Showing papers in "New Phytologist in 1979"

Seasonal patterns of fructan metabolism in forage grasses

Abstract: Summary Fructan levels and mean molecular weights were measured throughout the year in leaves and stems of four forage grasses. In contrast to other studies, the major period of fructan synthesis in all varieties was autumn and winter, with maximal values in December. Extensive hydrolysis, accompanied by a decline in mean molecular weight, occurred between January and April. Fructan accumulation was maximal in periods when growth was restricted and the properties of the synthetic system are discussed in relation to the patterns of growth of temperate forage grasses.

Photosynthesis, respiration and water content in bryophytes

Abstract: Summary Response curves of photosynthesis to water content of bryophytes of dry habitats (e.g. Tortula intermedia, Camptothecium lutescens) show an optimum, with photosynthesis declining again at high water contents. Respiration may be stimulated by water stress, but is unaffected by high water contents. The steep portions of the photosynthesis and respiration curves lie within a similar range at low water contents. Some species of constantly moist habitats (e.g. Pellia epiphylla, Hookeria lucens) show photosynthesis increasing progressively to water contents of 500 to 1000 % of dry weight, and affected at much lower water deficits than respiration as the plant dries out. The response of photosynthesis and respiration to water potential is broadly similar in the two groups. In the species investigated there was generally measurable photosynthesis at –60 to – 100 bar, but little or none at – 150 to –200 bar. Respiration continues to somewhat lower water potentials of which the limits were not determined. Field measurements of the water content of shoots of five species over a period of 12 months showed much greater variation in Tortula muralis than in the woodland species. Maximum water contents in the field generally lay close to the optima of the photosynthesis response curves. The lower water contents recorded in these and in published data are considered in relation to sorption isotherms for bryophytes and other plant materials. The water associated with bryophyte shoots can be divided into (1) water within the cell walls (apoplast water), (2) water within the cytoplasm (symplast water), and (3) external capillary water. Changes in water content below about –200 bar take place chiefly within (1), between c.– 200 and c. - 2 bar within (2), and at higher water potentials chiefly within (3). Water movement within the shoots is physiologically important; the distribution and movement of water are mediated by the geometry of the capillary spaces of the cell walls and the plant surface. In species with papillose leaves, rates of capillary conduction in the interstices between the papillae are more than sufficient to balance evaporation. Conduction within the cell walls is likely to be important in species with non-papillose leaves, hut other pathways may also be involved, and water movement in these species requires further investigation.

The biology of ambrosia trifida l.

Abstract: Summary Ambrosia trifida L. is a fast growing annual colonizer of disturbed ground. When present it drastically reduces kinds, numbers and growth of other annuals. Its seedlings emerge before any other annual in early spring. We studied seed germination in relation to temperature, moisture, depth of sowing, and seedling emergence, survivorship and performance of mature plants in relation to time and depth of sowing and seed size. Seeds germinated under a wide range of temperature (8 to 41°C) with an optimum between 10 to 24 °C. Further germination occurred after restratification suggesting germination polymorphism. The seeds also germinated under a wide range of soil moisture conditions (17 to 55 % dry wt) but highest germination occurred at 20 to 33 % soil moisture. Optimum depth of sowing was 2 cm; very little germination occurred very close to soil surface, and some occurred at the 16 cm depth. In the field seedlings emerged from shallow depths first and then from progressively deeper parts of the soil bank. There was positive correlation between seed size and maximum depth from which seeds of this species and those of five other associated annuals emerge. Time required for seedlings to emerge after germination was directly related to depth. Seedlings that emerged first had the highest probability of survival and those that emerged late suffered progressively higher mortality, irrespective of whether late emergence was caused by late germination or deep germination. Among the survivors that reached maturity, plant weight, height, and number of seeds per plant declined with delayed emergence. However, experimental manipulation showed that delayed emergence per se was not the cause of the mortality but rather competition with individuals which emerged earlier. Furthermore, delayed emergence of cohorts in separate plots did not significantly reduce plant height, weight and number of seeds per plant. Thus in the field and within a patch there may be strong selection for early germination and emergence. However, this selection may be opposed by the unpredictability of the time of disturbance, the spatial patchiness of disturbance, and the longevity and induced dormancy of Ambrosia seeds. Compared to its associated annuals, A. trifida has the largest seeds and seedlings, the earliest germination and emergence and a very high photosynthetic rates. These properties give A. trifida a decisive advantage over the other species.

