bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: GRIFFITHS H. , SMITH J. A. C. , LÜTTGE U. , POPP M. , CRAM W. J. , DIAZ M. , LEE H. S. J. , MEDINA E. , SCHäfer C. , STIMMEL K.‐H.
Published: April 2006

summary

A comparison of the performance of two epiphytes with crassulacean acid metabolism (CAM) was made during the rainy season and dry season at the Ciénega el Ostional, Chichiriviche in northern Venezuela. The epiphytic bromeliad, Tillandsia flexuosa has water‐retaining tanks and leaf trichomes, and propagates mainly vegetatively to produce large populations in the shrubby island vegetation. The epiphytic orchid, Schomburgkia humboldtiana formed smaller populations, and had large succulent leaves with uniform chlorenchyma and no distinct water‐storage parenchyma, unlike T. flexuosa. Both epiphytes were myrmecophilous.

Leaf succulence (kg m−2) declined by ∼ 10% in the dry season for both plants. Both epiphytes showed reduced CO2 uptake during Phase I (dark period) and (dawn‐dusk) titratable acidity (ΔH+) in the dry season. Water‐use efficiency (WUE) was higher for S. humboldtiana (16.0 × 10−3 mol CO2 per mol H2O compared with 5.0 × 10 −3 for T. flexuosa) although WUE remained constant during rainy and dry season for each species.

Sixty to seventy per cent of the dawn dusk titratable acidity was derived internally from respiratory CO2 (recycling) for both species, and in absolute terms, recycling decreased in the dry season, in contrast to the expected progression under drought stress. Recycling is an important facet of carbon balance for both species in both rainy and dry seasons.

Leaf Na+ concentration was higher than values quoted for terrestrial salt stressed CAM plants. Fructose and glucose declined in leaf bases of T. flexuosa during the dark period, but not in the more distal regions of the leaf. S. humboldtiana showed a decrease in sucrose at night, and mannitol was also an important constituent of the leaves.

Xylem sap tension maxima increased from 0.38 ± 0.09 MPa (rainy season) to only 0.55 ± 0.06 MPa (dry season) for T. flexuosa, these values being much lower than those found for terrestrial shrubs and herbs at the same site, the two epiphytes use CAM in conjunction with differing morphological adaptations to maintain growth throughout the year at the Ciénega el Ostional, but it would seem that T. flexuosa has better physiological characteristics for maintenance of carbon acquisition during the dry season.
Occurrence of fructans in the Gramineae (Poaceae)
Authors: SMOUTER HENK , SIMPSON RICHARD J.
Published: April 2006

summary

The occurrence and type of storage carbohydrate (fructan, starch or sucrose) was determined in stems of reproductive tillers of a number of species of the family Gramineae representing major taxonomic groups. Plants were collected from two grassland sites in Victoria (Australia). Fructans were detected in all species examined, but particularly high concentrations were found in species of the subfamily Pooideae where fructans accounted for 75–95% of the storage carbohydrates. In most other subfamilies, fructans varied between 5 and 30% of the storage carbohydrates. However, fructans accounted for 50% of the storage carbohydrates in species of the subfamily Arundinoideae. Separation of fructans (to DP 14) by thin‐layer chromatography demonstrated that different isomers of trisaccharides and different proportions of oligosaccharides were present, depending on the species. In some species there was evidence of continuous series of oligosaccharides between sucrose and high molecular weight polymers. However, these series differed markedly from the series of oligosaccharides present in Helianthus tuberosus.

The polymerization of fructans and trisaccharide forms present in the grasses examined were similar on generic and, in a number of cases, subtribal and tribal levels and reflected phylogenetic relationships between taxa. The possible presence of fructans in all subfamilies may indicate that fructan synthesis is not necessarily exclusive to the subfamily Pooideae.
Sugar unloading in roots of Ricinus communis L.
Authors: CHAPLEO S. , HALL J. L.
Published: April 2006

summary

Acid invertase (EC 3.2.1.26) is present in soluble and insoluble preparations from root and shoot tissue of Ricinus communis L. Greatest activity is found in expanding tissue, whilst very low activity is found in vascular and in Phloem‐enriched tissue from stem internodes. In most tissues less than 20% of the total acid invertase activity is insoluble, the exception being extrafloral nectariess where 65–82% is insoluble. The activity of sucrose synthase (EC 2.4.1.13) is low in leaves and apical regions of the primary root; the root stele contains greater activity than the cortex. Considerable diel variations in leaf carbohydrate content were demonstrated and the results suggest that variations for the young sink leaves might be out of phase with those of source leaves by as much as one Photoperiod. The results are discussed m relation to the metabolism and transport of sucrose, particularly in roots.
The activity and preliminary characterization of peroxidases in leaves of cultivars of date palm, Phoenix dactylifera L.
Authors: BAAZIZ M.
Published: April 2006

summary

Peroxidase activity was determined in leaves of 13 cultivars of date palm, Phoenix dactylifera L. Levels of Peroxidase in the crude extracts were found to differ significantly among the cultivars. The desalted 50–95% ammonium sulphate cuts of the crude peroxidase showed differences in heat inactivation. In studying the effect of assay pH on the activity of peroxidase, 6 of the 13 cultivars examined demonstrated a pH optimum at pH 4.6. Three other pH optima, 4.0, 5.0 and 5.6 were shown for 2, 3 and 2 other cultivars, respectively. Two anodic bands of peroxidase were present in all cultivars, when polyacrylamide gel electrophoresis was carried out and followed by staining the gels with guaiacol as substrate. The two anodic peroxidase bands showed little differences on the oasis of their relative mobility. Both of them were characterized by low electrophoretic mobility. The results are discussed with respect to the possible relationship of the peroxidase activity in the vascular fusariosis (Bayoud disease) of the data palm.
Cytology and development of a mycorrhiza‐like infection in the gametophyte of Conocephalum conicum (L.) Dum. (Marchantiales, Hepatophyta)
Authors: LIGRONE R. , LOPES C.
Published: April 2006

