Showing papers in "New Phytologist in 1977"

The development of endomycorrhizal root systems: i. spread of infection and growth‐promoting effects with four species of vesicular‐arbuscular endophyte

Abstract: SUMMARY Four vesicular-arbuscular endophytes were inoculated into onions cultured in soil in a growth chamber. Dry weight, root length, infected root length, phosphorus content and quantity of external mycelium were measured at intervals. Three endophytes produced similar hyphal inflows, growth increments and external mycelium. One endophyte produced no growth increase in the host, and had little external mycelium and slow increase in percentage infection.

Demographic analysis of the growth of linum usitatissimum

Abstract: SUMMARY Traditional growth analysis techniques have dealt with changes in plant weight and leaf area and have contributed a great deal to the understanding of plant growth. However, they have ignored the fact that the plant may be considered as a population of modules perfectly suited for studies of age structure. Plant growth has many analogies with the growth of a population of organisms. Plant modules (e.g. leaves) have a life cycle–birth, juvenile phase, ‘reproduction’ (i.e. contributing resources to the birth of other leaves and ultimately to flowering and seed set), senescence and death. Plants of Linum usitatissimum were grown in a glasshouse under full and 50% light and at densities of 3.9 and 30/flat. Leaf birth rates were reduced by shading and especially by increased plant density. Light and density also influenced the branching pattern, the intrinsic rate of growth (rm), leaf survivorship, life expectancy (ex), and leaf death rates. Leaf death was strongly influenced by the treatments. Regardless of leaf age, leaf area index, flowering time, density or light intensity, leaf death started when the total biomass of the plants was about 13 g/flat. This biomass apparently exceeded the carrying capacity of the soil medium. Experimentally withholding nutrients, shading the lower parts of the plants, and the removal of flower buds influenced the onset of leaf death but the variable that was most effective, was the withholding of nutrients. Death started in the lower leaves and proceeded upwards regardless of leaf age. The number of seeds per plant was more strongly correlated with the number of leaves than with the total leaf area per plant. This study shows that the application of life-table and other demographic analyses to leaf birth and death is feasible and permits an interpretation of plant response to environmental factors at a more sophisticated level than is possible from classical growth analysis.

Influence of mycorrhizal infection on competition for phosphorus and potassium by two grasses

Abstract: Summary Lolium perenne L. and Holcus lanatus L. were grown together in 125-mm pots in a factorial experiment combining mycorrhizal infection and root competition. Both root competition and mycorrhizal infection gave a slight advantage to H. lanatus but, in combination, these produced considerable suppression of Lolium perenne. Root length of L. perenne was reduced by mycorrhizal infection, which was itself increased by competition. The competitive effects can be explained solely in terms of mycorrhizal infection.

Upper critical levels of toxic elements in plants

Abstract: Summary This study examined the effect of Cu, Ni, Zn or Cd in the leaves and shoots of young barley on their yield of dry matter. As expected, the yield of dry matter, or the uptake of heavy metals from a given solution, varies considerably with growing conditions. However, the minimum concentrations of these elements in the plant tissue that was necessary before the yield of dry matter was reduced by their toxic effects (‘upper critical level’) proved to be independent of growing conditions varied enough for the control plants to have required 14–31 days to reach the five-leaf stage, and for the weights of the control plants to have ranged from 76 to 214 mg. This being so it is suggested that if young barley plants were used to monitor accumulations of heavy metals in the soil environment, the quantity would provide a good measure of the hazard of any accumulation relative to the onset of toxicity, where To and Tc are standard values for the background (unpolluted) and the upper critical level of the element in plant tissue, and Tits level in a test crop. This reduces to [m. Log10T/n] and if T is measured in ppm of dry matter, m and n are approximately, A graph of Relative Hazard against tissue concentration is presented.

