate dehydrogenase (GDH) are key enzymes for ammonium assimilation in Stichococcus bacillaris Naeg. (UTEX 314). Cells growing with different concentrations of nitrate and ammonium contain activities of both GS and NADPH‐GDH in excess of required nitrogen assimilation rates under autotrophic as well as heterotrophic conditions. The activity of GS increases 2 to 3 fold, and NADPH‐GDH 10 to 15 fold when the concentration of ammonium in the medium is lowered from 2 to 0–2 mM, or when nitrate is present as the nitrogen source. The activity of ferredoxin‐dependent glutamate synthase (GOGAT) is similar to, or high than that of GS. In this alga. NADPH‐GDH has a low Km for ammonium (1–6 mM), and is capable of functioning effectively over the pH range occurring in the chloroplast stroma. A possible role of NADPH‐GDH in nitrogen assimilation by S. bacillaris is supported by the observation that the alga grows normally in the presence of methionine sulphoximine (MSX), when high levels of this enzyme are present, while GS is almost completely inhibited. Stichococcus bacillaris also contains high activities of NADH‐GDH, but the Km for ammonium of this GDH (33 mM) appears too high for it to function effectively in nitrogen assimilation. The activity of NADH‐GDH increases 3 to 5 fold when cells growing photoautotrophically are transferred to heterotrophic conditions, suggesting a catabolic role for this enzyme.
THE STRUCTURE AND FUNCTION OF THE VEGETATIVE MYCELIUM OF ECTOMYCORRHIZAL PLANTS
Authors: FINLAY R. D. , READ D. J.
Published: May 2006

It is increasingly evident that in natural plant communities the vegetative mycelia of ectomy‐corrhizal fungi can form networks of hyphal interconnections which link the root systems of their host plants in both intra‐ and inter‐specific combinations. Root observation chambers have been used to examine the development of these mycelial networks and to assess their functional significance as pathways for the transfer of assimilate between individuals in a range of host‐fungus associations. Carbon transfer between plants of Pinus spp. is significantly increased by the presence of mycelial connections and preliminary evidence suggests that such transfer may be enhanced where concentration gradients are induced by shading. The significance of these experimental results is discussed in relation to nutrient cycling processes in natural ecosystems.
ANATOMY OF BRANCH ABSCISSION INLAGERSTROEMIA MICROCARPAWIGHT
Authors: BHAT K. V. , SURENDRAN T. , SWARUPANANDAN K.
Published: May 2006

Some anatomical details of branch abscission inLagerstroemia microcarpaWight (Lythraceae) are discussed. Repeated abscission of numerous annual twigs and subsequent healing of their scars produce irregular growth of the subjacent branch portions to give gall‐like structures. In the abscission zone, secondary xylem fibres are thin walled and poorly lignified, with dense protoplasmic contents and closely spaced septa. Disintegration of pith parenchyma cells and shrinkage of bark and wood tissues contribute towards weakening of abscission zone. The protective zone situated proximal to the abscission zone is strongly lignified and rich in extractives. Detachment occurs immediately above the protective zone leaving the encircling dormant buds intact. Abscission scars are healed centripetally by the usual method of callus formation from the cambial tissue. It appears that branch abscission inL. microcarpais a mechanism to withstand drought by reducing the transpiring surface.
THE CONTRASTING RESPONSE TO SIMULATED ACID RAIN OF LEAVES AND COTYLEDONS OF CABBAGE (BRASSICA OLERACEA L.)
Authors: CAPORN SIMON J. M. , HUTCHINSON THOMAS C.
Published: May 2006

