bluuebunny/crossref_metadata_2025 huggingface dataset:
Chloroplast development and nuclear gene expression in cotyledons of soybean seedlings
Authors: SAITO G. Y. , CHANG Y. C. , WALLING L. L. , THOMSON W. W.
Published: April 2006

With the greening of soybean cotyledons after germination, development of the photosynthetic membrane system and particularly granal stacking were correlated with decreasing chlorophyll a/b ratios. Chlorophyll a/b binding proteins are known to be localized mainly in the appressed membrane regions and to have a role in mediating granal membrane appression. The chlorophyll a/b binding protein genes became operative very early in the development of the photosynthetic membrane system and coincided with incipient granal formation. However, the accumulation of chlorophyll a/b binding protein mRNAs decreased as the chloroplasts approached full development. As predicted from the literature, an early amyloplast developmental stage was observed, and prolamellar‐like structures appeared early in the development of the chloroplasts, but subsequently disappeared. The reported amoeboid stage that follows the amyloplast phase was not observed, and starch persisted until quite late in development of the chloroplasts. Also, deformations in the shape of the developing chloroplasts indicated that they were amoeboid as they increased in size and as granal formation increased. Phytoferritin accumulations were observed at every stage of development, suggesting that it was not utilized during chloroplast development.
Internal secretory structures in Hypericum (Clusiaceae): H. perforatum L. and H. balearicum L.
Authors: CURTIS J. D. , LERSTEN N. R.
Published: April 2006

Hypericum species have translucent oil cavities; many species also have superficially similar black internal structures. Contradictory descriptions of both structures emerged from 19th century studies, which we review here. Our study of Hypericum perforation L. leaves and petals shows typical schizogenous translucent oil cavities that develop with a uniseriate epithelium. Black structures, in contrast, are nodules, each composed of several large cells lacking a central intercellular space and surrounded by a biseriate sheath of flattened cells. Nodule cells accumulate black, granular, but non‐resinous contents. The ‘streaks’ that traverse petals are elongate tubular cavities or nodules, except for some chimerical tubes composed partly of each. Hypericum balearicum L. leaves have bulging, pustular cavities. A large cellular nodule forms first, by non‐synchronous cell divisions within the leaf mesophyll, and is surrounded by a sheath of two to three flattened cell layers. The central cells then separate unevenly to form an irregular cavity into which isolated cells and clusters of cells intrude, some of which continue to divide as other cells degenerate. Little or no oil accumulates in the cavity, and the peripheral lining of cells is very irregular to flattened and empty. Both species studied exhibit secretory structures with previously undescribed anatomical features.
Metabolism of [15N]glycine and [13C]glycine by Dionaea muscipula studied by gas chromatography‐mass spectrometry
Authors: GREENAWAY W. , MAY J. , ENGLISH S. , WHATLEY F. R.
Published: April 2006

Plants of Dionaea muscipula Ellis fed for 24 h via trap lobes with [13C]glycine or [15N]glycine metabolized the glycine in the fed trap lobes only. Both 13C and 15N labelling was detected in glycine and serine and l5N labelling in alanine, aspartic acid, glutamic acid and 4‐aminobutanoic acid extracted from fed trap lobes. Limited amounts of [4‐15N]aminobutanoic acid and serine were translocated to the lamina of the fed trap lobes but neither these, nor other labelled amino acids, were detected in other parts of the plant. No 13C labelling was detected in compounds other than glycine and serine.
Mcchanism of flood tolerance in reed, Phragmites australis (Cav.) Trin. ex Steudel
Authors: GRIES C. , KAPPEN L. , LÖSCH R.
Published: April 2006

Important factors, such as porosity, respirational O2 consumption, O2 release of the roots and iron oxidation on the root surface, which are involved in the flood tolerance of Phragmites australis were investigated in northern Germany. The porosity of the different organs was determined as 58% for rhizomes, 42% for culms and 23‐38% for adventitious roots. Mean respirational O2 consumption of below ground organs was measured at 5, 10, 15 and 20°C as respectively 0.25, 0.5, 0.8 and 1.75 nmol O2 g−1dry mass s−1. The saturation concentration was estimated to be less than 0.017 mmol O2 1−1up to 15°C and 0.03 mmol O2 1−1at 20°C. From values of the root O2 gas exchange obtained from entire plants predictions are made concerning the O2 status of the roots under field conditions throughout the year. The O2 release for a reed stand was calculated as 65‐129 mg O2 m−2h−1in summer conditions. The oxidation power of the roots was further demonstrated by the development of iron hydroxide‐plaques on the root surface.
Iǹfectivity of pine and eucalypt isolates of Pisolithus tinctorius on roots of Eucalyptus urophylla in vitro
Authors: MALAJCZUK N. , LAPEYRIE F. , GARBAYE J.
Published: April 2006

Two isolates of the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch were inoculated on to roots of Eucalyptus urophylla S. T. Blake in vitro and a comparison made of the rate of ectomycorrhizal development. Both isolates initiated ectomycorrhizal roots but the time of onset of root colonization and the rate of formation varied with the isolate. An isolate cultured from a sporocarp collected from under eucalypts in Australia rapidly colonized roots of E. urophylla and initiated mycorrhizas after 2 d incubation, whereas an isolate obtained from sporocarps collected from under pines in the United States developed ectomycorrhizas only after 7 d incubation. Dual inoculation of E. urophylla seedlings using a paper‐sandwich technique again showed the rapid colonization of roots by the eucalypt isolate even when roots were inoculated 7 d previously with the pine isolate. These in vitro observations support field observations that there are variable degrees of plant species ‐ fungal isolate compatibility, implying specificity, and this is an important factor influencing successful ectomycorrhiza formation and development.
Ectomyeorrhiza formation in Eucalyptus
Authors: DELL B. , MALAJCZUK N. , THOMSON G. T.
Published: April 2006

