bluuebunny/crossref_metadata_2025 huggingface dataset:
DIFFERENTIAL ABAXIAL AND ADAXIAL STOMATAL RESPONSES TO INDOLE‐3‐ACETIC ACID INCOMMELINA COMMUNISL.
Authors: PEMADASA M. A.
Published: May 2006

Summary

The responses of abaxial and adaxial stomata to indole‐3‐acetic acid (IAA) were examined on isolated epidermis ofCommelina communis.IAA was remarkably effective in producing wide adaxial apertures accompanied by a massive increase in the stomatal K+content, and, therefore, eliminating the normal disparity in both the opening and K+accumulation between abaxial and adaxial stomatal cells; it also reversed the suppressive effect of abscisic acid. IAA may affect the transport of K+either directly or indirectly through its control of the proton pump. If the IAA‐induced adaxial opening and K+accumulation is a result of a stimulation of proton extrusion, then, under normal conditions, the proton pump should operate at a lower capacity in adaxial than in abaxial guard cells. Alternatively, the lack of stomatal sensitivity to IAA in the presence of Na+ions suggests a possibility that it might have a direct effect on the K+transport. In either case, as reported here, an external supply of IAA would enhance K+accumulation in adaxial guard cells. The inherent disparity in opening and accompanied K+accumulation between abaxial and adaxial stomatal cells is postulated to be a result of differences in endogenous auxin level between the two epidermes and/or of differential adaxial and abaxial sensitivity to auxin. Thus, the results indicate a hormonal basis for the differential adaxial and abaxial opening.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN NATURAL VEGETATION SYSTEMS
Authors: WHITTINGHAM J. , READ D. J.
Published: May 2006

Summary

The functional role of mycorrhizal interconnections between plants was investigated in pot experiments which were designed to simulate some of the circumstances of the regeneration niche in grassland.

Young plants of Festuca ovina L. and Plantago lanceolata L. were grown in pots in close association with adults of the same species in the mycorrhizal (M) and non‐mycorrhizal (NM) condition. 32P or nutrient solution was applied to isolated parts of mature ‘source’ plants and transport of the nutrients to younger ‘sink’ plants was examined in the mycorrhizal and non‐mycorrhizal condition. Transport was determined either by measuring 32P in, or total yield of, sink plants at sequential harvests.

Greater movement of 32P occurred into roots of mycorrhizal plants of both species. The differences were stastistically significant after only 24 h in F. ovina and after 48 h in P. lanceolata. Application of nutrient solution to source plants led to significantly greater yield in M sinks after 18 and 30 weeks.

It is concluded that direct transfer of nutrients between living source and sink plants occurs by way of connecting mycorrhizal hyphae. The significance of these observations for nutrition and survival of young plants is assessed and the broader implications for nutrient cycling in ecosystems considered.
THREE FLANDRIAN POLLEN PROFILES FROM THE TEITH VALLEY, PERTHSHIRE, SCOTLAND
Authors: LOWE J. J.
Published: May 2006

Summary

Deteriorated pollen grains have been recorded from Flandrian sediments in three sites near Callander in Perthshire, and diagrams are presented of deteriorated pollen as opposed to the overall pollen totals discussed in the previous paper. The problems of interpreting records of deteriorated pollen are discussed, a format for pollen diagrams conveying detailed information on deteriorated grains is introduced, and the palaeoenvironmental implications of the records are considered. It is shown that major changes in deteriorated pollen totals are common to all three diagrams, with low percentages in the early Flandrian, and pronounced increases in deteriorated totals coincident with the Corylus decline at each site. It is suggested that similar studies at other sites in northern Britain may prove these trends to be consistent features of Flandrian pollen diagrams.
THE ESTABLISHMENT OF THE PLASTID THYLAKOID SYSTEM
Authors: WHATLEY JEAN M. , HAWES C. R. , HORNE J. C. , KERR J. D. A.
Published: May 2006

Summary

Making use of serial thin sections of conventionally fixed tissue we have constructed a model of the thylakoid system in a pre‐granal, dividing chloroplast. The three‐dimensional configuration of this plastid is compared with the thylakoid configurations seen in 1μm thick sections of the zinc iodide‐osmium impregnated tissue which were examined with a high voltage electron microscope. A comparison has also been made between the differential staining characteristics of the various membranous invaginations, vesicles and tubules which are frequently associated with the plastid envelope and which may play a part in development of the thylakoid system.
PATTERNS OF TURNOVER OF FRUCTANS IN LEAVES OF DACTYLIS GLOMERATA L.
Authors: POLLOCK C. J.
Published: May 2006

Summary

The patterns of labelling of fructans with different molecular weights and of fructose residues within chains were determined after cold‐grown plants of Dactylis glomerata L. were fed 14CO2. The coincidence of fructan mobilization and chain elongation, together with the occurrence of asymmetry in the labelling of individual chains, was taken as evidence for reversible transfer of terminal fructose residues between fructan chains during accumulation. These patterns are discussed in relation to the role of fructans in winter growth and survival in temperate grasses.
THE DEVELOPMENT OF MYCORRHIZAL POPULATIONS ON POT‐GROWN SEEDLINGS OF EUCALYPTUS ST‐JOHNII R.T. BAK
Authors: CHILVERS G. A. , GUST L. W.
Published: May 2006

