bluuebunny/crossref_metadata_2025 huggingface dataset:
Mycorrhiza development in onion in response to inoculation with chitindecomposing actinomycetes
Authors: AMES ROBERT N.
Published: April 2006

Twelve actinomycetes, originally isolated from spores of Glomus macrocarpum Tul. & Tul., were inoculated into nonsterilized soil containing G. macrocarpum and G. mosseae (Nicol. & Gerd.) Gerd. & Trappe. The chitin‐decomposing actinomycetes were strongly antagonistic toward fungi, bacteria or actinomycetes, or combinations of these based on prior studies. Eight Streptomyces, two Nocardia, and two unidentified species were tested for their effects on mycorrhiza development in onion (Allium cepa L.), plant growth and nutrient content, soil hyphal density, and soil populations of bacteria and actinomycetes. None of the actinomycetes adversely affected plant growth or nutrient content. The lower foliar P content of two of the treatments could be explained as a dilution effect brought about by the significantly larger shoot growth. With few exceptions, the soil microbial populations and saprophytic fungal hyphal densities were not significantly different from the controls. Seven of the twelve actinomycetes significantly increased the percent mycorrhizal root colonization and four significantly increased the density of hyphae > 5μm in diameter, predominantly those of vesicular‐arbuscular mycorrhizal (VAM) fungi. This is the first study to demonstrate that actinomycetes isolated from spores of a VAM fungus can be beneficial to mycorrhiza development and growth of onion in a nonsterile soil system.
Interaction of soil bacteria, mycorrhizal fungi and orchid seed in relation to germination of Australian orchids
Authors: WILKINSON K. G. , DIXON K. W. , SIVASITHAMPARAM K.
Published: April 2006

Endotrophic bacteria were isolated from the mycorrhizal tissues of 12 out of 13 tested species of Western Australian terrestrial orchids. The bacteria were placed into eight groups based on u.v. light fluorescence, Gram staining and colony characteristics. The most commonly isolated bacteria from 9 out of the 12 orchid species sampled were strains within the Pseudomonas fluorescens‐putida group. The abundance of bacteria followed a seasonal pattern that differed between orchid genera especially on the basis of the morphology of fungus infected tissue. There was little evidence of specificity of bacterial groups to orchid taxa or part of the plant infected by the fungus. Symbiotic germination of Pterostylis vittata seed in association with seven bacterial isolates showed a significant promotion of germination and seedling development with three bacterial strains. The influence of a fourth strain was no different to the control while the remaining three strains significantly suppressed seedling development.
Fructan biosynthesis in excised leaves of Lolium temulentum L.
Authors: CAIRNS ANDREW J.
Published: April 2006

summary

Analyses of the kinetic properties and products of fructosyl transferases from Lolium temulentum L. suggest that these enzymes are artifacts of conventional extinction and/or assay methods. An alternative approach to the investigation of fructan biosynthesis in cell‐free extracts has been developed. This approach employs the Sensitivity of radiotraeers to overcome the limitations of conventional quantitative methods for the analysis of fructan.

Homogenates of leaves were prepared, which contained enzyme protein, endogenous sucrose and fructan. These extracts catalysed the rapid and efficient incorporation of radioactivity from [U‐14C]sucrose into material with a decree of polymerization greater than 2. The chromatographic pattern of these labelled products was identical to the pattern of native leaf fructan. Kestose, which does not accumulate to high concentrations in vivo but was a major product of our previous enzyme assay procedures, was not a product of these homogenates.

The flux of radioactivity into oligofructan was sufficient to account for observed rates of fructan accumulation in the leaf And fructosyl transfer was observed at sucrose concentrations between 15 and 30 mol m−3, which is within the probable physiological range of substrate concentration for L. temulentum leaf cells. Extracts derived from leaves which were not actively accumulating fructan were unable to label oligofructan. Labelling of fructan was not due to non‐enzymic isotope exchange.

Leal homogenates contained invertase and fructan hydrolase activities. Invertase activity was inhibited by pyridoxal HCl and pyridoxine MCI when these compounds were included in reactions at 20 mol m−3. Inhibition of invertase activity was correlated with a marked stimulation of fructosyl transfer, suggesting competition for substrate. Because this system functions at physiologically relevant sucrose concentrations and produces a pattern of labelled products identical to native leaf fructan, we suggest that it represents a more convincing starting point for studies of the enzymology of fructan biosynthesis than previous cell‐free extracts.
Distribution of photosynthetically fixed carbon within root systems of Eucalyptus pilularis plants ectomycorrhizal with Pisolithus tinctorius
Authors: CAIRNEY J. W. G. , ASHFORD A. E. , ALLAWAY W. G.
Published: April 2006

summary

In intact seedlings of Eucalyptus pilularis Stn. ectomycorrhizal with Pisolithus tinctorius (Pers.) Coker & Couch in growth pouches, and labelled photosynthetically with 14C4 more radioactivity was translocated into mycorrhizal than to non‐mycorrhizal roots. Results from autoradiography of intact root systems were supported by data from scintillation counting of individual root tips. Greater 14C accumulation occurred in young than in older mycorrhizas. It is proposed that individual mycorrhizal roots act most strongly as carbon sinks early in their life and that there is a progressive reduction in the amount of photosynthate translocated to them as they age.
Oxalic acid induced cytological alterations differ in beans tolerant or susceptible to white mould
Authors: TU J. C.
Published: April 2006

