bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of simulated acid rain on leaf wettability, rain retention and uptake of some inorganic ions
Authors: PERCY K. E. , BAKER E. A. 
Published: April 2006

summaryLeaves of Phaseolus vulgaris L., Vicia faba L., Pisum sativum L. and Brassica napus L. were exposed from emergence to full expansion to seven treatments of simulated acid rain at pH values between 5.6 and 2.6. Droplet leaf contact angles in all species decreased on leaves exposed to simulated acid rain at pH <4.6 relative to those exposed at pH 5.6. Retention of rain containing fluorescein increased on P. vulgaris leaves exposed to simulated acid rain at pH 4.6 and at pH < 3.8. Retention by B. napus leaves was increased at pH < 4.6. Uptake of the three ions studied was in the order 86Rb+≤35SO42−≤63Ni2+. Uptake of 86Rb+ increased into B. napus leaves and decreased into P. vulgaris leaves exposed at pH ≤ 3.4. Uptake of 35SO42− and 63Ni2+ by B. napus leaves increased after exposure to simulated acid ruin at pH 2.6 but it was unaffected in P. vulgaris. Up to 7%, of applied 35SO42−, was found in the epicuticular wax layer on B. napus leaves 48 h after application, most being found after exposure at pH 2.6. The order of lateral movement of ions within leaves paralleled the order of uptake. Movement of all three ions was increased in B. napus leaves exposed previously to simulated acid rain at pH 2.6. The increased retention of fluorescein on leaves exposed to simulated acid rain and the reduced contact angles for water are attributed to decreases in surface roughness. The altered ion uptake pattern could also be related to changes in surface wax structure or could be associated with observed changes in properties of cuticular membranes. These results demonstrate that the interaction of plants with their atmospheric environment could possibly be affected by pre‐exposure to acid rain in amounts and at pH values that occur in ambient rainfall.
Holocene history of the forest–alpine tundra ecotone in the Scandes Mountains (central Sweden)
Authors: KULLMAN LEIF 
Published: April 2006

summaryThe Holocene history of the forest‐alpine tundra ecotone in Central Sweden (Scandes Mountains) is inferred from radiocarbon analyses of subfossil wood remains. Pinus sylvestris was the dominant subalpine tree species during the early Holocene, when it ascended almost 200 m higher than currently. A short climatic episode (less than 100 years) is postulated to have triggered erosional processes around 6300 n.p., and extinguished the upper part of the subalpine pine woodland. Subsequently, a subalpine belt of Betula pubescens ssp. tortuosa and Alnus incana developed. A Holocene thermal optimum occurred around 6100 b.p., when the birch/alder belt nourished and the tree‐limits probably reached their highest levels during the Holocene. Shortly after 6000 b.p., a long‐term pine forest retrogression started and the birch/alder belt was disrupted by expanding snow‐beds. Pine receded slightly at its tree‐limit, but the uppermost belt of closed pine forest (presently dominated by birch) remained intact until c. 3300 b.p., when a severe climatic deterioration occurred. The present‐day subalpine belt of pure birch forest developed successively and increased in vertical extent after c. 5300 b.p., when summer temperature declined. The evolution of the birch belt is postulated to have been ultimately a response to decreased seasonally, which favoured birch at the expense of pine. Because of the ‘inertia’ characterizing the highest pine forest, the birch belt was relatively narrow until a major thermal decline e. 3300 b.p., when it made a massive downslope expansion. The latest phase of pine recession was during the Little Ice Age, 800–300 b.p.
The effects of root treatments on growth of the primary leaves of Phaseolus vulgaris L.: biophysical analysis
Authors: MILLIGAN S. P. , DALE J. E. 
Published: April 2006

