bluuebunny/crossref_metadata_2025 huggingface dataset:
A HISTOCHEMICAL STUDY OF PHENOLIC MATERIALS IN MYCORRHIZAL AND UNINFECTED ROOTS OF EUCALYPTUS FASTIGATA DEANE AND MAIDEN
Authors: LING‐LEE M. , CHILVERS G. A. , ASHFORD A. E.
Published: May 2006

The distribution of phenols in uninfected and mycorrhizal Eucalyptus fastigata roots has been examined by application of a range of histochemical tests to thin sections.

The vacuoles of most cap cells and many epidermal cells of E. fastigata mycorrhizas contain considerable quantities of phenolic materials. Cap cells of uninfected fine roots similarly contain materials with the staining properties of phenols, but uninfected root epidermal cells rarely do. It is suggested that accumulation of phenols in the epidermal cells of mycorrhizas is a response to the presence of the fungal symbiont. Further evidence is provided that the hyphae of the fungal symbiont penetrate and grow through the phenolic materials of the outer root cap cells. No evidence was found to suggest that these areas contain appreciable quantities of polysaccharide.

Phenols were also detected in the endodermis and outermost layer of cortical cells. Judged on their staining reactions, these seem to be chemically different from those of the cap and epidermis. They are present in both mycorrhizal and uninfected roots, but appear much closer to the tip in the former. The outer layer of cortical cells has other specialized features, including the presence of a suberin layer in the walls, which are characteristic of mature differentiated endodermal cells in E. fastigata. These features are discussed from the viewpoint that the outer cortical layer acts as a barrier to further hyphal penetration in eucalypt mycorrhizas.
THE LOCATION OF THE RESISTANCE TO WATER MOVEMENT IN THE SOIL SUPPLYING THE ROOTS OF TRANSPIRING PLANTS
Authors: FAIZ S. M. A. , WEATHERLEY P. E.
Published: May 2006

Previous work has shown that when plants are rooted in unsaturated soil and subjected to high rates of transpiration, the depression of water potential in the leaves (ΔΨ1) may rise to as much as 15 bars, but falls to less than half this value on reducing or stopping transpiration. This fluctuation in water stress in the plant has been interpreted as due to changes in the depression of water potential of the soil at the root surface (ΔΨs) arising dynamically as a result of the hydraulic resistance of the soil. Major gradients of ΔΨs could arise in the soil either around each individual root (perirhizal) or between the root zone and the surrounding root‐free water supplying zone (pararhizal).

To decide between these two hypotheses, experiments were made on Helianthus plants subjected to conditions in which pararhizal gradients were unlikely to arise. The above pattern of stress development and recovery were clearly demonstrated, thus favouring the perirhizal hypothesis. The data indicate that under these experimental conditions, the drop in water potential across the perirhizal soil was about the same as that through the plant (approx. 6 bars).
EFFECT OF GIBBERELLIC ACID ON POLYPHENOL OXIDASE ACTIVITY IN DE‐EMBRYONATED WHEAT AND BARLEY GRAINS
Authors: JENNINGS P. H. , DUFFUS C. M.
Published: May 2006

De‐embryonated grains of wheat and barley showed various responses when incubated with gibberellic acid (GA3). Amylase activity in the three cultivars studied showed similar responses to GA3 concentration and period of incubation. Changes in o‐diphenolase and monophenolase activities of polyphenol oxidase (o‐Diphenol: oxygen oxidoreductase, E.C.I. 10.3.1) which occurred when de‐embryonated grains were incubated in the absence of GA3, were enhanced by the hormone. Activity was promoted in extracts from wheat half‐grains, but inhibited in extracts from the two barley cultivars. Whereas monophenolase activity was detected primarily in extracts of the wheat aleurone layer, it was only detectable in the barley endosperm extracts. The inhibitory effect of GA3 on monophenolase activity in the barley cultivars is discussed.
GIBBERELLIN EFFECTS WITHIN HAZEL (CORYLUS AVELLANA L.) SEEDS DURING THE BREAKING OF DORMANCY I. A DIRECT EFFECT OF GIBBERELLIN ON THE EMBRYONIC AXIS
Authors: ARVIS B. C. J. , WILSON D.
Published: May 2006

Gibberellin Ai breaks the dormancy of hazel seed. Both GA1 and GA3 are transported more readily from embryonic axis to cotyledon than in the reverse direction. Since both gibberellins stimulate axis growth more rapidly when applied directly to it than when applied to the cotyledon, it seems likely that gibberellins directly affect the axis. This is confirmed by a rapid response of excised axes to gibberellic acid in liquid culture.
EFFECT OF GIBBERELLIC ACID AND SOME POLYPHENOLS ON THE FLOWERING OF IMPATIENS BALSAMINA
Authors: NANDA K. K. , KUMAR SURINDER
Published: May 2006

Chlorogenic acid, tannic acid and gibberellic acid (GA3) all induce floral buds in I. balsamina under strictly non‐inductive photoperiods. Floral bud initiation is hastened when 100 mg/l GA3 is used in combination with both polyphenols, the effect being most pronounced with 100 mg/l chlorogenic acid. 1 and 100 mg/l each of chlorogenic and tannic acids increase the number of floral buds also when used in combination with 100 mg/l GA3 as compared with 100 mg/l GA3 alone.
THE CYANOPHYTE‐HEPATIC SYMBIOSIS II. NITROGEN FIXATION AND THE INTERCHANGE OF NITROGEN AND CARBON
Authors: STEWART W. D. P. , RODGERS G. A.
Published: May 2006