summary

Leaf tissues of two white bean (Phuscolus vulgaris L.) cultivars, one susceptible and one tolerant to white mould [Sclerotinia sclerotinrum (Lib.) de Bary], were treated for different times with oxalic acid. Tissues were prepared by both thin sectioning and freeze‐fraeture techniques for electron microscopy. The plasma membrane of the resistant cultivar appeared more tolerant to damage induced by oxalic acid than that of the susceptible cultivar. At the same concentration of oxalic acid the plasma membrane and chloroplasts of the susceptible cultivar were affected more, and ruptured more quickly, than those of the tolerant one. In thin sections, the ruptured organelles were partially or completely disorganized. In replicas of freeze‐fractured preparations of the plasma membrane, increased protrusions, wrinkles, breakages and ruptures were associated with increasing exposure to oxalic acid. Damage was more severe in the plasma membrane of the susceptible cultivar than in that of the tolerant one. Measurements of the conductivity of water bathing leaf discs of the two cultivars showed that the susceptible cultivar led to a higher conductivity than the resistant one, indicating that the injury and rupturing of the plasma membrane were closely related to membrane stability.
Morphological features of pericycle cells in relation to their topographical location in onion adventitious roots
Authors: CASERO P. J. , GARCÍA‐SÁNCHEZ C. , LLORET P. G , NAVASCUÉS J.
Published: April 2006

summary

Analysis of cell length, cross‐sectional area and nuclear length of pericycle cells in adventitious roots of Allium cepa L. has revealed the existence of three cell types whose topographical location is related to the vascular pattern. Cells opposite the xylem are short and narrow with an elongated nucleus. The intervening cells are also short but their cross‐sectional area is much greater than that of cells at the xylem pofes, while their nucleus is relatively short. Cells opposite the phloem are long, with an elongated nucleus, and their cross‐sectional area is intermediate between that of the other two cell types. Lateral root primordia are always initiated from the population of short cells opposite the xylem. However, the different cell types appear in the pericycle before primordial initiation and not as a result of this event.
Fluxes of atmospheric hydrogen sulphide to plant shoots
Authors: DE KOK Luit J. , STAHL KLAUS , RENNENBERG HEINZ
Published: April 2006

summary

Short‐term exposure of maize, pumpkin, spinach and spruce to various atmospheric H2S concentrations resulted in high H2S fluxes to the shoots. In all species an almost linear relation was observed between flux and H2S concentration up to around 0.3 μl −1. At higher H2S concentrations the flux reached a maximum, which was about 0.08, 0.04, 0.1 and 0.03 μmol g f. wt−1 h−1 for maize, pumpkin, spinach and spruce, respectively. The transpiration rate was not affected during H2S exposure. Up to a level of 0.3 μl 1−1, the shoot conductance for a influx of the various species varied between 61 and 92% of that predicted from shoot conductance for aqueous vapour efflux. There was no relation between the H2S flux to the shoots and the sensitivity of the species towards H2S. A 12 days' exposure of maize, pumpkin and spinach to 0.75 μl 1−1 H2S resulted in a reduction of shoot yield of 1.36 and 69%, respectively. H2S flux to the shoots of pumpkin, spinach and spruce remained rather constant during exposure for three or four days to about 0.22μl l−l H2S. Even at a concentration of about 0.8 μl 1−1H2, which reduced the growth of pumpkin and spinach, the fluxes remained nearly constant. Fluxes of H2S to the shoots did, however, vary diurnally, being high during the light and low during the dark period. The H2S flux to transpiration ratio was constant during both light and dark periods, indicating that uptake was predominantly via the stomata. Only part of the total flux of H2S to the shoots of pumpkin and spinach could be recovered in the water‐soluble non‐protein sulphydryl fraction of the shoots (maximum 34%). It is proposed that cysteine synthase is directly involved in the fixation and metabolism of atmospheric H2S by the plant.
Fluoride‐induced enhancement and inhibition of shoot growth in four taxa of Pinus
Authors: DOLEY D.
Published: April 2006

summary

Pinus elliottii Englem. Var. elliottii (PEE) and three varieties of Pinus caribaca morelet [var. caribaca barr. Et Golf. (PCC), var bahamensisi Barr. et Golf. (PCB) and var. hondurensis (PCH)] were grown at gaseous hydrogen fluoride concentrations of 0.0, 1.2, 1.8 and 4.3 μ F m−3 during a period of 200 d. Extension growth of the mainstem and lateral branches was not significantly affected by fluoride in any taxon. Overbark diameter increment at the stem base was signicantly greater at 1.2 μg F m−3 than at 0, 1.8 or 4.3 μ F m−3 in all taxa, and also near the stem apex in PEE. Only in PEE was the stem base diameter increment lower at 4.3 μ F m−3 than in control plants. Lateral branch diameter increments were not signicantly affected by ambient fluoride concentration. Stem base diameter increments in all taxa linearly related to the rates of photosynthesis I needles 4–8 weeks old.
The effect of arginine on rates of internalization of other amino acids by symbiotic Chlorella cells
Authors: McAULEY P. J.
Published: April 2006

summary

Addition of arginine to the medium of symbiotic Chlorella freshly isolated from the European strain of green hydra increases the rate of uptake of other amino acids into the cells via a general amino acid permease. Uptake rates increase immediately upon addition of arginine, reaching a new stable level after 20–30 min. Removal of arginine causes an immediate decrease in uptake rates. Changes in the Km and Vmax of amino‐acid uptake in the presence of arginine, and the fact that cycloheximide treatment does not inhibit the arginine‐stimulated increase, suggest that arginine does not induce synthesis of new transport protein. Instead, arginine may alter properties of the cell membrane such as charge, thereby increasing the efficiency of uptake of amino acids by existing transport mechanisms. The significance of this novel effect is discussed in terms of possible control of amino acid supply to the symbiotic Chlorella.
Evidence from peroxidase polymorphism on the taxonomy and reproduction of some Sorbus populations in south‐west England
Authors: PROCTOR MICHAEL C. F. , PROCTOR MARGARET E. , GROENHOF ANDREW C.
Published: April 2006