Brassica oleracea L. (cabbage) was grown in glasshouse and controlled environments and exposed to simulated rains delivered as sprays at pH 5.6‐2.8. A single rain treatment of pH 3.0 given to 10 d old plants elicited a marked downward curvature in the cotyledons, occurring within the duration of the 30‐min spray. Subsequent to this initial response, the cotyledon surface was extensively damaged. In contrast, the older‘true’leaves showed little or no injury after similar treatments. Estimates of the contact angles between rain droplets and leaf surfaces, and SEM studies of adaxial surfaces, indicated that the contrasting morphology of the epicuticular wax on cotyledons and leaves was a major factor determining the extent of acid rain damage. Simulated rain treatments of pH 3.2 and 2.8, starting at the cotyledons stage, reduced plant growth by 17 and 15% respectively over a 20 d period. However, the same treatments given at later stages in development when the‘true’leaves were predominant, had no significant effect on growth. In the natural environment the occurrence of rate, highly acidic rain events during different stages of plant development may be an important determinant of the impact of rainfall on vegetation. The young, seedling stage of species, such as B. oleracea, in which cotyledons show poor development of surface wax, may be particularly vulnerable.
EFFECTS OF PHOSPHATE SUPPLY AND INOCULATION WITH A VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGUS ON THE DEATH OF THE ROOT CORTEX OF WHEAT, RAPE AND SUBTERRANEAN CLOVER
Authors: MacLEOD W.J. , ROBSON A. D. , ABBOTT L. K.
Published: May 2006

The effect of phosphorus supply and mycorrhizal infection on the death of the cortex of roots (RCD) was examined in two glasshouse experiments. RCD was observed in both Australian and English cultivars of wheat (Triticum aestivum L.), and in rape (Brassica napus L.), but not in subterranean clover (Trifolium subterraneum L.). It occurred most rapidly in wheat plants moderately deficient in phosphorus (i.e. in plants producing approx. 60% of shoot weight with phosphorus not limiting growth) but was delayed both in plants severely deficient in phosphorus and in plants with adequate and luxury supplies of phosphorus compared to those which were moderately deficient. Although inoculation with a vesicular‐arbuscular mycorrhizal fungus did not markedly affect plant growth, it delayed RCD in phosphorus‐deficient plants and accelerated RCD in phosphorus‐adequate plants. The effects of phosphorus supply and mycorrhizal infection on RCD cannot be readily explained by effects of these treatments on plant growth or phosphorus concentrations within plants. Moreover, it is unlikely that effects of these treatments on RCD are related to effects on the availability of assimilates required to maintain the cortex.
SITES OF FLAVONE ACCUMULATION IN SOME GENOTYPES OF SILENE PRA TENSIS (RAFN.) GODRON ET GREN. (CARYOPHYLLACEAE)
Authors: VAN GENDEREN H. H. , VAN HEMERT J.
Published: May 2006

Petal laminae in Silene pratensis (Rafn.) Godron et Gren, contain 60 to 80% of the flower flavonoids. The flavone content of the petal lamina on a fresh weight basis is about 10 times that of the petal claw and at least five times that of the calyx. The ratios between the different glycosides found in the stigmata or in the stamen usually differ from those in the rest of the flower. The highest flavone concentration is always found in the vacuoles of the epidermal cells in the most exposed parts of both leaves and the flower. The total flavone distribution pattern is not influenced by the type of glycosylation.
ENDOGENOUS ETHYLENE AFFECTS THE BEHAVIOUR OF STOMATA IN EPIDERMIS ISOLATED FROM RUST INFECTED FABA BEAN (VICIA FABA L.)
Authors: TISSERA PREENI , AYRES P. G.
Published: May 2006

Rust infection of proximal halves of leaves of Vicia faba L. potentiates the sustained production of ethylene by abiotically wounded but uninfected distal regions. When epidermal strips were isolated from distal regions, either before or after incubation in aqueous media, stomatal opening was inhibited compared to that in strips from leaves of healthy, control plants. This inhibition, and the even greater inhibition seen in strips from rusted tissues, was reversed to differing extents by inclusion in the medium of inhibitors of the action of ethylene, namely silver ions (6 × 10−2 mol m−3), or of its biosynthesis, namely cobalt ions and AVG (both at 1 × 10−1 mol m−3). When ACC, a precursor of ethylene, was supplied to healthy leaves it promoted ethylene evolution after wounding and inhibited stomatal opening in strips isolated from those leaves. The cytokinins zeatin and kinetin (1 × 101 mol m−3) also promoted opening in strips from both healthy and rusted regions of infected leaves, but only fusicoccin (1 × 10−2 mol m−3) promoted wide opening in rusted regions. It is proposed that endogenous ethylene is an effective regulator of stomatal behaviour in epidermal strips prepared from either healthy or rusted regions of infected leaves of V. faba.
THE RESPONSES OF CYNOGLOSSUM OFFICINALE L. AND VERBASCUM THAPSUS L. TO DEFOLIATION IN RELATION TO NITROGEN SUPPLY *
Authors: VERKAAR H. J. , VAN DER MEDIJDEN E. , BREEBAART L.
Published: May 2006