Summary

The development of a population of mycorrhizas on the root system of a pot‐grown Eucalyptus seedling has many of the characteristics of a disease epidemic. For example, the number of mycorrhizal apices tends to increase exponentially in the early stages. The disposition of these mycorrhizal apices is non‐random, a fact which should engender care when sampling during field surveys. The final pattern of distribution of mycorrhizal apices within the root system reflects the degree of pre‐infective ectotrophic spread, the frequency and location of primary infection events, the perpetuation of mycorrhizal apices by forward growth, the extent to which they proliferate by branching, and the contribution of later secondary infections from mycorrhiza‐derived inoculum. The relative importance of these different processes is determined, as in a plant disease, by interaction between prevailing fungal, plant and environmental factors. The importance of inoculum availability and the capabilities of the fungus with respect to different regions of the root surface are stressed. The different modes of origin of mycorrhizal apices must be taken into account in any studies which seek to understand the mechanisms involved in conversion of normal root apices into mycorrhizas.
COBALT AND THE CONTRIBUTION OF CROWN AND LATERAL NODULES TO NITROGEN FIXATION OF LUPINUS ANGUSTIFOLIUS L.
Authors: RILEY IAN T. , DILWORTH M. J.
Published: May 2006

Summary

The contribution of crown and lateral nodules to the nitrogen supply of inoculated cobalt deficient and sufficient narrowleaf lupin (Lupinus angustifolius L.) was studied in a glasshouse experiment using cobalt‐deficient Lancelin sand. As found earlier, cobalt deficient plants bore more lateral nodules but fewer crown nodules, than normal plants and the nitrogen fixing ability of the deficient plants improved throughout the growth period. This improved nitrogen fixing ability resulted solely from the increased lateral nodulation of cobalt deficient plants. Nitrogenase specific activity of the lateral nodules did not improve with time and crown nodule activity fell to effectively zero.
FLORAL BIOLOGY AND BREEDING SYSTEM OF STERCULIA CHICHA ST. HIL. (STERCULIACEAE)
Authors: TARODA NEUSA , GIBBS P. E.
Published: May 2006

Summary

The neotropical, monoecious, forest species Sterculia chicha has been shown to have flowers which are adapted for pollination by Diptera, such as medium‐sized species of the sapromyo‐philous genera Acroglossa, Cachliomya, Gaemnochaetopsis, Ornidia and Parasarcnphaga. Controlled pollination experiments show that the species is self‐incompatible. The fact that pollen tube growth proceeds to the ovule following both compatible and incompatible pollinations suggests that the incompatibility mechanism is based on the non‐fusion of gametes in the embryo sac, as in the Theohroma‐type, originally known only in the related Theobroma cacao.
PLANT‐INDUCED CHANGES IN THE RHIZOSPHERE OF RAPE (BRASSICA NAPUS VAR. EMERALD) SEEDLINGS
Authors: HEDLEY M. J. , WHITE R. E. , NYE P. H.
Published: May 2006

Rape plants that were grown in thin layers of 32P‐labelled Begbroke sandy loam (initial pH 6.1) attained such high root densities (> 90 cm cm−3) that after c. 14 days, all the soil volume became rhizosphere soil. At this time, the rhizosphere pH began to decrease and the quantity of plant available P in the rhizosphere soil, as measured by the L value, exceeded the isotopically exchangeable soil P (E value), determined on samples of incubated but unplanted soil. The P concentration of the rhizosphere soil solution dropped to a minimum of 0.6 μM at 14 days, and remained low, but the phosphatase activity of the rhizosphere soil increased to 10 times that of the control soil after 35 days.

In an identical experiment, after 20 and 41 days of growth, organic P (Po) and inorganic P (Pi) in the control and rhizosphere soils were fractionated into the following forms: that extractable by an anion‐exchange resin, 0.5 M NaHCO3 (pH 85), 0.1 M NaOH, 1 m NaOH, 1 m HCl and residual P. Fractionation of the soil P indicated that during the first 21 days, when the rhizosphere pH did not decrease, only resin Pi 0.5 m NaHCO3 Pi and 0.1 m NaOH Pi were significantly depleted by plant uptake. After 41 days, however, when the rhizosphere pH had fallen to 5.3, in addition to depletion of resin Pi 0.5 m NaHCO3 Pi and 0.1 m NaOH Pi there was substantial depletion of acid‐soluble forms of soil Pi and residual P. It is suggested that acidification of the rape rhizosphere (Parts I and II) led to the dissolution of acid‐soluble forms of Pi that were not exchangeable with 32P.

In these experiments, there was no evidence for significant hydrolysis of soil Po. Indeed, there was a slight increase in Po in the rhizosphere soil due to the accumulation of fine root debris and microbially immobilized Pi. A possible combination of processes leading to the solubilization of soil P in the rape rhizosphere is proposed.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS
Authors: MACFARLANE J. D. , KERSHAW K. A.
Published: May 2006

The potential control by temperature and moisture of the movement of glucose from the phycobiont in Collema furfuraceum, Peltigera polydactyla and Peltigera rufescens is examined. The ratio of labelled mannitol to labelled glucose after exposure to 14CO2 is used as a measure of the amount of glucose transported and converted to mannitol in the lichen thallus over a range of experimental temperatures and levels of thallus hydration. The results show that temperature has little effect on the proportion of the total label appearing in mannitol except at 5°C. This is interpreted as a minimum temperature requirement for the conversion of glucose to mannitol within the mycobiont. The effect of thallus hydration, however, shows that in Peltigera polydactyla the major movement of fixed carbon from the phycobiont to the fungal partner occurs at, or close to, full thallus saturation. Below 300% thallus moisture by weight the amount of label appearing in mannitol declines sharply. Conversely, in Collema furfuraceum and Peltigera rufescens, transport of glucose continues at a constant rate down to very low levels of thallus hydration.