The structure of mature tubercles collected from a Eucalyptus pilularis forest in Queensland, Australia, is described. The smooth, pale yellow tubercles (5‐20 mm diam.) consisted of a rind (200‐250 μm thick) enclosing a dense coralloid mass of ectornycorrhizas (150‐300 μm diam.) and rhizomorphs (200‐300 μm diam.). The outer rind region was cemented together with an interhyphal matrix of carbohydrate containing embedded lipid deposits. Dolipores were common in the inner rind indicating the fungal component to be a basidiomycete. Mycorrhizas had thin mantles and well‐formed Hartig nets. Protein and lipid reserves were present in mantle hyphae. Rhizomorphs formed around non‐mycorrhizal roots inside the tubercles. The central zone of rhizomorph tissue contained thick‐walled hyphae which stained positively for lignin‐like material. The tubercles are similar to structures formed in associations between Rhizopogon and conifers in the northern hemisphere.
Vesicular‐arbuscular mycorrhizas and the soil‐disturbance‐induced reduction of nutrient absorption in maize.
Authors: FAIRCHILD M. H. , MILLER G. L.
Published: April 2006

Maize seedlings have been shown to absorb more phosphorus (P) from soil from long term zero‐till plots than from the same soil after disturbance, apparently because of greater vesicular‐arbuscular (VA) mycorrhizal colonization in the undisturbed soil, A growth room experiment was conducted to determine the effect of soil P availability on this phenomenon. Maize was grown for three 3‐week cycles in initially disturbed soil. Phosphorus was mixed with the soil to create five P‐amendment rates: 0, 40, 80, 120, and 160 μg Pg−1soil. After each growth cycle, the soil in half the pots was disturbed and replanted, whereas the other half were replanted without disturbing the soil. In the third growth cycle, shoot dry weights were greater in the undisturbed soil than in the disturbed soil at the lower P‐amendment rates, but soil disturbance had no effect at the 120 and 160 μg P g−1soil amendments. Mycorrhizal colonization was much greater in the undisturbed soil at all P amendment rates. Shoot N, P, Mg, and Zn concentrations were higher in the undisturbed than in the disturbed soil at all P amendments, but only the increased P and Zn could be directly related to increased mycorrhizal colonization. While the benefit to the plant from mycorrhizal colonization induced by lack of soil disturbance can be quite large even at high rates of P amendment to the soil, the benefit achieved depends on the balance between the carbon (C) cost and P benefit to the host and may or may not favour the host.
K+(Rb+) uptake by intact Taraxacum plants: effects of nutrient status on K+uptake
Authors: HOMMELS C. H. , PRINS H. B. A. , KUIPER P. J. C. , TANCZOS O. G.
Published: April 2006

Microspecies of the genus Taraxacum differ in mineral ecology, spanning a range from nutrient‐poor and undisturbed soils to heavily fertilized grasslands. In this study, the principal features of K+uptake in Taraxacum plants were surveyed in order to design an appropriate test for an ecological study of K+uptake kinetics.

Mechanical stimuli induced transient K+efflux, combined with an alkalinization of the ambient solution; during this period, K+(Rb+) uptake was strongly inhibited. As a consequence, uptake experiments were conducted with intact plants in conditions of minimal disturbance.

K+uptake was studied as a function of the internal K+status, which was manipulated by various (pre)treatments including cultivation at different temperatures and various types of K+deprivation. NO−3‐dependent K+uptake in ‘high‐salt’ plants was abolished by pretreatments in which K+uptake was inhibited (i.e. cultivation in CaSO4 solution, or in complete nutrient solution with K+omitted, or in K2SO4 solution). In K+‐starved plants, NO−3‐dependent K+uptake was replaced by K+/H+exchange.
Characterization of the high‐affinity K+(Rb+)‐uptake system in roots of intact Taraxacum microspecies: comparison of 12 microspecies in relation to their mineral ecology
Authors: HOMMELS C. H. , SAAT T. A. W. , KUIPER P. J. C.
Published: April 2006

Taraxacum microspecies differ with respect to nutritional levels in their habitats. In the context of marked differences in growth response to internal potassium concentration between two ecologically contrasting microspecies, K+‐uptake characteristics, Vm and Km, of the high‐affinity uptake system of 12 microspecies were studied. In this comparative study, CaSO4‐pretreated plants were used.