The effects of defoliation of Cynoglossum officinale L. and Verbascum thapsus L. on growth, net assimilation rate and dry matter distribution were studied under various nitrogen regimes. At high levels of nitrogen supply, there was a higher net assimilation rate (NAR) and a higher leaf weight ratio in defoliated plants than in undefoliated plants resulting in a faster growth of defoliated plants. In V. thapsus growth of defoliated plants did not differ significantly from undipped plants. In a low nitrogen regime all defoliated V. thapsus plants died. In the same regime C. officinale had a low NAR and thus showed little regrowth. Leaf nitrogen content was not significantly different from control plants.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN FIELD‐GROWN CROPS
Authors: JAKOBSEN I.
Published: May 2006

The importance of vesicular‐arbuscular mycorrhiza (VAM) and P fertilizer for P nutrition and dry matter production in field peas (Pisum sativum L.) was studied in moderately P‐deficient soil. Half of the experimental plots were fumigated to reduce the level of VAM infection. Shoots and 0 to 30 cm soil cores were sampled on three occasions.

An extensive VAM infection was rapidly established in untreated soil, whereas infection levels were low in fumigated soil. Root growth responded to fumigation by increased root length and decreased root diameter. Fumigation reduced the P content in shoots considerably, and correspondingly the mean rates of P inflow per unit root length were 60% lower in fumigated than in untreated soil during flowering. These effects of fumigation were ascribed to the low levels of VAM infection in fumigated soil. The production of dry matter was not decreased accordingly in fumigated plots, although both it and P uptake were increased by adding P fertilizer. The possible reasons for this discrepancy are discussed.

A supplementary survey on infection development at five other field sites showed that peas are extensively colonized by VAM fungi, even in soils where a standard procedure is being used. These results indicate that VAM is of major importance to P uptake by the field‐grown pea.
INCREASED RATES OF PHOTOSYNTHESIS IN LOCALIZED REGIONS OF A BARLEY LEAF INFECTED WITH BROWN RUST
Authors: SCHOLES J. D. , FARRAR J. F.
Published: May 2006

The rate of photosynthesis was examined in whole leaves of barley infected with brown rust (Puccinia hordei Otth.) and within localized regions of the infected leaf, within brown rust pustules and in regions between them, from flecking to green island formation. In addition, oxygen evolution was measured from localized regions of a rusted leaf after feeding with inorganic phosphate (Pi) to investigate the hypothesis that fungal sequestration of Pi from the host cytoplasm may, totally or partially, be responsible for the decline in photosynthesis. The rate of net photosynthesis and the quantum yield of oxygen evolution declined in whole infected leaves as the disease progressed. However, the rate of gross photosynthesis (per unit chlorophyll) was increased in rusted leaves. Autoradiographic and oxygen evolution studies showed that the decline in net photosynthesis could be attributed largely to a reduction in the rate of photosynthesis in the regions between pustules. Within areas of the leaf invaded by the fungus, gross photosynthesis was increased in comparison to control tissue. Feeding leaf tissue with Pi did not significantly increase the rate of photosynthesis in pustules or regions between pustules, implying that Pi was not previously limiting the rate of photosynthesis. Possible mechanisms underlying the increase and decrease in photosynthesis in different regions of an infected leaf are discussed.
TOWARDS THE SELECTION IN VITRO FOR RESISTANCE TO ALTERNARIA BRASSICICOLA (SCHW.) WILTS., IN BRASSICA NAPUS SSP. OLEIFERA (METZG.) SINSK., WINTER OILSEED RAPE
Authors: MACDONALD MARY V. , INGRAM D. S.
Published: May 2006

Culture filtrates of Alternaria brassicicola (Schw.) Wilts, were found to be toxic to secondary embryoids of Brassica napus ssp. oleifera (Metzg.) Sinsk. The culture filtrates were partially purified and added to tissue culture media to produce a selection medium. Different secondary embryoid lines of B. napus were found to differ in their sensitivity to the selection medium, and it was possible to select lines which showed increased resistance to the selection medium. Some plants that were regenerated from secondary embryoids were found to be more resistant to the pathogen than were seed‐grown plants of the same cultivar, although there was no correlation between sensitivity to the selection medium and susceptibility to the pathogen.
COMPETITION BETWEEN THREE LICHEN SPECIES USING A FACTORIAL EXPERIMENTAL DESIGN
Authors: ARMSTRONG R. A.
Published: May 2006