These results are discussed in relation to our previous findings using Peltigera praetextata, and in relation to the balance of total photosynthate between the lichen symbionts during a drying cycle. It is evident that the rate of transport of glucose is closely controlled by the level of thallus hydration which in turn correlates with the xeric or mesic preference of each species. Alternate wetting and drying cycles effectively ensure that each biont obtains an adequate supply of the fixed carbon resources, thus maintaining the integrity of the lichen.
OXYGEN EXCHANGE WITH THE LACUNAE AND ACROSS LEAVES AND ROOTS OF THE SUBMERGED VASCULAR MACROPHYTE, LOBELIA DORTMANNA L.*
Authors: SAND‐JENSEN KAJ , PRAHL CLAUS
Published: May 2006

The oxygen dynamics of Lobelia dortmanna were examined by continuous oxygen measurements in the lacunae and in the water around leaves and roots during light/dark cycles. Lobelia exchanges about six times more oxygen over the root than the leaf surface. The exchange rates per unit of surface area are two or three times higher across roots than leaves in accordance with a similar difference in permeability constants. The delay in reaching constant rates of exchange across roots is about 45 min after switching to dark and about 25 min after switching to light. This delay corresponds to the time necessary to change the oxygen concentration in the lacunae to a new steady state gradient with the water around roots. The oxygen pools in lacunae and root‐water change at the same rate at equilibrium. During incubation in a closed system it is necessary to correct for changes in the lacunal oxygen pool when it is significant relative to the oxygen pool in the external water. The lacunae of Lobelia are an effective pathway for gas movements between leaves and sediment. The extensive lacunae, and the diffusional barrier for gases in Lobelia, should facilitate recycling of oxygen, and probably carbon dioxide, within the plant‐sediment system.
THE ADVANCEMENT INDEX VINDICATED
Authors: SPORNE KENNETH R.
Published: May 2006

In a recent publication, Muller has listed those families whose pollen can be recognized in the fossil record. Those recorded as being in existence before the Palaeocene have an average advancement index which is significantly lower than that of the present‐day world flora, while those which appeared only after the Oligocene have a significantly higher one. Statistical analysis shows that many primitive characters are more abundant in the early arrivals than in the present‐day world flora. Muller's data, therefore, provide strong support for the concept of an advancement index calculated on the basis of statistically correlated characters.
EARLY‐AND MID‐FLANDRIAN ENVIRONMENTAL HISTORY OF THE BRECON BEACONS, SOUTH WALES
Authors: WALKER M. J. C.
Published: May 2006

Pollen‐stratigraphic data are described from two sites on the northern face of the Brecon Beacons escarpment in South Wales, U.K. Pollen percentage, pollen concentration and deteriorated pollen diagrams are presented which contain details of vegetational changes in this part of Britain from the time period immediately following the wastage of the Loch Lomond Advance glaciers around 10000 radiocarbon years ago, until the establishment of oak and alder woodland in the mid‐ Flandrian some 4000 years later. An initial phase of juniper scrub was followed by the expansion of birch woodland over much of the area, and these forests were subsequently invaded by large numbers of hazel. Quercus, Ulmus and Pinus were present throughout the mid‐Flandrian, but increasing climatic wetness, possibly beginning around 7000 radiocarbon years ago, led to the decline of elm, pine and birch as woodland components in this part of South Wales, and to the expansion of Quercus and particularly Alnus. These vegetational changes are discussed in terms of vegetational developments at other sites in upland Wales and western Britain.
POTENTIATION OF SULPHUR DIOXIDE INDUCED INHIBITION OF PROTEIN SYNTHESIS BY DESICCATION
Authors: OKOLOKO G. E. , BEWLEY J. DEREK
Published: May 2006

In vivo protein synthesis in the gametophyte apices of Tortula ruralis (Hedw.) Gaertn, Meyer and Scherb was studied in relation to desiccation and sulphur dioxide stress. The latter was applied in aqueous form, at three levels (0.1, 0.5 and 1.0 mol m−3), while two drying regimes (slow and rapid) were employed. Desiccation by itself caused only a slight inhibition of protein synthesis following 30 min rehydration. SO2 at 0.1 mol m−3 was stimulatory to protein synthesis when applied alone (20%) or in combination with slow desiccation (14%). Combining 0.1 mol m−3 SO2 with rapid desiccation not only abolished this stimulation but further reduced protein synthesis to 70% of control. SO2 at both 0.5 and 1.0 mol m−3 was inhibitory to protein synthesis in the absence of desiccation. Desiccation applied after pretreatment in 0.5 mol m−3 and 1.0 mol m−3 SO2 caused a potentiation of SO2 inhibition, rapid desiccation having a stronger effect in this regard than slow desiccation.
TRANSPORT, TRANSLOCATION AND METABOLISM OF 14C‐PHOTOSYNTHATES AT THE HOST‐PARASITE INTERFACE OF PISUMSATIVUM AND ERYSIPHE PISI
Authors: MANNERS J. M. , GAY J. L.
Published: May 2006

Haustorial complex, mycelial and host (leaf without mycelia) samples were obtained from leaves of Pisum sativum infected with Erysiphe pisi either immediately following a 20 min exposure to 14CO2 (‘pulse’) or after a further 20 h ‘chase’ in 12CO2. After the ‘pulse’, labelled ethanol‐soluble sugars (glucose, fructose and sucrose) and mannitol predominated in the host and mycelial fractions respectively and lipids (mainly triglycerides) and an ethanol‐insoluble glucan (not α‐1, 4 linked) contained most of the 14C in the haustorial complexes. Ethanol‐soluble carbohydrates contained only 3% of the total 14C in the haustorial complexes with sucrose and glycerol as the major components. After the ‘chase’, the total 14C in host and mycelium declined but the proportions in starch or glycogen, protein, cell wall and nucleic acid fractions increased. Total 14C in haustorial complexes increased but that contained in sucrose and glycerol decreased and that in mannitol increased. During both ‘pulse’ and ‘chase’, the quantity of 14C in the haustorial complexes was small compared with that in the mycelial and leaf fractions.

These results indicate that transport of host sugars to the fungus is mediated by haustoria. Sucrose and glycerol are either translocates or metabolic intermediates in this process and mannitol is the major primary sink of the fungus. Glycogen and other macromolecules are produced at a later stage in the fungus. Polysaccharides and lipids are important sinks at the host‐haustorial interface. These results are discussed in relation to the regulation of transport at the host‐parasite interface.
Studies ON MUCORALEAN MYCOPARASITES
Authors: EVANS G. H. , COOKE R. C.
Published: May 2006

Diffusible, non‐volatile factors from hyphae of Mortierella vinacea and Mycotypha microspora directed growth of Piptocephalis fimbriata germ tubes towards them. Such factors were also present in Y‐phase cells of Mycotypha microspora but were not released from them. They were absent from hyphae of Circinella mucoroides which was nevertheless susceptible to attack by Piptocephalis fimbriata. Growth‐directing factors were extracted from sporelings of Mortierella vinacea and partially characterized. They were hydrophilic, thermo‐labile, positively charged and appeared to be either proteinaceous or bound to proteins. The consequences of directed growth of Piptocephalis fimbriata towards its hosts are discussed in relation to the process of mycoparasitism.
COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.
Authors: LACK ANDREW J.
Published: May 2006

If competition for pollinators is an important influence on populations of Centaurea scabiosa and C. nigra sensu lato one of the characters most likely to be affected is flowering time. Observations were made on the flowering period of several populations of the two species growing sympatrically and in isolation, and on plants from these and further populations transplanted into the Botanic Garden.

Conclusions from the study are:

Where C. scabiosa and C. nigra grow sympatrically, C. nigra flowers slightly later than C. scabiosa but there is a considerable period of overlap.

Populations of C. scabiosa differ slightly in flowering time, but there are large differences between C. nigra populations growing in isolation from C. scabiosa.

In many populations of both species there are large differences in flowering time between individuals.

The differences observed between plants in the field are maintained in cultivation.

Small differences are apparent between years and between aspects.

The large range of flowering time seen in C. nigra may be partly attributable to differences between ssp. nigra and ssp. nemoralis and hybridization between them, but local ecological factors are important influences on some populations. Competition for pollinators between C. scabiosa and C. nigra may maintain the difference in flowering time between the two species in some areas.
THE LATE DEVENSIAN VEGETATIONAL HISTORY OF THE WHITLAW MOSSES, SOUTHEAST SCOTLAND
Authors: WEBB J. A. , MOORE P. D.
Published: May 2006

Late Devensian Late‐glacial deposits are described from the Whitlaw Mosses, near Melrose, Roxburghshire (now Borders). Pollen diagrams and macro fossil lists are given for the bottom sediments of Beanrig Moss and Blackpool Moss, two small fens lying in hollows in the undulating boulder clay of Tweeddale. The succession of taxa through the sediments indicates interstadial conditions followed by stadial conditions.

Critical determinations of certain microfossil and macrofossil indicator taxa, permits the identification of certain plant communities. These are as follows: Communities identified from within the stadial are;

(1) bare‐ground communities of open, wind‐exposed areas with Artemisia cf. norvegica and Papaver spp. of the section scapiflora as the main indicator types;

(2) bare‐ground communities in sheltered areas of long snow‐lie with such species as Salix herbacea, Polytrichum norvegicum and P. alpinum.

The main communities identified in the interstadial are as follows:

(1) scrub with abundant Juniperus and sparse tree birches (e.g. B. pubescens);

(2) base‐rich, well‐drained short turf with abundant Helianthemum;

(3) damp, tall‐herb meadows in which Rumex acetosa is important;

(4) dwarf‐shrub heath with Dryas octopetala and Betula nana;

(5) open‐ground communities with Artemisia spp. and Hippophaë.

Communities identified from both the stadial and interstadial are:

(1) short‐turf calcareous flushes or springs with Selaginella and various mosses;

(2) fens and marshy lake margins with, e.g. Homalothecium nitens.

Several taxa have not hitherto been found in the Late Devensian of the British Isles, amongst which are Artemisia cf. campestris, A. sect. dracunculus, A. cf. maritima s.l., Gypsophila repens/fastigiata, Hedysarum cf. hedysaroides, Minuartia rubella, Rhacomitrium cf. canescens and Vactinium vitis‐idaea. The identification of the pollen grains and macro fossils is discussed and comments are made on the biogeographical and ecological implications of the records, especially of those species which are now no longer part of the British flora.
EVALUATION OF PUTRESCINE AS A BIOCHEMICAL INDICATOR OF THE POTASSIUM REQUIREMENTS OF LUCERNE
Authors: SMITH G. S. , LAUREN D. R. , CORNFORTH I. S. , AGNEW M. P.
Published: May 2006

The diamine putrescine was found to be a sensitive indicator of potassium requirements of lucerne. There was an inverse relationship between the concentration of putrescine and that of potassium and the lowest concentrations of putrescine occurred only in plants which produced in excess of 90 % of the maximum dry matter yield. Using the point where the concentration of putrescine reached a minimum as an indication of healthy growth, it was established that a potassium concentration of 3 % of the dry matter of the leaves would be required for optimum dry matter production of lucerne at the early bloom stage of development; the corresponding value in the stem was estimated to be 5 % of the dry matter. While a low supply of magnesium enhanced the accumulation of putrescine in potassium deficient plants, potassium was shown to be the major factor influencing the concentration of putrescine. The advantages of using the concentration of putrescine as a basis for estimating the potassium requirements of lucerne are discussed in relation to the difficulties encountered with the conventional critical levels concept.
COMPARISONS BETWEEN THE GROWTH RATES OF MYCORRHIZAS, UNINFECTED ROOTS AND A MYCORRHIZAL FUNGUS OF EUCALYPTUS ST‐JO HNII R. T. BAK
Authors: CHILVERS G. A. , GUST L. W.
Published: May 2006