Microspecies differences in Vmax were more abundant than in Km. Significant differences between kinetic parameters of ecologically related groups of microspecies were largely absent; only the (average) Vmax of the group of microspecies derived from heavily fertilized and moist grasslands was higher than those of the remaining three groups of microspecies. Within a taxonomically related group of eight microspecies, variation in Vmax (average) and Km (average) values was almost as high as total variation. The results on kinetic characteristics of the high‐affinity K+‐uptake system are discussed in the context of additional differences in physiology such as the critical internal K+concentration and growth potential between two representative microspecies of different mineral ecology.
The influence of ozone, acid mist and soil nutrient status on Norway spruce [Picea abies (L.) Karst.]
Authors: BARNES J. D. , EAMUS D. , BROWN K. A.
Published: April 2006

Three‐year old Norway spruce [Picea abies (L.) Karst.] trees established from two clones (4076 and 2470) of a medium‐altitude southern German provenance, were transplanted in May 1986 into two acid brown earth soils which differed particularly in the amounts of exchangeable Ca2+and Mg2+. During the summers of 1987 and 1988 trees were exposed in large‐scale fumigation chambers (solardomes) to ozone at 200 or 40 μg−3(control). Each day trees were treated with acid (pH 3‐6) or control (pH 5‐5) mist solution. In late autumn 1988 certain aspects of tree water relations were investigated. In clone 4076 ozone and acid mist reduced stomatal conductance in the light, but resulted in incomplete stomatal closure at night, reducing the diel range of stomatal conductance in treated trees grown on both soils. In addition, current year's needles excised from clone 4076 dried more rapidly following exposure to ozone and/or acid mist than needles from control trees, indicating impaired stomatal performance. However, evidence of both clonai and soil variation in this response was found. Cellular water relations of current year's shoots of clone 4076 were investigated using pressure‐volume analysis. Exposure to ozone and/or acid mist resulted in a marked increase in the plasticity of tissues (reduction in ɛ) compared with controls, indicating that the pollutants induced cell wall loosening. In trees exposed to acid mist this was associated with lower cellular solute concentrations and a decrease in maximum turgor. Throughout this study, where interactions between ozone and acid mist were significant, they were always antagonistic. It is concluded that effects of ozone and acid mist on stomata, which would be expected to enhance the sensitivity of trees to drought and winter desiccation, may be at least partially compensated for by concomitant changes in the turgor relations of individual cells. It remains to be established whether interactions between gaseous air pollutants and water stress are a factor contributing to the development of forest decline in central Europe and north eastern America.
An ozone‐low temperature interaction in loblolly pine (Pinus taedaL.)
Authors: CHAPPELKA ARTHUR H. , KUSH JOHN S. , MELDAHL RALPH S. , LOCKABY B. GRAEME
Published: April 2006

Loblolly pine (Pinus taedaL.) seedlings from two families differing in ozone sensitivity, were exposed to ozone and acidic precipitation in modified open‐top chambers, beginning in May of 1988. Visible injury (bleached needle tips) occurred after a late‐season frost in April, 1989 on newly emerging (length 5 cm) needles. After one week, needle tips turned brown and necrotic. Incidence of injury was recorded in April, May and June, 1989. Injury only occurred on trees exposed to ozone at above‐ambient concentrations (1.7 and 2.5 × ambient), and was significantly greater in the ozone‐sensitive family (GAKR 15‐91) suggesting that this response is under some genetic control. Incidence of injury decreased with time and was more noticeable in the ozone‐tolerant family (GAKR 15‐23). There was no effect of acid rain, or interaction between ozone and acid rain, revealed by visible injury. In addition, experiments were conducted to determine if ozone and/or freezing temperatures enhanced electrolyte leakage. There were no differences observed in diffusate conductivity among treatments. These findings suggest that the observed injury was due to photo‐oxidation induced by an ozone‐low temperature interaction, and represent the first report of this type of injury in loblolly pine.
The biology of mycorrhiza in the Ericaceae
Authors: SHAW G. , LEAKE J. R. , BAKER A. J. M. , READ D. J.
Published: April 2006

summary

The role of the ericoid mycorrhizal endophyte Hymenoscyphus ericae (Read) Korf & Kernan in the regulation of iron uptake by ericaceous plants is investigated. Growth of the fungus is not inhibited in solution cultures containing a range (0–144 [ig ml−1) of iron concentration ([Fe]ext) typical of those obtained in extracts from heathland soil. Absorption of iron by the fungus occurs rapidly at low [Fe]ext but more slowly as [Fe]ext increases. Concentrations of iron in the mycelium ([Fe]mye), reach 6000μg g−1dry weight. Mycorrhizal (M) roots of Vaccinium macrocarpon Ait. and Calluna vulgaris L. (Hull) showed a very high affinity for iron at low [Fe]ext, a feature not shown by non‐mycorrhizal (NM) roots. The involvement of a hydroxamate siderophore in the absorption of Fe by M plants at low [Fe]ext is suggested.

Concentrations of iron in shoots ([Fe]ext of NM plants of V. macrocarpon increase linearly with increasing [Fe]ext while those of M plants fall in the mid‐range of [Fe]ext relative to initial and final values. Ratios of [Fe]extto [Fe]ext are lower in M than in NM plants across the range of [Fe]ext examined. The extent of involvement of mycorrhizal infection in excluding the metal from shoots as [Fe]ext increases, is discussed, and the importance of the mechanisms of iron capture and storage in the root are assessed in terms of iron availability in natural heathlands.
Phosphorus relationships and production of extrametrical hyphae by two types of willow ectomycorrhizas at different soil phosphorus levels
Authors: JONES MELANIE D. , DURALL D. M. , TINKER P. B.
Published: April 2006

