bluuebunny/crossref_metadata_2025 huggingface dataset:
Accumulation and consumption of solutes in swards of Lolium perenne during drought and after rewatering
Authors: THOMAS HENRY
Published: April 2006

summary

Simulated swards of Lolium perenne were grown in containers 0.9 m deep in the glasshouse and subjected to drought for 0 (control) 2, 4, 6 or 8 wk. Leaf growth, water relations and accumulation of solutes (sugars, amino acids and minerals) were measured in mature leaf laminae and in young meristematic leaf bases. The swards were then rewatered and fertilized, and growth and solute changes measured over the next 8 d.

After 8 wk of drought leaf extension had stopped, leaf laminae were scorched at the tips, cell membranes were damaged, and osmotic potential (ψs) had fallen to −2.6 and −2.8 MPa in laminae and bases respectively. Hydration (ratio of tissue water to dry matter) declined steadily to less than half control values, but relative water content declined significantly only after more than 6 wk drought. Nearly all osmotic adjustment was the result of these changes in water content, since molarity of total measured solutes on a dry weight basis increased by only 11 % in laminae and fell by 6% in bases.

During drought, water soluble carbohydrate contents increased, mostly due to accumulation of large fructan molecules having little effect on ψs. In bases smaller fructans (having degrees of polymerization, DP, of 3–5), glucose and fructose decreased, whereas in laminae fructan of DP3 and sucrose increased. Relatively large amounts of neo‐ketose accumulated in laminae after 8 wk drought. Proline contents of bases increased steadily during drought, whilst in laminae proline contents were generally very low, and increased only after severe drought. Minerals made the major contribution to ψs. Total mineral contents of laminae rose slightly due mostly to accumulation of Ca2+ and Mg2+, whereas in bases mineral contents tended to decline. Phosphate content, however, declined in both bases and laminae.

Following rewatering, tissues rehydrated within 2 d. Water potential rose more rapidly than ψs, so that after 2 d turgor temporarily exceeded control values. Leaf extension rates changed almost in parallel with turgor. Carbohydrates in leaf bases changed rapidly: fructans of DP3–5 and fructose initially increased and then declined, whereas sucrose and glucose contents fell by more than 50% and remained low. Proline contents fell to control values within 1–2 d, whereas phosphate contents (already low) continued to decline. The changes were generally more rapid in the bases than in the laminae.

The roles of solutes in osmotic adjustment and as substrates for regrowth are discussed. The differences between slow, relatively natural drought and rapid stressing of pot‐grown plants are emphasized.
Evidence for the involvement of ethene in aerenchyma formation in adventitious roots of rice (Oryza sativa L.)
Authors: JUSTIN S. H. F. W. , ARMSTRONG W.
Published: April 2006

summary

Two varieties of rice (ev. Norin 36 and RB3) were either grown in stagnant or aerated 1/4‐strength Hoagland's solution with or without exogenous ethene and a range of silver concentrations (an ethene antagonist), or were grown in flooded and drained soils.

With cultivar Norin 36, AgNO3 was very effective in reducing porosity by inhibiting aerenchyma development. This effect was antagonized by gassing with increasing concentrations (1 or 2 μ1−l) of ethene. The results are consistent, therefore, with reports that cavity formation in roots is controlled by endogenous levels of ethene. Also, porosity varied with root length, and if a correction was made for this, the inhibitory effect of the silver ion on aerenchyma development appeared to be even greater.

For the cultivar RB3, root porosities in solution culture appeared initially to be unaffected by ethene or AgNO2, but root lengths were reduced and root numbers increased by increasing ethene concentration. When these effects on root length were taken into account, it was concluded that ethene had increased root porosity, and AgNO3, had decreased it. Consistent with earlier studies, and with the ethene hypothesis, aerenchyma development in both varieties was also enhanced by soil waterlogging, with percentage porosities 12 units higher in flooded than in drained soil. The porosities of cv, RB3 were higher than those for cv. Norin 36, however, and the regression line of porosity against root length was steeper, indicating a greater predisposition to form aerenchyma in cv. RB3. This was confirmed in solution‐grown roots, where AgNO3 had no significant effect on porosity in stagnant or in aerated roots of cv. RB3, and both 1 and 2 μ1−1 ethene increased the porosity in cv. RB3 roots to a similar level. Silver nitrate, however, did antagonize the effects of 1 and 2 μ1−1 ethene. In contrast, porosity in cv. Norin 36 was progressively reduced by AgNO3.

It is concluded that, although there are intervarietal differences in sensitivity, an ethene promotion of gas‐space formation can occur in rice, and ethene should not be ruled out as the endogenous promoter.
Histological analysis of the expression of Agrobacterium rhizogenes rolB‐GUS gene fusions in transgenic tobacco
Authors: ALTAMURA M. M. , ARCHILLETTI T. , CAPONE I. , COSTANTINO P.
Published: April 2006