summary

Peroxidase isoenzymes in stem tissue were investigated by polyacrylamide gel electrophoresis in Sorbus populations mainly from Devon, south‐west England, A total of 16 bands were recognized, of which 10 were variable between individuals or populations. The sexual diploid species S. aucuparia, S. aria and S. torminalis showed individual variation within populations. Six polyploid microspecies, S. anglica, S. porrigentiformis, S. rupicola, S. vexans, S. subcuneata and S. devoniensis, and an extensive unnamed rupicola‐like population on the coast of north Devon and west Somerset, consisted of individuals of essentially identical phenotype (with a few recognizable minor variants). Every microspecies had a distinctive peroxidase phenotype but S. porrigentiformis from Devon was not identical with a specimen from Leigh Woods, Bristol. Microspecies of the S. aria group have various combinations of seven bands which occur in diploid S. aria populations. S. anglica combines ‘S. aria’ bands with a prominent band from S. aucuparia. S. subcuneata and S. devoniensis possess four or five of the ‘S. aria’ bands, together with two bands which are apparently constant in S. torminalis; S. intermedia also has a peroxidase phenotype related to these species.
Effect of oxygen supply and temperature at the root on the physiology of kiwifruit vines
Authors: SMITH G. S. , BUWALDA J. G. , GREEN T. G. A. , CLARK C. J.
Published: April 2006

Summary

A severe leaf disorder currently affects kiwifruit vines (Actinidia deliciosa var. deliciosa) in New Zealand and a number of other countries. The symptoms, which develop in mid‐summer, include interveinal chlorosis, development of necrolic areas on the leaf and eventual leaf death. Field observations strongly indicated the involvement of the root system. The present study investigated the extent to which temperature and oxygen supply at the root influenced the physiology of kiwifruit vines.

Maximum root growth occurred at 20 °C, while temperatures in excess of 25 °C reduced growth. Shoot growth was also reduced by root temperatures above 20 °C. No obvious leaf symptoms developed on the vines affected by the high temperatures. Below 20 °C there was a marked reduction in growth with little or no growth occurring at 10 °C. While soil temperature can be expected to influence root growth per se, it would appear unlikely that it directly controls the seasonal pattern of root growth or greatly influences the physiology of the leaf.

This study showed kiwifruit vines are not well adapted to tolerate low concentrations of oxygen in their root zone. Growth was substantially reduced when the supply of oxygen to the roots was reduced. The extent of the reduction was proportional to the number of hours per day the vines were without aeration. Root growth was particularly affected. Distinctive leaf symptoms appeared on all oxygen‐stressed vines and included the sudden appearance of large necrotic areas on the older leaves, sometimes preceded by an interveinal chlorosis. Measurement of the porosity of the roots indicated that the average air space between the tightly packed cells accounted for 2% or less of the total root volume. There was no obvious change in root porosity with decreasing oxygen supply or difference between the solution grown vines and vines from the field.

Decreasing the supply of oxygen to the roots resulted in rapid reduction in the stomatal conductance of the leaves and the virtual elimination of the diurnal pattern. Associated with the decrease m the stomatal conductance was a marked increase in the maximum daily temperature of the leaves compared to the control vines. The difference between the two treatments increased with time. An estimate of the rate of consumption of oxygen per unit length of root (9.1 × 10−10 mol m−1 s −1) suggests that a mature kiwifruit vine could deplete the oxygen supply in a well aerated soil to an anoxic condition in about 5 hours. The relatively high consumption of oxygen coupled with the low porosity of the roots ensures that even short periods of low concentrations of oxygen in the root zone will seriously affect the physiology and growth of kiwifruit vines. It was concluded that poor aeration of the root system is likely to be a major factor in the incidence of the leaf disorder currently affecting kiwifruit vines in a number of countries.
A correlation in plastid development and cytoplasmic ultrastructure with nuclear gene expression during seed ripening in soybean
Authors: SAITO G. Y. , CHANG Y. C. , WALLING L. L. , THOMSON W. W.
Published: April 2006

Summary

With greening of soybean embryos during seed ripening, increased granal stacking directly correlates with decreasing chlorophyll a/b ratios. However, the intergranal fret system that is normally observed in chloroplasts is minimally developed during embryogenesis. Transitions in chloroplast development were correlated with coincident transitions in cellular ultrastructure. Levels of chlorophyll a/b binding protein mRNAs decreased prior to chloroplast dedifferentiation to eoplast during seed maturation. This suggests that the availability of chlorophyll a/b binding proteins is essential for maintenance of thylakoid appression and stacking against derivative processes.
The relationship between some morphological and chemical features of Sphagnum cuspidatum Ehrh. and physical characteristics of the environment
Authors: BAKER R. G. E. , BOATMAN D. J.
Published: April 2006

Summary

The frequency (No. 1000 fascicles−1) of innovations (branches resembling the parent shoot) on plants of Sphagnum cuspidatum Ehrh. was determined at IX sites on or near the Silver Flowe National Nature Reserve on six occasions. The capitula were analysed for nitrogen, phosphorus and potassium.

When the sites were arranged in order of increasing mean innovation frequency it was found that the frequency at ombrotrophic sites was less than that at rheotropic sites. Interfascicle length was directly related to innovation frequency but no evidence of a relationship between either interfascicle length or innovation frequency and capitulum dry weight was found. During the course of each growing season the variances of the means of interfascicle length and capitulum dry weight declined.

Multiple regression analysis indicated that the capitulum dry weight and interfascicle length were negatively and positively related respectively to the nitrogen content of the capitula. The regression of innovation frequency on N, P and K in the capitula was not significant (P > 0.05).

Two experiments were undertaken in which shoots of Sphagnum cuspidatum were reciprocally transplanted between a rheotrophic and an ombrotrophic site. During the course of a single growing season the mean interfascicle length, the mean capitulum dry weight and the mean concentrations of N, P and K in the capitula became much more similar to those of the controls. At the beginning of each experiment all visible innovations were removed from the plants. At the end of the experiment in 1983 innovation frequencies on the transplants were intermediate between those on the ombrotrophic and rheotrophic controls. In 1984 innovation frequencies on both controls and transplants were relatively low and an attempt is made to explain this in terms of the climatic conditions of that year.
Ultrastructure and cytochemistry of Dunaliella tertiolecta Butcher and Pavlova lutheri (Droop) Green grown on three different sources of organic nitrogen*
Authors: OLIVEIRA LUIS , HUYNH HANH
Published: April 2006

Summary

Phototrophic growth of Dunaliella tetiolecta Butcher or Pavloca lutheri (Droop) Greet) on hypoxanthine or allantoatc produces major ultrastructural changes, by comparison with nitrate‐ and urea‐grown cultures. These are particularly noticeable during growth on hypoxanthitie and affect mainly the endoplasmic reticulum, mitochondria and vacuoles. Cytochemical tests reveal the presence of both uricaase and cataJase activities in mitochondria. Since no mierobodies are observed m cells of these trncroaluac, it appears that mitochondria participate in the oxidativc degradation of putines and their derivatives. These oryancllcs may therefore play a major role m the organic N budget oi Dunaliella tertiolecta and Pavlova lutheri.
The temporal window of germination in oospores of Chara (Charophyceae) following primary dormancy in the laboratory
Authors: STROSS R. G.
Published: April 2006

Summary

Fully ripened oospores from two clones of Chara Zeylanica Klein ex Willdenow. were harvested in October. Initially, the oospores of one clone were all dormant, those of the second clone were non‐dormant. Postharvest temperatures influenced after‐ripening and dormancy initiation respectively. The temperature effect was reflected in the amplitude of germination, which ranged from 29‐100% hut not in the duration of the dormant interval. The germination window opened independently of temperature and was maximally open 6‐2 months postharvest. After‐ripening was augmented and germination was suppressed by oscillating temperatures. Light, given as prolonged exposures, was a necessary stimulus for activation. A secondary, or ‘Haupt’, messenger, diffusing from the bactoagar substratum, obscured the light reaction and disrupted the germination window. A ‘location awareness’ is suggested by an endogenous temporal window of germinability, superimposed on which are discriminators that sense appropriate conditions of light and temperature.
Compensation in growth and photosynthesis of wheat (Triticum aestivum L.) following early inoculations with Septoria nodorum (Berk.) Berk.
Authors: ROONEY J. M. , HOAD G. V.
Published: April 2006

Summary

Inoculations of winter wheat with Septoria nodorum (Berk.) Berk, at either the three or six Leaf stage in the glasshouse identified possible mechanisms of changes in the growth of winter wheat to compensate for the damaging effects of infection. Following inoculations at the three leaf Stage there was increased photosynthesis in healthy fourth leases on inoculated plants; no equivalent increase was shown for later inoculations. There was some indication that, after third leaf inoculation, photosynthesis was stimulated in healthy areas on infected leaves but depressed in infected areas. After inoculations at the third leaf stage, the shoot/root dry weight ratio increased compared with that of controls. No significant changes in dry matter production, at anthesis or during grain‐growth, followed inoculation at the six leaf stage. At anthesis there was an increase in the proportion of dry weight partitioned to stems, and tiller and leaf area of infected plants was greater than m the control plants.
Ectomycorrhizas and putative ecto‐mycorrhizal fungi of Afzelia africana Sm and Uapaca guineensis Müll. Arg. in southern Senegal
Authors: THOEN D. , BA A. M.
Published: April 2006

Summary

Ectomycorrhizas and ectomycorrhizal fungi of Afzelia africana Sm. and Uapaca guineensis Müll. Arg. are reported in forests of southern Senegal. Ectomycorrhizas occurred in dry and wet conditions, at different soil contents of available phosphorus (0–17.5 μg g−1). U. guineensis was confined to groundwater forests. Individual trees had both ecto‐ and endomycorrhizas, A. africana grew scattered in semi‐evergreen and riverside forests, whereas in the woodland it formed larger patches and could dominate the canopy. Eighteen putative ectomycorrhizal fungi grew under U. guineensis and thirty‐one under A. africana. Only six species were common to both trees, indicating an ecological and/or taxonomical selection. The fungi belonged to the following Orders: Russulales (16), Boletales (11), Agaricales (9), Cantharellales (2), Selerodermatales (2), Hymenogastrales (1), Gautieriales (1), Aphyllophorales (11). Some of them had a wide Sudano‐Zamhezian or Guineo‐Congolian distribution and reached their northern limit in Senegal.
Which steps are essential for the formation of functional legume nodules?
Authors: SPRENT J. I.
Published: April 2006

summary

Nodulation is reviewed in terms of the phenotypes proposed by Vincent (1980).

Individual legumes may be infectible by one or more of the three bacterial genera (collectively known as rhizobia)Rhizobium, Bradyrhizobium, orAzorhizobium.The type of infection process by which rhizobia gain entry is largely governed by the host genotype. In addition to the widely studied root‐hair pathway, infections may be associated with lateral root emergence or occur between root epidermal cells. The exact chemical and physical nature of the root hair/epidermal cell wall is likely to be a critical factor in determining whether infections can proceed. In addition to differing with species, wall composition may be influenced by soil chemical (e.g. Ca2+) and biotic factors (e.g. bacteria).

Rhizobial features essential for infection include particular surface polysaccharides and the induction of nodulation genes by plant root exudates. Neither of these is likely to be a major barrier to the extension of nodulation to new hosts.

Dissemination of rhizobia within developing nodules may be intercellular, via infection threads or by division of a small number of infected cells. All functional symbioses eventually have ‘intracellular’ bacteria, in the sense that rhizobia are geographically located within the boundary of the host cell walls. However, they remain extracellular in the sense that they are always confined by a membrane which is largely of host cell origin. In some genera they are also surrounded by infection thread walls, probably modified forms of ‘invasive’ infection thread walls, which allow differentiation of rhizobia into the nitrogen‐fixing form. Thus, natural, functional, symbioses may (a) never involve a stage in which bacteria are confined within tubular infection threads or (b) never release bacteria from infection threads. These features are determined by host genotype.

The one feature of legume nodules so far found never to vary is the stem‐like character of a peripheral vascular system. This contrasts with the central vascular system of actinorhizas and the rhizobial‐induced nodules on the Ulmaceous genusParasponia.Although of great intrinsic interest, this character is unlikely to present an insurmountable barrier to the extension of nodulation to new species. Other features, such as the ability to produce haemoglobin are now known to the in the genetic makeup of many higher plants.

The discovery of the wide range of nodule structures occurring in nature, together with work on mutant rhizobia which may bypass critical stages in the nodulation process, suggest various ways in which the extension of nodulation to non‐nodulated legumes and to other (initially at least, dicotyledonous) plants may be engineered.

CONTENTSSummary129I.Introduction130II.The symbionts130III.Stages in nodulation132IV.Stems and nodules143V.Prospects for finding/making new symbioses144VI.Conclusions145Acknowledgements147References147
Nitrogen uptake and growth of wheat during O2 deficiency in root media containing NO3− only, or NO3− plus NH4+
Authors: BUWALDA F. , GREENWAY H.
Published: April 2006

summary

The effects of hypoxia at 0.003 mol O2 m−3 on growth and nitrogen uptake of wheat seedlings (Triticum aestivum L. ev. Gamenya) was compared between plants growing in nutrient solutions containing either NO3− only, or NO3− plus NH4+.

Hypoxia reduced the uptake of N by the plants, however both at 0.28–0.31 mol O2 m−3 (aerated solutions) and 0.003 mol O2 m−3, rates of N uptake from solutions containing NO3− plus NH4+ were 34% higher than from solutions containing NO3− only. In aerated solutions, growth was faster when NO3− plus NH4+ was supplied. By contrast, at 0.003 mol O2 m−3 both N treatments had the same low growth rate (expressed on a dry weight basis) despite considerably higher internal N concentrations in the plants supplied with NO3− plus NH4+. It is concluded that N nutrition did not limit growth at 0.003 mol O2 m−3 in either N treatment. Other possible causes of the growth reduction and differences in uptake characteristics between NO3− and NH4+ are discussed.
Effects of cation leaching on mineral cycling and transpiration: investigations with beech seedlings, Fagus sylvatica L.
Authors: LEONARDI SILVIO , FLÜCKIGER WALTER
Published: April 2006

summary

Beech seedlings (Fagus sylvatica L.) were sprayed with acidic or ammonium‐rich solutions of different concentrations, 10−3 or 10−5 mol l−1 H+ or NH4+. Whilst the leaching of Ca and Mg was increased by the more acid treatment, the K leaching was decreased. On the other hand, the concentrated NH4+ mist led to a substantial increase in the leaching of K. As a consequence of the greater uptake of cations due to their leaching, more protons were released to the nutrient solution and into the rhizosphere of potted plants. Increased transpiration was observed following the application of acidic mist to the plants in nutrient solution but decreased stomatal diffusive resistance of potted plants was detected only at night. Acid mist caused changes in stomatal behaviour that were responsible for a rapid and greater water loss of detached leaves.
Effects of drought and CO2 enrichment on competition between two old‐field perennials
Authors: MARKS SUSAN , STRAIN BOYD R.
Published: April 2006

summary

We studied the effects of drought stress and CO2 enrichment on the competition between Aster pilosus Willd. (aster, C3) and Andropogon virginicus L. (broomsedge, C4) under two CO2 concentrations (350 and 650 μl l−1 CO2) and two water treatments (well‐watered and water‐limited). Although broomsedge is the more drought‐tolerant species, this did not increase its competitive ability against aster under drought conditions. With CO2 enrichment, aster was a stronger competitor than broomsedge and comprised 75% of above‐ground pot biomass in both water treatments. CO2 enrichment also increased aster survival when competing with broomsedge under extreme drought conditions. Although drought stress and CO2 enrichment interacted to affect the two species in different ways, there was no interaction of drought stress and competition; aster was a stronger competitor than broomsedge under CO2 enrichment in both well‐watered and water‐limited conditions. With future increases in the atmospheric CO2 concentration, aster may delay broomsedge dominance in old‐field communities.
Effects of low concentrations of ozone on the fine structure of radish leaves
Authors: MIYAKE H. , MATSUMURA H. , FUJINUMA Y. , TOTSUKA T.
Published: April 2006