summaryPlants of Phaseolus vulgaris L. were grown at 22.5 °C and transferred to nutrient solution held at that temperature or at 10 °C; other plants were subjected to a pruning treatment that removed all lateral roots and part of the main root. Both root treatments resulted in a substantial reduction in growth of the primary leaves but did not affect leaf water potential or its components, n and P, except briefly for the root‐cooled plants. Treatments did not increase the wall yield threshold, Y, of leaf tissue which was always lower than in control plants; consequently the effective turgor for growth, P–Y, was greater in treated plants. Both treatments reduced wall extensibility, measured by a modified Instron technique and from the relationship between growth of leaf pieces and their turgor, and it is suggested that this is responsible for the reduction in leaf growth.
Continuity of chloroplast and endoplasmic reticulum membranes in Chara and Equisetum
Authors: McLEAN B. , WHATLEY J. M. , JUNIPER B. E. 
Published: April 2006

summaryContinuity between the endoplasmic reticulum and the plastid envelope has often been reported, but has seldom been demonstrated convincingly. Using rapid‐freezing and freeze‐fracturing techniques, we have shown that in the green alga, Chara globularis var. capillacea, and the lower vascular plant, Equisetum telmateia, such continuity is of frequent occurrence. Comparable chemically fixed, resin‐embedded tissues hardly ever reveal connections between the two organelles.
Differences in the spectral characteristics of birch canopies exposed to simulated acid rain
Authors: ASHENDEN T. W. , WILLIAMS J. H. 
Published: April 2006

summarySeedlings of silver birch in a polythene tunnel were exposed to simulated acid rain at pH values of 2.5, 3.5, 4.5 and 5.6 while growing in pots of either John Innes No. 2 potting compost or an Arfon series soil. Measurements of visible and near infrared radiance were taken from the canopies of groups of plants exposed to each of the rainfall treatments, after 34 weeks for plants grown in John Innes compost, and after 75 weeks for plants grown in both soils. Plots of reflectance against wavelength revealed that only plants exposed to the control pH 56 treatment retained the shape of curve that is characteristic of healthy green vegetation. Discriminant analysis showed that the radiometer data could be used to distinguish between birch canopies which had been exposed to the different rainfall treatments after both 34 and 75 weeks.The potential use of radiometry is discussed for identifying plants growing under the stress of acid rainfall in both controlled environments and in the field. It is apparent that further research using the more sensitive scanners now available will be required in order to improve the accuracy of this survey technique.
Comparative studies of plant growth and distribution in relation to waterlogging
Authors: WALDREN S. , ETHERINGTON J. R. , DAVIES M. S. 
Published: April 2006

summaryPopulations of Geum rivale L. and G. urbanum L. were collected from a range of habitats; G. rivale usually occurred in wetter and less‐shaded habitats than G. urbanum. Populations differed significantly in a number of respects; most differences between G. rivale populations were related to the sizes of leaves produced and to plant stature, whereas most of the variation in G. urbanum was related to differences in growth rates. The two species responded very differently to waterlogging, but there was only slight intraspecific variation in waterlogging tolerance in either species. Progeny of hybrid individuals were raised as families; their response to waterlogging was similar to that of one or other of the parent species. In G. rivale and other relatively tolerant families waterlogging generally caused a slight increase in shoot: root dry weight ratio, a small decrease in root dry weight, and had little effect on specific leaf area. Waterlogging of G. urbanum and less‐tolerant families caused a large increase in shoot: root ratio, a large decrease in root dry weight, and a decrease in specific leaf area. Tolerant families always had pronounced axillary bud proliferation, usually accompanied by the development of a rhizome‐like caudex. Less‐tolerant families and G. urbanum lacked a caudex, and had reduced axillary bud proliferation. Many of these traits were found to be highly heritable in hybrid families. The ratio of drained: flooded values was used as a measure of response to waterlogging, and showed highly heritable differences between hybrid families for root dry weight, shoot: root ratio and specific leaf area, indicating that these measures of waterlogging tolerance are genetically determined. Families whose maternal parents were morphologically similar to G. rivale were always relatively tolerant of waterlogging, but some families that were similar to G. urbanum were also tolerant. The results emphasize the effect of waterlogging on plant root formation; while there were also important effects of waterlogging on shoot growth and development, the primary effect appeared to be on the root system. These results are discussed in relation to theories of hybrid ecology, and the need for further comparative studies of hybrid ecology is emphasized.
Interaction between the pollen tube and stigmatic cell wall following pollination inBrassica oleracea
Authors: ELLEMAN CAROLE J. , WILLSON CLARE E. , SARKER R. H. , DICKINSON H. G. 
Published: April 2006