summary

The gene rolB from the T‐DNA of Agrobacterium rhizogenes is capable of directing differentiation of roots in transformed plant cells. A detailed histological analysis of the expression of this gene in transgenic tobacco plants is presented here. Gene fusions between the promoter of rolB and the GUS reporter gene (encoding E. coliβ‐glucuronidase) were utilized: tissue and cell specific GUS activity as driven by a long (1185 base pairs) and a short (306 bp) version of the rolB promoter was visualized histochemically during different phases of plant development, from embryo to flowering. The extended (1185bp) rolB promoter is under developmental control and is specifically active in the initial cells of all types of meristems and in the vascular system (phloem, phloem parenchyma, xylem parenchyma, pericycle and pericycle‐like cells) of mature organs as well as in the central cylinder of the embryo. In contrast, the 306 bp deletion of the promoter is unable to drive expression in menstematic initials but is still active in the vascular system of the seedling.
Sulphate and ammonium in mist impair the frost hardening of red spruce seedlings
Authors: CAPE J. N. , LEITH I. D. , FOWLER D. , MURRAY M. B. , SHEPPARD L. J. , EAMUS D. , WILSON R. H. F.
Published: April 2006

summary

Two‐year‐old seedlings of red spruce [Picea rubens Sarg. syn. P. rubra (Du Roi) Link] were grown in open‐top chambers supplied with charcoal‐filtered air near Edinburgh, Scotland. Between May and November 1988, plants were exposed to mists containing NH4+, SO42− and NO3− ions at concentrations of 1.6 mol m−3 and H+ at 3.2 mol m−3, in pairwise combination and all together. The mists were applied twice weekly at a rate of 2 mm precipitation equivalent per application. Treatment with H2SO4 severely damaged the plants after 3 wk; the concentration for this treatment was therefore reduced from 1.6 mol m−3 to 0.5 mol m3, and new plants were substituted, in June 1988. Frost hardiness was assessed by freeze‐testing detached shoots, then measuring rates of electrolyte leakage. No effects of the mist treatments were detected during the early stages of frost hardening, but on 31 October, shoots that had received sulphate and ammonium ions were less hardy than ‘control’ shoots treated with deionized water. The temperature which killed 20% of shoots was 14 °C higher, and the temperature which killed 56% of shoots was 7 °C higher than for ‘control’ shoots. Acidity per se had no effect on frost hardiness; nitrate ions had no effect and may have mitigated the effects of sulphate when applied together.

The results confirm earlier data, and indicate that uptake of NH4+ and SO42− ions can disturb the frost‐hardening process. There are important implications for pollution control strategies in the northeastern United States, if damaging interactions between frost hardiness of red spruce and pollutant deposition are linked to ammonium and sulphate rather than nitrate ions.
Mineral nutrition and mycorrhizal infection of seedling oak and birch
Authors: NEWTON A. C. , PIGOTT C. D.
Published: April 2006

summary

In order to assess the importance of nutrient uptake and mycorrhizal infection for the establishment of seedlings of pedunculate oak (Quercus robur L.) and silver birch (Betula pendula Roth.), seedlings were grown on two nutrient‐poor soils and sequential harvests taken throughout the first growing season. Seedlings were artificially established in two woodland sites and in pots of soil collected from each field site.

The pattern of nutrient depletion from oak cotyledons indicated that the initial N and P contents were completely utilized by the production of the first flush of leaves after 7 wk. Similarly, growth of birth in acid‐washed sand ceased after the production of the first pair of leaves. Growth rates of field‐grown seedlings were lower than those of pot‐grown seedlings in each case, such that pot‐grown plants were three times larger than field‐grown plants by the final harvest. Nutrient losses in abscised foliage constituted a significant proportion of the total nutrient uptake of both species: between 14 and 35 % of N, P and K was abscised in the case of birch. Taking losses of nutrients in abscised foliage into account, nutrient budgets of field‐grown seedlings were either slightly positive, or not significantly greater than zero.

The onset of ectomycorrhizal infection of field‐grown plants was 2–4 wk more rapid than that of pot‐grown plants; initial infection of field‐grown seedlings was observed 3 wk after outplanting. Percentage infection of field‐grown seedlings tended to be higher than in pots throughout the growing season, by up to 40%. Different mycorrhizal types displayed contrasting patterns of development: for example, Paxillus involutus (Batsch) Fr. tended to increase rapidly, to maximum percentage infections of over 30 %; whereas Cenococcum geophilum Fr. was consistently recorded at 10% infection. The role of mycorrhizal infection during seedling establishment is discussed in the light of these results.
Mineral nutrition and mycorrhizal infection of seedling oak and birch
Authors: NEWTON A. C. , PIGOTT C. D.
Published: April 2006

summary

In order to determine the effect of fertilizers on the growth, nutrient uptake and ectomycorrhizal infection of seedling oak (Quercus robur L.) and birch (Betula. pendula Roth.), N, P and K fertilizers were applied in a factorial design to plots of seedlings artificially established ph two woodland sites on nutrient‐poor soils. A parallel series of pot experiments were undertaken using the sajne design, in order to eliminate the effects of neighbouring mature trees on growth and mineral uptake.

Fertilizer addition increased the growth of birch in both pot and field experiments, and on both soil types, by up to 39 %. In contrast, fertilizer addition had little effect on growth of oak, other than to increase dry mass by 11 % in one of the pot experiments. Application of N, P and K generally increased the foliar concentration of the respective nutrient, by up to 49%. However, a number of negative effects of fertilizer application were recorded, particularly in the case of foliar P. For example, application of N K and N × K reduced the foliar P of birch by up to 35 % in pots.