Competition between three foliose lichens common on slate rock in south Gwynedd, Wales was studied in the field using a factorial experimental design. The lichens were grown as fragments glued to pieces of slate in two‐ and three‐species mixtures. In the two‐species mixtures, Parmelia conspersa (Ehrh. ex Ach.) Ach. outcompeted Parmelia glabratula ssp. fuliginosa (Fr. ex Duby) Laund. strongly and Physcia orbicularis (Neck.) Poetsch less strongly, while P. orbicularis outcompeted P. glabratula weakly. Significant two‐factor interactions indicated that the results from the three‐species mixture could not be predicted from the two‐species mixtures. Parmelia glabratula and P. orbicularis grew better in the presence of two competitors than one. This result suggests that the three species may co‐occur on well‐lit rock surfaces at the site.
THE ASSESSMENT OF NITROGEN FIXATION AND THROUGHPUT BY LICHENS IV. NITROGEN LOSSES FROM PELTIGERA MEMBRANACEA (Ach.) Nyl. IN AUTUMN, WINTER AND SPRING
Authors: MILLBANK J. W. , OLSEN J. D.
Published: May 2006

Undisturbed associations of Peltigera membranacea and associated mosses were held under simulated autumn, winter and spring conditions in a specially constructed, controlled‐environment chamber providing an atmosphere enriched with labelled nitrogen. Simulated rainfall via a programmable sprinkler system was incorporated, and the liquid run‐off was collected during 4 week experimental periods. Dry weight, total nitrogen and 15N labelling of the moss, lichen and run‐off liquid were determined, and nitrogenase activity of the lichen thalli was estimated by acetylene reduction at the end of the tests. It was estimated that the mosses derived direct nutritional benefit from nitrogen compounds leached from the lichen thalli, but due to simultaneous nitrogen‐fixing activity by epiphytes strictly quantitative estimates of the beneficial effects of the lichen were unobtainable.
EFFECTS OF ZINC ON CELL, NUCLEAR AND NUCLEOLAR SIZE, AND ON RNA AND PROTEIN CONTENT IN THE ROOT MERISTEM OF A ZINC‐TOLERANT AND A NON‐TOLERANT CULTIVAR OF FESTUCA RUBRA L.
Authors: POWELL M. J. , DAVIES M. S. , FRANCIS D.
Published: May 2006

The effects of a 4 d exposure to Zn on some cellular characteristics in the root meristem were investigated in seedlings of a Zn‐tolerant cultivar of Festuca rubra L. (Merlin) and in a non‐tolerant cultivar (S59). In S59, 0.1 and 0.2 μg Zn cm−3 resulted in a 7% and 17% reduction, respectively, in the mean area of mitotic cells compared with controls grown in the absence of Zn. Moreover, mean nuclear volume (13% and 28%) and total nucleolar volume (43% and 65 %) of G2 cells and RNA content (9 % and 44 %) and protein content (6 % and 17 %) of mitotic cells were also reduced by Zn. In Merlin, however, the mitotic cell area was 4 % and 19 % larger at 0.1 and 0.2 μg Zn cm−3 compared with the controls. Treatment with Zn also increased nuclear volume (13% and 47%) and total nucleolar volume (42 % and 86%), of G2 cells and RNA content (40 % and 32 %) and protein content (8 % and 33 %) of mitotic cells. The concentration of protein in mitotic cells was also increased by Zn treatment in Merlin. The data are discussed in relation to the previously established effects of Zn on the duration of the cell cycle in these cultivars.
THE EFFECTS OF PHOTOPERIOD AND TREATMENT WITH GIBBERELLIC ACID ON THE CONCENTRATION OF SOLUBLE CARBOHYDRATES IN THE SHOOT APEX OF SPRING BARLEY
Authors: COTTRELL J. E. , DALE J. E.
Published: May 2006

Summary

Barley plants (Hordeum vulgare L. cv. Clipper) were grown in controlled environment rooms for varying periods. The total soluble carbohydrate concentration was determined for stem apices over the period of early ear development using the p‐hydroxybenzoic acid hydrazide method.