Sorbitol, a compatible osmotic solute in plantago maritima

Abstract: SUMMARY Plantago maritimna grown under saline conditions accumulates large quantities of sodium chloride. Salinity reduces tissue potassium, calcium and magnesium contents. Several enzymes from P. maritima are shown to be salt-sensitive. In contrast to many other higher plant halophytes, P. maritima shows no accumulation of either amino acids or methylated onium compounds. High levels of the polyhydric alcohol sorbitol are however accumulated under saline conditions. The possible role of sorbitol as a compatible cytoplasmic solute is discussed.

The development of endomycorrhizal root systems ii. effect of agronomic factors and soil conditions on the development of vesicular-arbuscular mycorrhizal infection in barley and on the endophyte spore density

Abstract: Summary The percentage of roots with vesicular-arbuscular mycorrhizal fungi and numbers of spores were measured over 2 years in a field experiment with different crop rotations of barley, kale and fallow. Spore numbers, and subsequent infections of barley crops, were largest following barley; both kale and fallow breaks reduced spore population and infection similarly. With all crop rotations there was a long delay before appreciable percentage infection of roots developed, followed by a rapid increase, and then a constant value. Such late infections appear unlikely to improve crop nutrition, and final yield was negatively related to per cent infection. A survey of barley crops in 2 years on commercial fields following at least 3 years barley showed that infection was rather similar in most fields. There was a very slight correlation between infection percentage, clay content and pH, but no other soil factor had any influence. Early-sown crops tended to have low infection.

The origin of pollen in lake sediments: an enclosed lake compared with one receiving inflow streams

Abstract: Summary The contribution from inflow streams to pollen in lake sediments was examined by comparison of percentage and absolute pollen data from sediment cores taken from two small lakes (5 and 10 h) within the same lowland region of south Cumbria; one in an enclosed basin (a large interdrumlin hollow) and the other receiving streams. The vegetation histories of the last 7000 years, interpreted from percentage pollen analysis, were similar. Calculated rates of annual influx of pollen to the sediments were at all times lower in the enclosed basin; in it they agreed with present deposition into pollen traps from respectively forest, incompletely vegetated land, and grassland. These rates are accepted as estimates of the amount of pollen per unit area which annually reaches a small lake by deposition from the air. Differences between these rates and those to the open lake, for each successive vegetation type, give estimates of the contribution from streams to sediments of the open lake. This contribution constituted 80 % at the horizon of extensive forest clearance. In the open lake, parallel changes in pollen and geochemistry at this clearance horizon show that the source of increased pollen influx lay in organic soils (mor); distribution of the tracer pollen Ilex shows that these soils must have formed on this catchment after initial disturbance of primary forest, and thereafter constituted a source of pollen of ages older than the time of deposition in the lake. Disruption of the vegetation cover on this catchment by deforestation and ploughing appears to have increased permanently the rate at which streams transported sediment, including pollen, to the lake. Only in the enclosed lake do rates of pollen influx remain in equilibrium with vegetation changes recorded in the percentage data. In this lake, with a similar history of changing land use, there is no perturbation of rates of annual pollen influx. The absolute pollen data for Tilia cordata in the enclosed lake confirm for this site the distribution history suggested for this species by Pigott and Huntley (1978).

Localization of heavy metals and other elements accumulated in the lichen thallus

Abstract: Summary This study demonstrates the extracellular deposition of particulate metallic fall-out accumulated in the lichen Caloplaca aurantia with the aid of scanning and transmission electron microscopy and the application of energy dispersive X-ray analyses. The elemental composition of particles integrated in the lichen tissue was compared with the elemental composition of dust particles collected from the surface of the lichen colonies. The different effect of heavy metals in particulate form or in solution, as reflected by lichen's tolerance or sensitivity, is discussed.

Enzymatic studies on the metabolism of vesicular‐arbuscular mycorrhiza. iii. ultrastructural localization of acid and alkaline phosphatase in onion roots infected by glomus mosseae (nicol. & gerd.)

Abstract: Summary The ultrastructural distribution of acid and alkaline phosphatase in 6-week-old onion roots infected by Glomus mosseae has been investigated cytochemically. Significant acid phosphatase activity was only observed in the little vacuolated, immature terminal arbuscule branches of the mycorrhizal fungus whilst strong alkaline α-naphthyl phosphatase and β-glycerophosphatase activities were localized within the vacuoles of the mature arbuscular and intercellular hyphae. In the host cells neither acid nor alkaline phosphatase distribution was modified with vesicular-arbuscular mycorrhiza formation. These results are discussed in relation to previously reported mycorrhiza-specific alkaline phosphatase (Gianinazzi-Pearson and Gianinazzi, 1976, 1978) and the metabolism of phosphorus in vesicular-arbuscular mycorrhizal systems.

Photosynthetic contribution of flowers and seeds to reproductive effort of an annual colonizer

Abstract: Summary The energetic cost for a plant to produce reproductive structures is termed reproductive effort and is most frequently expressed as the ratio of reproductive biomass to total plant biomass. This expression may lead to an incorrect analysis of reproductive effort unless an account is taken of (a) the cost of producing male flowers or male flower parts, and (b) the photosynthetic contribution (reproductive assimilation) of reproductive structures to propagule production. An analysis was made of the carbon budget for reproduction in Ambrosia trifida L., based on measurements of CO2 flux, and the elaboration of seed by excised immature pollinated inflorescences in the absence of carbohydrate from the main stem. Reproductive assimilation accounted for 41 and 57 % respectively of the carbohydrate required to produce male and female inflorescences on intact plants. Individual flowers retain their ability to elaborate seed even after being removed from the parent plant at the time of pollination.

The development of waterlogging damage in young barley plants in relation to plant nutrient status and changes in soil properties

Abstract: Summary When the soil in which 13-day-old barley plants were growing was flooded, the concentration of dissolved oxygen in the waterlogged soil declined to < 2 % (in the equilibrium gaseous phase) within 48 h. Within the same time there was injury to seminal roots and a reduction in the rate of leaf extension. The net rates of uptake of nitrogen, phosphate and potassium in shoots were reduced shortly after the onset of waterlogging, and because dry matter accumulation by shoots was initially little affected, the average concentration of these nutrients showed a marked decline after 48 h compared with aerated controls. The concentration of nitrate in shoots was particularly sensitive to waterlogging and after 48 h was about one third of that in controls. Analysis of individual leaves and tillers showed that with waterlogging, nitrogen was accumulated by the younger tissues at the expense of the older leaves. This trend, which was not observed with plants in aerobic soil, preceded the premature breakdown of chlorophyll in the older leaves. With prolonged anaerobiosis, there were increases in the concentration of potentially inhibitory soil products (ethylene, organic acids, manganese) and a decline in nitrate in the soil solution, but these changes, which mostly occurred after the onset of the characteristic symptoms of waterlogging damage were relatively small and unlikely to have led to injury to shoots. The possible relations between the low concentration of oxygen around roots, the inhibition of ion uptake, the redistribution of nutrients within the shoot, and the premature senescence of leaves are discussed.

Desiccation effects and cation distribution in bryophytes

Abstract: Summary Analysis of the cations in a range of bryophytes, using a differential ion displacement technique, has shown that potassium is mainly soluble within the cells, calcium is bound, exchangeably, to sites in the cell wall and is insoluble within the cell and magnesium is present in all three locations. After desiccation, soluble ions either leak into the rehydrating solution (e.g. potassium and some magnesium) or become bound to the cell-wall exchange sites (e.g. most of the magnesium). Leakage of intracellular ions can be used as a measure of membrane damage. An index of desiccation resistance (based on potassium retention within the cells after storage at 52 and 100% r.h.) is related to the availability of water in each bryophyte's habitat and is significantly correlated with the total potassium content of the plant. Reduced cation leakage occurred after material was transferred from either 52 or 0% r.h. to 100% r.h., indicating the ability of bryophytes to recover from such desiccation stress. An index of recovery is presented which shows that most bryophytes, unless excessively stressed, are able to repair the damage caused by desiccation.

The genecology of lawn weeds

Abstract: SUMMARY 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.

Clonal variation in populations of ranunculus repens

Abstract: Summary A computer simulation model is developed to examine the relationship between the population flux of ramets, the recruitment of seedlings and genet diversity in populations of Ranunculus repens in a North Wales pasture. The study is based on a continuous monitoring of the flux of ramets and recruitment of seedlings in eight populations over a period of 4 years. A simple flow diagram, which describes the life-cycle of R. repens and which incorporates the field census data, is used as the basis for a series of computer simulations. The computer model simulates the actual flux of ramets in each of the eight populations and, assuming no selection between families, is used to follow the fates of ramets and families of ramets. Comparisons between the numbers of families of ramets in the real and simulated populations provide little evidence for selection between families of ramets or against new seedling recruits. With no selection the number of original families present within a population declines at an approximately exponential rate and the contribution made by these families to the total genet diversity of the population rapidly becomes subordinate to the role of new seedling inputs. It is suggested that although the contribution of seedlings to maintaining the total number of individuals, Nη, in populations of plants which spread clonally may be very small, the occasional establishment of seedlings may nevertheless play a significant role in determining the number of clones or genets, N.

Presence of 14c activity in root exudates and guttation fluid from agropyron repens treated with 14c‐labelled glyphosate

Abstract: Summary The herbicide, N-phosphonomethyl glycine (glyphosate), is readily absorbed by the foliage and translocated in the phloem of Agropyron repent (L.) Beauv. The roots and rhizomes were active sinks and, 8 days following herbicide treatment, 14C accumulated at the rhizome nodes, especially at the apical buds. Appreciable amounts of [14C]glyphosate were exuded from intact roots into surrounding solutions but very low levels occurred in the guttation drops collected from the leaf tips. Some implications of the work are discussed.

Studies on the efects of low levels of sulphur dioxide on the growth of lolium perenne l.

Abstract: Summary Lolium perenne L. cv. S23 was grown in Perspex chambers situated out of doors and ventilated with clean air or controlled levels of sulphur dioxide (SO2). Fumigations were carried out with [SO2] ranging from 43 to 423 μg m−3 for periods up to 194 days under both summer and winter conditions. Concentrations as low as 43 μg m−3 for 173 days in winter and 106 μg m−3 for 194 days in summer could produce reductions in shoot dry wt but, in some experiments, similar or higher concentrations had no effect on growth. This difficulty in obtaining a clear dose/response relationship is possibly due to an interaction of environmental factors with the effects of the pollutants. In some of the experiments, growth was reduced in the absence of any detectable symptoms whereas, in other cases, the fumigated plants became chlorotic. There was some evidence for chronic SO2 injury being more severe on young plants. SO2 acted primarily through a depression in net assimilation rate. No clear correlation was found between either chlorophyll content or total sulphur content of the fumigated plants and a reduction in any of the growth parameters investigated. The results are discussed in relation to those of other workers and their relevance to conditions in the field in the United Kingdom.

Morphogenensis of the carpophore of coprinus cinereus

Abstract: Summary An interpretation of carpophore morphogenesis is presented which is derived both from the literature and from original observations. Cultured material of Coprinus cinereus (also called C. macrorhizus and C. lagopus) has been studied using biochemical assays together with light-, scanning- and transmission electron microscopy to provide details of histology and the levels and distribution of protein, glycogen and NADP-linked glutamate dehydrogenase during the course of development of stipe and cap. Initially, aggregates of hyphae form primordia which subsequently develop into mature carpophores. During stipe development glycogen deposition is at first restricted to cells forming a cup-shaped mass in the stipe base, but very early in primordium development this deposit is depleted and glycogen accumulates in the gills, particularly the subhymenium, where it probably serves as a reserve material for the later stages of cap development. The distribution of cytochemically detectable protein differs from that of glycogen in that the former initially accumulates in the upper regions of the primordial stipe and in the gill hymenium. The stipe showed no conspicuous change in its content of protein during development although in the cap the fraction of the dry wt represented by protein increased substantially. Primordial stipes are composed of overlapping cells of hyphal dimensions with dense cytoplasm and small vacuoles. Stipe development depends on cell enlargement, this seeming to be biphasic; an initial increase in volume being attributable to an increase in cell diameter to give an undifferentiated dikaryotic central region and a differentiated multi-nucleate cortex. Stipe growth depends on reallocation of cellular components, no one reserve material being identifiable as of prime importance although a few simple sugars do appear to be correlated with the osmoregulatory activity connected with the large scale uptake of water involved in stipe elongation. In the primordium cap the subhymenium is an open tissue of interwoven hyphae, the cells containing large accumulations of glycogen. The hymenium is formed from dikaryotic branches of the subhymenial hyphae to become an organised layer of hyphal tips. Subsequently, although the subhymenial hyphae remain as such, the hymenial cells become inflated. The paraphyses come to form a pavement of appressed and interlocked cells each containing a large central vacuole. Basidia are only slightly enlarged and contain dense cytoplasm with few vacuoles; they contrast with the much extended and inflated cystidia. Despite their inflation, all three cell types still show continuity with the subhymenial hyphae. During cap expansion the major inflationary force is paraphyseal enlargement but as the gill lamellae are removed by autodigestion further cell inflation in the pileal flesh enables it to assume a supportive role. In the earlier stages there is some correlation between declining glycogen content of the cap and increasing activity of NADP-linked glutamate dehydrogenase. It is suggested that cap expansion is driven osmotically and that at least some of the osmotically active materials are synthesised through the urea cycle. At first this activity could be supported by glycogenolysis and amination but later on substrates may be provided by autodigestion of spent gill tissues. It is concluded that cap development is regulated by a metabolism quite distinct from those of either the parental mycelium or the stipe, and that the fundamental metabolic changes occurring throughout carpophore development are orchestrated by light. As carbohydrate nutrients in the medium approach exhaustion suppression of mycelial morphogenesis into hyphal aggregates is lifted, but the subsequent switch from the vegetative pathway of sclerotium development to carpophore formation is normally dependent on illumination with low intensity blue light. Growth then becomes polarized to form a presumptive pileus and glycogen is mobilized from the surrounding mycelium to accumulate at the base of the stipe. Receipt of a second illumination inhibits further growth of the stipe base and causes glycogen reserves to be translocated to the cap. Glycogen is utilized in the cap to produce glycolytic intermediates, allowing regulation of many aspects of metabolism by catabolite concentration and contributiong to the diverse syntheses required for spore formation and dissemination.

Interaction between a vesicular-arbuscular mycorrhiza and rhizobium and their effects on soybean in the field

Abstract: Summary Interaction between Glomus fasciculatus and Rhizobium japonicum and their effects on soybean in the field was studied in a phosphorus deficient sandy loam soil with pH 5·6. The number, dry weight and nitrogen content of the root nodules in plants inoculated with Glomus plus Rhizobium were significantly more compared to plants inoculated with only Rhizobium. Rhizobium inoculation did not have any significant effect on sporulation of G. fasciculatus in the rhizosphere. Although soybean plants inoculated with G. fasciculatus recorded increased phosphorus content, dry weight and grain yield than uninoculated plants the differences were not statistically significant. In Rhizobium only inoculation markedly increased the nitrogen content of the plant and grain yield. Dual inoculation with both the symbionts increased significantly the dry weight of the shoot and its nitrogen content over single inoculation with either Glomus or Rhizobium. These results suggest that vesicular–arbuscular (VA) mycorrhiza can greatly assist nodulation and nitrogen fixation in field growth soybean inoculated with rhizobia.

SALT TOLERANCE IN THE WILD RELATIVES OF THE CULTIVATED TOMATO: PROLINE ACCUMULATION IN LYCOPERSICON ESCULENTUM MILL., L. PERUVIANUM MILL. AND SOLANUM PENNELLI COR. TREATED WITH NaCI AND POLYETHYLENE GLYCOLE

Abstract: Summary The cultivated tomato Lycopersicon esculentum cv. Rhemlands Ruhm and the two wild species L. peruvianum and Solomon pelnnellii which originated in dry habitats were compared with respect to accumulation of free proline, chloride and succulence under NaCl stress, and accumulation of proline and succulence under water stress produced by polyethylene glycole. Proline accumulation increased in all three species under both types of stress. Increase under salinity stress, however, was smaller in the two wild species which accumulated more chloride and were more succulent. Under water stress, the increase of proline level was greatest in is. pennellii, in which succulence decreased drastically, and smallest in L. peruvianum. The possible role of salt tolerance in enabling wild tomato species to endure drought, and the difference between them with respect to proline accumulation, are discussed.

Lichen water relations under drying conditions

Abstract: Summary The loss of water by evaporation in various species of lichens has been examined under a range of controlled windspeed/radiation regimes. Temperate and arctic species both show a type of morphological control of evaporation. Such control varies, however, with the nature of the surrounding environment. Evaporation from those species which show a very low resistance to evaporative water loss such as Bryoria nitidula, Umbilicaria deusta and U. veiled appears to be relatively insensitive to increases in radiant flux. Conversely those species, or specific growth forms, which show a high resistance to evaporative water loss, such as Cladina stellaris and U. muhlenbergii, appear to be sensitive to increases in supply of radiant energy. These results suggest that the morphological control of evaporation in lichens is significant to the ecology of this group of plants.

Seasonal and edaphic variation in vesicular‐arbuscular mycorrhizal infection of grasses by glomus tenuis

Abstract: SUMMARY Seasonal differences in percentage length of gramineous host root infected with Glomnus tenuis were measured in three field sites in Pennsylvania, U.S.A. Highest G. tenuis infection levels were generally found in the spring in very phosphorus-deficient soils low in moisture. In roots sampled from soils with a high spring soil-moisture content, fine endophyte infection increased to a maximum later in the growing season. A higher percentage frequency of fine endophyte infection on fine grass feeder roots in spring is taken as evidence for the hypothesis that G. tenuis is a vesicular-arbuscular mycorrhizal fungus particularly adapted to penetrating host roots during brief seasonal fluxes of phosphorus availability. The implications of these data are discussed in relation to mechanisms in grasses which adapt them to nutrient stress.

Alleviation of waterlogging damage to young barley plants by application of nitrate and a synthetic cytokinin, and comparison between the effects of waterlogging, nitrogen deficiency and root excision

Abstract: Summary A study was made of the effects of either 6-benzylaminopuiine (BAP), a synthetic cytokinin, or calcium nitrate on the response of the shoots of 13-day-old barley plants to soil waterlogging. Spraying leaves daily with BAP resulted in small improvements in leaf extension and retarded the premature loss of chlorophyll in the older leaves after 7 days waterlogging, but the rates of accumulation of dry matter and inorganic nutrients in shoots were reduced to the same extent as in unsprayed plants. After a further 7 days waterlogging, during which spraying was discontinued, plants treated with BAP were no longer appreciably different from untreated ones. When calcium nitrate was added daily to the surface of the waterlogged soil, no symptoms of waterlogging damage appeared. Leaf extension, shoot weight, emergence of tillers, chlorophyll concentrations and the accumulation of inorganic nutrients in shoots were similar to those in plants in non-waterlogged soil after 7 and 14 days. The effect was dependent on the presence of a narrow zone of aerated soil close to the surface, in which root growth and function could continue. When plants were grown for 13 days in aerated nutrient solution, and then transferred to solutions lacking nitrate, the development of leaf chlorosis, the decrease in the concentration of nitrogen in the shoots and their retarded accumulation of dry matter were all similar to that caused by waterlogging. The premature loss of chlorophyll in the older leaves was retarded by spraying with BAP. Chlorosis of the older leaves could also be promoted in plants in aerated nutrient solution by excising part of the root system. Mechanisms by which BAP and calcium nitrate alleviate symptoms of waterlogging damage, and the significance of nitrogen deficiency and root excision in relation to waterlogging damage, are discussed.