Fertilizer application to both species tended to reduce ectoniycrrhizal infection, both in pots and in the field. These effects were more pronounced for birch than oak, and a greater number of effects were recorded in pots than in the field. In general, N had the greatest effect. For example, the number of mycorrhizal tips of birch in pots was reduced to 38 % of the control value, following N application. Application of P and K also reduced mycorrhizal infection, although the results of the analyses differed depending on how mycorrhizal infection was assessed.

The relative proportions of a number of the ectomycorrhizal types were also influenced by fertilizer addition. Although the proportion of most types was reduced, two types [formed by Paxillus involutus (Batsch) Fr. and Scleroderma citrinum Pers.] increased in some of the treatments where they were dominant. For example, application of N to birch in pots increased the proportion of P. involutus mycorrhizas to 172% of the control.

The interactions between the effect of fertilizers on growth, nutrient uptake and mycorrhizal infection are discussed, and some implications for forest management are highlighted.
Seed developmental patterns inBanksia attenuataR. Br. andB. laricinaC. Gardner in relation to mechanical defence costs
Authors: STOCK W. D. , PATE J. S. , RASINS E.
Published: April 2006

summary

A comparison is made of the phenologies of infructescence, follicle and seed growth development of two species ofBanksiawith particular reference to nutrient provision of dissimilarly sized seeds and associated mechanical defence costs. Follicles and seeds ofB. attenuatadeveloped sequentially while the smaller seededB. laricina, exhibited an almost synchronous pattern of development. Seed nitrogen loading, assayed by temporal changes in amino pool sizes in different parts of the seed, was confined to a relatively short period (± 3 months) prior to infructescence desiccation in both species. Prolonged infructescence development in the larger seededB. attenuatacannot therefore be interpreted simply as a mechanism for extending time available for mobilization of scarce nutrients within the plant, but may be a result of selective pressures related to the development of large woody structures around the seeds which provide mechanical defence against predators. BothBanksiaspp. make relatively large investments of carbon, but not of nitrogen, in defence structures (up to 5·5 g per seed inB. attenuata) which in plants with low photosynthetic rates could have associated penalties in terms of N required for photosynthetic enzymes. Sequential development of follicle and then seed assumes significance, since nitrogen used in photosynthesis to provide carbon to the follicle can subsequently be mobilized from the leaf and redeployed in seed protein synthesis. The often held view that larger seeds require longer maturation periods is not universal as, in theBanksiaspp. examined, defence costs and photosynthetic capacity might play a more dominant role in determining seed developmental patterns.
Population variation in Spartina anglica C. E. Hubbard
Authors: THOMPSON J. D. , McNEILLY T. , GRAY A. J.
Published: April 2006

summary

Clonal replicates of Spartina anglica C. E. Hubbard were reciprocally transplanted into cleared plots and undisturbed vegetation in three adjacent zones on the Dee Estuary salt marsh, Cheshire, England. The aim of the investigation was to examine whether clones from these populations show a differential response to the range of naturally occurring environmental variation. Clone survival was significantly lower in the pioneer zone relative to the sward and mature marsh zones and was greatest in plants from the pioneer population in all transplant sites. Tiller number per plant was consistently greater in the pioneer population, increased with increasing marsh elevation and the removal of natural vegetation in the mature zone, and, for the pioneer and mature populations, showed a significant clone x environment interaction effect. The norms of reaction showed marked differences between clones in the pattern of response to environmental variation, but joint regression of clone means on overall means showed that very few clones had a linear response. Several morphological characters showed significant interactions with environmental effects in ANOVA, but only for total plant biomass in the pioneer population did this reflect a linear increase in more favourable environments. Differences in overall stature quantified by the pattern of morphological character correlations indicated the occurrence of different morphological forms within the populations. The differences in performance and plasticity are discussed in the context of the successional development of these populations, and the possible influence of age‐related somatic variation.
Population variation in Spartina anglica C. E. Hubbard
Authors: THOMPSON J. D. , McNEILLY T. , GRAY A. J.
Published: April 2006

summary

The response of clonal replicates of nine populations of Spartina anglica C. E. Hubbard to environmental variation was examined in three pot environments, designed to test for differences between the populations in their response to environmental variation. ANOVA showed that the effect of environment was highly significant for all morphological and yield characters, and that the populations were also significantly different for several characters. For above and below ground vegetative biomass, there was a significant population x environment interaction, indicative of differences in plasticity between the populations. Linear regression of the population mean value in each environment on the mean value of all populations in each environment was performed for these two traits. This showed that the response to environmental change was not significantly due to a linear relationship in some populations, hence, the method could not be used to compare the response of each population. Nevertheless, norms of reaction plots for each population showed that the three populations collected from successionally mature sites showed less response to more favourable conditions. The three mature populations also had significantly lower tiller numbers per plant in all environments. These results substantiate previous results which suggest a decline in vigour and plasticity in successionally mature populations. Morphological characters, except third leaf width and culm diameter, all proved to be significantly correlated in pairwise comparisons. This is further evidence for the occurrence in S. anglica of ‘graceful’ and ‘stocky’ variants which contrast with the highly plastic ‘anglica’ growth form.
Precociously developing individuals in populations of chickweed [Stellaria media (L.) Vill.] from different habitat types, with special reference to the effects of weed control measures
Authors: BRIGGS D. , HODKINSON H. , BLOCK M.
Published: April 2006

summary

Long‐term weed control in gardens and arable areas is likely to be a potent selective force favouring precocious development of annual weed species. In an experiment with Stellaria media (L.) Vill., we grew progenies from open‐pollinated seed of a number of seed‐parents collected from 12 British populations of five habitat types. We raised plants in a temperate glasshouse and a garden plot, to see if plants from areas subject to weed control ‐gardens and arable fields – had a quicker rate of development from germination to flowering and fruiting than plants from habitats subject to less weed control (waysides) or no weeding pressure (seasonally exposed river sediments and bird colonies).