Concentration of soluble carbohydrates rose during the photoperiod and was lower in the apices of plants subjected to shade. It also increased as the ear enlarged, irrespective of photoperiod. In 8 h photoperiods plants initiated many more spikelets, but at a lower rate, compared to those grown in 16 h days. Apices of plants grown in 8 h days showed a lower relative growth rate, but despite this at the end of spikelet initiation concentration of soluble carbohydrates was about 30% higher than for apices from plants in 16 h photoperiods. Where plants were grown in 8 h high intensity light followed by 8 h low intensity light soluble carbohydrate content was slightly more than in the apices of plants kept throughout 16 h in high intensity light. Treatment of plants grown in 8 h photoperiods with gibberellic acid accelerated the rates of initiation and development of spikelets. Treatment caused a substantial but ephemeral increase in soluble carbohydrate content, although by the time that spikelet initiation ceased the concentration was similar in control and treated plants.

It is concluded that total soluble carbohydrate concentration in the apex is not related to either rate of initiation or rate of development of spikelets. It is suggested that rate of utilisation of available soluble carbohydrate is subject to photoperiodic control and restricts growth and development of the ear.
TRANSPIRATION AND THE WATER RELATIONS OF FABA BEAN (VICIA FABA) INFECTED BY RUST (UROMYCES VICIAE‐FABAE)
Authors: TISSERA PREENI , AYRES P. G.
Published: May 2006

Summary

Transpiration and the water relations of faba bean (Vicia faba L.) were studied in healthy tissues of plants infected by rust (Uromyces viciae‐fabae (Pers.) Shroet). Water relations measurements on infected plants were made either on uninfected, healthy halves of otherwise infected lower leaves or on wholly uninfected upper leaves and, thus, they excluded the direct influence of fungal tissues. Rust caused increased transpiration from infected tissues after sporulation but, even in well‐watered plants, infection of proximal halves lowered leaf water potentials and inhibited transpiration from distal regions of the same leaf. The normal relationship between leaf water potential and stomatal diffusion resistance was not affected in the uninfected distal part of the leaves. Relationships between soil water potential and leaf water potential were affected by rooting patterns. Increased transpiration caused by rust accelerated drying of the soil, and consequent lowering of leaf water potentials, when plants were grown singly in small unwatered pots.

When healthy and rusted plants grew together in pairs in the same small unwatered pots of soil, and therefore at the same soil water potentials, healthy regions of proximally rusted leaves, and healthy leaves near the shoot apex of rusted plants, had lower leaf water potentials and were less turgid than comparable tissues of healthy plants. However, rust did not impair the ability of these same tissues to recover normal leaf water potentials and turgor when plants were rewatered.

When healthy and rusted plants shared soil columns that allowed unrestricted downward growth of roots and soil was cooled to temperatures similar to those in the field, roots grew faster in well watered soil than in unwatered soil. Rust inhibited the growth of roots in the mid‐depth (mid soil water potential) region of unwatered soil columns. Although the pattern of water potentials and changes in turgor that developed in unwatered plants after 15 d was similar to that seen previously in unwatered plants grown in small pots, differences in root growth would probably give healthy plants and increasing advantage over rusted plants in water uptake during longer periods of drought.
THE EFFECT OF MYCORRHIZAL INFECTION ON THE RESPONSE OF BETULA PAPYRIFERA TO NICKEL AND COPPER
Authors: JONES MELANIE D. , HUTCHINSON THOMAS C.
Published: May 2006