summary

Radish (Raphanus sativus L.) plants were fumigated with 0.1 or 0.05 μl l−l O3 for 8 or 24 h a day for 6 to 18 d and the leaf tissues examined by light and electron microscopy. Ultrastructural damage was apparent in the leaves fumigated with as low as 0.05 μl l−1 for 8 h a day for 6 d. Ozone induced an increase in both the number and size of the plastoglobules but a decrease in chloroplast dimensions. These changes in the chloroplasts developed further even after O3 fumigation had been discontinued. The plastoglobules were electron dense in the early stages of exposure to O3 but subsequently became electron translucent. Finally large plastoglobules were extruded into the vacuole, a phenomenon which may partly account for the reduction in chloroplast size. Ozone also caused disruption of the tonoplast and this was followed by collapse of the cells. Low concentrations of O3 appear to accelerate senescence of the chloroplasts.
Intercellular infection in the meristematic region of ‘Piceirhiza gelatinosa’ mycorrhizas
Authors: HAUG I.
Published: April 2006

summary

‘Piceirhiza gelatinosa’ mycorrhizas from Schluchsee, but not from two other sites in the Black Forest, showed intercellular hyphae in the apical region of unbranched and finger‐like branched roots. The hyphae of the fungus were able to penetrate between the meristematic and immature cortical cells. In outer regions of the root, hyphae were arranged in layers one to two cells deep but towards the middle, single hyphae were most commonly encountered. The method of penetration and a possible relationship with abnormal growth are discussed.
Shoot: root interrelationships in leeks infected with the rust, Puccinia allii Rud.: Growth and nutrient relations
Authors: ROBERTS A. M. , WALTERS D. R.
Published: April 2006

summary

Growth and nutrient relations were examined in healthy leeks and in leeks inoculated with the rust, Puccinia allii, to give three different intensities of infection (i.e. 10, 20 and 30%). Experiments were conducted over an 8‐week experimental period, although only data from 5 weeks after inoculation are shown. The dry weights of rust‐infected plants were substantially reduced compared with controls over the entire experimental period. Although shoot: root (S: R) ratios were increased in rusted plants 2 weeks after inoculation, the trend was reversed thereafter and for the remainder of the experiment S:R ratio was reduced in comparison with healthy controls.

The contents of nitrogen, phosphate, potassium and calcium were reduced in rusted plants compared to controls. On the other hand, with few exceptions, the concentrations and specific absorption rates of these minerals increased in rusted plants compared with healthy controls. The ability of infected plants to maintain a functional S:R equilibrium with respect to nutrient uptake was examined using an analysis based on comparing changes in incremental plant dry weight with incremental nutrient weight. Calculated values of functional equilibrium for control and rusted plants showed that rust infection altered functional equilibrium with respect to uptake of the four nutrients. The possible mechanisms underlying these changes in physiology and the analysis of such changes are discussed.
Histochemical localization of desoxyhemigossypol, a phytoalexin in Verticillium dahliae‐infected cotton stems
Authors: MACE M. E. , STIPANOVIC R. D. , BELL A. A.
Published: April 2006

summary

The terpenoid phytoalexin desoxyhemigossypol (dHG) was detected histochemically in the stem xyiem of Verticillium dahliae Kleb‐infected, wilt‐resistant Seabrook Sea Island cotton as a green product on V. dahliae mycelium within vessel lumens and in specialized, often solitary, paravascular parenchyma cells. The SbCl3‐HClO4 histochemical reagent yielded a green‐coloured Sb‐dHG product specific for dHG when used as a spray on chromatograms of extracts from Verticillium‐infected stele tissue. Both dHG and related terpenoid aldehyde derivatives occurred together in parenchyma cells and on V. dahliae mycelium. The presence of dHG on Verticillium mycelium reinforces previous studies that identified dHG as the most toxic and possibly most important phytoalexin in the resistance of cotton to V. dahliae.
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: LÜTTGE U. , MEDINA E. , CRAM W. J. , LEE H. S. J. , POPP M. , SMITH J. A. C.
Published: April 2006

summary

In an ecophysiological field investigation of plant communities of vegetation islands of an alluvial plain in northern Venezuela the members of the Cactaceae, Pereskia guamacho, and a columnar ceroid cactus, Subpilosocereus ottonis, were studied. The alluvial plain was flooded by fresh water in the rainy season in November/December 1985 and was dry and saline in the dry season in March/April 1986. The highly succulent leaves of P. guamacho were shed in the dry season. They performed C3 photosynthesis in the wet season and did not show signs of considerable salt accumulation. P. guamacho avoids stress due to drought and salinity by leaf‐shedding. The columnar stem succulent ceroids are salt‐excluding plants with crassulacean acid metabolism (CAM). Rapid die back and regeneration of absorptive roots, water parenchyma and CAM, with the possibility of nocturnal stomatal closure and CO2 recycling, are traits of adaptive value under fluctuating conditions between rainy and dry seasons on the alluvial plain.
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: LÜTTGE U. , POPP M. , MEDINA E. , CRAM W. J. , DIAZ M. , GRIFFITHS H. , LEE H. S. J. , SCHÄFER C. , SMITH J. A. C. , STIMMEL K.‐H.
Published: April 2006

summary

The perennial halophytes, Batis maritima L., Sesuvium portulacastrum L., and Portulaca rubricaulis H.B.K. which inhabit the extreme environment on parts of the salt plain and at the edges of the vegetation islands of Ciénega el Ostional were examined to determine their strategies for growth and survival in the rainy and dry seasons.

All of the three species are leaf‐succulents. High leaf‐sap osmotic pressures, xylem tensions and Na+ and Cl− levels indicated that S. portulacastrum and B. maritima are salt‐accumulating halophytes. Succulence, leaf‐sap osmolalities and Na+ and Cl− levels increased in the dry season in B. maritima by a factor of 1.5‐2.0 and in S. Portulacastrum by a factor of 1.9–2.7. B. maritima also accumulated sulphate with a two‐fold increase of concentrations in the dry season. In S. portulacastrum Na+ accumulation much exceeded Cl− accumulation and oxalate synthesis was found to serve charge balance. In this species the compatible solutes, proline and pinitol, were clearly detectable in both seasons; their levels increased by a factor of about 6 in the dry season.

Exchange of water vapour and CO2 was measured with a portable steady‐state porometer. Photosynthesis in B. maritima showed little response to the transition from the rainy to the dry season while S. portulacastrum was severely impaired in the dry season, showing pronounced midday depressions of gas exchange and about 40% inhibition of light‐saturated rates of CO2 uptake. P. rubricaulis shed its leaves in the dry season.

According to carbon isotope ratios (δ13C), B. maritima (δ13C =−26.4‰) and S. portulacastrum (δ13C =−25.8 ‰) are C3 plants while P. rubricaulis (δ13C =−12.3‰) performed C4 photosynthesis.
Iron plaque on roots of Aster tripolium L.: interaction with zinc uptake
Authors: OTTE M. L. , ROZEMA J. , KOSTER L. , HAARSMA M. S. , BROEKMAN R. A.
Published: April 2006

summary

The iron plaque on roots of Aster tripolium L. growing in waterlogged salt marsh soil adsorbed appreciable amounts of Zn and Cu, with maximum Zn/Fe and Cu/Fe ratios of 0.1 When concentrations of Zn or Cu adsorbed in the iron plaque are expressed as mg metal kg−1 FeOOH (assuming that iron plaque consists mainly of FeOOH), the Zn and Cu concentrations of the iron plaque was up to 680 and up to 2000 times higher than in the surrounding sediment, respectively. The Zn concentration in red roots (with iron plaque) was higher than in white roots (without iron plaque). Zn concentrations in field sampled roots were correlated with the amount of Zn on the roots and the Zn concentration in the soil, whereas Cu concentrations in the roots were only significantly correlated to the Cu concentration in the soil. In vitro experiments showed that red roots take up more Zn than white roots. Measurement of Zn uptake by excised roots showed that the uptake of Zn into the xylem fluid was significantly higher in roots with 500–2000 nmol Fe cm−2 on the root surface compared to roots with less than 500 or more than 2000 nmol Fe cm−2 on the root surface. The results indicate that iron plaque enhances uptake of Zn by the roots but may act as a barrier when large amounts of Fe are deposited on the root surface. The role of the iron plaque on roots of salt marsh plants growing in soil contaminated with heavy metals is discussed.
Sugar unloading in roots of Ricinus communis L.
Authors: CHAPLEO S. , HALL J. L.
Published: April 2006

summary

The accumulation of exogenous D‐fructose, D‐glucose and sucrose into root tips of Ricinus communis was studied. Accumulation of sucrose is biphasic with respect to substrate concentration, both saturable and non‐saturable Phases being discerned. Accumulation is sensitive to pH, the exogenous solute potential, PCMBS, and other sugars. Sap representative of the apoplast was collected by centrifugation and contains approximately 40 mol m−3 hexose equivalents. Plants were labelled to the steady state with respect to cotyledonary sucrose derivatives; whole roots were then analysed by compartmental analysis and the results indicated similar apoplastic hexose concentrations. The vacuoles of roots grown in low salt solution contain most of the root soluble sugars, at a concentration of about 70 mol m−3 hexose equivalents. The sugar content of such roots decreases with availability of KCl to an extent which indicates that this involves a replacement of vacuolar hexose by alternative osmotica, supporting the results from compartmental analysis.
Sugar unloading in roots of Ricinus communis L.
Authors: CHAPLEO S. , HALL J. L.
Published: April 2006

summary

The intercellular pathway of sugar transport within tissues of Ricinus communis roots, which are available to exogenous solutions, was investigated to identify the route of phloem unloading. Less than 3%, of soluble translocate within the root system accumulates in root bathing media designed to influence the apoplastic movement of soluble sugars. Sucrose and hexoses make up 80% of the leaked translocate. The influence of plant growth regulator substances and of amino acid analogues upon the accumulation of translocate into the primary root has been evaluated and is discussed in relation to the symplastic transport of carbohydrate.
A 13C NMR study of photosynthate transport and metabolism in the lichen Xanthoria calcicola Oxner
Authors: LINES C. E. M. , RATCLIFFE R. G. , REES T. A. V. , SOUTHON T. E.
Published: April 2006

summary

13C nuclear magnetic resonance (NMR) spectroscopy was applied to the lichen Xanthoria calcicola Oxner. The in vivo spectra were poorly resolved and although the line‐broadening effect of variations in the bulk magnetic susceptibility could be eliminated by spinning the sample at the magic angle, the spectra were still relatively Uninformative in comparison with the spectra of methanol extracts of the tissue. The synthesis of ribitol by the algal symbiont and its subsequent metabolism to mannitol by the fungus was followed using pulse‐chase experiments. The fine structure in the spectra provided support for the role of the pentose phosphate pathway in the conversion of ribitol to mannitol. Preliminary experiments, in which the conditions of the pulse‐chase experiment were altered, showed that the incorporation of 13C into mannitol was reduced at a lower temperature, and in thalli of low moisture content, and was abolished by darkness.
Effects of the bisulphite ion on growth and photosynthesis in Sphagnum cuspidatum Hoffm.
Authors: BAXTER R. , EMES M. J. , LEE J. A.
Published: April 2006