summary

There is much circumstantial evidence for a role of increased P uptake in the growth response of plants to ectomycorrhizas. Full response curves with and without mycorrhizal infection along a P gradient in soil are, however, required to test this hypothesis fully. In this experiment, rooted cuttings of Salix viminalis L. cv. Bowles Hybrid were grown in a 1:2 mixture by volume of gamma‐irradiated soil and sterile sand, with bicarbonate‐extractable P concentrations of 4, 6, 10, 21, 60 or 90 mg P kg−1. The cuttings were inoculated by mixing peat/vermiculite spawn of Laccaria proxima (Boud.) Pat., or Thelephora terrestris (Ehrh.) Fr., or autoclaved spawn 1: 5 by volume with the soil: sand mixture. The plants showed a positive growth response to mycorrhizal infection by either fungus at the two lower P levels, and to L. proxima only at 10 mg P kg−1. At 21 mg kg−1and above, infection was reduced and neither mycorrhizal inoculation nor further P additions caused significant growth increases. These results imply that the growth responses to ectomycorrhizas in this experiment were solely due to increases in P uptake. Cuttings infected with L. proxima tended to be larger than those infected by T. terrestris. Estimates of percent mycorrhizal infection did not differ between the fungi at the lower P levels. However, overall production of extramatrical hyphae per gram of soil was highest in soil inoculated with L. proxima. At 10 mg P kg−1the length of L. proxima hyphae per unit length of mycorrhizal root, P uptake per unit root weight, and total P content in plants infected with L. proxima were significantly higher than for T. terrestris. This study confirms that increased P uptake can be an important component of growth stimulation by ectomycorrhizas. It also presents the first quantification of extramatrical ectomycorrhizal hyphae in soil and suggests a role for them in the growth response.
Carbon–sink stimulation of photosynthesis in Douglas fir seedlings by some ectomycorrhizas*
Authors: DOSSKEY M. G. , LINDERMAN R. G. , BOERSMA L.
Published: April 2006

summary

Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings responded differently regarding rate of photosynthesis when inoculated with three different ectomycorrhizal fungi. Rhizopogon vinicolor FSL788‐5 caused a significant increase in net photosynthesis rate compared to non‐mycorrhizal controls, while Hebeloma crustuliniforme HeCr2 and Laccaria laccata S238‐A had no effect. Colonization by Rhizopogon and Hebeloma caused increased osmotic potential in the leaf symplast compared to controls, while Laccaria did not. Colonization levels for Rhizopogon, Hebeloma and Laccaria were 36, 93 and 73 % of root tips, respectively. Rhizopogon and Hebeloma produced abundant extramatrical hyphae and/or rhizomorphs, while Laccaria was smooth‐mantled. Hebeloma‐colonized seedlings were significantly smaller than non‐mycorrhizal controls; Rhizopogon seedlings were smaller, but significantly so only at P < 0.10. Laccaria did not affect seedling size. Only smaller Hebeloma seedlings exhibited elevated concentrations of N, P, K, and Ca over non‐mycorrhizal controls. These data demonstrate a non‐nutritional basis for increased rate of photosynthesis caused by some ectomycorrhizal fungi that can be explained by the increased photosynthate sink generated by extensive fungal growth associated with the mycorrhizas.
Recovery of kiwifruit vines from transient waterlogging of the root system
Authors: SMITH G. S. , JUDD M. J. , MILLER S. A. , BUWALDA J. G.
Published: April 2006

summary

The extent to which kiwifruit vines (Actinidia deliciosa var. deliciosa) recovered from transient waterlogging of the root system was determined under controlled conditions. Vines were waterlogged for periods varying from 1 to 7 days. The effects of decreasing concentrations of oxygen in the root zone on growth of the vine were rapid with substantial reductions occurring after being exposed to oxygen concentrations in the surrounding water of less than 0.125 mmol l1for as little as 1 day. There was no evidence of recovery of growth once aeration was restored to the roots, except for the appearance of new roots at the base of the stems of vines that had been waterlogged for less than 5 days. The quantity of new roots grown was inversely related to the time of waterlogging. Although new roots were also found on the control vines, the quantities involved were very much less than for the vines stressed for up to 4 days. No new roots were found for vines waterlogged for more than 4 days.

The substantial loss of dry weight of roots of vines waterlogged for more than 3 days was due in part to a lack of growth and to a physical loss of root tissue. The loss of tissue resulted from the detachment of the cortex from the central stele through the dissolution of an entire layer of cortical cells which, in the control vines, were filled with starch. A microscopic examination of the cells of the root from waterlogged vines showed the cortical cells to be generally distorted with much of the intercellular material missing.

The closure of the stomata within 2–3 h of the roots being waterlogged and the rapid desiccation of the leaves that followed the closure, was consistent with earlier findings with kiwifruit vines. Some recovery of stomata activity occurred for vines that had been waterlogged for less than 4 days once the oxygen supply to the root was restored. For vines that had their roots submerged for only 1 day, stomatal activity was fully restored 3 days after the vines were removed from the water. In contrast, there was no recovery of stomatal activity for vines that had been waterlogged for more than 3 days.

A feature of stomatal behaviour that was not related to the effects of oxygen stress was the cyclic pattern which developed. Each cycle repeated itself every 4–6 days and consisted of a period of high stomatal conductance followed by a sharp decline to a much lower level. A highly significant negative relationship was found between the level of photosynthetically active radiation and stomatal behaviour.