On soil‐grown seedlings in pots, and on pure‐cultured seedlings in bottles, mycorrhizas grew at approximately one‐fifth the rate of equivalent uninfected apices. It was seen in bottle cultures that, because the growth rates of primary and secondary roots usually exceeded the growth rate of the fungus, only a few of these apices came into contact with the inoculum. The slower growth rate, later appearance and the positioning of tertiary root apices, led to many of these becoming invested by fungal mycelium and a considerable proportion of them became converted to mycorrhizas. Mycorrhizal apices were seen to remain active for longer periods, and to grow at more constant rates, than uninfected apices. Possible reasons for this are discussed.
FACTORS AFFECTING BUD INDUCTION IN THE MOSS HYOPHILA INVOLUTA
Authors: RAHBAR KAVITA , CHOPRA R. N.
Published: May 2006

Protonema of Hyophila involuta remains bud‐free on basal medium (Knop's Major and Nitsch's Minor salts). Auxins, gibberellic acid, abscisic acid, chelates, vitamin B12, activated charcoal, coconut milk; and altered hydration, pH, temperature, light intensity and duration do not induce buds. Cytokinins initiate multicellular gemmae on the protonema. Buds are induced only by the interaction of IAA with kinetin or DMAAP, and these develop into normal gametophores.
PRODUCTION OF HAPLOID PLANTS FROM ANTHER CULTURES AND SECONDARY EMBRYOIDS OF WINTER OILSEED RAPE, BRASSICA NAPUS SSP. OLEIFERA
Authors: CHIANG SHIONG LOH , INGRAM D. S.
Published: May 2006

Following anther culture of a range of cultivars of winter oilseed rape, Brassica napus ssp. oleifera, approximately 15 to 70 % of the resulting embryoids developed directly into plants. The rest grew abnormally in culture, giving rise to abnormal plantlets which formed large numbers of secondary embryoids on their surfaces (up to 100 per abnormal plantlet). The secondary embryogenic plantlets were haploid, and the secondary embryogenic potential was maintained for over a year in culture without diminution. More than 70% of the secondary embryoids, and the plants regenerated from them, were haploid. These results are discussed in connection with the possibility of producing large numbers of haploid plants throughout the year for breeding purposes and for the production of novel disease resistant plants through genetic manipulation in culture.
CRYSTALLINE STRUCTURE OF PLANT EPICUTICULAR WAXES DEMONSTRATED BY CRYOSTAGE SCANNING ELECTRON MICROSCOPY
Authors: JEFFREE C. E. , SANDFORD A. P.
Published: May 2006

The epicuticular wax structure of several species was investigated, using plant material frozen rapidly in liquid nitrogen, and observed by means of a cryogenic specimen stage fitted to a scanning electron microscope. The wax was found to have a crystalline fine structure identical with that observed using conventional techniques for the preparation of plant surface specimens for transmission and scanning electron microscopy. The findings are discussed in relation to recent reports that the waxes are amorphous at low temperatures, and that the generally‐accepted crystalline fine structure of plant epicuticular waxes is an artefact of conventional specimen preparation procedures.
NIACIN BIOSYNTHESIS IN LEAF DISCS AND SEEDLINGS OF CATTLEYA SKINNERI (ORCHIDACEAE)
Authors: COOPER JAN L. , HILTON BRENDA L. , ARDITTI JOSEPH , TARR JOHN B.
Published: May 2006

Summary

Seedlings and leaf discs of Cattleya skinneri incorporated label from 14C‐ and 3H‐labelled tryptophan into niacin. Label from [14C]glycerol and[14C]aspartate was not significantly incorporated into the vitamin.
THE ROLE OF ORGANIC ACIDS IN ZINC TOLERANCE IN DESCHAMPSIA CAESPITOSA
Authors: THURMAN D. A. , RANKIN J. L.
Published: May 2006

Summary

The relationship between metal tolerance and accumulation of organic acids has been investigated using zinc‐cadmium tolerant and non‐tolerant clones of Deschampsia caespitosa. Zinc significantly increased citrate and malate levels in the roots of the tolerant clone but had no significant effect on the levels of these acids in the roots of the non‐tolerant clone. Cobalt, copper, mercury and nickel had no significant effect on the levels of these acids in either clone. A number of enzymes involved in organic metabolism were extracted from the roots of the two clones, but no difference in their sensitivities to zinc was found. Changing the citrate levels in the roots by growing plants under different iron regimes did not change tolerance indices. Grown in the presence of zinc, both clones contained enough citrate and malate to complex only approximately half of the zinc present in their roots.
PHYTOLECTINS FROM THE NITROGEN‐FIXING LICHEN PELTIGERA HORIZONTALIS: THE BINDING PATTERN OF PRIMARY PROTEIN EXTRACT
Authors: PETIT PATRICE
Published: May 2006

Summary

A protein fraction containing phytolectins was isolated from the nitrogen‐fixing lichen Peltigera horizontalis. These lectins were thermostable, truly non‐specific and were more effective on human erythrocytes A, B and O than concanavalin A. Phytolectins originate from the mycobiont and do not bind any of the freshly isolated phycobionts tested, but with slight differences bind the cultured phycobionts isolated from three Peltigera spp. It is suggested that the production of phytolectins may be characteristic of the lichen symbiosis and that they may be involved in the recognition or initial interactions between compatible lichen symbionts.
THE FINE STRUCTURE OF EPIDERMAL CELL MUCILAGES OF ROOTS
Authors: FOSTER R. C.
Published: May 2006

Summary

Transmission electron microscope studies of epidermal cell mucilages of roots of various species show that the nature of mucilage and the boundaries between the cell wall and the soil depend on the age of the epidermal cells concerned and the degree of bacterial lysis experienced.
CHANGES IN CELL POPULATION KINETICS IN AN OPEN MERISTEM DURING ROOT GROWTH
Authors: CLOWES F. A. L.
Published: May 2006

Summary

The problem of root meristems, previously considered to exchange cells between the stele and the cap as well as between cortex and cap, has been solved by using DNA‐labelling and stathmokinetic methods to observe the change in behaviour of the meristem as the primary root ages in Cucurbita pepo L.

The stelar pole is quiescent and can contribute few, if any, cells to the cap. During early growth the tiers of cells of the columella meristem are intermittently quiescent and active. This causes the highest average rate of mitosis in the cap to occur in a tier of the columella that is not adjacent to the stelar pole. It also interrupts the patterns of cells in the columella to form up to four complexes of cells along its length. As the root ages, rates of mitosis become generally lower, except in the quiescent stelar pole, and fewer tiers of the columella stay meristematic. The proximal tier of the columella, adjacent to the stelar pole, now acquires the highest rate of mitosis in the meristem. This simplifies the columella pattern, but the meristem never becomes closed because no quiescent buffer establishes itself between the stele and the central cap meristem and so a boundary between the cortex and peripheral cap meristems never becomes stabilized.
THE GENETIC CONTROL OF A NON‐RADIATE CONDITION IN SENECIO SQUALIDUS L. AND SOME OBSERVATIONS ON THE ROLE OF RAY FLORETS IN THE COMPOSITAE
Authors: INGRAM RUTH , TAYLOR LYNN
Published: May 2006

Summary

The genetic control of a non‐radiate mutant of Senecio squalidus has been found to be identical with the genetic control of the non‐radiate character in S. vulgaris. The biological effects of the same gene in the two species are discussed. The morphology of the radiate florets in the heterozygotes of 5. squalidus has been investigated, and some implications for the evolution of protogyny are discussed.
ULTRASTRUCTURE OF TALL FESCUE (FESTUCA ARUNDINACEA SCHREB. CV. S170) CELLS FIXED WHILE EXPOSED TO LETHAL OR NON‐LETHAL EXTRACELLULAR FREEZING
Authors: PEARCE R. S.
Published: May 2006

A freeze‐substitution method was used to fix tissues (from roots, leaf laminae and leaf meristem of tall fescue) subjected to lethal or non‐lethal extracellular freezing, which induced intracellular dehydration. There was no evidence of direct (tearing) damage by extracellular ice. In the tissues fixed while so frozen, the cytoplasm was coherent and the plasmalemma was present but the trilamellar structure of membranes was not always evident, e.g. it was usual in thylakoid membranes but was rare in the peripheral membranes of chloroplasts. An abnormal feature was the presence of strongly osmiophilic material, often associated with membranous structures and possibly of more than one type. The appearance of the frozen tissues and the amount of strongly osmiophilic material did not vary with hardiness. When a lethal freezing treatment was given, strongly osmiophilic material occurred at the same sites in both frozen and thawed tissues, but it was largely absent from thawed non‐lethally frozen tissues, though present in the same material before thawing. The occurrence of intact plasmalemmata in tissues fixed while lethally frozen and of strongly osmiophilic material in tissues fixed while non‐lethally frozen, are in contrast to some other recent work.
ROOT CONTRACTION IN TRANSPIRING PLANTS
Authors: FAIZ S. M. A. , WEATHERLEY P. E.
Published: May 2006

Experimental data published previously (Faiz and Weatherley, 1977) emphasized the existence of considerable hydraulic resistance in the perirhizal soil of rapidly transpiring plants. This was evident when soil water potential (Ψs in the root zone was as high as −2 or −3 bars. In a further paper (Faiz and Weatherley, 1978) the hypothesis was put forward that it is the soil‐root interface which presents a high resistance to the flow of water through the soil‐plant system. This resistance, it was thought, could increase as a result of contraction of stressed‐roots, with the formation of vapour gaps between soil and root.

In this paper we demonstrate that the root tissues may contract by as much as 25 % of their turgid volume when the water potential of the leaves (Ψl) falls to around −15 bars. Under such conditions the extensive formation of vapour gaps would be expected and a reduction of water stress should therefore follow if the gaps could be closed mechanically. Such closure was attempted by either squeezing or vibrating the soil mass containing the root system. Both of these treatments led to a temporary reduction in water stress in the plants and the existence of vapour gaps was thus supported.
EFFECT OF LOCAL CONCENTRATIONS OF ACETIC ACID AROUND BARLEY ROOTS ON SEEDLING GROWTH
Authors: GUSSIN E. J. , LYNCH J. M.
Published: May 2006

Acetic acid was applied to localized regions of barley roots. Treating a single root tip with a small concentration (5 mol m−3) of the acid stimulated root and shoot growth. No stimulation was observed when more than one root was treated or with greater concentrations of the acid. Treating 2 cm lengths along the root axis distal to the root tip region (2 cm long) gave a greater inhibitory effect on root and shoot growth than the corresponding root tip treatment. Treatment of tips and 2 cm lengths resulted in some compensatory growth in the non‐treated roots.
RELATIVE PERFORMANCE OF CONIFER POPULATIONS IN VARIOUS TESTS FOR SENSTIVITY TO SO2, AND THE IMPLICATIONS FOR SELECTING TREES FOR PLANTING IN POLLUTED AREAS
Authors: GARSED S. G. , RUTTER A. J.
Published: May 2006

The sensitivity of five Pinus and three Picea populations to SO2 was compared in various types of fumigation experiment (i) > 9 months at 200 μg m−3, (ii) 6 h at 8000 μ m−3, (iii) 9 weeks at 800 μg m−3, (iv) 12 h (overnight) at 17 000 μg m−3 preceded by either 42 days or 6 h at 800 μg m−3. To complement the fumigation experiments the growth of four of the populations was compared at a polluted (London) and a control site (Silwood Park).

There was no relationship between the relative sensitivity of the populations to 200 μg m−3(measured as relative growth rate) and the degree of acute injury at 8000 μg m−3. In general the populations of Picea were more sensitive to low concentrations of SO2 but more resistant to acute injury than those of Pinus. At 800 μg m−3 the initial symptoms were of acute injury, but later whole needles died and were shed. Populations prone to the initial injury were not necessarily sensitive to the later type, and vice versa.

Leaf fall was accelerated and dry wt gain depressed at the polluted site compared with the control and these effects were much greater in Picea than in Pinus populations.

It is concluded that the order of sensitivity obtained in screening experiments depends largely on the conditions used, and that short‐term experiments with high concentrations of SO2 cannot be used to predict the responses of conifers to low concentrations of SO2 in the field.
ASPECTS OF RAINFOREST REGENERATION
Authors: CHANDLER G. , GOOSEM S.
Published: May 2006

Measurements in two sub‐tropical rainforests demonstrated that (i) in one rainforest succession, total soil phenols varied dramatically throughout the study year with soils from the ‘climax’ rainforest exhibiting highest phenol levels, the nature of these phenolic compounds was not investigated; (ii) in the other rainforest succession, the 55‐year‐old regrowth exhibited highest total phenols, but the level of condensed tannins increased throughout the succession. The highest level of nitrification was observed in soils containing highest total phenols but the addition of ferulic acid decreased nitrification. Studies on Argyrodendron trifoliolatum demonstrated that addition of the phenol, caffeic acid, to nutrient media enhanced leaf concentrations of Zn, Mn and P. Increasing light intensities, however, decreased foliar concentrations of Fe, Zn, Mn and P but had no effect on Ca or N. Plants raised on ammonium −N exhibited higher levels of Fe, Zn, Mn and P than those raised on nitrate–N.

Glasshouse trials showed that at low light intensities omission of N, P and N + P did not dramatically enhance leaf phenol production. Almost invariably, an increase in light intensity increased leaf phenols but only one of the four species examined (Syzygium floribundum) exhibited marked responses to nutrient deficiencies at high light intensities, with the omission of nitrogen leading to highest leaf phenols.
THE UPTAKE AND TRANSLOCATION OF TRI‐AND HEXA‐VALENT CHROMIUM AND EFFECTS ON THE GROWTH OF OAT IN FLOWING NUTRIENT SOLUTION AND IN SOIL
Authors: MCGRATH S. P.
Published: May 2006

Tri‐ and hexa‐valent chromium (Cr) were both absorbed by oat and were equally toxic when supplied at 2 to 200 μM in nutrient solution. The proportion of Cr translocated to the shoots was similar, regardless of the form supplied to roots.

Adding 750 μg of hexa‐valent Cr per gram of either acid or alkaline soil resulted in large, toxic concentrations of Cr in soil solution. The same amount of trivalent Cr gave smaller Cr concentrations in the soil solution, with more Cr present from acid than from alkaline soils. Nevertheless, increased uptake of Cr and reduced plant yields occurred on both soil types with added trivalent Cr.
MYCORRHIZAL ASSOCIATIONS IN SOME WOODLAND AND FOREST TREES AND SHRUBS IN TANZANIA
Authors: HÖGBERG P.
Published: May 2006

The mycorrhizal associations in 47 indigenous Tanzanian trees and shrubs, mainly from less humid areas, were studied. Forty species were found to be endomycorrhizal. One,Uapaca kirkianaMull. Arg. (Euphorbiaceae) was ectendomycorrhizal while six, fourBrachystegiaspp.,Julbernardia globiflora(Benth.) Troup. (Caesalpiniaceae) andMonotes elegansGilg. (Diptero‐carpaceae), were ectomycorrhizal. The results demonstrated a dominance of endomycorrhizal species, which is typical for the tropics and is further reinforced by taxonomic considerations. However, in the Miombo (Brachystegia–Julbernardia) woodlands, a major ecosystem in East and South Central Africa, ectomycorrhizal trees predominate in volume. In three other ecosystems studied – aCombretumwoodland, a groundwater forest and a semi‐evergreen forest–ectomycorrhizal species were absent or almost absent. Nodulated leguminous species appeared to be more common in the fire‐induced woodlands than in the closed forests.
ULTRA‐STRUCTURE AND MICRO ANALYSIS OF THE POLYPHOSPHATE GRANULES OF THE ECTOMYCORRHIZAS OF FAGUS SYLVATICA
Authors: STRULLU D. G. , HARLEY J. L. , GOURRET J. P. , GARREC J. P.
Published: May 2006

Evidence is presented that the granules visible in the vacuoles of the hyphae of the sheath of Fagus sylvatica mycorrhiza in electron microscope (EM) preparations contain phosphorus and calcium. Little phophorus or calcium is present in the clear regions of the hyphal vacuoles. Calcium but not phosphorus is present in considerable quantity in the hyphal walls of the fungal sheath.
ULTRASTRUCTURAL STUDIES ON ARCHEGONIAL DEVELOPMENT IN THE MOSS PHYSCOMITRIUM CYATHICARPUM
Authors: LAL M. , KAUR G. , CHAUHAN E.
Published: May 2006

Oogenesis in the moss Physcomitrium cyathicarpum is characterized by a copious secretion of mucilage into the venter of the archegonium due to the extrusion of numerous vesicles from the egg. Maturation of the egg is not attended by any special event in the nucleus. The cell organelles become redistributed into zones as the egg matures before fertilization.
RHYTHMICITY IN NITRATE REDUCTASE ACTIVITY IN WHEAT EMBRYOS DURING GERMINATION
Authors: DISA SUHAS , GUPTA ADITYA , RAJASEKHAR V. K. , GUHA‐MUKHERJEE SIPRA , SOPORY SUDHIR K.
Published: May 2006