summary

Shoots of Sphagnum cuspidatum Hoffm. were collected from two sites: one, a relatively unpolluted site in N. Wales, remote from pollution sources and the other, a grossly polluted site in the South Pennines.* Material from both sites was grown in the laboratory and exposed to artificial rainwater solution with and without bisulphite (HSO3) amendment (0.1 mM). Effects of exposure to HSO3 for up to 21 days on growth, photosynthesis, chlorophyll a fluorescence and chlorophyll concentrations were studied in the two Sphagnum populations.

Application of HSO3 produced significantly less than maximum growth in Sphagnum from both sites. This effect was far greater, however, in the material from the unpolluted Welsh site.

Photosynthesis in the Welsh material treated with HSO3 decreased steadily with time; after 21 days of exposure, photosynthetic oxygen evolution had ceased. This decrease was accompanied by a decrease in fluorescence quenching (as [(P – T)/P]), suggesting a gradual loss of water‐splitting activity.

In contrast, HSO3 initially stimulated photosynthesis in Sphagnum from the polluted site. Chlorophyll concentration was decreased in Spliagmtm from both sites in the presence of HSO3

Possible mechanisms of tolerance to HSO3 are discussed.
The relationship between extracellular metal accumulation and bisulphite tolerance in Sphagnum cuspidatum Hoffm.
Authors: BAXTER R. , EMES M. J. , LEE J. A.
Published: April 2006

summary

Sphagnum cuspidatum Hoffm. was collected from a remote site in N. Wales, and a polluted site in the S. Pennines. When added to artificial rainwater solution, HSO3− was oxidized to SO42−. The rate at which this oxidation occurred was modified differentially by the mosses from the two sites.

S. cuspidatum from the S. Pennines promoted a rapid oxidation rate and disappearance of HSO3− was complete in 6 h. S. cuspidatum from N. Wales, on the other hand, achieved a very slow oxidation rate and HSO3− persisted in solution for more than 24 h. Prolonged exposure to HSO3− in the Welsh material caused damage to, and eventual death of, this material but not of the S. Pennine moss.

The rates of HSO3− oxidation promoted by the mosses from the two sites appear to be related to the concentration of the transition metal ions, Fe(III), Mn(II), and Cu(II), present on the cell‐wall cation‐exchange sites. These metals, particularly Fe, present on the surface of the S. Pennine material catalysed a rapid chemical oxidation of HSO3− to SO42−. The increased levels of transition metals associated with the S. Pennine moss originate in the peat as a legacy of past pollution events at this site.

Levels of Fe were approximately 100 times greater than those for Mn or Cu and 5–10 times higher on the S. Pennine moss than on that from N. Wales. Removal of these metal ions (using EDTA) from the surface of the S. Pennine material removed the HSO3− oxidizing ability of the moss, leading eventually to cell death.

The ability to withstand high levels of HSO3− was conferred upon the Welsh moss by supplying Fe(m) in artificial rainwater solution under laboratory conditions. Transplanting Sphagnum from the Welsh to the S. Pennine site gave rise to a similar response. Nomenclature of mosses follows Smith (1978).
The effects of oxides of nitrogen and carbon dioxide enrichment on photosynthesis and growth of lettuce (Lactuca sativa L.)
Authors: CAPORN SIMON J. M.
Published: April 2006

summary

The response of glasshouse crops to the nitrogen oxide pollutants which may be generated during enrichment with O2 has been studied in controlled environments. Lettuce (Lactuca sativa L. cv. Ambassador) was grown in air containing either low CO2, (380μmol mol−1), high CO2, (1200 μmol mol −1), or high CO2 plus oxides of nitrogen? (NOx)‐ Carbondioxide enrichment increased the rate of emergence and expansion of leaves and the growth of Young plants. Addition of NOx (2μmol mol−1 NO and c. 0.5 μmol mol−1 NO2) to CO2‐enriched air significantly reduced the yield, compared with the ‘clean, high CO2 treatment, without producing visible symptoms of toxicity. Fumigation of single plants in high CO2, with NOx rapidly inhibited photosynthesis per unit leaf area. This did not appear to be due to a reduction in stomatal conductance. Removal of NOx from the atmosphere caused a rapid and complete recovery in the rate of photosynthesis. Studies were made of the effects of growing Plants for long periods in atmospheres containing high CO2 and NOx on the photosynthetic capacity of single leaves when measured in NOx‐free air. The decrease in photosynthetic rate as the fourth leaf aged occurred earlier in plants grown in CO2‐enriched air than in those from the low CO2 treatment. Leaves which developed in the CO2‐enriched air containing NOx did not suffer any long‐term damage to photosynthetic activity in comparison with those of the ‘clean’ high CO2. In mature leaves the principal long‐term effect of enrichment (with or without NOx was to reduce the rate of photosynthesis in saturating CO2. In contrast, there was less effect on the rate of Photosynthesis in low CO2. The absence of a long‐term effect of NOx, on the photosynthetic capacity suggested that photosynthesis by the lettuce crop will be inhibited only during the transient periods of NOx accumulation in the glasshouse.