Summary

The role of ectomycorrhizas in the metal tolerance of birch seedlings from Sudbury, Ontario was investigated. Betula papyrifera Marsh, is one of the few tree species able to survive in the copper‐ and nickel‐polluted area near Sudbury. Two types of birch seedlings were tested; those inoculated with Laccaria proxima (Boud.) Pat., Lactarius hibbardae Peck, Lactarius rufus (Scop, ex Fr.) Fries, or Scleroderma flavidum E. & E. isolates originating from the Sudbury area, and those which were not inoculated. Once the seedlings were infected, they were grown in sand culture containing 34 or 85 μM Ni, 32 or 63 Cu, or a control solution. At the low nickel concentration, the mycorrhizal plants, especially those infected with S. flavidum, grew significantly better than did non‐mycorrhizal plants. At the higher nickel concentration, S. flavidum‐infected seedlings weighed 86% of controls without nickel, while the other seedlings weighed only 52 to 61 % of control. The good growth of S. flavidum‐infected birch seedlings may have been due to retention of nickel in the mycorrhizas. These seedlings had the highest root nickel contents and the lowest stem nickel contents. At the high concentration of copper, growth of the mycorrhizal seedlings was significantly reduced compared with the non‐mycorrhizal seedlings. This reduction in growth of infected seedlings did not relate to an increase in the uptake or translocation of copper. Under the low copper treatment, infection with mycorrhizal fungi did not affect seedling growth. The potential role of iron and phosphorus in affecting host metal tolerance was investigated. Changes in the tissue concentrations of these elements did not relate to the effect of the fungi on metal tolerance.
TREATMENT OF THE STIGMA WITH AN EXTRACT OF A COMPATIBLE PISTIL OVERCOMES SELF‐INCOMPATIBILITY IN PETUNIA
Authors: SHARMA NEELAM , SHIVANNA K. R.
Published: May 2006

Summary

Treatment of the stigma with an extract of a compatible pistil, just before pollination, was very effective in overcoming self‐incompatibility in Petunia hybrida Vilm. Progressive delay either in the application of the extract, or in pollination markedly reduced its efficacy in overcoming self‐incompatibility‐ The treatment seems to mask the self‐incompatibility recognition molecules of the pistil.
POLYPLOIDY AND HABITAT DIFFERENTIATION IN DESCHAMPSIA CESPITOSA
Authors: ROTHERA S. L. , DAVY A. J.
Published: May 2006

Summary

The chromosome numbers of 114 populations of the Deschampsia cespitosa (L.) Beauv. complex, widely distributed in the British Isles, were determined from root‐tip squash preparations. This revealed two widespread morphologically cryptic chromosomal races of seminiferous D. cespitosa (2n= 26, 52). The tetraploid is found throughout Britain; its range of habitats includes meadows, pastures, woodland, plantations, verges and waste ground. This is the first report of an extensive geographical distribution for tetraploid seminiferous D. cespitosa. The diploid appears to be mainly restricted to woodland, of mostly ancient, semi‐natural origin. Populations with both chromosome numbers are rare. The tetraploid is usually found where invasive colonization has clearly occurred.

The closely related proliferous taxon, D. alpina (L.) Roem. & Schult., was tetraploid, in agreement with published data. The prolifery itself induces changes in floret morphology. The floral morphology and cytological data together suggest that sub‐specific rank is appropriate for this variant in British material.
GLUTAMATE METABOLISM IN INTACT SEEDLINGS AND SEEDLING SEGMENTS OF PEAS
Authors: MELCHER INGA M.
Published: May 2006

Summary

Glutamate metabolism in intact cotyledons of pea seedlings (Pisum sativum L.) differs considerably from that in cotyledon slices. No decarboxylation of glutamate was found in intact cotyledons, whereas the decarboxylation in sliced cotyledons was so large that γ‐aminobutyric acid (γAbu) was by far the predominant metabolic product of glutamate. A number of mechanisms that could trigger glutamate decarboxylase activity are discussed.
PROTEIN CONTENTS OF SEED YIELDS OF FIELD‐GROWN SOYBEANS EXPOSED TO simulated ACIDIC RAIN: ASSESSMENT OF THE SENSITIVITIES OF FOUR CULTIVARS AND EFFECTS OF DURATION OF SIMULATED RAINFALL
Authors: EVANS LANCE S. , SARRANTONIO MARY J. , OWEN ELIZABETH M.
Published: May 2006