Comparison of the behaviour of plants in the glasshouse and out‐of‐doors revealed a broadly similar pattern of behaviour. However, for some, but not all seed‐parents, rate of development was different in the two sets of conditions.

In conformity with hypothesis, plants from one of the gardens were quick to reproduce, but plants from Ness Botanic Garden and arable fields were more variable than expected. Plants from less well weeded and non‐weeded sites did not conform to expectation. Plants from waysides were quick to reproduce, so too was much of the material from a bird colony on the island of Skomer. While some late‐developing plants were detected from a second bird colony (Fame) and from exposed river sediments by the Tweed and Manifold, we found a small number of precocious and some intermediate individuals in the progeny of some seed‐parents.

It is possible that bird colonies and exposed river sediments are heterogeneous habitats, in which there are niches where ‘native’ variants with different rates of development are at a selective advantage.

However, there is another explanation of our results. First, we discovered that, while some of the seed‐parents were probably behaving as homogeneous lines for rate of development, others show ed segregation, providing evidence that a degree of outcrossing is possible in populations of Stellaria. Secondly, there is evidence that human activities have led to habitat disturbance in and around the bird colonies and riverside vegetation we have studied. Our findings are consistent with the hypothesis that, gene flow by pollen and/or seed of precocious weedy plants has occurred in these man‐disturbed sites, leading to different patterns of variation involving hybridization between ‘introduced’ precocious plants and ‘native’ slow‐developing variants.
Studies in the vegetational history of the Northern Pennines
Authors: TURNER JUDITH , HODGSON JOYCE
Published: April 2006

summary

Tree pollen data in the form of mean frequencies for the late Flandrian were collected from 46 sites in the Northern Pennines. They indicate that as in the early and mid‐Flandrian spatial variation in the species composition of the woodlands is related to local geology, topography and climate.

A sub‐set of the data was compared with published mid‐ and early Flandrian data from the same sites. Temporal variation in Betula, Pinus and Alnus is related to changes in climate, in Ulmus and Corylus to Dutch elm disease and in Fraxinus to human disturbance. Spatial diversity is at least as strong as temporal.
Accumulation of phenolic compounds in the necrotic areas of Austrian and red pine needles after spraying with sulphuric acid: a possible bioindicator of air pollution
Authors: ZOBEL ALICJA , NIGHSWANDER JAMES E.
Published: April 2006

summary

Austrian pine (Pinus nigra Arn.) and red pine (P. resinosa Ait.) were tested for needle damage caused by sulphuric acid spray. Morphology and histology of newly grown needles were compared in 3‐ and 6‐yr‐old plants growing in the greenhouse under controlled conditions. Potted plants covered with plastic bags were sprayed daily either with distilled H2O or sulphuric acid of pH 2.5, 3.5 and 4.5. Needle tips, mid‐parts and bases were fixed after 1, 3 and 24 h, and 3, 7 and 30 d in glutaraldehyde + 0.1% caffeine for intracellular precipitation of phenolics. Histochemical reactions and electron microscopic observations showed that the morphological damage is linked to increased deposition of phenolic compounds in mesophylla cells, beginning directly under the stomata. Disorganization of membranes leads to death of the mesophyll cells, even before morphological damage is recognizable as brown spots on the needle surface. Thus the histochemical reactions and observations of cell structure revealed damage earlier than macroscopic observations.
Effect of a vesicular–arbuscular mycorrhizal fungus and rhizosphere micro‐organisms on manganese reduction in the rhizosphere and manganese concentrations in maize (Zea maysL.)
Authors: KOTHARI S. K. , MARSCHNER H. , RÖMHELD V.
Published: April 2006

summary

Maize (Zea maysL. ev. Tau) plants were grown in a calcareous soil for six weeks in pots having separate compartments for growth of roots and vesicular‐arbuscular (VA) mycorrhizal fungal hyphae. Soil was sterilized and either left non‐inoculated (sterile treatment), or was inoculated with rhizosphere micro‐organisms only (MO–VA) or with rhizosphere micro‐organisms together with a VA mycorrhizal fungus [Glomus mosseae(Nicol & Gerd.) Gerdemann & Trappe (MO +VA)]. Concentrations of Mn in roots and shoots, as well as exchangeable Mn in rhizosphere soil, decreased in the order MO–VA < MO + VA < sterile treatment. In all treatments, the concentration of exchangeable Mn was lower in the rhizosphere soil (0–5 mm distance from the root surface) than in the bulk soil (5–15 or 15–25 mm distance from the root surface). In the rhizosphere soil, the total microbial population was similar in mycorrhizal (MO + VA) and non‐mycorrhizal (MO–VA) treatments, but the proportion of Fe‐ or Mn‐reducers was 20‐ to 30‐fold higher in the non‐mycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbial populations upon root infection with the mycorrhizal fungi. The Mn+Iv‐reducing potential (net balance between reduction and oxidation) in the rhizosphere soil was also distinctly lower in mycorrhizal treatment compared to non‐mycorrhizal treatment.

In the sterile treatment, low Mn+IV‐reducing potential and correspondingly low concentration of exchangeable Mn in soil, compared to the other treatments, indicates the importance of micro‐organisms in Mn reduction in soil and acquisition of Mn by plants. Therefore, the lower Mn concentrations in mycorrhizal plants are most probably caused by a shift in composition and activity of rhizosphere micro‐organisms. As a side effect of the treatments, improved soil aggregation, as indicated by soil adhering to the nylon net (facing hyphal compartments) after plant harvest, occurred in non‐mycorrhizal and sterile treatments but not in the mycorrhizal treatment.
A light and electron microscope study of rhizoid–ascomycete associations and flagelliform axes in British hepatics with observations on the effects of the fungi on host morphology
Authors: DUCKETT J. G. , RENZAGLIA K. S. , PELL K.
Published: April 2006

summary

Ascomycetous fungi, identified by the presence of simple septa and Woronin bodies, form a range of highly specialized associations with the unicellular rhizoids of 46 (16.2%) of the 284 species of British liverworts. The majority of these are in the two jungermannialian suborders Lepidoziineae and Cephaloziineae. Thirty three species (11.6%) also possess flagelliform axes. These extend to depths of 20–30 cm in peaty substrata and in most species bear abundant fungus‐infected rhizoids. When grown in sand or water culture, isolated from their natural substrata (sandstone rocks, peat, Sphagnum, rotten wood), the hepatics are free from rhizoid infections. On returning the plants to their native substrata, the rhizoid‐fungus associations are re‐established.

Each rhizoid or fascicle of rhizoids is infected independently and a continuous strand of fungus‐containing cells is absent. Internally the flagelliform axes contain elongate parenchyma cells with abundant plasmodesmata in their transverse end walls. The apices of the axes are invested by mucilage and subapical amyloplasts appear to act as graviperceptive particles.

The morphology of the flagelliform axes and the ultrastructure of the rhizoid‐fungus association varies greatly between taxa. The Lepidoziaceae and Calypogeiaceae produce fascicles of rhizoids from the bases of rudimentary leaves whereas the flagelliform axes in the Cephaloziaceae are leafless. In Cladopodiella the fungus forms a pseudoparenchymatous sheath around the rips of swollen rhizoids. Development of swollen rhizoids precedes fungal infection in Lepidozia, Kurzia and Telaranea but not in other genera. Hyphae penetrating the basal walls of the rhizoids in Cephalosia, Nowellia, Calypogeia and Odantoschisma are ensheathed by host Wall material. These diverse patterns of fungal infection suggest independent, and probably relatively recent, evolution in the various genera.

The flagelliform axes in hepatics appear to be major organs of assimilation and perennation structurally and functionally analogous in the former capacity to vascular plant mycorrhizas and particularly the hairs roots in Ericaceae.
An alternative nitrogenase is not expressed in molybdenum‐deficient legume root nodules
Authors: DILWORTH M. J. , LONERAGAN J. F.
Published: April 2006

summary

Three legume root nodule bacteria systems (Medicago polymorpha L. ‐Rhizobium meliloti, Ornithopus sativus Brot. ‐Bradyrhizobium lupini and Trifolium subterraneum L.‐ Rhizobium leguminosarum by. trifolii) were grown in solution culture under conditions likely to lead to the production of alternative nitrogenases (molybdenum‐deficient, or molybdenum‐deficient but supplemented with vanadium). Addition of 1 μM molybdenum produced significant responses in both nodule and top weights while 2 μM vanadium did not. Ethane, which is produced as well as ethylene when acetylene is reduced by vanadium nitrogenase or nitrogenase‐3 from Azotobacter, was not found in significant amounts during assays of acetylene reduction in either molybdenum‐deficient or molybdenum‐deficient, vanadium‐supplemented treatments, suggesting that no non‐molybdenum nitrogenase was produced by these root nodule bacteria.
Low temperature‐enhanced inhibition of photosynthesis by oxides of nitrogen in lettuce (Lactuca sativa L.)
Authors: CAPORN S. J. M. , MANSFIELD T. A. , HAND D. W.
Published: April 2006

summary

The response of photosynthetic gas exchange to oxides of nitrogen (NOx) was studied in leaves of lettuce (Lactuca sativa L.) at different temperatures. Exposure to > high concentrations (e.g. 13 μmol NOx mol−1), similar to those often found in commercial glasshouses, caused a rapid inhibition of the net assimilation of CO2. This appeared to be by a direct effect on photosynthesis rather than by a change in the stomatal conductance. In ambient CO2, (345 μmol mol−1), the percentage inhibition at 10 and 5°C was approximately 3× and 5×, respectively, that measured at 20°C. This effect of temperature also occurred when measured in CO2, enriched air (1050 μmol mol−1), which would normally accompany NOx in a glasshouse. The extent of photosynthetic inhibition caused by NOx was, however, always less in high than in low CO2.

The results suggest that when burning fuel to raise the CO2, concentration and heat the glasshouse air, growers should avoid generating high concentrations of NOx, in conditions of low temperature.
Root and soil respiration responses to ozone inPinus taedaL. seedlings*†
Authors: EDWARDS NELSON T.
Published: April 2006

summary

Respiration rates of roots of loblolly pine (Pinus taedaL.) seedlings decreased in response to elevated ozone (O3) concentrations. Estimated annual root respiration rates were 12% less in seedlings exposed to twice‐ambient O3(7 h mean = 70.110 nl 1−1) than in seedlings exposed to sub‐ambient O3(7 h mean = 20.40 nl 1−1). Measurements taken during periods of relatively rapid and of negligible root growth suggest that the reduced root respiration may be due to both reduced maintenance respiration and reduced growth respiration. Respiration rates of the soil substrate of the O3‐exposed seedlings were also below those of the substrate of seedlings exposed to sub‐ambient O3. The study supports the theory that there is a reduced supply of photosynthates to the roots of plants exposed to elevated O3. It is hypothesized that a reduced supply of photosynthates to the roots may affect soil respiration rates by reducing root exudation rates and, consequently, reducing rhizosphere microbial populations.
Seasonal changes in antioxidants in red spruce (Picea rubensSarg.) from three field sites in the northeastern United States
Authors: MADAMANCHI NAGESWARA R. , HAUSLADEN A. , ALSCHER RUTH G. , AMUNDSON R. G. , FELLOWS S.
Published: April 2006

summary

Changes in antioxidant levels were investigated in red spruce (Picea rubensSarg.) from three field sites in the northeastern United States. Whiteface Mountain, NY at an elevation of 1090 m, represents a red spruce population in decline, while Millinocket and Howland, Maine are at 518 and 105 m above sea level, respectively, and have red spruce stands that show no symptoms of decline. The Millinocket site with saplings that are 15–20 yr old was compared with the Howland site with 60‐yr‐old trees to test the effect of age on antioxidant levels. The Howland site was compared with the Whiteface Mountain site, which has trees more than 100 yr old, to test the effects of air quality and elevation. Foliage developed in 1987 (87 needles) and in 1988 (88 needles) was sampled from May to November and from July to November, 1988, respectively. Quadratic polynomial and linear regressions were used to model the relationships through time of each variable measured. Regression coefficients were obtained by one‐way analysis of variance. The means for total glutathione and oxidized glutathione were higher at Whiteface Mountain in 87 needles, and needles of both age classes sampled in November had significantly higher oxidized glutathione at Whiteface Mountain compared to those at Howland. No significant difference was observed in the mean ascorbate content of either needle class at all the three sites. The activity of superoxide dismutase declined with time in 87 needles at Whiteface Mountain and the mean activity was lower at Whiteface Mountain than at Howland. The effects of ozone concentration, site elevation and other environmental factors on seasonal changes in antioxidant levels and superoxide dismutase activity are discussed.
Changes in germinability, ABA content and ABA embryonic sensitivity in developing seeds of Sorghum bicolor (L.) Moench. induced by water stress during grain filling
Authors: BENECH ARNOLD R. L. , FENNER M. , EDWARDS P. J.
Published: April 2006

summary

The effect of intermittent water stress during grain filling on the germinability of developing seeds of S. bicolor was investigated. The drought treatment was imposed in cycles within the maturation period by withholding water for 5–6 days, rewatering at the end of each drought cycle and withholding water again. Changes in abscisic acid (ABA) content and embryonic sensitivity to ABA in the maturing seeds were also monitored in order to find out if there were any parallel changes with seed germinability resulting from drought conditions. Seeds developing in plants subjected to drought showed a high level of germinability earlier in the maturation period than did control seeds; consequently, they were less resistant to pre‐harvest sprouting as shown when panicles were exposed to high humidity conditions. Very high levels of ABA accumulated in the early stages of development in seeds maturing on water‐stressed mother plants; however. ABA content fell markedly when the seeds stopped growing, and remained significantly below those recorded in control seeds until the end of the maturation period. Development under drought conditions decreased the sensitivity of the isolated embryo to exogenous ABA by about 10‐fold. The good agreement found between germinability, endogenous ABA concentrations and embryo sensitivity to ABA at different stages of development, suggests a key role for ABA as a major inhibitor of precocious germination and shows that changes in germinability caused by water stress during grain filling are likely to be related to changes in ABA pool size in the developing seed.
Studies on the localization of a protein, immunologically similar to a 62‐kilodalton sucrose‐binding protein isolated from developing soybean cotyledons, in the shoot and root of spinach
Authors: WARMBRODT ROBERT D. , VANDERWOUDE WILLIAM J. , HITZ WILLIAM D.
Published: April 2006