summary

An aseptate fungus associated with the gametophyte of the hepatic Conocephalum conicum (L.) Dum. was studied by light and electron microscopy. The fungus forms a highly branched mycelium external to the plant. Fungal hyphae colonize the smooth‐walled rhizoids, through which they pass into the gametophyte parenchyma of the midrib. The fungus in the parenchyma is entirely intracellular. Vesicles are found in rhizoids and a few ventral layers of parenchyma cells. Prominent arbuscules develop in more internal cells from lateral branches of infecting hyphae that spread from cell to cell. Infected host cells show cytoplasmic proliferation, especially of ribosomes, Plastids and mitochondria, The arbuscules eventually degenerate leaving clumps of collapsed hyphae. Reinfection of cells with degenerate arbuscules was not observed. The ultrastructural and developmental characteristics of the fungus and its high cytological compatibility with the host are indicative of a well integrated symbiotic association similar to the vesicular–arbuscular mycorrhizas of higher plants.
The development of endomycorrhizal root systems
Authors: AMIJEE F. , TINKER P. B. , STRIBLEY D. P.
Published: April 2006

summary

Leek plants (Allium porrum L.) were grown in a controlled environment on a mixture (2: 1 w/w) γ‐irradiated (1.0 Mrad) sandy loam and sand, at six concentrations of bicarbonate‐soluble phosphorus (P) ranging from 22 to 344 mg P kg−1 (soil basis). Inoculum of the vesicular‐arbuscular (VA) mycorrhizal fungus Glomus mosseae (Nicolson & Gerdemann) Gerdemann and Trappe was placed (M) or not (NM) in a layer 3 cm below the soil surface.

At intervals of 10 d, lengths of main axes of roots and their lateral branches, and of the segments of infection within them, were measured. From these data we calculated the mean (harvest interval method} rates of linear extension of root tips and of infection fronts for each member of root, averaged over the whole root system. The mean delay, d, between a root encountering the layer of inoculum and the subsequent formation of internal infection, was also derived.

Addition of P to soil did not affect rates of extension of roots, but increased the initiation of main axes and laterals. Infection segments extended twice as fast in laterals as in main axes. At low rates of addition, P did not affect fungal behaviour but increased the length of root available for colonization.

When bicarbonate‐soluble P exceeded 140 mg kg−1, the rates of extension of infection fronts in both main axes and laterals were approximately halved, and d was considerably increased. The density (the area ratio of fungal to host tissue in a longitudinal squash) of the hyphae and arbuscules respectively, and the number of entry points per unit length of root, were greatly reduced by added P. However, the ratios of numbers of entry points/hyphal density and of arbuscule density/hyphal density were unaltered, and the morphology of the fungus was not noticeably affected.

It is probable that formation of entry points was the rate‐limiting step for colonization, and that this rate was reduced by added P.
Response of white clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) to acid rain in situations of species interferences
Authors: MENCHACA L. , HORNUNG M.
Published: April 2006

summary

Pure stands of Trifolium repens L. N.Z. Huia and Lolium perenne L. S32 and mixtures of various densities and frequencies were treated with sulphuric acd solutions of pH 2.5, 3.5 and 5.6. The species yield was recorded over five sequential harvests. Multifactorial response equations were used to describe the behaviour of the species yield as a function of acidity and the density of both species. Predictions, made through these models, showed that the response of yield of these species to simulated acid rain treatments Varied greatly depending on the planting density, the time of harvesting and on whether the plants were growing in monoculture or in mixture. This suggests that it is not sufficient to consider the effects of experimentally applied acid rain on single individuals or low density stands, since the results obtained will not reflect the response in a close canopy sward.
Growth dynamics and water use of seedlings ofQuercus albaL. in CO2‐enriched atmospheres
Authors: NORBY RICHARD J. , O'NEILL E. G.
Published: April 2006

summary

White oak (Quercus albaL.) seedlings were grown from a half‐sib collection of acorns in pots containing a nutrient‐Poor forest soil and maintained in controlled‐environment chambers having mean atmospheric CO2concentrations of 389, 496, and 793 cm3m−3. Additions of nitrogen and phosphorus to the soil increased plant growth, indicating that the unfertilized plants were nutrient deficient. Despite the nutrient deficiency, the plants grown in elevated concentrations of CO., generally were larger than those in ambient CO2, but dry weight data from harvests at 5, 12, 24, and 36 weeks provided insufficient evidence of an effect of CO2because of the high variability associated with the recurrently‐Hushing habit of these seedlings. Mathematical growth analysis based on periodic non‐destructive measurements allowed comparisons of the continuous growth patterns of the plants and avoided the problems of ontogenetic variation. CO2, enrichment was thus shown to increase plant growth rate primarily through increased unit leaf rate rather than increased leaf area production. Unit leaf rate during the second half of the experiment was 22 and 27% higher in the medium and high concentrations of CO2compared with that in low CO2instantaneous measurements of foliar gas exchange also showed that CO2, assimilation increased with CO2, enrichment. The most pronounced effect of CO2, enrichment was increased water‐use efficiency, which was shown both through whole‐plant gravimetric analysis and instantaneous gas exchange measurements. Whole‐plant water‐use efficiency for the duration of the experiment was increased by 52 and 82% by the mdium and high concentrations of CO2. Limitations of resources, including water and nutrients, do not preclude plant growth responses to CO2enrichment of the atmosphere.
Holocene to Middle Last Glaciation vegetation history at Newall Creek, western Tasmania
Authors: VAN DE GEER G. , FITZSIMONS S. J. , COLHOUN E. A.
Published: April 2006

summary

Pollen analysis and 14C dating of 5.5m of organic‐rich soil and fluviatile deposits from Newall Creek (altitude 140 m) indicate that temperate rainforest (0‐11 K yr B.P.) was preceded by grassland‐herbland (11 to 21 K yr B.P.), and then by open grassy Eucalyptus woodland.

Comparison with a lake‐swamp site at Tullabardine Dam showed that the main vegetation changes were comparable making allowance for some spatial variations in the taxa represented and the lower quantity of pollen in the fluviatile deposits.

The inferred sequence of climatic change was from a cool moist interstadial through a cold last glacial maximum to a warm moist Holocene environment, a sequence also indicated at Tullabardine.
Occurrence of nodulation in the Leguminosae
Authors: DE FARIA S. M. , LEWIS G. P. , SPRENT J. I. , SUTHERLAND J. M.
Published: April 2006

summary

Reports of nodulation in the Leguminosae are examined in the light of current views on the taxonomy of the family. In the subfamily Caesalpinioideae, nodulation is largely restricted to the tribe Caesalpinieae and the genus Chamaecrista from the Cassieae. All nodules studied have rhizobia retained within infection threads during the nitrogen fixing period.

In the Mimosoideae, nodulation is general, except for 4 groups within the tribe Mimoseae, and a very few species of Acacia. The only tribe from the Papilionoideae which appears not to nodulate is the Dipterygeae, although the monogeneric Euchresteae has not been examined. A number of genera in the Swartzieae do not nodulate. Taking tile family as a whole, nodulation appears to be very uniform – certain sections nodulate, others do not.
Responses to high temperature of the Azolla–Anabaena association, determined in both the fern and in the cyanobacterium
Authors: WATANABE I. , LIN CHANG , SANTIAGO‐VENTURA TERESITA
Published: April 2006

summary

The responses to high temperature of the cyanobacterial symbiont and the host fern in tile Azolla–Anabaena symbiosis were studied by using Azolla strains with heterologous Anabaena azollae Strasburger of without Anabaena. At 26/18°C, symbiotic Azolla grew better than the corresponding Anabaena‐free Azolla. A high temperature‐sensitive species Azolla filiculoides Lamarck, produced smaller biomass under conditions of 37 °C (day)/29 °C (night) than the corresponding Anabaena‐free Azolla grown in N‐containing medium. A. filiculoides with Anabaena from temperature tolerant Azolla microphylla Kaulfuss was more effective at N2 fixation than A. filiculoides with homologous Anabaena. A microphylla with Anabaena from A. filiculoides grew more slowly and fixed less N2 than the strains with homologous Anabaena. In the presence of combined N at 37°/29 °C, A. microphylla grew better than A. filiculoides with Anabaena from A. microphylla. Tolerance of the Azolla‐Anabaena association to high temperature is, therefore, determined both in the host fern and symbiont Anabaena.
The effects of nickel, calcium and magnesium on the acid phosphatase activity of two Alyssum species
Authors: GABBRIELLI R. , GROSSI L. , VERGNANO O.
Published: April 2006

summary

Root Surface acid phosphatase activity was assessed in seedlings of two species of Alyssum, one endemic to Tuscan serpentines (Alyssum bertolonii Desv.) and the other of wide occurrence (Alyssum saxatile L.), cultivated in solutions to which various concentrations of Ni2+, Ca2+ and Mg2+ were added. Treatments were applied in two factorial experiments of type 2n. A concentration of 0.01 mM Ni2+ markedly stimulated phosphatase activity in A. bertolonii, but slightly decreased it in A. saxatile. Increased Ca2+ concentration stimulated enzyme activity in both species, hut in A. bertolonii the highest activity was obtained with low Ca2+ concentrations, whilst the opposite occured in A. saxatile. A. bertolonii instead required high Mg2+ concentrations to increase phosphatase activity significantly. The same concentrations were toxic to A. saxatile. In the serpentine species, favourable conditions for the increase of phosphatase activity were induced by a high Mg2+/Ca2+ ratio, which also favoured dry mass production. Therefore it is possible that the increase of phosphatase activity might be an aspect of plant adaptation to serpentines.
Effects of O3 on alder photosynthesis and symbiosis with Frankia
Authors: GREITNER CAROL S. , WINNER WILLIAM E.
Published: April 2006

summary

Alnus serrulata (Aiton) Willdenow seedlings with and without root nodules formed by the nitrogen‐fixing actinomycete Frankia were exposed to clean filtered air or ozone (O3) at 0.12 μl l−1 for 27 d (approximately 164 h total exposure). Gas exchange measurements on leaves and transmission electron micrographs of root nodule cells were made to detect any O3 effects on the functioning of leaves and the root symbiont.

Photosynthesis, stomatal conductance, and internal CO2, concentration were calculated for all plants in clean O3‐free air more than three weeks after the fumigations began. Significant positive correlations between photosynthesis and conductance were found for leaves of control nodulated and unnodulated alders and O3‐treated nodulated alders. There was a weak positive correlation between photosynthesis and conductance for unnodulated O3‐treated seedlings measured in clean air. When O3‐treated leaves were measured during fumigation with O3, no positive correlation between photosynthesis and conductance was found for either nodulated or unnodulated seedlings. Photosynthetic rates of leaves having the highest stomatal conductance values were decreased by O3for both nodulated and unnodulated plants.

Transmission electron microscopy (TEM) revealed that after a 27 d exposure of shoots to O3, host root cells of nodules from O3‐treated plants lacked organelles and showed extensive cytoplasmic breakdown. Hyphae and N2‐fixing vesicles of Frankia appeared normal. The Frankia endophyte seems to be more resistant to O3 than is the host root nodule cell. These results show that ambient levels of O3 may reduce photosynthesis and bring about associated degradation in rhizosphere symbiosis.
The effects of temperature and moisture on CO2 uptake and total resistance to water loss in the antarctic foliose lichen Umbilicaria antarctica
Authors: HARRISSON P. M. , WALTON D. W. H. , ROTHERY P.
Published: April 2006

summary

Maximum net photosynthesis of field‐fresh thalli, illuminated at 200 μmol photons m−2 s−1 (PAR), was attained at 13 °C and 1.10 g g−1 water content. Small but significant rates of photosynthesis were measured at −5.5 °C. Depression of net photosynthesis at high thallus water contents is explained in terms of thallus anatomy. Calculation of evaporative resistance of the thallus by a new method showed a moisture‐dependent response pattern, and was in agreement with direct observations made on other foliose species.
Developmental changes in the aperture during pollen grain ontogeny in Olea europaea L.
Authors: FERNÁNDEZ M. C. , RODRÍGUEZ‐GARCÍA M. I.
Published: April 2006

summary

Changes in both size and form of the structures making up the apertural region, a modified part of the pollen grain wall, were studied during development in Olea europaea L. The very young microspores initially show thickening of the endexine around the apertural zone. This is followed by the appearance of an exinous oncus and subsequently an intinous oncus. The intinous oncus contains tubules derived from evaginations of the plasmalemma. These tubules increase in number and diameter during development.
Biomass production and gas exchange of winter wheat as affected by flag leaf inoculations with Septoria nodorum
Authors: ROONEY J. M.
Published: April 2006

summary

Inoculation of flan leaves of winter wheat with Septoria nodorum (Berk.) Berk was more effective in reducing final grain weight when inoculation was at anthesis than when it was at flag leaf emergence, either during or following leaf expansion; grain number was not significantly affected by the timing of inoculation. The greatest senescence was observed with late inoculations with correspondingly lower flag leaf weight at grain maturity. It is suggested that flag leaves become more susceptible to S. nodorum with increasing time after emergence. Inoculation did not result in any significant redistribution of assimilate from stems to ears as it did not affect stem weight. The reduction in photosynthesis at high irradiance was proportional to infection‐induced senescence. Change in the total resistance to the diffusive flow of carbon dioxide was controlled by the mesophyll resistance, i.e. that remaining following subtraction of boundary layer and stomatal components.
A comparative study of plant responsiveness to the duration of episodes of mineral nutrient enrichment
Authors: Campbell B. D. , Grime J. P.
Published: April 2006

summary

Growth, dry matter partitioning and nitrogen capture were compared in two grasses of contrasted ecology, subjected to treatments involving pulses of nutrient enrichment of various durations supplied every 6 d over a period of 6 weeks. The potentially fast‐growing Arrhenatherum elatius ssp. bulbosum (Willd.) Schubler and Martens was superior in rates of nitrogen capture and dry matter production when exposed to long (≥ 10 h) nutrient pulses whereas the slow‐growing species Festuca ovina L. enjoyed an advantage in treatments providing nutrient pulses of between 0.1 and 10 h duration. These results are consistent with differences in mechanisms of resource foraging predicted by the C‐S‐R model of plant strategies and related models. It is concluded that the lower rates of turnover of tissues and the capacity of roots to remain viable under chronic nutrient stress are important components of the ability of Festuca ovina to exploit brief pulses of mineral nutrient enrichment. The range in duration of the pulses advantageous to F. ovina corresponds to that which might be expected to arise from the death and recovery of microbial populations in infertile soils.
The population genetics of Armeria maritima (Mill.) Willd. on the River South Tyne, UK
Authors: RICHARDS A. J. , LEFEBVRE C. , MACKLIN M. G. , NICHOLSON A. , VEKEMANS X.
Published: April 2006

summary

A. maritima inland in England and Wales is largely confined to metal‐rich soils, where it has probably evolved metal tolerance. Similar populations are found in Belgium, Germany and Poland. Numerous large populations occur on river terraces beside the rivers South Tyne and Tyne in Northumberland. These terraces were mostly formed between 1850 and 1940, and have high levels of toxic heavy metals which result from mining activities within the catchment. It is probable that A. maritima occurred on naturally metalliferous soils high in the Pennine catchment prior to mining, and colonized metalliferous river terraces downstream after 1850.