A histochemical investigation of lead uptake in raphanus sativus

Abstract: SUMMARY A histochemical method was used to investigate the distribution of applied lead in the seed and seedling stage of Raphanus sativus. Lead contamination of the embryo was inhibited by the testa until it ruptured during imbibition. In seedlings, lead moved into the root cortex predominantly along the cell walls as far as the endodermis. Beyond the endodermis lead was localized extensively in the vascular tissues. There was little movement of lead from the vascular tissue into the surrounding tissue of the stem and cotyledons.

H+ AND Ca2+ IN PHLOEM AND SYMPLAST: RELATION OF RELATIVE IMMOBILITY OF THE IONS TO THE CYTOPLASMIC NATURE OF THE TRANSPORT PATHS

Abstract: SUMMARY The capacity of the symplast and the phloem to transport Ca2+ and H* (OH−) is discussed in relation to the concentrations of free and bound Ca2+ and H* in these transport systems, and the general restrictions on the concentrations of free Ca2+ and H* in cytoplasm. It is concluded that the low Ca2+ and H+ transport capacity of symplast and phloem are consequences of the cytoplasmic nature of these transport systems. The significance of the low transport capacity for these two ions relative to the rate at which the plant produces or consumes H+ or can take up Ca2+ and transport it in the xylem is discussed. Other transport characteristics of the phloem can also be related to the cytoplasmic nature of the transport conduit: the nature of the transported organic C and N compounds is partly dependent on the requirement that high concentrations of these solutes can be tolerated by cytoplasmic enzymes, i.e. sucrose, mannitol and amino-acids are ‘compatible solutes'. The properties of the intracellular transport systems (symplast and phloem) are contrasted with those of extracellular transport systems such as plant xylem and animal blood.

Variations in the basic pathway of chloroplast development

Abstract: SUMMARY The sequence of ultrastructural changes which take place during chloroplast development in leaves of plants of Phaseolus vulgaris grown in the light is compared with that of plants grown in the dark. Further comparisons are made with the developmental sequence found in the hypocotyls of Phaseolus and in the leaves of Zea mays. It is concluded that there is a single basic pathway of chloroplast development. Variations in this pathway are related to blocks in the sequence resulting in the accumulation of storage materials such as phytoferritin and prolamellar bodies, characteristic of the species or tissue concerned. An attempt has been made to assess the ubiquity and duration of an association between plastids and the E.R. in lower plant species compared with the angiosperms. A plastid-E.R. association is common and persistent in lower plant species whereas in angiosperms it is apparently transitory and confined to immature or specialized cells.

Tolerance of anoxia and ethanol metabolism in germinating seeds.

Abstract: SUMMARY Seeds resistant to soaking injury and the associated condition of anoxia regulate glycolysis so that there is minimal production of ethanol. This regulation is achieved by low anaerobic respiration rates, the minimization of the Pasteur effect, and by the production of lactate as an alternative to ethanol during the early stages of anaerobiosis. Resistant seeds differ from those intolerant of soaking where anoxia causes an acceleration of glycolysis, an induction of alcohol dehydrogenase activity and the production of large quantities of ethanol as the exclusive end-product of glycolysis. Seeds tolerant of soaking are therefore similar to the roots of flood-tolerant plants where ethanol production is also limited during periods cf anoxia.

A histochemical study of phenolic materials in mycorrhizal and uninfected roots of eucalyptus fastigata deane and maiden

Abstract: SUMMARY The distribution of phenols in uninfected and mycorrhizal Eucalyptus fastigata roots has been examined by application of a range of histochemical tests to thin sections. The vacuoles of most cap cells and many epidermal cells of E. fastigata mycorrhizas contain considerable quantities of phenolic materials. Cap cells of uninfected fine roots similarly contain materials with the staining properties of phenols, but uninfected root epidermal cells rarely do. It is suggested that accumulation of phenols in the epidermal cells of mycorrhizas is a response to the presence of the fungal symbiont. Further evidence is provided that the hyphae of the fungal symbiont penetrate and grow through the phenolic materials of the outer root cap cells. No evidence was found to suggest that these areas contain appreciable quantities of polysaccharide. Phenols were also detected in the endodermis and outermost layer of cortical cells. Judged on their staining reactions, these seem to be chemically different from those of the cap and epidermis. They are present in both mycorrhizal and uninfected roots, but appear much closer to the tip in the former. The outer layer of cortical cells has other specialized features, including the presence of a suberin layer in the walls, which are characteristic of mature differentiated endodermal cells in E. fastigata. These features are discussed from the viewpoint that the outer cortical layer acts as a barrier to further hyphal penetration in eucalypt mycorrhizas.