Free‐living and symbiotic phycobionts of Anthoceros punctatus and Blasia pusilla reduce acetylene and fix 15N2; gametophytes and sporophytes without algae do not. Nitrogenase activity by free‐living and symbiotic Nostoc is higher under microaerobic than aerobic conditions in the light, and is higher in the light than in the dark. The free‐living Blasia phycobiont grows heterotrophically on sucrose and less well on fructose and glucose; hetero‐trophic growth on galactose is negligible. There is a transfer of 15N from the alga, via the gametophyte to the sporophyte of Anthoceros. About 98% of the extracellular nitrogen liberated into the medium by excised Nostoc colonies is in the form of ammonia; there is negligible liberation of peptides and amino acids. The capacity to excrete ammonia is lost after 72 h of growth free from the liverwort. Excised Nostoc colonies show a negligible capacity to fix CO2 photosynthetically and autoradiographic studies show a transfer of fixed carbon from Blasia gametophytes to the algal cavities. Sucrose may be the main extracellular carbon compound liberated by Blasia gametophytes. In Anthoceros, nitrogenase activity can be sustained for days when alga‐containing gametophytes are placed in the dark, if the sporophytes remain exposed to the light. This indicates a transfer of photosynthate from the sporophyte, via the gametophyte, to the alga.
THE RESPONSE OF LICHEN GROWTH TO TRANSPLANTATION TO ROCK SURFACES OF DIFFERENT ASPECT
Authors: ARMSTRONG R. A.
Published: May 2006

Thalli of four saxicolous lichens on slate rock fragments were transplanted from rock surfaces to horizontal boards and then to south‐east‐facing and north‐west‐facing rock surfaces. The radial growth rate of Physcia orbicularis and Parmelia conspersa thalli declined after transplantation to north‐west‐facing rock surfaces and was unchanged after transplantation to south‐east‐facing rock surfaces compared with growth rate on the boards. The radial growth rate of P. glabratula ssp. fuliginosa thalli declined after transplantation to south‐east‐facing rock surfaces and was unchanged after transplantation to north‐west‐facing rock surfaces compared with growth rate on the boards. The radial growth rate of P. saxatilis thalli was similar on the horizontal boards, south‐east‐facing and north‐west‐facing rock surfaces. Those results are discussed in relation to the aspect distributions of the four lichens in South Gwynedd, Wales.
THE EXTRACTION, COMPOSITION AND INTRA‐CELLULAR DISTRIBUTION OF PROTEIN IN EARLY MAIZE GRAINS FROM AN ARCHAEOLOGICAL SITE IN N.E. ARIZONA
Authors: DERBYSHIRE E. , HARRIS N. , BOULTER D. , JOPE E. M.
Published: May 2006

Maize grains from an archaeological site in N.E. Arizona have been examined by light microscopy and electron microscopy. Their endosperm tissue was intact and was similar to that of modern maize although some of the features seen in other non‐viable seeds were present; the embryos, however, were discoloured and damaged. Protein has been extracted from both endosperm and embryos although only a small quantity was extracted from the latter. The protein sub‐unit profiles of these extracts and of storage protein fractions prepared by serial extraction of endosperm meal in salt, alcohol and sodium dodecyl sulphate (SDS) solutions have been determined after electrophoresis in SDS‐acrylamide gels. The data obtained indicate that zein and glutelins similar to modern maize proteins were the major storage proteins but that their proportions differed to those in modern maizes; these conclusions are supported by the amino acid composition of the wholse seed meal. It is suggested that these procedures may be applicable to other archaeological samples of seeds including those of other species and that the data so obtained may be of use in cultural studies and in botanical studies of crop plant origins and evolution.
EFFECTS OF PLANT HORMONES PRESENT IN BACTERIAL CULTURES ON THE FORMATION AND RESPONSES TO VA ENDOMYCORRHIZA
Authors: AZCÓN R. , DE AGUILAR C. AZCÓN‐G , BAREA J. M.
Published: May 2006

The growth and infection levels in mycorrhizalLavandula, LycopersicumandMedicagoplants were compared after treatment with preparations fromRhizobium, Azotobacterand phosphobacteria (aPseudomonas).The bacterial cultures are known to contain growth substances. Ceil‐free supernatants and in some instances, the whole bacterial culture, behaved as the pure plant hormone in improving dry weight and infection levels compared with mycorrhizal control plants.
A PROCEDURE FOR THE SIMULTANEOUS MEASUREMENT OF NET CO2‐EXCHANGE AND NITROGENASE ACTIVITY IN LICHENS
Authors: CRITTENDEN P. D. , KERSHAW K. A.
Published: May 2006

A sensitive and rapid procedure is described for the simultaneous measurement of mean rates of net CO2‐exchange and nitrogenase activity (acetylene reduction) in cyanophilic lichens. It involves a reaction gas chromatographic technique for the determination of CO2 and ethylene. Data on concurrent rates of net CO2‐exchange and nitrogenase activity in Peltigera canina (L.) Willd. var. praetextata (Florke em. Sommerf.) Hue and Stereocaulon paschale (L.) Hoffm. at different levels of thallus water content are presented in order to illustrate the application of the new method.
LICHENS OF THE SUGAR LIMESTONE REFUGIUM IN UPPER TEESDALE
Authors: GILBERT O. L. , EARLAND‐BENNETT P. , COPPINS B. J.
Published: May 2006

Though the grassland associated with the sugar limestone outcrops in Upper Teesdale supports the richest terricolous lichen assemblage of any calcareous site so far discovered in England or Wales it may not have acted as a significant refugium for late‐glacial lichens. A possible reason for this is suppression by open canopy forest during the boreal and atlantic periods. The current high density of terricolous lichens may, to some extent, be a result of intensive grazing over the last few centuries which has favoured the development of an extremely short, open sward offering a wide range of microhabitats.
Studies IN THE VEGETATIONAL HISTORY OF SCOTLAND
Authors: BIRKS HILARY H. , MATHEWES ROLF W.
Published: May 2006

This paper describes palaeoecological studies at Abernethy Forest by means of pollen and macrofossil analysis and radiocarbon dating. It also illustrates the value of stratigraphic macrofossil analysis in conjunction with pollen analysis in increasing the range and detail of palaeoecological reconstructions of past vegetation and environment.