Summary

Analyses of seeds harvested from field‐grown soybeans (Glycine max Merrill) demonstrated that simulated acidic rainfalls can significantly decrease total protein contents. In an experiment conducted in 1983, seed yields of plants exposed twice weekly to long duration rainfalls showed no significant differences in seed protein contents among the acidity levels tested. In contrast, significant differences in protein contents were found for seed samples from the short duration, daily rainfalls. Seeds of plants exposed to simulated rain of pH 5.6 had average protein contents of 37.9% compared with a range between 30.6 and 32.1 % from plants exposed to lower pH values. Overall the protein contents of seeds of acidic rainfall treatments, expressed on a per plant basis, ranged from 23 to 34%. The results suggest that the response of soybean seed yields to acidity are affected by duration and frequency of simulated rainfalls. In the 1984 growing season, four commercial cultivars were tested under conditions of longer duration rainfalls, applied twice weekly. Significant treatment effects occurred only to the Amsoy cultivar and not to Asgrow, Corsoy or Hobbit. For the latter three cultivars the protein contents of samples were all relatively high (means were all between 35 and 39%). The relatively low protein content of Amsoy soybeans exposed to simulated rainfalls of pH 2.7 was apparently responsible for the statistical significance among treatments. These and previous results demonstrate that rainfall acidity can significantly affect protein contents of seeds of field‐grown soybeans and that effects on protein content are independent of changes in plant seed yields.
LEAF‐SURFACE PROPERTIES IN RELATION TO TOLERANCE OF SALT SPRAY IN FESTUCA RUBRAssp. LITORALIS (G. F. W. MEYER) AUQUIER
Authors: HUMPHREYS M. O. , KRAUS M. P. , WYN JONES R. G.
Published: May 2006

Summary

Leaf‐surface properties were investigated in F. rubra ssp. litoralis (G. F. W. Meyer) Auquier cv. Hawk, which is tolerant of salt spray, and cv. Aberystwyth S.59, which is susceptible. Salt retention and leaf wettabilities were measured and leaf‐surface structure was observed using a scanning electron microscope. In both cultivars stomata were confined to adaxial leaf surfaces which were less wettable than abaxial surfaces probably because of ridging and wax deposits. Salt retention after spraying was much higher per unit dry weight in S.59 than in Hawk, although salt retention per unit of projected leaf area was similar in both cultivars. This was because leaves were folded about the midrib in Hawk but were much flatter in S.59. Folding reduced the exposure of adaxial leaf surfaces to salt spray. The adaptative significance of this is discussed together with its broader physiological implications.
PRODUCTION OF INDOLE‐3‐E THANOL AND INDOLE‐3‐A CETIC ACID BY THE MYCORRHIZAL FUNGUS OF OPHRYS LUTEA (ORCHID ACEAE)
Authors: BARROSO J. , NEVES H. CHAVES , PAIS M. S.
Published: May 2006

Summary

The GC/MS analysis of trimethylsilyl derivatives of extracts from the culture medium and from the mycelium of Ophrys lutea Cav., a mycorrhizal fungus grown in a liquid culture medium, revealed the ability of this fungus to synthesize indole‐3‐ethanol and indole‐3‐acetic acid.

The identification of these compounds in the liquid medium and in the mycelial extracts suggested their transference from the fungus to the host during the establishment of mycorrhizas.
ULTRASTRUCTURAL STUDIES IN LICHENS
Authors: HONEGGER ROSMARIE
Published: May 2006

Summary

The cytology of the relationship between evolved lecanoralean lichen mycobionts and their trebouxioid photobionts were studied in the foliose Cetrelia olivetorum (Nyl.)Culb. & C. Culb., Platismatia glauca (L.)Culb. & C. Culb., and Parmelia tiliacea (Hoffm.)Ach., and in the fruticose Pseudevernia furfuracea (L.)Zopf (all Parmeliaceae) using SEM and partly TEM techniques. In freeze‐dried SEM preparations of all four species crystalline secondary metabolites of fungal origin were detected on the surface of the algal symbiont. Extracellular lichen products crystallized within and on the outermost surface layer of the cell wall which spreads from the mycobiont over the surface of the photobiont. This outermost wall layer revealed an irregularly tessellated pattern in freeze‐fracture preparations and was recognized as a very thin, electron‐dense layer in ultrathin sections. According to histochemical tests the surface layer of medullary hyphae and algal cells is largely composed of proteins and polyesters of fatty acids. Published data on the in vitro effects of phenolic lichen products on the metabolism of isolated, cultured photobionts are summarized, and possible roles of these secondary metabolites at the myobiont‐photobiont interface within the lichen thallus are discussed.