In comparison with the British populations of subspecies maritima, the Tyne populations are unique in being polymorphic for scape hairiness. This character is also found in European mine populations. The Tyne populations also share with European mine populations some degree of self‐fertility, but selfing was insufficient to give rise to detectable excesses of the papillate morph. Nevertheless, in at least one population, excesses of papillates may occur. The papillate morphs tend to be more self‐fertile than the cob morph. The recessive homozygous papillate phenotypes flower later, and tend to predominate in the densest parts of the population It is suggested that heterotic genes may be linked to the loci studied. This may account for the late dowering and high density of homozygous phenotypes.
Ultrastructure, development and cytochemistry of storage cells in the‘tubers’of Phaeoceros laevis Prosk. (Anthocerotophyta)
Authors: LIGRONE R. , LOPES C.
Published: April 2006

summary

The gametophyte of Phaeoceros laevis Prosk. forms small parenchymatous tubers as perennating organs. The development of tuber cells is characterized by marked cytoplasmic proliferation. The chloroplasts are packed with starch and abundant lipid bodies (spherosomes) are produced in the cytoplasm in association with rough endoplasmic reticulum. The vacuoles become pleomorphic and accumulate electron‐dense deposits. These were negative to PATAg staining for carbohydrates and were digested by pronase; therefore they are assumed to be protein. No ultrastructural evidence was found for the participation of either ER or dictyosomes in the biogenesis of the protein‐storing vacuoles. The mature tubers have a distinct layer of epidermal cells with thick external walls, and frequently harbor intercellular cyanobacteria.
Effects of salinity and relative humidity on growth and ionic relations of plants
Authors: SALIM M.
Published: April 2006

Growth and ionic relations of mung bean (Vigna radiate L.), sunflower (Helianthus annuus L.), red kidney bean (Phaseolus vulgaris L.), tomato (Lycopersicum esculentum L.) and Atriplex spongiosa L. were studied with three concentrations of NaCl up to 100 mM in the root medium and at either 30% or 90% relative humidity (RH). Two harvests (7 days apart) of all five plant species were taken. Increase in root zone salinity and relative humidity significantly decreased the transpiration rates of all except A. spongiosa. Fresh weight/dry weight ratios of the shoots were unaffected by salinity, except in mung bean, whereas increased RH generally increased the ratios. Shoot/root ratios of mung bean and A. Spongiosa plants were unaffected by both salinity and humidity but increased salinity decreased these ratios in the other three species. In sunflower and tomato greater RH increased the shoot/root ratios at all salt levels. Generally, increased salinity decreased the relative growth rates of mung bean, red kidney bean and sunflower whereas increased RH improved the relative growth rates of mung bean. A. Spongiosa and sunflower.

In most of the species, concentrations of [K + Na] and Cl in the shoot tissue water increased, and those of Ca and Mg decreased, with increase in NaCl concentration in the root medium up to 100 mM. However, in some cases, the concentrations of inorganic ions in the shoot tissue water decreased at all levels of NaCl when the RH in the growth cabinet was increased up to 90%. Concentrations of K in root tissue water of all five species decreased and their Na and Cl concentrations generally increased with increasing salinity of the root medium. Although rates of Na transport relative to that of K through the roots of all the species significantly increased with salinity, red kidney bean roots conducted more Na relative to K under low RH compared with high RH. Similarly the roots of sunflower and A. spongiosa conducted more Cl relative to [K + Na] when the RH was decreased. Higher rates of net ion transport from roots to shoot of mung bean and A. spongiosa plants resulted in higher concentrations of K, Na and Cl in their shoot tissue water when the RH was decreased from 90% to 30%.
The response to salinity at the microscopic level of the marine fungus Dendryphiella salina Nicot and Pugh as investigated stereologically
Authors: CLIPSON N. J. W. , JENNINGS D. H. , SMITH J. L.
Published: April 2006

A stereological analysis of the response of cellular characteristics of hyphae of the marine hyphomycete Dendryphiella salina to salinity is presented. Analyses of volume fractions, compartmental volumes, membrane surface densities and membrane areas have been made. A major finding has been that the wall forms 40 % of the compartment volume. Total hyphal compartment volume was maximal at 200 mM NaCl at 109μm3 with compartments increasing in width and decreasing in length with salinity. Maximal protoplasmic and cytoplasmic volumes were also found at 200 mM. Electron microscopy demonstrated three different vacuolar types differentiated by their staining characteristics. A light‐staining vacuolar type increased in total volume from 4.5 to 12.2μm3 from 0 to 1 M NaCl. Data are considered not only in terms of hyphal anatomical characteristics but also in terms of those physiological processes occuring in D. salina which allow it to grow in saline media.
Vesicular‐arbuscular mycorrhizas increase chloride concentration in citrus seedlings *
Authors: GRAHAM J. H. , SYVERTSEN J. P.
Published: April 2006