Changes in chlorophyll and carotenoid content, specific leaf area and dry weight fraction in sitka spruce, in response to shading and season

Abstract: SUMMARY The response of chlorophyll and carotenoid concentration, specific leaf area and dry weight fraction in shoots of Sitka spruce (Picea sitchensis (Bong.) Carr.) to season and photon flux density has been measured. Shoots were sampled from different heights in the canopy at two forest sites, one thinned, the other unthinned. An increase in specific leaf area and a decrease in dry weight fraction was found in shaded shoots. At both sites, there was a seasonal variation in pigment content, with a summer maximum for chlorophyll and a winter maximum for carotenoid. Pigment content was constant throughout the canopy on the thinned site, but was higher in shaded shoots from the unthinned site.

Vesicular‐arbuscular infection and soil phosphorus utilization in lupinus spp.

Abstract: SUMMARY Lupinus angustifolius, L. cosentinii and L. luteus were weakly infected (<10% of root length) with vesicular-arbuscular endophytes and hence VA mycorrhizas were not considered of any value in their phosphorus uptake on the nutritionally poor sandy soils of Western Australia. Vesicles were present in approximately 30% of field plants and less often in the glasshouse. Arbuscules were observed on only one specimen of L. cosentinii in a restricted section of one lateral root. Infection was reduced further when soil moisture was high and by small additions of phosphorus to the soil. Under certain conditions, VA mycorrhizal infection in L. cosentinii was stimulated by the growth of red clover. ‘Proteoid’ -like rootlets were observed on lupins and these had specialized root-soil surface properties that may be responsible for improved phosphorus uptake.

Glutamine synthetase and nitrogenase activity in the blue‐green alga anabaena cylindrica

Abstract: Summary On adding NH4+ to nitrogen-fixing cultures of Anabaena cylindrica, the glutamine pool of the intact filament increases within seconds. Nitrogenase activity and then glutamine synthetase activity decline. There are no changes in the activities of glutamate-aspartate aminotrans-ferase, or in the pools of alanine, glycine and aspartate during this period. Nitrogenase activity is usually inversely related to the size of the glutamine pool and shows little correlation with glutamine synthetase activity per se. There is no evidence of adenylylation or dead-enylylation of glutamine synthetase (snake venom phosphodiesterase has no effect on activity, there is no serological homogeneity with the Escherichia coli enzyme which shows a covalent modification; the ratio of biosynthetic: transferase activity does not change markedly on the addition of NH4+ and the kinetics of decrease in glutamine synthetase activity are not consistent with adenylylation of the enzyme). Feed-back inhibition occurs, with alanine and glycine being particularly effective inhibitors and with some inhibition occurring with AMP, carbamoyl phosphate and aspartate. Histidine, lysine, ornithine, citrulline and arginine were non-inhibitory at the concentrations used. There is no evidence of inhibition of glutamine synthetase by glutamine. The addition of azaserine inhibits glutamine uptake by intact filaments and reduces the subsequent conversion of glutamine to glutamate within the filament by 77%. Such results are consistent with the operation of the glutamine synthetase-glutamate synthase pathway in Anabaena cylindrica.

Early effects of flooding on nitrogen deficiency and leaf chlorosis in barley

Abstract: SUMMARY Effects of flooding the root system on nitrogen status, leaf chlorosis and shoot growth have been studied in barley seedlings. Within 2 days, oxygen in the soil water decreased to a low concentration (< 2%), and net uptake of nitrogen to shoots was inhibited. Simultaneously, there was a decrease in the average concentration of nitrogen in shoots, due to translocation from older leaves to younger expanding ones. These changes pieceded the onset of chlorosis of the older leaves. It is suggested that inhibition of nitrogen uptake, and the consequent redistribution of nitrogen within the shoot, are important contributory factors in the early senescence of leaves and the retarded growth of shoots in flooded plants.

The cyanophyte-hepatic symbiosis i. morphology and physiology

Abstract: SUMMARY The Anthoceros punctatus-Nostoc and Blasia pusilla-Nostoc symbioses were investigated. In both associations the Nostoc colonies develop in mucilaginous cavities on the undersurface of the gametophyte. The sporophytes of Anthoceros have no Nostoc colonies; no sporophytes of Blasia were found. The symbiotic algae have been identified as Nostoc sphaericum ex. Born et Flah. The heterocyst frequency of the free-living isolates is 3–6% but this increases to 30% (Blasia) and 43% (Anthoceros) when the algae are growing symbiotically. On infecting alga-free gametophytes of Blasia pusilla with Nostoc, algal colonies develop in the cavities within 72 h. The developing Nostoc colonies stretch the cells of the cavity wall and there also arise from a point on the host cavity wall, usually opposite the cavity pore, septate, branched, filamentous protrusions, which increase the surface area of contact between phycobiont and host by about 30% within 4 weeks of colony formation. Such outgrowths may facilitate interchange of metabolites between the alga and liverwort. The Nostoc phycobiont of Anthoceros may infect Blasia and vice-versa. A strain of Nostoc punctiforme isolated from Gunnera also infects Blasia, but four other Nostoc isolates, including one from cycad root nodules, do not. Five other heterocystous algae, five non-heterocystous filamentous algae and one unicellular alga tested do not infect Blasia. The nitrogen contents of thalli with Nostoc colonies are significantly higher than those treated with algae which do not develop colonies. The symbiotic algae differ physiologically and biochemically from free-living algae. They show higher rates of nitrogenase activity (acetylene reduction assay), are depleted of nitrogen-storing phycobilin pigments and structured granules and although metabolically active do not evolve O2 or fix CO2 photosynthetically, but do have polyhedral bodies which contain the key CO2-fixing enzyme ribulose-l,5-diphosphate carboxylase. The Blasia symbiosis grows well and remains established in the pH range 4–8, at low levels of combined nitrogen (<100 mg I−1 of nitrate-nitrogen) but not at high levels (100–1000 mg I−1), in the temperature range 10–25°C, and under moist but not waterlogged or desiccated conditions.

Pollen transfer and pollination in the common fig (ficus carica l.)

Abstract: Summary The traditional ideas, as to how pollination is achieved in the common fig (Ficus carica L.), are untenable because the very narrow entrance slits of the ostiole render it very difficult for the pollen vector (the agaonid wasp Blastophaga psenes L.) to introduce pollen on its body surface into the female receptive fig. The process is now shown to entail: (a) loading of pollen in the polleniferous fig into intersegmental and pleural invaginations which form in the shrunken body of the wasp following water loss; (b) unloading of pollen in the receptive fig, as a result of partial swelling and contortion of the wasp's body during oviposition attempts. Conditions in the cavities of polleniferous and receptive figs are discussed in connection with the pollination process.

Seed activation and seed germination under moisture stress

Abstract: SUMMARY Seeds of calabrese and carrot were held at 10°C or 20°C for periods of up to 21 days in water or polyethylene glycol ‘6000’ solutions of from −5 to −20 bars. Seeds were subsequently placed to germinate in a favourable environment or were first dehydrated before transfer to this environment. The seeds’ ability to germinate was virtually unaffected by any of the temperature, water potential or duration treatments. Increasing water stress progressively reduced the levels of water content and oxygen uptake rates after initial imbibition, and delayed the onset of germination with the accompanying increase in these factors. At −15 and −20 bars, water content remained approximately constant throughout the experiment but oxygen uptake rates fell after day 6. The results have a direct bearing both on the seed ‘priming’ treatment used to accelerate seed germination and on the tolerance to drought of seeds in the field.

The role of anabaena in the azolla-anabaena symbiosis

Abstract: SUMMARY The Anabaena cells in Azolla undergo a developmental pattern of differentiation parallel to that of the fern. At the apex, the algal cells are small and rapidly dividing, and do not fix atmospheric nitrogen. After the leaf cavities are colonized, the algal cells form heterocysts, fix nitrogen and the vegetative cells enlarge considerably. The synchrony between the two partners appears to break down under certain environmental conditions leading to alga-free fern fronds.

Mycorrhizal endogonaceae in a new zealand forest

Abstract: SUMMARY Most vascular plants and some liverworts in a New Zealand coniferous-dicotyledonous forest harboured typical vesicular-arbuscular endophytes, Rhizophagus tenuis or mixtures of the two. At least nine sporing fungi were present but non-sporing races probably predominated. Spores were present in variable densities (2–17 × 103 1−1) in forest soils but their distribution was not obviously related to that of host plants. In inoculation experiments, fungi had a wide host range and, in terms of growth response, hosts showed no clear preferences for particular endophytes. There was some indication of fungi being specific to soil type. Many tree seedlings begin growth perched on rocks or logs and Rhizophagus tenuis is a pioneer endophyte there.

The cyanophyte-hepatic symbiosis ii. nitrogen fixation and the interchange of nitrogen and carbon

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

Effects of aqueous sulphur dioxide on chlorophyll destruction in pinus contorta

Abstract: SUMMARY The effects of aqueous SO2 on chlorophyll breakdown in lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were determined under laboratory conditions. Aqueous SO2 concentrations ranging from 100 to 500 ppm resulted in a sharp decrease in total chlorophyll content. Chlorophyll a was more sensitive to SO2 than chlorophyll b. Quantitative determinations of various pigments suggested that's SO2 causes the conversion of chlorophyll a into phaeophytin a (100–500 ppm SO2) and chlorophyll b into chlorophyllide b (10–50 ppm SO2). The suggested conversion of chlorophyll into chlorophyllide induced by SO2 was supported by increased activity of pine needle chlorophyllase at low aqueous SO2 concentrations (10–50 ppm). The breakdown of chlorophyll molecules by SO2 as measured by loss of Mg++ and total chlorophyll was accompanied by a decreased ability of pine needles to photosynthesize H14CO3. The effect of SO2 on pigment breakdown and rate of photosynthesis was due mostly to the specific direct actions of SO2 and was not a function of increased acidity.

The hormonal control of cell wall turnover in pisum sativum l.

Abstract: SUMMARY A tentative structure for the polysaccharides of pea epicotyl cell walls is presented. The turnover of these polysaccharides has been followed by gravimetric and pulse chase studies. It is suggested that an important effect of IAA is the promotion of turnover in certain wall hemi-celluloses, notably xyloglucan; moreover, such turnover appears to be inhibited by kinetin. The relevance of these findings is discussed in terms of longitudinal and lateral cell expansion.

Potassium efflux by lichen thalli following exposure to aqueous sulphur dioxide

Abstract: Summary Potassium efflux is a useful experimental quantity for assessing damage to lichens exposed to SO2. This SO2-induced K+ efflux is biphasic in response to increasing concentrations of aqueous SO2. The first phase can be extrapolated to identify the SO2 concentration at which no K+ release occurred above the control values. This threshold concentration was used to determine the relative sensitivities of various lichen species. Good agreement was observed between the total K+ lost and the reduction in the total photosynthetic 14C-fixation rates. The magnitude of the SO2-induced K+ efflux indicated that release occurred from intra-cellular sources. The kinetics of the release process and the effects of SO2 on membrane integrity are discussed.

A comparison of the characteristics of glutamine synthetase and glutamate dehydrogenase from lemna minor l.

Abstract: SUMMARY The high affinity of Lemna minor glutamine synthetase for ammonium (Kappm 1.2 – 1.5 × 10−5 M) and its strong inhibition by ADP and 5-AMP contrasts with the low affinity (Kappm 3 × 10−2 M) for ammonium and lack of inhibition by ATP shown by glutamate dehydrogenase. Glutamine synthetase was inhibited by alanine, aspartate, glycine and serine while glutamate dehydrogenase was not affected by any amino acid, other than the product of the reductive amination reaction, glutamate. The properties of glutamine synthetase and glutamate dehydrogenase are consistent with the view that the glutamine pathway is the major route for ammonia assimilation when there is a restricted availability of ammonia. The characteristics of glutamate dehydrogenase, when contrasted with those of glutamine synthetase, and considered in relation to the concurrent regulation of the two enzymes, support the view that the glutamate pathway may contribute towards ammonia assimilation under conditions of high ammonia availability or low energy charge. Comparison of the properties of glutamate dehydrogenase purified from ammonium- and nitrate-grown plants suggests that only a single form of the enzyme is present.

A cytological analysis of the nostoc‐bryophyte relationship

Abstract: SUMMARY A comparative light and electron microscope study has been made of the Nostoc colonies within the thalli of Blasia pusilla and the three British species of Anthoceros, and also of the Nostoc isolated from each bryophyte. From their morphology in culture two taxa of Nostoc have been identified; N. sphaericum from Anthoceros punctatus, A. husnotii and A. laevis, and N. calcicola from other gatherings of Anthoceros laevis and Blasia. These findings support the notion that the algal-bryophyte associations are none specific. Within bryophyte thalli, the Nostoc trichomes are closely packed and specific features cannot be recognized. Mucilaginous sheaths are much less extensive and there is no evidence that the alga thrive in mucilage produced by the adjacent bryophyte cells. Heterocyst frequencies as high as 50% in the bryophytic Nostoc spp. strikingly recall the Azolla, Gunnera and cycad-blue-green algal symbioses. Akinetes, readily produced in culture were only seen in the Nostoc from dormant Anthoceros. The absence of phycobilisomes and high heterocyst frequencies in the bryophytic Nostoc spp. corroborates physiological data that the algae receive organic carbon from their hosts which enable them to fix nitrogen heterotrophically. The Nostoc colonies in both Blasia and Anthoceros are extensively penetrated by multi-cellular bryophytic filaments. Whereas in Anthoceros these comprise highly vacuolate, thin-walled cells, which sometimes contain intracellular Nostoc trichomes, in Blasia the filaments are thick-walled and often develop labyrinthine wall ingrowths. This transfer cell morphology may be interpreted as an adaptation facilitating interchange of metabolites between Blasia and Nostoc. Its absence in Anthoceros perhaps indicates a far less harmonious relationship or may be related to the higher nutrient status of the habitats where the Anthoceros spp. were collected.

Self‐pollen reduces the number of cross‐pollen tubes in the styles of brassica oleracea l.

Abstract: SUMMARY The number of cross-pollen tubes in the styles of self-incompatible kale plants was reduced by 46–94% when self-pollen was applied to the stigma immediately before the cross-pollen. Similar reductions were found when the cross-pollen was applied at time intervals of 2–16 h after the self-pollen, but little or no reduction occurred when the time interval was 24 h or 32 h. No reductions were found when cross-pollen was applied before self-pollen nor when dead cross-pollen was applied before the live cross-pollen. Application of onion pollen before cross-pollen gave a mean reduction of 69%. The results are discussed in the context of current views on the mechanism of self-incompatibility in Brassica, and their practical implications for the breeding of F1 hybrid brassicas.

Effects of light intensity on the formation of vesicular-arbuscular endomycorrhizas on allium cepa by gigaspora calospora

Abstract: SUMMARY Four different light intensities exerted distinctly different effects on the formation, reproduction and influence of vesicular-arbuscular mycorrhiza on onion plants. Over a growth period of 100 days, the rate of infection under low light intensities (5 and 10 klux) was more rapid and the percentage of infection higher than on mycorrhizal plants cultivated under a light of 15 and 20 klux. The production of spores increased with light intensity. A plant growth enhancement occurred at all light levels but was most pronounced under a 10 klux light regime.