A new, large diameter core from Abernethy Forest was radiocarbon dated, and the presence of Late Devensian sediments was confirmed. Clear vegetational changes were recorded. A pioneer grass‐sedge vegetation colonized the bare moraine. It developed into a shrub tundra, dominated by Empetrum and Be tula nana as a result of the climatic warming during Allerød time. The Younger Dryas climatic deterioration led to the formation of species‐rich open vegetation, in which Artemisia was very abundant.

At the opening of the Flandrian, at about 9700 B.P., Juniperus and Betula nana scrub developed, which was later colonized by tree Betula and then Corylus. From about 7225 B.P. Pinus dominated the forest.

Throughout, the specific determinations and local derivation of macrofossils enhanced the reconstruction of the upland vegetation. In addition, macrofossils provided the majority of the evidence for the progression of the hydrosere through lake to bog communities.

The complementary nature of pollen and macrofossil analyses from the same core is emphasized by a direct comparison of seed and pollen influxes.
CELL WALL STRUCTURE AND ELONGATION GROWTH IN ZEA MAYS COLEOPTILE TISSUE
Authors: DARVILL A. G. , SMITH C. J. , HALL M. A.
Published: May 2006

Data from pulse‐chase studies on the turnover of glycosidic linkages in cell walls of maize coleoptile sections and other work on the effect of auxin or low pH on sugar release from ‘sheets’ of cells derived from the same tissue are presented. The qualitative and quantitative effects of auxin and low pH on sugar release from cell sheets are almost identical in the short term. Using a recently derived model of the maize coleoptile cell wall, a hypothesis is proposed concerning the role of auxin‐induced proton release in the cleavage of glycosidic linkages in relation to growth.
PLANT AND LEAF RESISTANCE TO GASEOUS AIR POLLUTION STRESS
Authors: TAYLOR G. E.
Published: May 2006

Levitt's (1972) revision of stress phenomena in plants provides a scheme for analysing the response of vegetation to gaseous air pollution. Total plant resistance is a consequence of two general mechanisms, (i) pollution stress avoidance and (ii) stress tolerance. Stress tolerance is subdivided further into strain avoidance and strain tolerance. Many of the environmental, physiological and morphological factors known to influence the susceptibility of plants to air pollution are discussed using this format. The value of this approach is the systematic framework it provides for analysing, relating and interpreting the factors affecting variable leaf and plant resistance to gaseous air pollution stress.
RESPONSE TO SOIL MOISTURE SUPPLY IN THREE LEGUMINOUS SPECIES
Authors: FOULDS W.
Published: May 2006

Detached nodules of Medicago lupulina, Lotus corniculatus and Trifolium repens were able to reduce acetylene for a period of 8 h in moist conditions, but the rate fell after 2 h when water stress was applied. Under moist conditions, nodules of Medicago lupulina and Trifolium repens, when measured while attached to or detached from the host plant, possessed the most rapid rate of N2(C2H2)‐fixation. Nodules of Lotus corniculatus showed by far the slowest rates. Relatively mild drought had less effect on N2(C2H2)‐fixation of L. corniculatus than the other two species. This legume also suffered fewer fatalities, maintained a relatively high shoot turgidity and shedded fewer root nodules during periods of desiccation. Under similar drought conditions, the N2(C2H2)‐fixation rate of Medicago lupulina nodules was drastically reduced and about half of the root nodules were lost. However, only half the plants died. The same severity of desiccation caused similar reductions of N2(C2H2)‐fixation in Trifolium repens as well as a very high fatality rate and massive loss of nodules. Severe and prolonged desiccation greatly affected N2(C2H2)‐fixation in all three species.
HORMONES IN PLANTS BEARING NITROGEN‐FIXING ROOT NODULES: THE NODULE AS A SOURCE OF CYTOKININS IN ALNUS GLUTINOSA (L.) GAERTN.
Authors: WHEELER C. T. , HENSON I. E.
Published: May 2006

Levels of endogenous cytokinins in various parts of nodulated and non‐nodulated alder plants were estimated using the soybean callus bioassay. In three separate experiments, differences in levels of total plant cytokinin activity were attributed primarily to growth differences between plants, other than nodulation. The higher percentage of total plant cytokinin activity found in the leaves of non‐nodulated plants may be related at least in part to the better development of the root system of these plants compared to those with nodules.

In other experiments growth differences were minimized by comparing intact plants with plants which were either denodulated or root‐pruned or both. All three surgical treatments had similar effects, reducing levels of cytokinins in the stems, while leaf cytokinin levels were not affected greatly. The relative stability of leaf cytokinin levels was also evident following leaf detachment. Factors responsible for the maintenance of cytokinin levels in the leaf are discussed.

The results suggest that nodules are unlikely to make a major contribution to shoot cytokinin content, although export of endogenous cytokinins from the nodules cannot be excluded entirely.
INTERACTION BETWEEN A VA MYCORRHIZA AND AZOTOBACTER AND THEIR EFFECTS ON RHIZOSPHERE MICROFLORA AND PLANT GROWTH
Authors: BAGYARAJ D. J. , MENGE J. A.
Published: May 2006

Larger populations of bacteria and actinomycetes were recovered from the rhizospheres of tomato plants inoculated with the mycorrhizal fungus Glomus fasciculatus and Azotobacter chroococcum, either individually or together, than from those of non‐inoculated plants. Plants inoculated with both Glomus fasciculatus and Azotobacter chroococcum had greater numbers of bacteria and actinomycetes in the rhizosphere than plants inoculated with either Glomus fasciculatus or Azotobacter chroococcum alone. The fungal population of the rhizosphere was unaffected by inoculation with Glomus fasciculatus but reduced by inoculation with Azotobacter chroococcum. Inoculation of tomato with Glomus fasciculatus increased the Azotobacter chroococcum population in the rhizosphere which was maintained at a high level for a longer time. Inoculation of tomato roots with A. chroococcum enhanced infection and spore production by Glomus fasciculatus. The dry weights of tomato plants inoculated with both G. fasciculatus and Azotobacter chroococcum were significantly (62%) greater than non‐inoculated plants. These results suggest a synergistic or additive interaction between Glomus fasciculatus and Azotobacter chroococcum.
A SCANNING ELECTRON MICROSCOPY STUDY OF ‘VESICULAR BODIES’ IN MYCORRHIZAL ROOTS OF PINUS MUGO (TURRA)
Authors: WILLS B. J. , COLE A. L. J.
Published: May 2006

The formation of vesicular bodies in mycorrhizal short roots of Pinus mugo has been investigated using the scanning electron microscope. They appear to bear a relationship to the Hartig net but their exact nature is as yet unexplained.
UPTAKE OF FUBERIDAZOLE AND THIABENDAZOLE BY PENICILLIUM DIGITATUM, CUNNINGHAMELIA ECHINULATA AND POTATO SLICES
Authors: GREENAWAY W. , WARD S. , WHATLEY F. R.
Published: May 2006

The resistance of Cunninghamella echinulata to the systemic fungicides fuberidazole (FEZ) and thiabendazole (TBZ), and that of Penicillium digitatum to TBZ, may be due to active secretion of the fungicides from the hyphae. There was no clear evidence that secretion of FEZ was the cause of FEZ resistance in P. digitatum.

Both the uptake and release of FBZ and TBZ by potato slices appeared to be passive processes.
SALT TOLERANCE IN PASTURE GRASSES
Authors: VENABLES ANNE V. , WILKINS D. A.
Published: May 2006

Samples of six species of grass from a salinized pasture were grown in culture solution with varying concentrations of sodium chloride added. The rates of root growth showed a high correlation with the conductivity of water extracts of the soils of origin. The results can be interpreted as evidence for strong selection for the appropriate level of response to salt at each point on the salinity gradient. Salt tolerance was found to be highly heritable in Festuca rubra.
ECOPHYSIOLOGICAL ASPECTS OF ZINC TOLERANCE IN SILENE MARITIMA WITH.
Authors: BAKER A. J. M.
Published: May 2006

Zinc uptake by a range of zinc‐tolerant and non‐tolerant populations of Silene maritima was studied by means of long‐term water‐culture experiments. The pattern of zinc uptake and transport in mine populations differed from coastal and arctic‐alpine populations. All mine populations showed some degree of restricted transport from root to shoot; some also accumulated zinc in the roots. Uptake characteristics could be correlated with soil zinc analyses but did not relate directly to indices of zinc tolerance obtained by short‐term measurements of radicle elongation.
AUXIN TRANSPORT CHARACTERISTICS AND CELLULAR ULTRASTRUCTURE OF DIFFERENT TYPES OF PARENCHYMA
Authors: WANGERMANN ELISABETH , WITHERS LYNDSEY ANN
Published: May 2006

Secondary xylem tissue of Coleus and Helianthus internodes, and both parenchyma and vascular tissue of Zea and Triticum coleoptiles, were found to be capable of active polar auxin transport; pith parenchyma from Coleus and Helianthus internodes was not. Electron microscopy revealed the presence of ‘plasmalemmasomes’ in parenchyma cells from tissues known from present and previous work to contain the transport system, and their absence from cells of tissues known to lack the transport system. A possible link between the presence of plasmalemmasomes and the capacity for polar auxin transport is discussed.
FURTHER INVESTIGATIONS INTO THE LOCATION AND MAGNITUDE OF THE HYDRAULIC RESISTANCES IN THE SOIL:PLANT SYSTEM
Authors: FAIZ S. M. A. , WEATHERLEY P. E.
Published: May 2006

In a previous paper (Faiz and Weatherley, 1977), evidence was put forward for the development of steep gradients of water potential in the soil surrounding the individual roots of rapidly transpiring plants (perirhizal gradients). In this paper, similar experiments are described in which additional data on the dimensions of the root system, distribution of soil water potentials within the rooting zone and the water potentials of the roots themselves were obtained. It was found with experiments on soil that the surface area of the root system was × 60 the cross‐sectional area of the pararhizal pathway (cross‐sectional area of the pot) through which water moved to the root zone from the water table below. Since the volume rate of flow through the peri‐ and pararhizal zones was the same, the velocity of movement up to the individual root was therefore only 1/60 of that through the soil supplying the root system. Under conditions of rapid transpiration, the gradient of water potential in that part of the pararhizal pathway immediately beneath the root zone was found to be about 1 bar cm−1. Thus it would be expected that the perirhizal gradient would be 1/60 of this, i.e. it would be negligibly small. However, the actual perirhizal drop in water potential was found to be about 8 bars through a distance of 0.1 cm, i.e. the gradient was 80 bars cm−1. Such a steep gradient would require the hydraulic conductivity of the soil in the perirhizal zones to be 4 orders of magnitude lower than that in the pararhizal pathway. An even greater discrepancy was found with fine sand. The soil within the rooting zone had a somewhat lower water content than that in the pararhizal zone, but it is not thought that this, and some other imponderables which are discussed, could account for this enormous discrepancy. It is concluded that in these experiments, measurable perirhizal gradients were unlikely to develop. Nevertheless, a considerable drop in water potential (about 8 bars in these experiments) between the soil and the root surface remains to be explained. The hypothesis is put forward that it is at the soil:root interface that a high resistance barrier can arise.
THE DISTRIBUTION OF FRUCTANS IN ONIONS
Authors: DARBYSHIRE B. , HENRY R. J.
Published: May 2006