summary

Previous work, using antisera developed against a 62 kDa sucrose‐binding protein isolated from developing Soybean cotyledons, resulted in the identification of an immunologically similar protein on the sieve‐tube plasma membranes of the small minor veins of spinach (Spinacia oleracea L. var. Bloomsdale Dark Green). These studies have been expanded to determine the extent of the immunologically similar protein throughout the shoot and root of the mature spinach plant. lndirect immunogold labelling of resin‐embedded leaf and stem tissues resulted in the specific localization of colloidal gold on the plasma membrane of mature sieve tubes in the major veins and large minor veins of the lamina as well as sieve tubes of the petiole and stem. The amount of label associated with the petiole and stem sieve tubes was less than in the sieve tubes of the lamina. In all cases, the label was evenly distributed along the plasma membrane and, except for a small amount of background label on the cell walls, was not associated with any other cellular component including organelles, membranes or membrane systems. Other cell types of the vascular and ground tissues were also essentially free of label. Control sections treated with non‐immune rabbit IgG were free of label. Sections of root tissue treated with the 62 kDa antisera contained immunolabel on the plasma membrane of the sieve tubes and, in addition, the plasma membrane of various parenchymatic elements including companion cells and vascular parenchyma cells. In both root and shoot tissues, the plasma membrane of sieve tubes considered to be structurally and physiologically immature did not contain label. These results are discussed in relation to the apoplastic and symplastic transport of solutes in source and sink tissues.
Development of the ovular structures in peach [Prunus persica (L.) Batsch]
Authors: ARBELOA ARANCHA , HERRERO MARIA
Published: April 2006

summary

Changes in the ovular tissues of peach (Prunus persica (L.) Batsch) were studied from anthesis to fertilization or degeneration in pollinated and unpollinated flowers. During this time the ovule undergoes a continuous developmental process. At anthesis the megagametophyte is immature and is not fully developed until 12 days later. During the first three weeks following anthesis the ovule increases in length from 400 to 1200μUm, and the nucellus and integuments undergo various changes particularly in the distribution of starch and cutin. These appear to be connected with early embryo sac nutrition and protection. As the ovule matures, starch accumulates mainly in the embryo sac, integuments and at the nucellar tip. This starch disappears during early embryo sac elongation. Concomitant with starch depletion, the cutin that separated the integuments from the nucellus vanishes. Other cutin accumulates between cells in the nucellar tip, thus protecting and isolating the embryo sac. Most of these changes appear to be a fixed feature of ovule development since they were also observed in a few long lived ovules in unpollinated flowers. However, in unpollinated flowers development of most of the ovules is soon interrupted: callose accumulates af the chalaza, starch disappears and the ovules degenerate.
The branch roots of Zea. II. Developmental loss of the apical meristem in field‐grown roots
Authors: VARNEY G. T. , McCULLY M. E.
Published: April 2006

summary

Most of the first‐order branches of field‐grown maize roots are short (around 10 mm). An anatomical and morphological survey of the tips of branches from nodal roots showed that almost all branches lacked a normal apex. Most tips were broken off (e.g. 74% in the mid‐regions of roots from node 1, 95% in the same region of node 3 roots), with living, mature tissues right to their end. The remaining tips were of 3 types: (a) Determinate tips with rounded off ends, no root cap, and mature tissues right at the tip;(b) Normal tips which were miniaturized versions of main root apices with a meristem, root cap and long zone of elongation; (c) Intermediate tips in which cap loss, meristem outgrowth and differentiation were incomplete. Normal tips were mainly on branches of the youngest roots and determinate tips were the predominant intact tips of old roots. This distribution, together with anatomical features of the three tip types indicates that Determinate tips form from Normal tips by a controlled pattern of cell enlargement, differentiation and possibly, cell division. Many tips must be broken accidentally by excavation, or earlier by browsers or pathogens. There was some evidence, however, that some broken tips are formed by developmentally controlled abscission both before and after the formation of determinate tips.
Effects of phosphate supply on wheat seedlings infected with powdery mildew: carbohydrate metabolism of first leaves
Authors: ZULU J. N. , FARRAR J. F. , WHITBREAD R.
Published: April 2006

summary

Wheat (Triticum aestivum L. cv. Longbow) was grown hydroponically with either 0, 0.33 or 3.3 mol Pi m−3 and, after 12 d, was infected with powdery mildew (Erysiphe graminis D.C. ex Merat f.sp. tritici). Fructan content of infected first leaves was increased by mildew infection but infection increased starch content only at 0 Pi. Photosynthetic 14CO2 fixation was reduced by infection, especially at 0 Pi. Accumulation of 14C in fructan rose with reduced Pi supply but was unaffected by mildew; accumulation of 14C in starch was lower in infected leaves. Pi deficiency increased the content of sugars in the apoplast, as did mildew infection, the greatest content being in infected leaves of low Pi status. Acid invertase activity was increased by infection but was not affected by Pi status. Thus P‐deficiency alone does not mimic the effects of mildew but Pi status and mildew interact in their effect on leaf carbohydrate metabolism.
Biology and effectiveness of Uromyces heliotropii Sred., a potential biological control agent of Heliotropium europaeum L.
Authors: HASAN S. , ARACIL E.
Published: April 2006

summary

The rust fungus Uromyces hellotropii Sred. shows potential for the biological control in Australia of the common heliotrope (Heliotropium europaeum L.), an annual weed of European origin. Teliospores of the pathogen remained viable when stored for one year at temperatures between −8 and 20°C, and carried infection over from one summer growing season to the next under a Mediterranean‐like climate. Both in glasshouse and field inoculation experiments, the rust rapidly killed infected plants and reduced or prevented seed production. U. heliotropii appears capable of surviving in the Mediterranean‐like climatic areas of Australia where common heliotrope is a problem weed and is sufficiently virulent to cause significant field infection.
The influence of an inhibitor of phytochelatin synthesis on root growth and root meristematic activity in Festuca rubra L. in response to zinc
Authors: DAVIES K. L. , DAVIES M. S. , FRANCIS D.
Published: April 2006

summary

Six‐day‐old seedings of three cultivars of Festuca rubra L. (Merlin, Hawk and S59) were grown in aerated calcium nitrate solution at various concentrations of Zn in the presence or absence of buthionine sulfoximine (BSO), a potent inhibitor of phytochelatin synthesis.