Seedlings of sour orange (Citrus aurantium L.) and sweet orange (C. sineusis (L.) Osbeck) were grown in a sandy soil low in phosphorus (P) and either inoculated with Glomus intraradices Schenck & Smith (vesicular‐arbuscular mycorrhizal; VAM) and/or fertilized with soluble KH2PO4 (nonmycorrhizal: NM). Eight‐month‐old VAM and NM seedlings of similar shoot size and P concentration were salinized with 30 and 60 mM NaCl in one experiment for 6 weeks until growth reductions were observed, and in another experiment, seedlings were salinized for 4 weeks before growth reductions occurred. Salinization did not affect colonization by G. intraradices but reduced growth, hydraulic conductivity of roots, and transpiration of shoots. There were no significant growth or physiological interactions between mycorrhizas and salinity which indicates that G. intraradices did not affect salinity stress tolerance of either species. In the first experiment, mycorrhizas increased Cl concentration in shoots and total Cl per plant of sweet orange but not sour orange. NM seedlings fertilized with KH2PO4, had significantly higher levels of P and K than in VAM plants which may have led to the observed differences in the leaf concentrations of Cl and cations. In the second experiment, VAM plants were also supplemented with KH2PO4 before salinization. This resulted in similar leaf and root concentrations of P, K, and other cations. Root Mn was lower and leaf Cu and root Cu and Zn were higher in VAM seedlings. Salinization negated the mycorrhizal effect on Cu to an extent depending on NaCl level. Mycorrhizas increased Cl concentration in leaves and roots of salinized sweet orange and sour orange in the apparent absence of a P‐nutritional effect.
Anther dehiscence in Lycopersicon esculentum Mill. I. Structural aspects
Authors: BONNER LYNDA J. , DICKINSON H. G.
Published: April 2006

The structure and chemistry of anther dehiscence in Lycopersicon esculentum (Solanaceae) has been examined using a range of microscopic techniques. No Single event or process has been identified as being solely responsible for the release of the pollen grains, instead, an integrated programme of development across a number of tissues appears to be involved. The earliest events in this process are changes in the intersporangial septa and growth of specific epidermal cells. Large numbers of calcium oxalate (druse) crystals accumulate in the septa and may play a part in the weakening and eventual enzymic dissolution of this cell layer. The differential growth of epidermal cells fulfils two roles; firstly it serves to define the point of rupture or stomium and, secondly the enlarged cells generate and transmit the force required to disrupt the unenlarged stomial cells. Adjacent loculi are unified within the anther first by the enzymic degradation of the crystal‐filled septal cells, which is followed by similar degradation of the remaining connective tissue cells and the eventual rupture of the remnants of the tapetal walls.

Once the epidermal cell system has been established, and adjacent loculi unified, the endothecium develops in the anther wall, but only in the region adjacent to the stomium in the distal third of the anther. Opening of the anther is achieved by a combination of the mechanical forces generated by tile enlarged epidermal, and possibly the endothecial, cells operating on the previously weakened stomial cells, which at the time of rupture have started to desiccate. Following rupture of the anther wall, the stomium is transformed from a slit to a wide‐mouthed pore via the ordered desiccation and contraction of the endothecial and surrounding tissue. Although these final stages of dehiscence show some sensitivity to ambient vapour pressure differences, there is little doubt that the process of dehiscence is not purely a desiccatory one, indeed only specific localised areas of the anther degenerate and dehydrate, whilst the bulk of the anther tissue remains turgid and metabolically active.

This multicomponential type of anther dehiscence is discussed in the perspective of other models proposed to explain anther opening in members of the Solanaceae, as well as systems suggested for other plants which clearly possess very different methods of dehiscence.
Analysis of specific leaf area and photosynthesis of two inbred lines of Plantago major differing in relative growth rate
Authors: DIJKSTRA PAUL , LAMBERS HANS
Published: April 2006

Two inbred lines of Plantago major L., differing in relative growth rate (RGR), were studied in order to elucidate physiological factors responsible for this difference. The slow growing inbred line of P. major ssp. major L. (line W9) had a lower specific leaf area (SLA) compared with that of the fast growing P. major ssp. pleiosperma Pilger (line A4). Photosynthetic activity per unit leaf area was higher than that of A4, but expressed per unit leaf dry weight W9 exhibited a lower activity than A4. Photosynthetic capacity (per unit leaf dry weight or nitrogen) was identical for both lines. The amount of chlorophyll a per unit dry weight or leaf area was higher for line W9. Differences in the chemical composition of the leaf dry weight of the two lines did not explain the lower SLA or lower photosynthetic activity per unit leaf dry weight of the slow growing line. The lower SLA of W9 was mainly caused by the lower water content per unit dry weight. A higher amount of cell wall material per unit leaf dry weight was found.

We conclude that the lower SLA of W9 resulted in a greater shading within the leaf, a lower light absorption and lower photosynthetic rate per unit leaf dry weight. Consequently, this resulted in a lower RGR. The significance of these characters for growth under trampling and soil compaction is discussed.
Purification and some properties of an aminopeptidase from endosperms of ×Haynaldoticum sardoum Meletti et Onnis
Authors: GALLESCHI L. , PELLEGRINI L.
Published: April 2006

Aminopeptidase activity was detected in dry and germinating seeds of x Haynaldoticum sardoum. The enzyme was partly purified from germinating seeds and preliminary characterization was carried out.

The aminopeptidase showed a pH optimum of 8.0, a molecular weight estimated at 89 000 by Sephadex G‐100 gel filtration and an isoelectric point of 4.5. The enzyme hydrolysed p‐nitroanilides, but was unable to break down exogenous native proteins. Activity was severely inhibited by p‐chloromercuribenzoate, p‐hydroxy‐mercuribenzoate and bestatin, slightly inhibited by iodoacetamide and ethylenediaminetetraacetic acid and not influenced by 2‐mercaptoethanol, phenylmethanesulphonyl fluoride and polyamines.

A possible physiological role for the enzyme in the final stages of storage protein degradation is suggested.
Visible foliar injury of red spruce seedlings subjected to simulated acid mist
Authors: LEITH I.D. , MURRAY M. B. , SHEPPARD L. J. , CAPE J. N. , DEANS J. D. , SMITH R. I. , FOWLER D.
Published: April 2006

Two‐year‐old red spruce seedlings [Picea rubens Sarg. syn. P. rubra (Du Roi) Link] were subjected to 6 simulated acid mist treatments (pH 2.5, 2.7, 3.0, 3.5, 4.0, 5.0) in a replicated experiment using open‐top chambers. Acid mist solutions containing equimolar (NH4)2SO4, and HNO3 were applied twice weekly for 22 weeks, each application being equivalent to 2 mm of precipitation.

Visible symptoms of foliar damage were observed on the 3 most acidic mist treatments (pH 2.5, 2.7, 3.0). The inputs of nitrogen, sulphur and acidity in the most acidic treatment were 55, 42, 1,3 kg ha‐1, respectively, over a 10 week period. The plants subjected to the pH 2.5 treatment were found to be most severely damaged with approximately 40% foliar necrosis after 10 weeks of treatment.

On approximately 80% of seedlings, necrosis was confined to current year needles only. These damaged needles were initially light brown or light orange in colour turning a deeper red 3 to 5 weeks after initial necrosis. Percentage foliar damage was linearly related to concentration (of NH4+, NO3‐, SO42– and H+) with 62% foliar damage in the pH 2.5 treatment after a 22–week period.

Spray application stopped in December 1987. Observations during the following spring showed that the pH 2.5 and pH 3 treatments induced earlier Hushing, requiring 60 day °C less thermal time than the pH 5–0 treatment. In 1988, this decrease in thermal requirement was equivalent to flushing 11 days earlier. There was no evidence of acid mist treatments inducing bud mortality.
Effects of acid mist on the frost hardiness of red spruce seedlings
Authors: FOWLER D. , CAPE J. N. , DEANS J. D. , LEITH I. D. , MURRAY M. B. , SMITH R. I. , SHEPPARD L. J. , UNSWORTH M. H.
Published: April 2006

Seedlings of red spruce [Picea rubens Sarg. syn. P. rubra (Du Roi) Link] were exposed to mists containing equimolar (NH4, SO4 and HNO3 at pHs of 2.5, 2.7, 3.0, 35, 4.0 or 5.0. The mists were applied twice each week, amounting to 2 mm precipitation equivalent on each occasion, between July and December, to open‐top chambers supplied with charcoal‐filtered air.

Frost hardiness of shoots excised from seedlings was determined on 6 occasions starting on 21 September, and was found to be strongly influenced by acid mist treatments, seedlings subject to the most acidic mists being the least frost hardy. On 21 September when the first sample was taken the lethal temperature for killing 50% of shoots (LT50) was – 11 °C for the least acidic (pH 5.0) mist and – 7 °C for the most acidic (pH 2.5). By 19 October, the LT50s of pH 5.0 and pH 2.5 mists were –27 and –15 °C respectively. All intermediate treatments ranked according to treatment concentration, with the smaller concentrations causing lower LT.50 values.

The treatment at pH 30 provided S and N inputs to the seedlings similar to those experienced by red spruce at elevations of about 1000 m in the southern Appalachians. At pH 3.0, the frost hardiness LT10 during October was typically 8 °C higher than the pH 5.0 treatment, leading to a significant increase in the probability of frost damage at the LT10 level in an average October.

The proximity of minimum night temperatures during September to December to the LT10 temperatures of red spruce shoots receiving large inputs of SO42‐, NO3‐, NH4+ and H+ suggests that decreases in frost hardiness caused by intercepted cloud water containing large concentrations of these ions may play a significant part in the observed decline at mountain‐top locations.
Interaction ofGlomusspecies andVigna unguiculatain an oxisol subjected to simulated erosion
Authors: AZIZ T. , HABTE M.
Published: April 2006

An experiment was conducted in the greenhouse to determine the effectiveness of three species of vesicular‐arbuscular (VA) mycorrhizal fungi in an oxisol subjected to simulated erosion using cowpea [Vigtta unguiculata(L.) Walp, cv.‘California Black Eye’] as an indicator host. Inoculation of the eroded soil resulted in increased VA mycorrhizal colonization of roots without enhancing shoot P concentration and dry matter yields. Inoculation of the uneroded soil, however, led to significant improvement in infection level as well as in symbiotic effectiveness. Based on the results of this study, it appears that the lack of expression of mycorrhizal effectivness in the eroded soil is a result of nutrient deficiency. The results thus suggest the importance of restoring lost nutrients before the benefits of VA mycorrhizal inoculation could be effectively exploited for a successful establishment of a mycorrhizal cowpea in eroded soils.
Control of stomatal aperture by calcium in isolated epidermal tissue and whole leaves of Commelina communis L.
Authors: ATKINSON C. J. , MANSFIELD T. A. , KEAN A. M. , DAVIES W. J.
Published: April 2006

Plants of Commelina communis L. were grown in media containing different concentrations of calcium from 1 to 8 mol m −3. After 4 weeks' growth stomatal behaviour was studied both on the intact plants and on isolated abaxial epidermis. The effect of Ca nutrition on stomatal opening was apparently different according to these two methods of observation. The apertures measured in light and in absence of CO2 were smaller on abaxial epidermal strips from plants grown at larger Ca concentrations than those grown at smaller concentrations. The inhibition of opening was thought to be due to the presence of free Ca2+ ions because inhibition was not found when EGTA was included in the medium used for incubating the isolated epidermis, and significant quantities of Ca were lost to the medium by epidermal tissue from plants grown on high concentrations of Ca.

Studies on the leaves of intact plants were made with a diffusion porometer and by gas exchange techniques using a leaf cuvette in which the environment was closely controlled. A/c1 curves were used to partition non‐stomatal and stomatal limitations to gas exchange. Porometer measurements of stomatal conductance, determined within the growth room, indicated reduced values for plants grown at low Ca compared with those grown at high Ca, i.e. the observations contradicted those obtained with isolated epidermis.

Biomass production increased with Ca up to 4 mol m −3. Analysis of A/c1 curves indicated that plants grown at the larger Ca concentration showed significantly greater values for carboxylation efficiency (dA/dc1). Partitioning of stomatal and non‐stomatal limitations to carbon fixation indicated that the gas‐phase limitations of CO2 were similar at different Ca concentrations. Differences in carboxylation efficiency could account for the greater biomass accumulation found at the larger Ca concentration.

Calcium analysis indicated that plants grown at high Ca contained greater bulk leaf Ca concentrations, and a difference in Ca concentration was also evident in epidermal tissue, but the relative distribution of fractionated epidermal Ca was similar. Xylem sap Ca analysis also revealed more Ca in the apoplast of high Ca grown plants.

The differences in stomatal behaviour in isolated epidermis and in the intact leaves suggest that in Ca‐rich plants, the level of free Ca2+ ions in the vicinity of guard cells is controlled, thus preventing inhibition of stomatal opening and interference with gas exchange. The loss of this control when epidermis is detached implies that the presence of the mesophyll tissue is important.
Appropriate controls for vesicular–arbuscular mycorrhiza research
Authors: KOIDE ROGER T. , LI MINGGUANG
Published: April 2006

Sunflower (Helianthus animus L.) and mustard (Brassica hirta Moench.) plants were grown in autoclaved soil to which was added various components of soil inoculum. Use of inocula containing mycorrhizal propagules ultimately resulted in growth promotions which were related to improved phosphorus nutrition. Inoculation with soil containing mycorrhizal propagules caused an initial growth depression in comparison with plants receiving no inoculation, but inoculation with washed spores did not. For several reasons, the growth depression caused by inoculation with soil was not attributable to mycorrhizal infection. First, the growth depression was evident before mycorrhizal infections had become established. Second, the growth depression was also evident when either soil or soil sievings, both lacking mycorrhizal propagules, were used. Third, similar growth depressions were observed in mustard. The results suggest that careful selection of appropriate controls for mycorrhizal plants must be made, particularly if the emphasis is on early phases of plant growth. Use of non‐sterile soil reduced the extent of mycorrhizal infection.
Spread of endomycorrhizal colonization and effects on growth of apple seedlings
Authors: DOUD MILLER DIANE , BODMER MAJA , SCHÜEPP HANNES
Published: April 2006

An experiment to determine the short‐term characteristics of root colonization by two vesicular‐arbuscular (VA) mycorrhizal fungi with apple (Malus × domestica Borkh.) was initiated concurrently with an experiment to determine longer‐term effects of colonization by these fungi on the growth of apple seedlings. Short‐term characteristics of colonization were determined by sequential harvesting of a cuvette system which also allowed monitoring of hyphal spread from inoculated ‘spreader’ plants, through a root‐free soil region, to non‐inoculated ‘receiver’ plants. Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe exceeded Glomus macrocarpum Tul. & Tul. in rate of initial colonization, amount of maximum colonization, and persistence of arbuscules and external hyphae. Colonization by either fungus reduced shoot fresh weight 11 days after inoculation but increased shoot and total fresh weight by day 38. Hyphae of G. mosseae had traversed through 2 and 3 cm of root‐free soil to colonize non‐inoculated ‘receiver’ roots by 29 days, and hyphae of G. macrocarpum by 38 days. G. mosseae colonized ‘receiver’ roots more intensely than did G. macrocarpum at 2 and 3 cm, and 3 and 4 cm distance, at subsequent harvests. The fungi were effective, singly and in combination, in increasing apple plant biomass, as compared to non‐mycorrhizal controls. Relative height growth rate, and colonization at harvest, of G. macrocarpum‐inoculated plants were less than those of G. mosseae‐inoculated or G. mosseae + G. macrocarpum‐ inoculated plants, but greater than those of the non‐mycorrhizal control trees.
Chitin‐decomposing actinomycetes associated with a vesicular–arbuscular mycorrhizal fungus from a calcareous soil
Authors: Ames R. N. , Mihara K. L. , Bayne H. G.
Published: April 2006

Spores of Glomus macrocarpum Tul. & Tul. were sieved from a calcareous, silty clay loam soil, washed in sterile water, and plated on chit in agar for the isolation of actinomycetes. Of the 190 spores examined, 100 were colonized by one or more chitin‐decomposing microorganisms: 82% were colonized by actinomycetes, 17% by bacteria, and 1 % by fungi. Fifty‐one actinomycete isolates were classified on the basis of morphological, cultural and biochemical criteria. Tentative identifications to genera and numbers of different isolates are as follows: Streptomyces (29); Nocardia (3); Streptosporangium (1); Streptoverticillium (1); Intrasporangium (1); Nocardiodes (1); and unidentified (15). This is the first study to report the prevalence and diversity of chitin‐decomposing actinomycetes associated with spores of a vesicular‐arbuscular mycorrhizal fungus in field soil.