The non‐structural carbohydrate content of individual leaf bases of onion bulbs was determined, and confirmed the presence of glucose, fructose, sucrose and a series of fructans as the only components. The fructans decreased in concentration with increasing molecular weight and those with a DP (degree of polymerization) of up to 10 were estimated. Total fructan concentration decreased from the youngest to the oldest leaf bases of the bulb, while fructose levels increased and glucose and sucrose levels tended to remain constant.
VESICULAR‐ARBUSCULAR MYCORRHIZAS IN PLANTS COLONIZING BLACK WASTES FROM BITUMINOUS COAL MINING IN THE ILLAWARRA REGION OF NEW SOUTH WALES
Authors: KHAN A. G.
Published: May 2006

Three commercial coal tips in the Illawarra region of New South Wales were investigated for the incidence of VA mycorrhizas in plants growing on them. All the plants examined except species of Personia and Banksia (Proteaceae) were infected by VA mycorrhizal fungi. Infection level ranged from 0 to 88%. Three main types of fungal endophytes, namely Glomus macrocarpus var. macrocarpus, Glom us mosseae, and Sclerocystis rubiformis, were identified. The possible role of VA mycorrhizas in plant colonization of coal spoil areas is discussed. The method of colorimetric quantification of VA infection was found a useful alternative to the slow and tedious method of clearing and staining. But the pigment‐extraction method is reliable only for measuring mycorrhizal infection in controlled short term experiments. This method, however, cannot be used to analyse infection in field‐grown, long established roots.
THE COLONIZATION OF A SLATE ROCK SURFACE BY A LICHEN
Authors: ARMSTRONG R. A.
Published: May 2006

Thalli of Parmelia glabratula ssp. fuliginosa on a vertical slate rock surface in South Gwynedd were significantly larger at the top of the face than at the bottom. The radial growth rates of the thalli measured over 1 year were not correlated with height on the face or with variation in thallus diameter down the face. These results suggest that the lichen thalli may be older at the top than at the bottom and are consistent with the hypothesis that the lichen colonized the top of the face first and then gradually spread downwards.
THE PARTITION COEFFICIENT OF 14C2H4 IN PLANT TISSUE AS A SCREENING TEST FOR METABOLISM OR COMPARTMENTATION OF ETHYLENE
Authors: JERIE P. H. , SHAARI A. R. , ZERONI M. , HALL M. A.
Published: May 2006

A method is described for the direct measurement of 14C2H4 in toluene scintillator and for the measurement of toluene‐soluble 14C accumulated in tissue during 14C2H4 (0.7–1.0 μ1/l) treatment. Using these methods the partition coefficient for ethylene between air and plant tissues was estimated. Tissues from a substantial proportion of 36 species tested gave partition coefficients significantly higher than that for water (0.11) indicating either the sequestration of 14C2H4 or the accumulation of toluene‐soluble metabolites. Steam‐killed tissue gave partition coefficients similar to that of water.
THE CARBON FIXATION CHARACTERISTICS OF ISOLATED CODIUM FRAGILE CHLOROPLASTS. CHLOROPLAST INTACTNESS, THE EFFECT OF PHOTOSYNTHETIC CARBON REDUCTION CYCLE INTERMEDIATES AND THE REGULATION OF RuBP+ CARBOXYLASE IN VITRO
Authors: COBB A. H. , ROTT JACQUELINE
Published: May 2006

Chloroplasts of the siphonaceous marine alga Codium fragile exhibit different carbon fixation characteristics in vitro from those of higher plants. A simple extraction medium, 0.8 M osmoticum and a saturating light intensity of 25 W.m−2 produced maximum rates of 40–60 μmoles CO2 fixed mg. chlorophyll−1 h−1 at 20°C, depending on the age and condition of the parent tissue. No marked lag phase was apparent and fixation proceeded at a linear rate for up to 60 min.

Incubation with 10 mM PGA enhanced the fixation rate, as did 10 mM SBP, 10 mM FBP and 5 mM R5P to a lesser extent, whereas 6 PGlu, S7P, F6P, Ru5P and PEP produced no measureable effect. This lack of marked response to the addition of exogenous photosynthetic intermediates is correlated to a lack of induction by these chloroplasts.

Using the retention of the soluble stromal enzyme RuBP carboxylase as a criterion of intactness, freshly isolated C. fragile chloroplasts were approximately 80% intact, and were still 40% intact after 96 h storage in the dark on ice.

RuBP carboxylase was shown to resemble the higher plant carboxylase, existing in either an active or inactive form depending on the prevailing levels of RuBP and Mg2+, and to be metabolically regulated by PGA, 6PGlu, SBP, FBP and Pi. Maximum rates obtained with a chloroplast extract were 155 jumoles CO2 fixed mg chlorophyll−1 h−1, at 20°C.
ROOT EXUDATION IN RELATION TO SUPPLY OF PHOSPHORUS AND ITS POSSIBLE RELEVANCE TO MYCORRHIZAL FORMATION
Authors: RATNAYAKE M. , LEONARD R. T. , MENGE J. A.
Published: May 2006

The mechanism responsible for inhibition of the establishment of mycorrhizal associations inSorghum vulgarePers. (herbaceous monocot) andCitrus aurantiumL. (woody dicot) under high levels of soil phosphorus (P) was studied. Plants were grown on low fertility loamy sand (4.5 ppm P), receiving superphosphate [Ca (H2PO4)2H2O] at 0, 6, 28, 56, 228 and 556 ppm P along with all the other necessary nutrients. The percentage P content of root tissue was correlated with the amount of P added to the soil. Root exudation, measured in terms of the net leakage of soluble amino acids and reducing sugars from the roots within a 17–h period, was significantly higher under low P levels (0, 6 and 28 ppm P) than under high P levels (56, 228 and 556 ppm P). The amount of exudation was correlated with a P‐induced decrease in phospholipid levels and associated changes in permeability properties of root membranes, rather than with changes in the root content of sugars and amino nitrogen. The hypothesis is proposed that phosphorus inhibition of mycorrhizal symbiosis is associated with a membrane‐mediated decrease in root exudation.
NUTRITIONAL REQUIREMENTS OF ORCHID ENDOPHYTES
Authors: HADLEY G. , ONG S. H.
Published: May 2006

Four geographically distinct isolates of Tulasnella calospora (Bourdier) Juel exhibited a similar nutritional pattern and utilized a wide range of carbon compounds including cellulose. None would grow on a mineral salts/glucose medium unless undefined materials were present. Growth occurred when a mixture of ten amino acids and ten vitamins was used, and all four isolates were heterotrophic for thiamine and p‐amino benzoic acid. They were also exacting for nitrogen. Growth on ammonium ions was very limited but asparagine, glycine and urea were good nitrogen sources while glutamine, arginine and alanine were less adequate.

Isolates of Ceratobasidium cornigerum (Bourd.) Rogers and a Rhizoctonia sp. were self‐sufficient for vitamins and grew well on nitrate or other nitrogen sources tested. They were more efficient than Tulasnella calospora isolates in their nitrogen economy.

T. calospora isolates may obtain vitamins and nitrogen compounds from their orchid hosts and may exhibit a limited phase of biotrophic nutrition.
POLYPHOSPHATE GRANULES IN THE FUNGI OF TWO LICHENS
Authors: CHILVERS G. A. , LING‐LEE M. , ASHFORD A. E.
Published: May 2006

Using Toluidine Blue‐stained sections, metachromatic granules have been detected in the fungi of two different lichens. These are histochemically identical with similar granules found in the fungal component of mycorrhizas and, like those, appear to consist largely of poly‐phosphate. Small numbers of polyphosphate granules have been previously reported from the algal component of a lichen, but not from the fungus. In the material examined here, the size and number of granules in the fungus greatly exceeded those in the algae. These granules merit further investigation to evaluate their significance in ion uptake and accumulation within this symbiotic system.
STUDIES ON THE GROWTH OF THE ENDOPHYTE OF OLALNUS GLUTINOSA (L.) VILL. IN NUTRIENT SOLUTIONS
Authors: QUISPEL A. , TAK T.
Published: May 2006

During incubation of nutrient solutions heavily inoculated with an axenic suspension of spore‐nodules of Alnus glutinosa (L.) Vill. we observed an increase in infective capacity. This effect was only obtained with nutrient solutions to which an extract with petrol ether‐soluble substances from roots had been added.

The reproducibility of the experiments is definitely increased when the active lipid factor(s) is further purified by silicagel column chromatography. Aerobic conditions are essential. Microscopic examination of the infective nutrient solutions showed the presence of Actinomycete‐like hyphae. These hyphae were never observed in controls where the lipid extracts had been omitted. After several transfers to fresh media, cultures are still highly infective and microscopically characterized by growth of these hyphae.

After inoculation with axenic suspensions of spore + nodules, neither an increase of infectivity nor growth of hyphae was observed.
SPORE FORMATION AND ENDOPHYTE DIVERSITY IN ROOT NODULES OF ALNUS GLUTINOSA (L.) VILL.
Authors: VAN DIJK C.
Published: May 2006

Analysis of root nodules of Alnus glutinosa sampled in a natural alder vegetation revealed two types, one containing clumps of endophytic spores and one without spores. The distribution pattern of both types, but especially the latter, showed considerable clustering. Both types of nodule sometimes occurred on the same tree, and some information on the dynamics of the distribution pattern was obtained from age analysis of nodules of both types. Since cross‐inoculation experiments showed a genetic basis for the presence or absence of spores in root nodules, the existence of two endophytic strains differing in their ability to produce spores seems likely. Different concentrations of ammonium and nitrate incorporated into the nutrient solution of nodulated test plants had only a slight influence on spore‐clump abundance in root nodules, and complete inversion of the spore type was not observed. Attempts to find additional strain differences led to the comparison of isomers of diamino‐pimelic acid (DAP) from the cell wall of both types of endophyte. DAP isomer analysis of genetically more distinct ‘Alnus‐type’ root nodules, i.e. those of Myrica gale and Hippophae rhamnoides, were used as reference. No additional taxonomic differences were found between the nodule types in Alnus glutinosa, but spore‐free nodules of Hippophae rhamnoides and Myrica gale differed with respect to the DAP isomer composition. Test plants of Alnus glutinosa provided artificially with either spore‐rich or spore‐free nodules did not differ significantly in acetylene reduction rate.
STUDIES ON MUCORALEAN MYCOPARASITES
Authors: EVANS G. H. , LEWIS D. H. , COOKE R. C.
Published: May 2006

At 15°C, axenically germinated spores of Mycotypha microspora gave rise to transient yeast‐phase growth before the establishment of hyphal development. At this temperature, germination in the presence of spores of Piptocephalis fimbriata resulted in the persistence of the yeast‐phase, few hyphae being formed. Where hyphae were produced these either reverted to the yeast‐phase, became severely attenuated, gave rise to dwarf sporophores or died. Such mycoparasite‐mediated effects did not occur at 20°C. When Mortierella vinacea was used as a host in similar experiments there was no yeast‐phase growth but severe stunting of hyphae occurred initially, followed by recovery and normal growth. Using Circinella mucoroides, there was again no yeast‐phase but there was massive death of host hyphae without any apparent disturbances to their morphology. These observations are discussed in relation to the physiological and ecological consequences of mycoparasitism.
THE HETEROCYSTS OF THE BLUE‐GREEN ALGA NOSTOCHOPSIS LOBATUS: EFFECTS OF CULTURAL CONDITIONS
Authors: TIWARI D. N.
Published: May 2006

The branched filaments of Nostochopsis lobatus form infrequent intercalary heterocysts in the main trichome while the short lateral branches (1–4 celled) characteristically produce only a terminal heterocyst when the alga is grown in a medium devoid of combined nitrogen. In the presence of ammonium nitrogen, intercalary heterocysts are not formed but the lateral heterocysts enlarge to assume a balloon‐like appearance; they undergo division in situ and liberate 3–5‐called germlings. These germlings grow and produce similar heterocysts and the cycle is repeated until growth ceases. Heterocysts are produced at the terminal ends of the long lateral branches during the later stages of growth in ammonium medium; they are not formed, in this position, in cultures grown in nitrogen‐free medium. The possible role of lateral heterocysts in controlling growth and development of long laterals is discussed.
REGENERATION OF CHLOROPLAST STRUCTURE IN TALBOTIA ELEGANS: A DESICCATION‐TOLERANT PLANT
Authors: HALLAM N. D. , GAFF D. F.
Published: May 2006

Talbotia elegans (Velloziaceae) is a desiccation‐tolerant plant whose dry leaves contain chlorophyll. The plastids of dry viable leaves retain some semblance of thylakoid structure and organization but are in a loose array. This contrasts with desiccation‐tolerant plants that lose chlorophyll during dehydration and reduce the chloroplast to pro‐plastid like bodies containing vesicles and numerous plastoglobuli. During rehydration, the existing thylakoid stacks are rehabilitated by the production of a ‘chloroplast designate’ volume surrounding the mass of thylakoids. This region is delimited by a double membrane and the thylakoids stack to form grana and intergranal lamellae by 24 h of hydration. Few organelles other than the chloroplast initials are easily recognizable in dry leaves but mitochondria, reduced to membrane‐bound sacs in the dry state, reform cristae after full hydration has been achieved.
DEVELOPMENT OF THE SHOOT APEX IN ZEA MAYS
Authors: CLOWES F. A. L.
Published: May 2006

Intact embryos of Zea mays have been studied by stathmokinesis and DNA labelling to find rates of cell proliferation in the regions of the developing shoot apex, and these have been compared with rates for seedlings, whose apices have to be partially uncovered for this purpose. In young embryo shoots, cells divide faster than they do in seedlings and rates at the summit do not differ greatly from those in the rest of the apex. The tunica, which contains about half the cells in the apex, contributes a decreasing fraction of the total cell production as the embryo ages. The results are discussed in relation to the maturation of the seed and the changes in the numbers of cells in the regions of the meristem.
TEMPERATURE AND THE COORDINATION OF CELL CYCLES WITHIN THE ROOT MERISTEM OF ALLIUM SATIVUM L.
Authors: TAYLOR A. T. , CLOWES F. A. L.
Published: May 2006

Cell cycling has been surveyed throughout the meristem over a range of temperature by stathmokinetic and DNA‐labelling methods.

There is a quiescent centre of ninety cells either out of cycle or with prolonged cycles. The cap initials have the highest rate of cell production, but only over a short temperature range. Outside that range the distal stelar cells have higher rates. The numbers of cells in the cap and its initials fall off with increasing temperature and there is a twelve‐fold variation in the rate at which the initials can refurnish the cap with new cells. The reduction in cell production that occurs towards the proximal margin of the meristem is due solely to lowering the growth fraction and the meristem contracts at high temperatures.

The phases of the cycle as fractions of the whole vary from region to region and with temperature in the same region. G1 is the most variable phase though it is never eliminated as it is in Zea and the shortening of the mean cycle of cycling cells in the stele from the tip to the proximal margin of its meristem is brought about largely by the reduction of G1 and, to a lesser extent, of G2 while both S and M lengthen. S and M decrease as the temperature increases from 20 to 30°C while G1 and G2 are minimal at 25°C. The coordination of cycle parameters in Allium is discussed in relation to the anatomical features of its meristem and contrasted with that in Zea.
HIGHER PLANT NUCLEOSOMES. A MICROMETHOD FOR ISOLATING AND DISPERSING CHROMATIN FIBRES
Authors: MORENO M. L , SOGO J. M. , DE LA TORRE C.
Published: May 2006

A one‐step method to isolate and disperse chromatin fibres from unfixed plant tissues is described. Nucleosomes as units of chromatin organization in Allium cepa L. root meristems are demonstrated by this simple technique.
NOVEL TECHNIQUES OF GENE TRANSFER AND PLANT IMPROVEMENT: AN APPRAISAL OF TRANSFORMATION IN EUKARYOTES
Authors: PANDEY KAMLA KANT
Published: May 2006

Certain recent theoretical and technological advances make possible the development of new techniques for combining genes from diverse sources without normal sexual hybridization. These include: (1) DNA‐ and phage‐induced transformation; (2) protoplast fusion and organelle transfer; (3) gametic transformation; and (4) graft hybridization. The essential feature of these novel techniques is ‘transformation’, broadly defined here as a phenomenon in which a part of the genetic information of one organism is combined with the entire genome of another. The present article reviews these topics briefly with reference to their potential value in plant improvement, and their contribution to a better understanding of induced transformation in flowering plants.

A critical consideration of differences between prokaryotic and eukaryotic DNA leads to a better appreciation of possible natural constraints operating against gene transfer across this major evolutionary line. Since transformation is essentially a natural mechanism in prokaryotes, and occurs in place of true sexuality and recombination, the occurrence of artificial transformation in eukaryotes may be considered to indicate an inherent capacity for recombination by transformation which has been superceded by the evolutionary development of the sexual mechanisms, meiosis and syngamy, but which may still be expressed if appropriate conditions can be generated. Future major developments may lie in discovering factors and techniques which would make eukaryotic organisms ‘competent’ as donors and recipients in transformation. It is suggested that the egg, zygote, and early embryonic cells may be better targets for transformation than differentiated somatic cells. The rapid successive divisions following fertilization of a eukaryotic egg cell presumably place heavy demands on DNA metabolism, and this may allow exogenous fragments to compete more favourably for integration into new DNA strands.

It is pointed out that in nature, as far as is known, none of the beneficial, healthy symbiotic or associative systems between eukaryotic and prokaryotic organisms involve gene transfers. The only case where gene transfer is known to occur is that of crown‐gall tumour disease–an unhealthy development.

It is concluded that although simple genes comprising short nucleotide sequences, or certain major genes for which genetic homology may exist between the two partners, may be transferred and expressed across the prokaryotic‐eukaryotic boundary, major advances may be achieved by altering the structure or expression of genes within their respective boundary limits. It is suggested that the most promising form of genetic engineering involving prokaryotic and eukaryotic genomes may be the fostering of a new, or improved, symbiosis or association of two genetically engineered partners, without actual transfers of genes between them.
THE GENECOLOGY OF LAWN WEEDS
Authors: WARWICK S. I. , BRIGGS D.
Published: May 2006

In order to investigate the hypothesis that disruptive selection is acting on Poa annua L. populations within a mosaic environment of bowling greens and flower beds, two experimental approaches were employed.

(1) Studies of samples of seedlings, raised from the seed present in soil and surface debris from the two bowling greens and one flower bed, established that in each site the seed population was more variable than the adult. This result is compatible with the notion of disruptive selection.

(2) An experiment was set up to examine the response of the two growth forms to clipping and to estimate the effectiveness of clipping as a selective force in the bowling green environment. In the control (unclipped treatment), the erect and prostrate variants differed both in total production and in their relative energy allocation to both vegetative and floral reproduction. These differences have been discussed in relation to r and K selection strategies.

Differential response to clipping was observed; the groups in descending order of relative fitness consisted of prostrate individuals from the two bowling green populations > prostrate individuals from the flowerbed populations > erect individuals from flower bed populations. Clipping appears to have two effects on the erect forms resulting in: (1) a greater percentage decrease in total dry matter production in the erect compared with the prostrate forms, and (2) a greater percentage of the dry weight produced being removed by the cut in the erect forms compared with the prostrate forms.

Coefficients of selection acting against erect plants under a regime of clipping ranged from 0.53 to 0.68. A selection coefficient of 0.77 was obtained for prostrate plants in the absence of clipping. In the light of the management of the lawns and flower beds, evidence for selection and gene flow is discussed.
THE GERMINATION AND VIABILITY OF FESTUCA VIVIPARA (L.) SM. PLANTLETS
Authors: HARMER R. , LEE J. A.
Published: May 2006

Festuca vivipara plantlets were collected from a site in the English Lake District at several dates during the summer and autumn 1976. Various germination tests showed that plantlets from the early harvests were non‐viable. Viability increased towards the end of the growing season and, at the last harvest, approximately 90% of the plantlets were capable of germinating. Plantlets showed no innate dormancy. However, the majority of plantlets were not dehisced from the panicle and establishment was largely through the collapse of the culm. Seeds of the closely related species, F. ovina, dehisced in July and exhibited a low primary dormancy. This could be broken by stratification and was lost after 2‐3 months dry storage. Plantlets retained a greater capacity than seed to germinate at low temperature (3°C) and field observations show that F. vivipara plantlets establish after culm collapse in the autumn whereas F. ovina seeds may not germinate until the following spring. However, plantlets were capable of surviving for at least 25 weeks in conditions of high relative humidity and low temperature in the laboratory, suggesting that they have the capacity to survive the winter if they do not reach a suitable substrate for establishment.
AN EXPERIMENTAL STUDY ON TWO POPULATIONS OF CHAMAENERION ANGUSTIFOLIUM (L.) SCOP. (=EPILOBIUM ANGUSTIFOLIUM L.) OCCURRING ON CONTRASTING SOILS, WITH PARTICULAR REFERENCE TO THE RESPONSE TO BICARBONATE
Authors: VAN ANDEL J. , BOS W. , ERNST W.
Published: May 2006

Two populations of Chamaenerion angustifolium occurring on contrasting soil types (alkaline v. acid) were studied with regard to mineral nutrition. Plants were grown from seeds of both populations on each of the soils and in culture solution with different levels of sodium bicarbonate.

Differentiation between the populations in a strictly ecological sense was not established. The main effects on the growth and mineral nutrition of the populations were correlated with characteristics of the root medium rather than with the origin of the seeds. Neither chlorosis under alkaline, nor toxicity under acidic conditions occurred. There were, however, some differences between the nutritional behaviour (Ca, Fe, Na) of the natural populations and their seedlings so that the overall potential of the seeds might be much wider than that of the already‐selected, natural populations. This seemed to be confirmed by the high percentage mortality in water cultures. Amongst the plants which survived some slight physiological differences appeared but not ones which influenced dry‐weight production.

It can be concluded that C. angustifolium is indifferent with regard to the soil factor pH, or better; that the species is adapted both to acid and alkaline soil. This was discussed with reference to Ca, Fe and HCO3+.