summaryElectron microscopic observations have revealed the stigmatic papilla wall ofBrassica oleraceaL. to be composed of several distinct layers. Measurement of the thickness of the major components of this wall has demonstrated a significant difference in cuticle thickness between the two S (incompatibility) genotypes under study. It is suggested that cuticle thickness is responsible for differences observed in the rates of pollen hydration on the stigma surface. The relevance of tins finding to the genetical control of pseudocompatibility is discussed. Unusually, the pectocellulosic component of the papillar cell wall is composed of three layers. On pollination, the outer layer detaches to permit the elongating pollen tube to pass down the papilla within the wall itself. At the base of the papilla, the tube becomes truly extracellular, growing down in the intercellular spaces between stylar parenchyma cells. Following a bud pollination, the pollen tube may even penetrate the complete cell wall and grow down the length of the cell, invested on one side by the plasma membrane and on the other by the inner face of the pectocellulosic wall. These tubes experience some difficulty in traversing the cell wall at the base of the papillar prior to entering the intercellular spaces of the style.
Metabolic changes associated with akinete germination in the cyanobacterium Anabaena doliolum
Authors: RAI A. N. , RAO V. V. , SINGH H. N. 
Published: April 2006

summaryThe energy requirements of akinete germination in A. doliolum were met initially from aerobic oxidation of endogenously stored carbon reserve. The germination of non‐photosynthetic akinetes commenced in light with new protein synthesis followed by the simultaneous development of oxygenic photosynthesis, nitrate reductase activity, glutamine synthetase activity and aspartate dehydrogenase (AsDH) activity by 24 h and heterocyst formation and nitrogenase activity by 60 h. Glutamate‐oxaloacetate transaminase (GOT) and glutamate‐pyruvate transaminase (GPT) activities were present in mature akinetes and only GPT activity increased during akinete germination. The simultaneous appearance during the course of germination of oxygenic photosynthesis, nitrate reductase activity and glutamine synthetase activity much before that of N2 fixation, implies that oxygenic photosynthesis is more closely associated developmentally with carbon dioxide and nitrate assimilation than with N2 assimilation. The activities of the transaminases (GOT and GPT) during the initial stages of germination suggest a significant role for these enzymes in amino‐acid metabolism associated with germination. The appearance of nitrate reductase activity under N2‐fixing conditions, in the absence of nitrate, suggests that the nitrate assimilating enzyme is not nitrate inducible.
The inhibition of ammonium uptake by nitrate in wheat
Authors: DEIGNAN M. T. , LEWIS O. A. M. 
Published: April 2006

summaryThe improvement of root growth in hydroponically grown crop plants such as wheat when nitrate is added to an ammonium‐only nitrogen source is possibly brought about by a suppression of the over‐rapid absorption of ammonium by nitrate, thus alleviating the stress imposed by root‐based ammonium assimilation on the supply of carbon skeletons required for root growth.The degree of suppression of ammonium absorption by nitrate in hydroponically grown wheat was investigated by measuring the relative rates of absorption of 15N from nutrient solutions containing 2 mM l6N nitrate, 2 HIM 15N ammonium, 2 mM 14N nitrate + 2 mM 15N ammonium, 2 mM 14N nitrate + 2mM 14N ammonium or 3 mM 14N nitrate + 1 mM 15N ammonium.After 8 h 15N feeding, 24% more 15N was found in ammonium‐only fed plants than in nitrate‐only fed plants. The l5N content of plants fed equal concentrations of 14N nitrate and l5N ammonium was 44 % lower than that of 15N ammonium‐only fed plants; those fed a 3:1 mixture of 14N nitrate and l5N ammonium had a 15N content 68%, lower than that of 15N ammonium‐only fed plants. The l5N nitrate +14N ammonium fed plants possessed a 15N content 32% below that of 15N nitrate‐only fed plants.It thus appears that not only is there a measure‐able suppressive effect of ammonium on the uptake of nitrate ions by wheat plants but that the inverse effect is even more pronounced and could account for observed effects of mixed ammonium + nitrate nutrition on root growth.
Influence of light and form of nitrogen on chlorine requirement of kiwifruit
Authors: SMITH G. S. , CLARK C. J. , BUWALDA J. G. , GRAVETT I. M. 
Published: April 2006

summaryThe extent to which light, potassium, and form of nitrogen (ammonium and nitrate‐nitrogen) modified the requirement by kiwifruit (Actinidia deliciosa var. deliciosa) for chlorine was examined in solution culture. A greater concentration of chloride was required in the nutrient solution for maximum growth under low irradiance than under high irradiance. In the absence of chloride, growth was severely restricted and the response to potassium was significantly reduced, especially under low light.Greater concentrations of chloride accumulated in the leaves of plants grown under high irradiance than under low irradiance. Increasing the concentration of nitrate in the leaves either by growing the plants under low light or by increasing the quantity of nitrate in the nutrient solution, substantially reduced the accumulation of chloride. The decrease in the concentration ot chloride was accompanied by an increase in the concentration of nitrate. Thus the combined concentration of nitrate and chloride was relatively constant over a wide range of treatments suggesting that a negative feedback mechanism may be operating in this species. However, while nitrate was preferentially accumulated by kiwifruit plants it could not substitute fully for chloride. Once the concentration of chloride in the leaves was decreased below 70μmolg−1 d. wt by competing nitrate ions, growth was substantially reduced. It is concluded that the effect of light on the chloride status of kiwifruit plants can largely be explained in terms of the strong competitive effect from nitrate ions, with greater concentrations of nitrate accumulating in the leaves under low irradiance than under high irradiance.The negative effect of potassium on the chloride status of the plants is not considered to be a specific physiological effect but rather the consequence of chloride, along with other non‐limiting nutrients, accumulating in the tissues of the severely potassium deficient plants.The ecological implications of the results are discussed in relation to features of the habitat in China where kiwifruit vines have evolved. The results of the present study are entirely consistent with this species having evolved in an environment where the availability of chloride and ammonium is relatively high while that of nitrate is severely restricted. It is concluded that the high concentration of chloride required in the tissues of kiwifruit vines is an adaptation which minimizes the expenditure of energy on the generation of osmotic pressure in the tissues rather than specifically maintaining charge balance.
Selection of lines with high and low sodium transport from within varieties of an inbreeding species; rice (Oryza sativa L.)
Authors: YEO A. R. , YEO M. E. , FLOWERS T. J. 
Published: April 2006

summaryVarieties (including designated cultivars) of Asian rice (a predominantly inbreeding species) show large individual variability in sodium transport and salinity resistance. Recurrent selection has been carried out over five generations with populations of Oryza sativa L. cv. IR36 and cv. IR20. Large numbers of individuals were exposed to a low concentration of NaCl in solution culture, and their sodium uptake determined non‐destructively by sampling the third leaf. The range of sodium concentrations in the leaf was two or three orders of magnitude. Individuals showing both high and low extremes of sodium uptake were selected and allowed to self‐pollinate. The sodium uptake by the progeny was measured in the same way, and the selection repeated. Significant differences in the frequency distribution of sodium transport between the selected lines were evident in both varieties after three cycles of selection. The lines continued to segregate in the fourth and fifth generations by which time the high and low selected lines showed substantial differences in sodium uptake. It is concluded that useful genetic diversity for sodium uptake and hence salt resistance exists within modern rice varieties.
Mycelial uptake, translocation and assimilation of nitrogen from 15N‐labelled ammonium by Pinus sylvestris plants infected with four different ectomycorrhizal fungi
Authors: FINLAY R. D. , EK H. , ODHAM G. , SÖDERSTRