Showing papers in "New Phytologist in 1981"

Quantifying vesicular-arbuscular mycorrhizae: a proposed method towards standardization *

Abstract: SUMMARY A standard method for the quantification of root colonization by vesicular-arbuscular (VA) mycorrhizal fungi is needed. From the examination of roots from three different host species, the estimation of the percentage of the length of root segments containing VA mycorrhizal fungal structures was found to be more accurate than the determination of the percentage of root segments with VA mycorrhizal fungal structures. It was no more time consuming, and was not influenced by segment size. Examination of a minimum of seven samples, each with 25 randomly selected 0 5 to 1 0 cm root segments, was needed for confidence limits to be within 10 % of the mean. It is proposed that, for the sake of comparability between studies, this procedure be

Variability in the resistance of sodium chloride salinity within rice (oryza sativa l.) varieties

Abstract: Varieties of rice differ in their resistance to sodium chloride salinity. Within varieties, which are not homozygous lines, there is very high variability in sodium uptake and in survival under saline conditions by the individual plants. This is in contrast with the relative uniformity in (for example) potassium uptake, dry wt and transpiration rate. There is a negative correlation between sodium (and chloride) accumulation by individual plants and their survival in saline conditions, demonstrating that variability amongst individuals fits the same pattern as has become generalized for varietal differences in glycophyte species. Possible reasons for this variability in sodium and chloride uptake within varieties, and its relevance to selecting salt-resistant varieties of rice, are discussed.

Observations on the mycorrhizal status of some alpine plant communities

Abstract: SUMMARY In some Austrian alpine plant communities, levels of vesicular-arbuscular mycorrhizal infection are highest in closed herb-rich communities of intermediate altitudes (1900 to 2500 m). In fertilized hay meadows of lower altitudes (1600 m) and in the nival zone above 3000 m, endogonaceous infection is light. In the latter, it is mainly by the fine endophyte, Glomus tenuis. Many plants throughout the altitudinal range of the survey are infected with dark septate hyphae and, in the Cyperaceae, this is the dominant infection. Ectomycorrhizas occur on some herbaceous species as well as on Salix up to 2500 m. The possible significance of the infection patterns is discussed.

Polarographic measurement of photosynthetic oxygen evolution by leaf discs

Abstract: Summary A simple polarographic device is described which permits the measurement, in the gas-phase, of O2 evolved by leaf discs during photosynthesis and O2 consumed in respiration. A method of calibration is described and results are included which illustrate the performance of the apparatus in typical experiments.

Factors affecting the vesicular-arbuscular infection and mycorrhizal dependency of thirteen wheat cultivars

Abstract: SUMMARY Wheat cultivars inoculated with Glomus mosseae show different degrees of mycorrhizal infection and mycorrhizal dependency. Mycorrhizal dependency was affected by root and root/shoot (R/S) ratio dry wts, but neither mycorrhizal dependency nor mycorrhizal infection levels were directly affected by N, P, K, Ca or Mg concentrations in plant tissues. Absence of mycorrhizal infection in some wheat varieties was associated with lack of sugar exudation from the roots rather than with the sugar content of the roots. VA infection led to a decrease in the reducing and total sugar content of root extracts, and this effect was correlated with the degree of mycorrhizal infection.

Comparative water relations and photosynthesis of mycorrhizal and non-mycorrhizal bouteloua gracilis h.b.k. lag ex steud.

Abstract: SUMMARY The rangeland grass, Bouteloua gracilis was inoculated with its mycorrhizal symbiont, Glomus fasciculatus, to determine the influence of vesicular-arbuscular mycorrhizae on water status, stomatal behaviour and photosynthesis as well as gross plant morphology, biomass and phosphorus content. Mycorrhizal infection increased transpiration rates by over 100% with 50 to 70% lower leaf resistances to water vapour diffusion. Leaf xylem pressure was not different between mycorrhizal and non-mycorrhizal plants indicating that whole-plant resistance to water transport was reduced by more than 50%. Photosynthetic rates under saturating light conditions increased 68% with infection as a consequence of a 33% reduction in stomatal resistance and a 67% reduction in mesophyll resistance to CO2 uptake. Mycorrhizal infection did not affect biomass or gross plant morphology after 30 weeks of growth, but increased chlorophyll and phosphate concentrations by 28% and 70% respectively. These physiological changes indicate that mycorrhizae may substantially alter survival ability of Bouteloua gracilis.

The differential ability of aquatic plants to utilize the inorganic carbon supply in fresh waters

Abstract: SUMMARY The photosynthetic activity of 15 species of microalgae and macrophytes was measured by continuous recording of oxygen concentration, and/or the change in pH, in bathing solutions of known alkalinity and carbon concentration. The microalgae had considerably greater apparent affinities for HCO3− and slightly greater apparent affinities for CO2, than the macrophytes (including several previously established HCO3-users), while the macrophytes had larger apparent affinities for CO2 than for HCO3− and larger diffusive resistances to CO2. For species with different affinities for CO2 and HCO3−, assimilation rate in a solution of constant alkalinity showed a distinct reduction when the CO2 concentration decreased to a value typical of each species; a list of such ‘CO2 compensation points’ is presented. (The same CO2 compensation point was obtained for Elodea canadensis by extrapolation of rate-substrate curves in solutions of which the pH was varied at each of three constant total carbon concentrations). At still lower total carbon values, any assimilation was held to be due to HCO3− uptake, and HCO3− compensation points for some species are given. Rather than ‘users’ and ‘non-users’ of HCO3− it is concluded that a gradation exists, use depending on HCO3− as affected by alkalinity and pH of the bathing solution, and on the species' HCO3-compensation point. Natural rates of photosynthesis of macrophytes and some microalgae are usually functions of exogenous [CO2] while those of other microalgae are functions of [CO2] and [HCO3−], with competitive effects at high pH in solutions of prevailingly low alkalinity. In characterizing the response of aquatic plants to inorganic carbon supply, a knowledge of CO2 and HCO3− compensation points is therefore essential.

Factors controlling the distribution of tilia cordata at the northern limits of its geographical range iii. nature and causes of seed sterility

Abstract: SUMMARY Failure of regeneration of Tilia cordata in north-west England is associated with almost complete sterility of the seeds. Between 1964 and 1979 significant numbers of fertile seeds were recorded only after the exceptionally warm summer of 1976. In contrast, large or moderate crops of fertile seed were produced at sites in central and southern England in at least 8 of these years. Comparative studies of pollination, fertilization and seed development at sites in north-west England, central England and northern France show relatively small differences in the proportions of flowers which are pollinated but significant differences in the rates of extension of pollen-tubes. In samples collected in 1977 from north-west England germinated pollen was present on most receptive stigmas but many pollen-tubes extended only a short distance down the style and the few which reached the base appeared to be arrested in the ovary wall. In French samples pollen had germinated on all receptive stigmas and numerous pollen-tubes had reached the ovary within 2 days of pollination. These differences cannot be attributed to variation in the incidence of self-pollination, as at least some trees of T. cordata in northern populations are almost certainly self-fertile. The differences are correlated with temperatures at the time when the samples were collected. When pollen-tubes are growing in sucrose solutions, their rate of extension shows a large response to temperature over the same range (15 to 25°C). Analysis of records shows that temperatures in north-west England at the time of flowering are frequently too low to permit fertilization. This is confirmed by studies of the development of ovules. Although a high proportion of ovules in T. cordata lack embryo sacs, normally at least one is functional in each ovary. In over 90% of fruit formed in north-west England, embryos are contained in none of the 10 ovules. In less than 10% of fruit partly developed embryos are present, suggesting that temperatures are also too low in late summer to allow completion of their development.

The mycorrhizal relationships of australian orchids

Abstract: SUMMARY The symbiotic associations of Australian orchids have been examined by isolating Rhizoctonia endophytes from orchids growing in the field and by symbiotic germination of orchid seed. Many Rhizoctonia isolates fruited and were identified to their perfect states. The isolation studies showed considerable specificity in association between many orchids and their endophytes. In particular Sebacina vermifera was generally associated with Caladenia and several related genera. Tulasnella calospora was closely associated with Diuris and Orthoceras and it and other species of Tulasnella with Thelymitra and Dendrobium. Ceratobasidium cornigerum was associated with Prasophyllum and Pterostylis and, with other species of Ceratobasidium, with orchids of the subtribe Sarcanthinae. Specificity, however, was not absolute for different Rhizoctonias may occur in an orchid either alone or with the more usual endophyte. A few orchids had a wide range of endophytes commonly present. Symbiotic germination studies generally substantiated the field isolations but showed further levels of specificity in that isolates of a fungus often differed markedly in their ability to germinate seed of a host or of different hosts under the conditions used. With orchids specificity seemed to occur at different levels, from species to at least subtribe, though the data are imprecise. If there is specificity to subtribe then there are some anomalies in classification. For instance all Caladeniinae sampled were associated with Sebacina vermifera except Lyperanthus which was associated with a wide range of other fungi. Microtis and Prasophyllum, though not considered closely associated, are placed together in the Prasophyllinae; their endophytes are quite different.

The influence of vesicular-arbuscular mycorrhiza on growth and water relations of red clover

Abstract: Summary Vesicular-arbuscular (VA) mycorrhizal infection of red clover grown in phosphate deficient soils enhanced the concentration of P in the tissues, stimulated growth of root and shoot but reduced the root/shoot ratio. Addition of phosphate to well below the optimum level also stimulated growth and enhanced P status of non-mycorrhizal plants, but their yields and P concentrations were much smaller than those of mycorrhizal plants and their root/shoot ratios were unaffected. The hydraulic conductivities of the root systems were very much higher in mycorrhizal than in uninfected plants. This could be partly attributed to the greater lengths and diameters and hence total surface areas of the mycorrhizal roots. Per unit length of root, the conductivities of the mycorrhizal roots were still two to three times higher, suggesting that this was mainly due to hyphal growth in the soil. When soil water was not limiting, the lower root resistances combined with larger leaf surface areas and possibly also lower leaf diffusion resistances resulted in very much higher transpiration rates and fluxes in mycorrhizal than in non-mycorrhizal plants. Under conditions of water stress, however, the leaf diffusion resistances of mycorrhizal plants were higher and transpiration fluxes lower compared with uninfected plants but, because of their higher total water demands, they wilted more rapidly. Mycorrhizal plants were able to extract soil moisture down to lower water potentials than non-mycorrhizal plants (difference about 1 MPa) but, possibly because of their lower leaf water potentials and higher root conductivities, they recovered turgor more rapidly than non-mycorrhizal plants when soil water was restored. Thus, the mycorrhizal habit is an advantage to the host plant in times of moisture stress.

Differences in fructan content and synthesis in some allium species

Abstract: SUMMARY In Allium cepa (cv. Creamgold), A. cepa (cv. Bunching Onion), A. porrum (leek) and A. sativum (garlic), fructans were the only nonstructural carbohydrates detected apart from glucose, fructose and sucrose. No starch or members of the raffinose series of oligosaccharides were detected. Both cultivars of A. cepa, and A. porrum had fructan polymers of the same length. The maximum DP (degree of polymerization) detected was 12. However, maximum carbohydrate concentration occurred in DP5 for A. cepa (cv. Bunching Onion) and DP12 for A. porrum. A. sativum was different from the other species in that larger polymers were present, reaching a DP of 50. The trisaccharides, 1F-fructosylsucrose and 6G-fructosylsucrose were found in all species. A. cepa and A. sativum contained similar fructan: fructan frutosyltransferases. Enzymes from both plants transferred fructosyl residues from trisaccharide to form tetrasaccharide and sucrose as the major products. This self-transfer predominated even in the presence of higher molecular weight acceptor molecules.

Biochemical explanations of more than additive inhibitory effects of low atmospheric levels of sulphur dioxide plus nitrogen dioxide upon plants

Abstract: SUMMARY Three clones of Lolium perenne L. known to show different sensitivities to SO2 pollution, together with other grasses (Dactylis glomerata L., Phleum pratense L. and Poa pratensis L.), were fumigated with low levels of SO2, NO2 and SO2+ NO2. Ratios of glutamate dehydrogenase activity (GDH) to that of glutamine synthetase (GS) were significantly raised by SO2 (6·8 parts 10-8 for 11 weeks) or SO2+ NO2 in the SO2-sensitive cloned cultivar S23 of L. perenne and by SO2+ NO2 in cloned Lolium perenne material which has high resistance to SO2 (S23 Bell resistant). In Lolium derived from Pennine upland (Helmshore clone) GDH/GS ratios were unchanged in the presence of SO2 or SO2+ NO2 but all three clones showed slight elevations in ratios in response to NO2 fumigation alone. Within a week after treatment with NO2, all grasses had significantly higher nitrite reductase activities than similar plants given clean air, SO2 or SO2+ NO2 treatments. The presence of SO2 appeared to destroy the ability of the plant to respond to NO2, and this inhibition of a potential detoxification mechanism of nitrite is believed to be one of the main reasons why the SO2+ NO2 combination exhibits more than additive effects upon the growth of grasses. All three clones of Lolium perenne and also Phleum pratense showed enhanced ATP formation in the presence of low (6·8 parts 10-8 for 20 weeks) levels of NO2, but reduced cyclic photophos-phorylation in the presence of either SO2 or SO2+ NO2. At higher levels of shorter duration (25 parts 10-8 for 11 days), rates of ATP formation, ATP content and energy charge ratios were higher in NO2 fumigated tissue than in controls, but lower in SO2+ NO2 treated tissue, although basic electron transport systems were unaffected. It is believed that the principal effect of the pollutant combination is upon proton gradients within the photosynthetic membranes leading to general deficiency in ATP which is necessary both for growth and the repair of secondary pollutant damage elsewhere. Parts 10-8 (parts per hundred million) = quantity in μ m-3× (1/mol. wt × 106) × 0·0224 × 108 at s.t.p. * for 11 weeks) or SO2+ NO2 in the SO2-sensitive cloned cultivar S23 of L. perenne and by SO2+ NO2 in cloned Lolium perenne material which has high resistance to SO2 (S23 Bell resistant). In Lolium derived from Pennine upland (Helmshore clone) GDH/GS ratios were unchanged in the presence of SO2 or SO2+ NO2 but all three clones showed slight elevations in ratios in response to NO2 fumigation alone.

A quantitative study of mycorrhizal infection in trifolium: separate determination of the rates of infection and of mycelial growth

Abstract: Summary We present a simple mathematical model of the infection of roots of Trifolium subterraneum by vesicular-arbuscular mycorrhizal fungi. The model permits separate calculation of the following. (1) The frequency of infection in unit length of root in unit time from mycorrhizal propagules distributed uniformly and randomly in soil. A value of 40·8 m−1 day−1 was found for the soil used in the experiments. (2) The rate of fungal growth along the root cortex from a single entry point, which was found to be 12·2 × 10−4 m day−1 for infections derived from propagules in the same soil. An alternative method of estimating the frequency of infection close to the root tip (from measurements of the rate of root growth and distance between the apex and the most apical entry-point) is presented. Comparison of values obtained suggests that the root tip is nearly 10 times more infectible than the average for the whole root system. Some of the assumptions implicit in the model have been investigated experimentally and the results are reported here. The model should be useful in distinguishing between environmental effects on the phases of colonization occurring in the soil, and at the root surface and within the root.

Control of development in chenopodium album l. by shadelight: the effect of light quantity (total fluence rate) and light quality (red.far-red ratio)

Abstract: In nature, fluence rate and the red: far-red ratio are reduced in shadelight beneath vegetation; both show similar exponential decays with increasing canopy density. An assessment of the degree to which each of these factors controls development in natural shade was made by comparing Chenopodium album plants grown under vegetational shade with those grown under the controlled environment light treatments of low fluence rate, and combined low fluence rate and low red:far-red ratio. The observations of stem extension and specific leaf area from vegetational shade were entirely consistent with the effects of the controlled environment light treatments. The increase of specific leaf area in natural shade was probably due to the low fluence rate; the initial rapid stem extension in natural shade was probably due to the reduced red: far-red ratio. There is good evidence to suggest that the latter is a phytochrome-controlled phenomenon.

Comparative inoculum potential of spores of six vesicular‐arbuscular mycorrhizal fungi

Abstract: Summary Using the most probable number method, differences in inoculum potential between six vesicular-arbuscular (VA) mycorrhizal fungal isolates were demonstrated. Inoculum of Glomus mosseae had the highest inoculum potential while G. constrictus, and G. fasciculatus isolate 92, and isolate 0–1 were approximately 1/5, 1/6 and 1/12 as effective. G. fasciculatus isolate 185 and G. epigaeus were approximately 1 /50 as effective. These differences were not correlated with differences in spore viability or germinability since approximately 75 % germination occurred in all species after 3 weeks. While G. mosseae has the largest spore size and had the highest inoculum potential, no further correlation between spore size and inoculum potential was observed. The rate of increase of infection by these six VA mycorrhizal fungi differed more when equal spore numbers were used as inoculum than when equalized inoculum potentials were used. The percentage root infection, subjected to the multiple infection correction, was regressed against log of inoculum density and yielded slopes of 063 to 070 for all VA mycorrhizal fungi tested. The inoculum density-infection relationships of mycorrhizal fungi are discussed with respect to Baker's epidemiological models.

Influence of plant interactions on vesicular‐arbuscular mycorrhizal infections.

Abstract: SUMMARY The effects of crop rotation on mycorrhizal development were examined in pot experiments, using sterilized soil inoculated with Glomus fasciculatus‘E3’ or Gigaspora margarita or unsterile soil containing mainly a type of Glomus macrocarpus var. geosporus. In four crop pairs tested, the amount of VA mycorrhizal infection in a host plant was not depressed in soil previously cropped with a ‘non-host’ plant, even where roots of the preceding ‘non-host’ plant were retained intact in the soil. Indeed the early establishment of VA infection in barley, lettuce and maize inoculated in sterilized soil was stimulated by the ‘non-hosts’ oilseed rape, cabbage and sugar beet, respectively. VA hyphae were sometimes observed growing in moribund ‘non-host’ roots. Effects of crop rotation in unsterile soil were similar but less marked. G. margarita in sterilized soil infected lettuce considerably less than other crops.

The reproductive biology of asclepias tuberosa

Abstract: SUMMARY Individual flowers of the self-incompatible milkweed Asclepias tuberosa are available to pollinators for 7 or 8 days; however, there is a large overlap in flowering time (4 to 5 weeks) within and among inflorescences on a single plant and therefore the possibility of high levels of self-pollination. Pollinator activity closely follows availability of flowers, although the more rapid decline of the former may indicate switching of pollinators to other plant species flowering simultaneously. These observational data are combined with experimental crossing data to write probability functions for a simple multiplicative model incorporating both extrinsic and intrinsic factors determining fruit-set. Fruit-set predictions from the model are very close to the 033% observed in natural populations of A. tuberosa.

An ecophysiological study of the salt secretion of four halophytes

Abstract: Summary Plants of Spartina anglica, Limonium vulgare, Armeria maritima and Glaux maritima were collected in the field and grown on different concentrations of NaCl, KCl and CaCl2. Salt secretion, ion content, water content and transpiration rates were determined. The highest sodium secretion was found in Spartina anglica, a species from the most saline habitat; and a somewhat lower secretion rate in Limonium vulgare. The lowest rates were found in Glaux maritima and Armeria maritima. The sodium secretion efficiency, i.e. the ability to maintain an unchanged internal sodium content, was highest in Spartina anglica. Spartina anglica is the most successful in the removal of excessively absorbed salt, since it secretes 60% of the absorbed sodium. The values for Limonium vulgare, Glaux maritima and Armeria maritima were 33, 20 and 4% respectively. The species studied differ in the preferential sequence of ion secretion as well as in secretion rate and efficiency. This preferential sequence of ion secretion seems to be similar in members of the same taxonomic group (Plumbaginaceae). The comparability of the secretion parameters is discussed with regard to morphological differences between the species.

The role of electricity in plant movements

Abstract: SUMMARY A survey has been made of the different types of reversible movements in the plant kingdom (including those of carnivorous traps, leaves, floral parts, root tips, cytoplasmic streaming, cilia and flagella) and it is suggested that many are mediated by changes in electrical potential Many touch-sensitive movements in higher plants are regulated by propagating electrical signals (action potentials), which relay excitation from the site of stimulation to the motor organ(s), where collapse of sensitive motor cells is brought about The resulting change in volume of the motor cells causes movement of the entire motor organ In some cases additional localized changes in electrical potential (receptor potentials) can be induced by external stimuli, which convert specific characteristics of the stimulus into an electrical analogue before triggering an action potential The role of electrical activity in other plant movements is more speculative Action potentials do not arise in light- or endogenous rhythm-regulated movements, but changes in the membrane potential of motor cells concerned with these movements may also help to drive the ionic transport which leads to their turgor-mediated motion The significance of electrical activity associated with intracellular movements is less certain, but may become the focus of increasing attention as the regulation of actin-directed cellular movements is further investigated Electrical impulses comparable to those in higher plants may, however, regulate ciliar and flagellar activity in the motile gametes and spores of lower plants Thus, it is clear that electrophysiology is an important aspect of many plant movements, and bears a remarkable similarity to excitation in animal nervous systems CONTENTS

Metal uptake in terricolous lichens

Abstract: Summary The nature of the accumulation patterns within the lichen is assessed in terms of metal localization within the different thallus components (i.e. rhizinae, thallus without rhizinae, phycobiont, mycobiont) and the importance of substrate concentrations in controlling localization. Peltigera canina, P. polydactyla, P. rufescens, Cladonia furcata, C. impexa and C. uncialis from a wide range of natural and man-influenced sites in the British Isles were analyzed for Cr, Cu, Fe, Mn, Ni, Pb and Zn; Cladonia spp. were used for comparative purposes. Metal accumulation capacity (μg g−1) of the rhizinae was maximum for Fe, Mn and Pb. However, the phycobiont was found to have maximal accumulation capacity for Cu, Ni and Zn. The metal accumulation capacities by rhizinae and thallus without rhizinae as well as phycobiont and mycobiont without rhizinae were found to be interrelated and were dependent upon the biologically-available metal concentrations in their associated soils as well as the type of substrate. The total amounts (g) of metals localized within the different thallial components, from two major types of environment (i.e. with background and enhanced metal concentrations), are presented; rhizinae accumulate the highest concentrations of all metals under enhanced environments.

The influence of soil aeration on the efficiency of vesicular‐arbuscular mycorrhizas

Abstract: SUMMARY Oxygen concentrations in the soil atmosphere greatly influenced the growth and mineral uptake of Eupatorium odoratum inoculated with Glomus macrocarpus. Shoot and root dry weights and length of mycorrhizal plants increased with O2 concentration up to 16%. Mycorrhizal plants at 21% O2 or non-aerated controls were smaller than those at 12 and 16% O2. Non-mycorrhizal plants had lower shoot and root dry wts than mycorrhizal plants at all O2 levels except at 0%. Phosphorus concentration in mycorrhizal and non-mycorrhizal plants differed significantly but did not increase with increasing O2. Mycorrhizal plants contained higher quantities of N, K, Ca and Mg than non-mycorrhizal and showed positive response in nutrient uptake to increase in soil O2. Inoculation and increased soil O2 resulted in higher concentrations of K and Mg but not of N and Ca. The development of Glomus macrocarpus exhibited quantitative and qualitative response to different soil O2 levels.

An unusual heteromorphic incompatibility system

Abstract: By means of intra- and intermorph crosses it has been shown that the distyly in Anchusa officinalis L. is governed by a single diallelic locus with dominance. Presence of the dominant allele is reflected in the short-styled morph, while homozygous recessives become long-styled. Most of the short-styled plants are heterozygous, but homozygotes have been found among the raised progeny resulting from crossings. Diallel crosses have revealed that at least two incompatibility loci must exist. These and the morphological locus segregate independently. The type of incompatibility system is as yet unknown, though the great frequency of non-reciprocal incompatibility points to a sporophytic system.

Responses of leaves of phaseolus vulgaris l. to simulated acidic rain

Abstract: SUMMARY Relative rates of nutrient penetration, nutrient leaching, and cell permeability of first trifoliate leaves of Phaseolus vulgaris L. cv. Univ. of Idaho 111 were examined after exposure to simulated acidic rain. In buffer solutions 35SO42- penetrated leaves faster at pH 2·7 than at 5·7. In contrast, 86Rb+ pervaded fastest at pH 5·7, and 3H2O entered foliage at similar rates at all pH levels tested. When plants were exposed to simulated rains of various pH levels, calcium, nitrate and sulphate were preferentially leached from whole leaves by rainfalls of low pH, whereas potassium and chloride leached more at pH 5·7 and 3·4 compared with 2·7 and 2·9. Isotope tests indicated that cells within leaves were more permeable to 35SO42- and 3H2O and less permeable to 86Rb+ at pH 2·7 than at higher pH levels. These results suggest a wide diversity of leaf and cell permeability responses to various ions after exposure to acidic rain. In general, an increased rate of nutrient leaching at more acidic levels was correlated with a lower adaxial leaf resistance during leaf development.

Plant growth responses to vesicular-arbuscular mycorrhiza xii. field inoculation responses of barley at two soil p levels

Abstract: SUMMARY The results are described of a field experiment in which barley was inoculated in the field by-placing 20 g of soil containing infected roots below each sowing position Three VA endophytes were used as inoculants and half the plots were given phosphate before sowing Growth and infection were recorded twice during the experiment and at harvest In the plots without added phosphate the fresh wt of ears was doubled by inoculation to approximately 100 gm-2irrespective of endophytes Added phosphate increased this more than inoculation and weight of ears rose to 200 to 300 gm-2 With one inoculant dry wt of ears was 35% greater than with phosphate only, but with the other two it was marginally less The results are discussed in relation to other experiments with barley and to the levels of infection throughout the experiment

Influence of phosphate source on vesicular-arbuscular mycorrhizae of bouteloua gracilis

Abstract: SUMMARY Non-mycorrhizal and vesicular-arbuscular mycorrhizal Bouteloua gracilis infected with Glomus fasciculatus were grown in defined media containing different phosphate sources and compared with respect to phosphate content and form, biomass, chlorophyll concentration, and root phosphatase activity. The phosphate sources were sodium monobasic phosphate, a mixture of sodium monobasic phosphate and calcium phytate, and calcium phytate. Inositol and inositol plus calcium were added to the sodium phosphate medium as additional treatments. Mycorrhizal infection was highest in roots of plants grown in the presence of phytate (75%). Lower root infection levels were noted in plants from the sodium phosphate (19%) and mixed phosphate (22%) media. No penetration by fungi occurred in plants from the sodium phosphate plus inositol or inositol and calcium media. Dry wts of non-mycorrhizal plants were highest when grown in media containing phytate and sodium phosphate plus inositol and calcium followed in decreasing order by sodium phosphate plus inositol, mixed phosphates, and sodium phosphate. Mycorrhizal infection increased leaf dry wt in plants from the sodium phosphate medium and root dry wt from the phytate medium. Phosphate concentrations in the plants were highest when grown in mixed phosphate medium followed by sodium phosphate and phytate. Mycorrhizal infection always increased significantly leaf phosphate concentrations but increased root phosphate concentrations only in the phytate medium. Phosphates were found predominantly as organically-bound compounds in leaves of mycorrhizal plants whereas in leaves of non-mycorrhizal plants, most of the phosphate was inorganic. Chlorophyll concentrations increased significantly with mycorrhizal infection with no change in a/b ratios. Mycorrhizal plants grown in the phytate medium had substantially higher alkaline phosphatase activity than did non-mycorrhizal plants; acid phosphatase activity was not affected by mycorrhizal condition. These results suggest that form of the phosphate in the root environment influences mycorrhizal establishment and effect of mycorrhizae on plant growth.

Ultrastructural and ultracytochemical features of a glomus tenuis mycorrhiza

Abstract: SUMMARY The ultrastructural organization and some cytochemical features (protein and polysaccharide distribution) of the mycorrhiza formed by Glomus tenuis in raspberry roots have been investigated. Certain aspects of the fine mycorrhizal endophyte (smaller hyphae, thinner walls, distinct two-layered wall structure following the PATAg test for polysaccharides, complete absence of septa) distinguish it from the coarse vesicular–arbuscular mycorrhizal fungi. The modifications occurring in the host-fungus interface during Glomus tenuis mycorrhiza development are however very similar to those that have been described in several mycorrhizae formed by coarse vesicular-arbuscular endophytes.

Observations on the mechanism of chloroplast division in higher plants

Abstract: SUMMARY The sequence of changes in membranes that occur during the division of young green chloroplasts is described from observations in the electron microscope of thin sections of leaf tissue of Triticitm aestivum var. Maris Dove, Atriplex semibaccata R.Br. and Sesamum indicum var. glauca. Comparative observations of the morphological forms of dividing chloroplasts present in suspensions from young wheat leaves were made using phase contrast and Nomarski interference optics and from thin sections. The isthmus region of the dividing chloroplasts has a similar form in all three species and fuzzy plaques of electron opaque material and some invaginations in the isthmus were frequently observed. The significance of these fuzzy plaques is discussed and a possible mechanism for chloroplast division suggested.

Developmental changes in leaf epicuticular waxes in relation to foliar penetration

Abstract: SUMMARY Changes in surface properties during expansion of the leaves of eight plant species have been examined in relation to the uptake of 1-naphthylacetic acid. Rates of wax production ranged from 0·1 ng cm-2 h-1 for sugar beet leaves to 6.2 nm cm-2 h-1 for leaves of Eucalyptus globulus. Individual leaves of all species maintained different rates of wax production at their adaxial and abaxial surfaces. Rates of synthesis of wax fractions and their constituent homologues varied with surface and leaf age. The homologue distribution shifted towards components of longer chain length as the leaves expanded. Morphological changes in wax deposits were small and limited largely to increases or decreases in the density of the plate waxes. Rates of penetration of 1-naphthylacetic acid varied between species, between leaf surfaces and with age of tissue. The highest rates of uptake were confined to the period when the leaves expanded most rapidly. The decrease in penetration rate with increase in age of the tissue, common to most plants, was greatest for grape vine and Eucalyptus globulus leaves both of which maintained high rates of wax production during expansion.

Resistances to carbon dioxide fixation in four submerged freshwater macrophytes

Abstract: Summary Discs (0·6 cm diameter) from submerged leaves of Potamogeton lucens L., P. perfoliatus L., P. polygonifolius Pourr. and P. praelongus Wulff were allowed to photosynthesize in well stirred conditions at pH 4·3, 20 °C, and a saturating light intensity of 120 W m−2 (400 to 700 nm) in a range of free CO2 concentrations for 1 h, and the rates were calculated from 14CO2 uptake. Total resistance (1/k+ 1/P) was calculated from these data, using a modification of Fick's first law. 1/k+ 1/P was found to vary between 3·7 × 104 and 5·9 × 104 s cm−1 in the four species. The internal diffusive resistance (l/D) only made up 2·6 to 4·3 % of this total. Estimates were made of the proportions of 1/k (the chemical resistance), 1/P (the diffusive resistance) and δ/D (the boundary layer diffusive resistance) to the total resistance over a range of possible values for the concentration of CO2 at the site of carboxylation: 1/P was always greater than 1/k, and δ/D was always the single largest resistance. The average boundary layer thickness for the leaf discs was calculated as 340 μm; for whole leaves of these species, also well stirred, the boundary layer thickness was estimated to range between 440 and 1090 μm. The ecological significance of the boundary layer to freshwater macrophytes in standing waters is discussed.