It was concluded that the speed with which the roots die and the associated damage to the leaves under anoxic conditions greatly limits the ability of kiwifruit vines to resume growth once oxygen supply to the root has been restored.
Long‐term exposure of Norway spruce,Picea abies(L.) Karst., to ozone in open top chambers
Authors: SUTINEN S. , SKÄRBY L. , WALLIN G. , SELLDÉN G.
Published: April 2006

summary

One clone of spruce,Picea abies(L.) Karst., was exposed to different concentrations of ozone in open‐top chambers for three seasons. The treatments were filtered air (CF), non‐filtered air (NF) and non‐filtered air + ozone (NF+). Changes in ultrastructure occurring in the 1985 flush of needles were followed for three years. Ultrastructural changes due to ozone first occurred in the chloroplasts. A decrease in length of the chloroplasts, an increase of the density of the stroma, an accumulation of ribosome‐like granules and a decrease in the size of starch grains, were observed. The second organelle to be affected was the microbody and the last the mitochondria. At this later stage the cytoplasm had also disintegrated. Structural changes always appeared first in the outer cell layer facing the sky. The changes then gradually advanced in the tissue towards the lower part of the needle. In the NF+ treatment changes were observed at the first sampling event in November, 1 month after the end of the first exposure period. At this time the needles were about 6 months old. In the NF treatment the same changes appeared when the needles were about 14 months old. No changes were observed in the CF treatment. Changes of the same type as those observed in the mesophyll tissue were also seen in stomatal and endodermal cells. In albuminous cells a general breakdown of the organelles was observed.
The effects of long‐term open‐air fumigation with SO2 on a field crop of broad bean (Vicia faba L.)
Authors: KROPFF M. J.
Published: April 2006

summary

Effects of SO2 on growth and production of broad bean, observed in three open‐air fumigation experiments, were interpreted in terms of damage components with a mechanistic simulation model. The model consisted of an elementary model for crop growth, extended with submodels for the microclimate in the crop and with a submodel for uptake of SO2 by leaves and for effects on leaf photosynthesis.

The major part of the observed reduction in total dry matter production could be explained by leaf injury observed in the oldest leaves of the fumigated plants at the end of the growing period. The effect consisted of dry matter loss through leaf abscission and a reduced growth rate at the end of the growth period due to reduction of the amount of absorbed radiation by the canopy. Direct effects of SO2 on leaf photosynthesis explained an extra 10% of the observed yield loss (losses ranged from 7 to 17% of control yield). This small effect was confirmed by field measurements which showed no detectable effects of SO2 on leaf and canopy photosynthesis. Increased leaf respiration, which was observed in the 1988 experiment, explained another 10% of the observed yield reduction.

Total SO2‐sulphur uptake by the fumigated crop, which is an important component of dry deposition of SO2, was accurately simulated by the model.
Anther dehiscence in Lycopersicon esculentum
Authors: BONNER LYNDA J. , DICKINSON H. G.
Published: April 2006

summary

Water tracers have been used to demonstrate the continued functioning of the anther filament during dehiscence in Lycopersicon esculentum Mill. Since Lycopersicon possesses neither nectar nor nectaries dehiscence cannot be related to sugar secretion, as has been demonstrated for other plants. The anthers seem structurally adapted for water conservation and the only transpirational loss of the flower appears to be through the petals. Transpiration from the anthers themselves thus appears not to be involved in regulating dehiscence. Anther opening is preceded by dehydration of the locule and circumstantial evidence indicates it to be an active process, with water being exported through the filaments to the petals along an osmotic gradient generated by starch/sugar interconversion. Measurement of water potential differentials between the petals and anthers points to the mechanism driving this export of water from the anthers. Interestingly, turgor pressure is maintained in the majority of the anther tissues until senescence, remaining remarkably constant against a background of dramatic changes in osmotic potential. These data, combined with the observation that the hydration level of the anthers falls only to 70% at senescence, indicates that dehiscence cannot primarily be a desiccatory process. Some domains within the anther do desiccate, but these are strictly localized. Thus, while hydration levels of living tissues remain independent of the environment, those observed to undergo protoplast degeneration and wall collapse exhibit environmentally‐linked hygroscopic absorption. Dehiscence thus emerges as an orchestrated programme of structural and physiological events leading to the desiccation of specific domains of the anthers. These findings are discussed in terms of current models for anther dehiscence in flowering plants.
Recent landscape history from a Co. Down lake deposit
Authors: HALL VALERIE A.
Published: April 2006

summary

A radiocarbon‐dated pollen diagram from a lake deposit at a lowland site in Co. Down, Northern Ireland showed mixed agriculture had been continuous over much of the last two millennia. The introduction of cereal cultivation at between the 3rd and 5th centuries A.D. is earlier than usual at sites with heavy soils in Ireland. There was no palynological evidence to support the historical view that there had been substantial woodland clearance in the area during the 17th century. Landscape enclosure by hedges, starting in the 18th century, was detectable in the fossil pollen record. The pollen evidence for flax cultivation showed that this was relatively recent. Throughout the diagram the continual presence of Ulmus pollen demonstrated that, in contradiction of the historic view, the taxon was extant in the area throughout the period A.D. 600 to A.D. 1700.
Tansley Review No. 24 Why are atmospheric oxides of nitrogen usually phytotoxic and not alternative fertilizers?
Authors: WELLBURN ALAN R.
Published: April 2006

Atmospheric pollution by the oxides of nitrogen, NO and NO2, can cause reductions in growth but rarely visible injury. This review considers their uptake into foliage, as well as their subsequent metabolism and physiology, and attempts to explain why these gases are often phytotoxic. The combined stresses of resisting cellular acidification, enhanced levels of nitrite (and ammonia), and the direct interference of the free radical ('N=O) with critical enzymes, reaction centres and regulatory mechanisms are thought to be the main reasons why oxides of nitrogen, especially NO, inhibit growth. If other air pollutants such as SO2are also present with NO or NO2then free radical‐induced injury, similar to that caused by O3alone, also occurs.