In the absence of BSO, increasing Zn concentrations reduced the root length of all three cultivars but the Zn‐sensitive cultivar (SS9) showed the greatest Zn‐induced reduction and the Zn‐tolerant cultivar (Merlin) the least. The presence of BSO in the medium, contrary to expectation, ameliorated the inhibitory effect of Zn on root growth in all three cultivars.

Treatment with 0.2 μg Zn cm−3 reduced the length of the root apical meristem in Merlin and S59. The presence of BSO in the culture solution did not affect the length of the apical meristem in Zn‐treated roots in any cultivar but, in the absence of Zn, BSO increased the length of the apical meristem by an average of 14.0% compared with the controls (0 Zn minus BSO). The mean length of epidermal cells in the region between the proximal boundary of the root meristem and the first root hair was reduced by an average 43% in the three cultivars following treatment with 0.2 μ Zn cm−3. However, the presence of BSO in the rooting medium did not influence epidermal cell length in Zn‐treated or untreated roots in any cultivar.

The presence of BSO resulted in an average 1.7–fold increase in the mitotic index in the root meristem of Zn‐treated roots; a comparable BSO‐induced stimulation of mitotic index has been found in roots grown without Zn. However, BSO did not affect the relative frequency of the four stages of mitosis. This preliminary evidence suggests that BSO stimulates cell division activity in roots of F. rubra.

The unexpected effect of the phytochelatin‐inhibitor, BSO, in increasing the Zn‐tolerance of roots argues against a key role of phytochelatins in the Zn‐tolerance mechanism of roots of F. rubra
The micromorphological distribution of bound calcium in needles of Norway spruce [Picea abies (L.) Karst.]
Authors: FINK SIEGRIED
Published: April 2006

summary

The distribution of bound calcium in spruce needles is visualized by various microscopical techniques. Ca pectate occurs in the middle lamellae of cell walls and in a surprisingly great concentration in the thick cell walls of the sieve cells and transfusion parenchyma. The major fraction of the calcium, however, is bound in the form of insoluble Ca oxalate crystals, which occur extracellularly on the outside of the walls of mesophyll cells which face the intercellular spaces. Furthermore, numerous small crystals appear within the cell walls of the epidermal cells, especially in the cuticular layer. The development and distribution of these apoplastic crystals is described in detail. Some hypotheses are finally presented for possible interpretations of these unusual patterns of the crystallization of Ca oxalate outside the vacuole.
Physiological response of two soybean cultivars to simulated acid rain
Authors: SMITH C. R. , VASILAS B. L. , BANWART W. L. , WALKER W. M.
Published: April 2006

summary

Simulated acid rain has been reported to cause physiological changes in various plant species. Studies were conducted in 1983, 1984, and 1985 to determine the effect, of acid rain on physiological parameters in two soybean [Glycine max(L.) Merr.] cultivars. Simulated acid rain of pH 3.0, 4.2 and 5.6 was applied throughout the growing season to plots protected from ambient rain and grown on a Flanagan silt loam (fine, montmorillonitic, mesic Aaquic Argiudoll). Individual plants were evaluated for CO2fixation, leaf water potentials, and leaf chlorophyll content. Microplots were evaluated for flowering and podding patterns, and dry matter and N partitioning. Rain pH did not affect CO2fixation, water potentials, chlorophyll content, seed yield, shoot dry weight, or N accumulation. At pH 4.2 Amsoy 71 produced fewer flowers and pods than at pH 3.0 or 5.6. Abscised leaf dry weight of Amsoy 71 was greater at pH 3.0 and 4.2 than at pH 5.6 pH effects were detected for N partitioning, but these responses were dependent on year and cultivar. No physiological basis for reported soybean yield responses to acid rain of pH 3.0 was identified.
Influence of host (Alnus and Myrica) genotype on infectivity, N2 fixation, spore formation and hydrogenase activity in Frankia
Authors: HUSS‐DANELL KERSTIN
Published: April 2006

summary

Nine species of Alnus, two of them represented by several provenances, and Myrica gale were inoculated with a ‘local source’ of Frankia. The inoculum is an effective (N2‐fixing), spore‐Forming type of Frankia that lacks H, uptake (hydrogenase) activity in symbiosis with A. incana. Despite their wide geographical origin (Europe, China, North America) and their various taxonomie grouping within the genus, all Alnus species/provenances formed Infixing nodules. In all studied nodules Frankia had the phenotype Spore+. None of the studied symbioses had hydrogenase activity. The Frankia inoculum was infective also on M. gale, and gave effective nodules without hydrogenase activity. Unlike some other spore‐forming types of symbiotic Frankia, all studied symbiotic phenotypes of the ‘local source’ of Frankia were thus stable characters not influenced by the various host genotypes included in the study.