Nitrate reductase (NR) activity, induced by germination in KNO3 showed a strong rhythmicity during the early stages of germination of wheat embryos. Peaks of activity occurred approximately every 12 h. There was no relationship between the amounts of nitrate in the embryos and enzyme activity. The fluctuations in enzyme activity did not appear to be due to reversible inactivation of the enzyme. Some evidence suggests that the fluctuations in enzyme activity may result from a more rapid degradation of enzyme during the decreasing phase of the rhythm.
SURVIVAL OF MYCORRHIZA FORMED BY CENOCOCCUM GEOPHILUM FR. IN DRY SOILS
Authors: PIGOTT C. D.
Published: May 2006

Seedlings and 2‐year old saplings of Tilia cordata growing in the shade on sandy‐textured soils can survive periods when the water potential of the soil decreases to −18 to −55 bars. Their mycorrhiza formed by Cenococcum geophilum is shown to remain alive. Measurement of rates of water‐loss from seedlings in similar conditions decreases from 16.0 to 26.2 mg h−1 when the soil is wet, to 4.1 to 4.6 mg h−1 when the soil is dry. Calculation of the volume of the mycorrhiza shows that its water content would support transpiration for periods not exceeding 1 h. Survival of the mycorrhiza through long periods of drought is apparently related to the ability of the fungal partner to withstand desiccation.
ACCUMULATION OF CALCIUM OXALATE IN THE MANTLE OF ECTOMYCORRHIZAL ROOTS OF PINUS RADIATA AND EUCALYPTUS MARGINATA
Authors: MALAJCZUK N. , CROMACK K.
Published: May 2006

Calcium oxalate crystals occur in the mantle of ectomycorrhizal roots of Firms radiata and Eucalyptus marginata. Dense concentrations of these crystals were observed in association with the fungal symbiont of both tree species. It is suggested that oxalate production may enhance nutrient uptake by ectomycorrhizal roots of forest species growing in nutrient impoverished soils. Concentrations of Ca, S, K and P were similar in mycorrhizal root masses of P. radiata and E. marginata.
ULTRASTRUCTURE OF PTEROSPORA ANDROMEDEA NUTTALL AND SARCODES SANGUINEA TORREY MYCORRHIZAS
Authors: ROBERTSON DIANE C. , ROBERTSON J. A.
Published: May 2006

Mycorrhizas of Pterospora andromedea Nuttall and Sarcodes sanguinea Torrey were examined with light and electron microscopes. Both plants were found to have a multi‐layered fungal sheath covering the surface of their roots and a Hartig net surrounding the epidermal cells but not penetrating the underlying cortex. Dolipore septa are present in the fungi of both plants. Individual determinate hyphae enter each epidermal cell through the radial wall which is oriented toward the tip of the root. As they penetrate, the epidermal cell wall appears to invaginate forming a fungal peg. The wall of the peg produces numerous protuberances similar to those found in transfer cells. In the combined fungal‐epidermal cell wall of the fungal peg the two walls do not remain distinct and it is impossible to be certain if both continue to the tip. Eventually, the tip of the fungal peg appears to open and form a mebranous sac, delimited by the epidermal cell plasmalemma, containing granular material with fibrillar inclusions which are approximately the size of microtubules. The relationship of the contents of the membranous sac to the contents of the fungal peg is discussed.
ULTRASTRUCTURAL CHANGES OF NOSTOC OF PELTIGERA CANINA IN PRESENCE OF SO2
Authors: SHARMA PAWAN , BERGMAN BIRGITTA , HÄLLBOM LARS , HOFSTEN ANGELICA V.
Published: May 2006

The effect of various concentrations of sulphur dioxide (SO2) (0, 10, 100, 1000 p.p.m.) on the infrastructure of the Peltigera canina (L.) Willd ‐ Nostoc symbiosis was investigated in vitro. Ten days incubation with SO2 resulted in the following changes: decreasing number of carboxysomes, increasing number of cyanophycin granules and initiation of akinete‐differentiation. No changes were observed in the general arrangement of the thallus, the wall of either fungus or Nostoc cells, polyglucoside granules and polyphosphate bodies. A decrease in number of carboxysomes indicates a disturbance in photosynthetic ability of the lichen. It also appears that SO2 acts as a stress factor leading to akinete‐differentiation as evidenced by increased number of cyanophycin granules and appearance of akinetes.
EVIDENCE FOR THE ABSENCE OF ECOTYPIC DEVELOPMENT IN ANDROPOGON VIRGINICUS (L.) ON METALLIFEROUS MINE WASTES
Authors: GIBSON D. J. , RISSER P. G.
Published: May 2006

Populations of broomsedge (Andropogon virginicus L.) were studied from three sites in northeastern Oklahoma, U.S.A. The sites differed in the levels of the heavy metals lead, zinc and cadmium which had become incorporated into the soil; the highest concentrations were recorded from a mine site, intermediate levels at a nearby old field and normal soil levels at a control site. A greenhouse transplant experiment utilizing clonal segments of the three populations grown on field (mine, old field and control) and artificial (mine tailings and quartz sand) soils showed that on the field soils the mine and control populations demonstrated similar growth characteristics. The old‐field population differed from these populations in terms of ramet survivorship on the soils. These observations do not support the hypothesis of ecotypic differentiation in response to heavy‐metal contaminated soils, but suggest that the control and mine populations were genetically similar in their ability to tolerate the edaphic conditions of the mine site. The old‐field population may have differentiated in response to the high intraspecific competitive regime on its site.