Floral morphology and pollen flow in the heterostylous species pulmonaria obscura dumort (boraginaceae)

Abstract: Summary Pollen flow in the heterostylous species P. obscura was studied in two localities in Denmark. Various floral characters of the two morphs were measured, but differences were found only in height of stamens and stigma, and size of pollen. In studies with a scanning electron microscope (s.e.m.) pollen was discovered to have a continuous, equatorial girdle formed by the transverse furrows extending laterally from the ora. The stigmatic papillae were composed of a stalk with a many-armed crown. The ratio of number of thrum to pin plants was approximately 1:1 fulfilling theoretical expectations. Six different Bombus spp. and a specimen of Psithyrus bohemicus were observed as visitors to P. obscura, which displays a range of adaptations to Bombus pollination. Thirty per cent of the Bombus specimens had corbicular pollen loads, which were almost 100% pure Pulmonaria pollen. Pollen flow was revealed by analysing the pollen loads on stigmas and proboscides. Both stigma types had more illegitimate pollen than expected on the basis of the ratio of production of the two pollen types. This could be caused by a high degree of intrafloral pollen flow. Since heterostyly does not apparently enhance the transport of legitimate pollen the adaptive role of the system is unclear.

Pollintation ecology of, and hybridization between, orchis coriophora l. and o. collina sol. ex russ. (orchid aceae) in israel

Abstract: Summary The flower of Orchis coriophora L. contains free nectar in the spur and is very fragant; it attracts a large gallery of pollinators mainly Apis mellifera. The capsule production rate is about 90% O. collina Sol. ex Russ. has empty spurs and is scentless; pollinators are scarce and capsule production rate is about 25%. The species are sympatric in some habitats in Israel and create rare hybrids which seem to be the result of common pollinators. It is suggested that each of the two species represents different pollination strategy in the genus. This view and the implications on self and cross pollination are discussed.

Legumin of pisum sativum and vicia faba

Abstract: Summary The legumins of Pisum and Vicia have been compared and the proteins have been shown to differ in molecular weight, subunit molecular weights and amino acid composition. Legumin of Pisum however has a similar disulphide bridged subunit construction to that of Vicia and consists of basic (pI's greater than 7) and acidic subunits (pI's less than 7). Of the two molecules, Pisum legumin was shown to be more acidic at pH values of neutral and above. The protein from Pisum has all the antigenic determinants of Vicia legumin and one or more determinant groups in addition. Tryptic peptide maps indicate that legumin is an homologous protein in Vicia and Pisum.

Inoculation of white clover and ryegrass seed with mycorrhizal fungi

Abstract: Summary Seeds of white clover and ryegrass were pelleted with soil heavily infested with the indigenous mycorrhizal fungi or efficient strains of Glomus tenuis and Gigaspora margarita and laid out on unsterilized pasture soils. Ryegrass plants inoculated with Glomus tenuis produced up to 48% more shoot growth than plants infected with the indigenous mycorrhizal fungi in Dunmore soil in glasshouse conditions. Similar inoculation of clover increased shoot growth by up to 91 % in Te Kuiti soil in the glasshouse and 37% in the field. Inoculation of clover with Gigaspora margarita increased dry matter of shoots by 79 % in Te Kuiti soil in the field.

The uptake of urea by the diatom, phaeodactylum

Abstract: Summary Urea-grown cells of Phaeodactylum absorbed [14C]urea by an active mechanism. Most of the urea taken up was present in the cells as free urea and the ratio of internal to external concentration could exceed 3000. The activity of the transport mechanism was greatly increased by depriving the cells of nitrogen for up to 24 h. The uptake mechanism had a high affinity for urea, the half-saturation constant being about 1·0 μM. Active uptake of urea occurred in darkness, particularly in nitrogen-deprived cells, but uptake was markedly stimulated by light. Uptake was not inhibited by DCMU but was abolished almost completely by 10−4m CCCP. It is concluded that active uptake is driven by phosphorylation. Uptake of [14C]urea continued until a constant level within the cells was attained, the plateau value probably resulting from a balance between rate of active uptake and rate of passive loss by diffusion. The transport mechanism was absent from cells grown with ammonium as nitrogen-source. The urea uptake mechanism developed in such cells when they were deprived of nitrogen; cycloheximide prevented the development of the mechanism. The mechanism was lost when urea-grown cells were incubated in ammonium medium for 24 h but ammonium (at concentrations up to 10 mM) did not inhibit short-term uptake of urea into urea-grown cells.