CONTENTSSummary395I.Introduction396II.Uptake and cycling of oxides of nitrogen396III.Biochemical responses to NO and NO2405IV.Physiological responses to NO and NO2410V.Combinations of NO and NO2with other pollutants416VI.Recapitulation and beyond418Acknowledgements420References420
Seasonal changes in antioxidants in red spruce as affected by ozone
Authors: HAUSLADEN A. , MADAMANCHI N. R. , FELLOWS S. , ALSCHER R. G. , AMUNDSON R. G.
Published: April 2006

Two‐year‐old red spruce (Picea rubens Sarg.) seedlings were exposed to various levels of ozone, from 0.4 to 3 times ambient levels, in open‐top chambers in Ithaca, NY, USA. Exposures, which varied with changes in day length, were from 30 May to 16 December 1987 and 1 June to 1 December, 1988. During the second exposure period, ascorbic acid, total and oxidized glutathione, α‐tocopherol, and superoxide dismutase were measured in current and previous year's needles at monthly intervals from May to July, and at bi‐weekly intervals from September to December. Orthogonalized polynomials were used to model the response through time of each variable measured. A one‐way analysis of variance model was fitted to every regression coefficient in each polynomial model to test for ozone effects on seasonal patterns of antioxidant levels. Ozone influenced seasonal changes in total glutathione, the oxidized/total glutathione ratio, and α‐tocopherol in previous years's needles and α‐tocopherol and superoxide dismutase in current year's needles. Averaged over the whole growing season, the oxidized/total glutathione ratio and superoxide dismutase showed an ozone treatment effect in both age classes. Mean total glutathione content increased in previous year's needles, but was not influenced by ozone in current year's needles. Mean oxidized glutathione content was higher with ozone exposure in current year's needles, but not in previous year's needles. The role of antioxidants in cold hardiness and ozone detoxification is discussed.
The influence of acid mists on growth, dry matter partitioning, nutrient concentrations and mycorrhizal fruiting bodies in red spruce seedlings
Authors: DEANS J. D. , LEITH I. D. , SHEPPARD L. J. , CAPE J. N. , FOWLER D. , MURRAY M. B. , MASON P. A.
Published: April 2006

Two‐year‐old spruce (Picea rubens Sarg.) seedlings were exposed to acid mists containing equimolar ammonium sulphate and nitric acid giving treatments of pH 2.5, 3.0 and 5.0. Acid mist treatments were applied twice weekly from late July until early October, 1987, when the plants were harvested.

There were no significant differences in biomass accumulation or in height growth between treatments, but marked differences in root morphology were found. Significantly larger amounts of coarse roots were produced in the pH 5.0 acid mist treatment and plants in the pH 3.0 treatment produced significantly greater amounts of fine roots. Plants receiving acid mists of pH 3.0 or less had a greater frequency of fine root branches along their coarse roots. Production of mycorrhizal fruiting bodies of Thelephora terrestris Ehrenb.: Fr. was significantly greater (P < 0.001) at pH 5.0 than in the other treatments.

Plants in the pH 2.5 and 3.0 treatments contained larger concentrations of N, 1.54 and 1.12% and S, 0.52 and 0.28% respectively, than those receiving acid mist at pH 5.0, i.e. 1.00 and 0.21% respectively. However, the between treatment differences of tissue nutrient concentrations were small relative to the differences in inputs between treatments. Foliar S exceeded concentrations recommended for nursery stock by 50 and 150% at pH 3.0 and 2.5 respectively.
Effects of sulphur dioxide fumigation on Phleum pratense and vesicular‐arbuscular mycorrhizal fungi
Authors: CLAPPERTON M. JILL , REID DAVID M. , PARKINSON DENNIS
Published: April 2006

Two experiments were conducted using controlled environment SO2 fumigation chambers which allowed only the shoots of Phleum pratense to be fumigated. Experiment 1 examined the effect of SO2 fumigation on the ability of vesicular‐arbuscular (VA) mycorrhizal fungi to infect roots. Experiment 2 examined the effect of SO2 fumigation on the proliferation of VA mycorrhizas in the roots. There was a significant decrease in the amount of infection in the roots of plants exposed to SO2. Low concentrations (0.05‐0.07 μ 1−1) of SO2 affected the ability of VA mycorrhizal fungi to colonize and, also, to proliferate within roots. In both experiments, root colonization was the overriding factor affecting the number of tillers, leaf area, and shoot and root dry weights of infected plants. Increased VA mycorrhizal infection resulted in reductions in the plant growth parameters.
Population structure and dynamics in Suillus bovinus as indicated by spatial distribution of fungal clones
Authors: DAHLBERG ANDERS , STENLID JAN
Published: April 2006

The spatial distribution of clones in the ectomycorrhizal fungus Suillus bovinus (L. ex Fr.) O. Kuntze was studied from somatic incompatibility pairings of isolates in four Scots pine (Pinus sylvestris L.) stands with different forest history. A pattern of increasing clonal size, decreasing clonal number, and decreasing fruiting per unit area, was found with increased forest age and relatively little disturbance. Establishment by spores was important on disturbed sites, while mycelial spread increased in importance with decreased disturbance. The number of clones was found to be 800 ha−1 in younger forest stands and decreased to between 25–130 ha−1 in mature stands. At the same time the diameter of the area occupied by a single clone increased from 1–3 m to 30 m. Implications of the observations are discussed in terms of ecological strategies and population dynamics.
Drought acclimation and the morphology of mycorrhizal Rosa hybrida L. cv. ‘Ferdy’ is independent of leaf elemental content
Authors: HENDERSON JANET C. , DAVIES FRED T.
Published: April 2006

Rosa hybrida L. cv. ‘Ferdy’ is a low maintenance landscape plant which is considered drought resistant. To determine the effects of endomycorrhizae on plant water relations and growth, rooted cuttings of uniform size were established in containers under moderately high P fertilization. Vesicular‐arbuscular (VA) mycorrhiza inoculated and noninoculated plants were placed under three water regimes: drought acclimated, non‐acclimated and later exposed to drought, or non‐stressed. Acclimated plants were conditioned by four 3‐d and three 4‐d drought cycles. Non‐acclimated plants received water daily prior to a single 4‐d drought cycles, and non‐stressed plants were watered daily throughout the study. Under water deficits, non‐acclimated plants had lower leaf water potentials (ΨL), transpiration rates (E) and stomatal conductances (g), than acclimated or non‐stressed plants. Non‐acclimated plants also had a greater leaf area, leaf number and shoot dry weight than acclimated plants, yet had a comparable leaf area ratio (LAR) and root‐shoot ratio. Mycorrhizal plants had a higher E, than non‐mycorrhizal plants, even though non‐mycorrhizal plants were of comparable biomass (leaf area, shoot and root dry weight and LAR). However, the root‐shoot ratio was greater with mycorrhizal plants which had fewer leaves (due to abscission), and lower cuticle and epicuticular wax weights than non‐mycorrhizal plants. There was no affect of VA mycorrhiza on leaf osmotic potential (Ψn) stomatal density, leaf cell density, leaf area, or macronutrient uptake. Acclimation of this low‐maintenance landscape rose cultivar to water deficits and the mechanism of drought avoidance via leaf abscission, were as beneficial to drought resistance as was mycorrhizal symbiosis.
Fine veins of dicotyledon leaves as sites for enrichment of solutes of the xylem sap
Authors: CANNY M. J.
Published: April 2006

The apoplastic tracer sulphorhodamine G (SR) was used as an indicator of the flumes, the sites where water left the apoplast and entered the symplast, in a selection of dicotyledon leaves. At these flumes the dye is deposited as crystals after a pulse of dye is fed to the transpiration stream, followed or not by a water chase. In contrast to wheat, the dicotyledons showed SR cystals inside the tracheary elements of the finest leaf veins. At short pulse times the crystals were in the stems of the branch‐trees of the fine veins, but after longer pulses, had moved to the vein termini. The dye solution was moving very slowly in the tracheary elements as it approached the ends of the branch‐trees, since the axial flow there is nearly balanced by radial leakage. These results are interpreted as evidence that most of the transpiration water enters the symplast in the vein sheaths of the fine veins, and that these veins are places where many of the natural solutes of the xylem sap will be enriched to quite high concentrations.
The metabolism and biological activity of ABA analogues in normal and flacca mutant tomato plants
Authors: LINFORTH R. S. T. , TAYLOR I. B. , DUCKHAM S. C. , AL‐NAIEB R. J. , BOWMAN W. R. , MARPLES B. A.
Published: April 2006

The metabolism of deuterium‐labelled analogues of ABA by normal and flacca mutant tomato plants was investigated. Comparison of the biological activity of ABA, ABA alcohol, ABA aldehyde and their 2‐trans isomers was made in both mutant and non‐mutant genotypes. While in normal plants ABA alcohol and ABA aldehyde were as effective as ABA in inducing stomatal closure, in the flacca mutants only ABA itself was biologically active. Both ABA alcohol and ABA aldehyde were converted to the inactive compound trans‐ ABA alcohol instead of ABA when fed to flacca plants. As trans‐ABA aldehyde was also readily converted to trans‐ABA alcohol by flacca plants, it was not possible to establish whether isomerization precedes reduction or vice versa in the synthesis of trans‐ABA alcohol from ABA aldehyde.
Effects of nutrient depletion on growth ofHolcus lanatusL. andFestuca ovinaL. and on the ability of their roots to absorb nitrogen at warm and cool temperatures
Authors: KACHI N. , RORISON I. H.
Published: April 2006

To examine the ecological relevance of slow growth for survival in unproductive environments, responses to nutrient depletion were compared between two ecologically contrasted grasses with reference to their ability to utilize a nutrient flush. Dry weight growth, ability of roots to absorb nitrogen and subsequent distribution between root and shoot were determined forHolcus lanatusL. andFestuca ovinaL. before and after subjecting them to nutrient depletion at warm and cool temperatures. Initially, the relative growth rates (RGR) ofH. lanatuswere much higher than those ofF. ovina, but after 21 days of nutrient depletion,F. ovinaattained higher RGR. During nutrient depletion,F. ovinamaintained higher shoot N concentrations thanH. lanatus, mainly due to lower rates of dry matter accumulation inF. ovina.Maintenance of N concentrations inF. ovinamay contribute to sustaining of the shoot activity under N‐depleted conditions. Nutrient depletion caused an increase in the proportion of N allocated to roots relative to shoots, butF. ovinaexhibited less plasticity thanH. lanatus.Following nutrient depletion, the ability of roots to absorb nitrate declined markedly inH. lanatusand to a much lesser extent inF. ovina.The ability to absorb ammonium was also reduced at warm temperatures, while at cool temperatures it was unchanged inH. lanatus, but increased inF. ovina.These results suggest thatF. ovinahas a greater potential to exploit ‘nutrient flushes’ thanH. lanatusunder unproductive conditions, especially at cool temperatures.
Physiological ecology of seed respiration in some tropical species
Authors: GARWOOD NANCY C. , LIGHTON JOHN R. B.
Published: April 2006

We examine the relationship of seed oxygen consumption rate (V̇o2) to seed moisture content, seed mass, and seed age in 22 ecologically diverse tropical species. These seeds vary greatly in moisture content, age, mass, mechanism of dormancy and length of viability. We quantify each relationship with a power equation, V̇o2=aXb, where X is the independent variable. Seed moisture content (MC) explains 80% of the variation in mass‐specific V̇O2 (ml O2 g−1 h−1) among seeds of all species, whereas seed mass explains < 1%. However, when seeds are reclassified as moist (> 28% MC) or dry (≤ 28% MC), seed mass explains 54% of the variation in mass‐specific V̇o2 (ml O2 g−1 h−1) within dry seeds, but no significant variation within moist seeds. In dry seeds, seed age explains only 27% of the variance in mass‐specific Vo2, although seed age and moisture content are negatively correlated. On a per seed basis, seed mass explains 54% of the variation in mass‐specific V̇o2 (ml O2 h−1 per seed) in dry seeds and 83 % of the variation in moist seeds: the exponents of the power function, 0.54 in dry seeds and 0.78 in moist seeds, are within the range reported for the allometric relationship of oxygen consumption and body size in animals and prokaryotes. We present a framework for future studies that recognizes seed respiration as an important, yet unstudied, component of tropical seed ecophysiology. We discuss the ecological significance of seed respiration in three groups of tropical species which differ in seed moisture content, mass, viability, and post‐dispersal moisture regimes: (1) shade‐intolerant pioneer species with small, dry, orthodox seeds; (2) seasonally dormant species; and (3) shade‐tolerant primary forest species with large, moist recalcitrant seeds.
Numerical taxonomy of the wild bananas (Musa)
Authors: SIMMONDS N. W. , WEATHERUP S. T. C.
Published: April 2006

The wild bananas (Musa) were described in numerical terms many years ago, well before ‘numerical taxonomy’ became popular. Those descriptions, slightly supplemented, are here subjected to analysis by modern methods. Principal co‐ordinate and clustering techniques give essentially similar results. Five groupings, rather than the four sections traditionally recognized, can be discerned. The fifth group contains five taxa previously included in section Musa (informally ‘Eumusa’) or of uncertain affinity. This group is only somewhat weakly distinguishable from section Australimusa. Several species previously regarded as of uncertain affinity seem to find ‘natural’ places. The results are by no means revolutionary but do encourage modest alteration of traditional views.
The history and vegetation dynamics of a yew wood (Taxus baccata L.) in S.W. Ireland
Authors: MITCHELL F. J. G.
Published: April 2006

Reenadinna Wood is one of the largest Taxus baccata dominated woods in the British Isles. It is therefore of considerable ecological and conservation interest. To investigate the history and dynamics of the wood, pollen data from a small hollow within the wood are described. These data are compared with the regional pollen record and local historical and archaeological information. The yew wood appears to have developed at least 3000, but probably 5000 years ago from a wood previously dominated by pine, oak, elm and hazel. There is evidence to suggest that the wood has been disturbed by periods of patch cultivation and site occupancy.
Uptake of amino acids by the cyanobacterium Anabaena ATCC 27893
Authors: PING XU , MCAULEY P. J.
Published: April 2006

summary

Active uptake of phenylalanine has been characterized in a species of cyanobacterium, Anabaena sp. ATCC 27893. Phenylalanine was apparently taken up by only one transport system over the concentration range 2–50 μM. Inhibition of phenylalanine uptake by glutamate and a range of neutral amino acids suggested that these were internalized by the same system. At least one other system appeared to be present, transporting the basic amino acids arginine and lysine. The Km and Vmax of phenylalanine uptake were comparable to those of phenylalanine uptake in eukaryotic unicellular freshwater algae. Uptake was energy dependent and internalized phenylalanine was rapidly incorporated into trichloracetic acid‐insoluble material.
Extracellular hexacyanoferrate III inhibits cytoplasmic streaming in the algaLamprothamnium papulosum
Authors: THIEL GERHARD , KIRST GUNTER O.
Published: April 2006

summary

Internodal cells of the euryhaline charophyteLamprothamnium papulosumexhibited a transient slow down of the cytoplasmic streaming when transferred to a medium containing hexacyanoferrate III (HCF III). The reduced form, hexacyanoferrate II, was without effect. The extent of the streaming inhibition, which appeared with a time lag of ≃ 3 min after addition of the redox reactant, was a function of the HCF III concentration. The inhibition could be prevented by preconditioning cells in the Ca2+‐channel antagonist LaCl3or by lowering the Ca2+concentration in the external medium even though these treatments did not greatly affect the rate of extracellular HCF III reduction. We therefore conclude that HCF III generates a Ca2+influx into the cytoplasm. The resulting transient increase in cytoplasmic free Ca2+inhibits the Ca2+‐sensitive streaming mechanism. Streaming inhibition was observed in acid (pH 55) and alkaline (pH 8) media. Because HCF III induced only a marked depolarization in alkaline medium, Ca2+influx is not a consequence of a decrease in transmembrane voltage.

The treatments that protected cytoplasmic streaming from inhibition by HCF III did not affect the decrease in membrane resistance caused by the redox reactant. Ca2+influx is therefore unlikely to be a major mechanism by which HCF III affects membrane transport pathways.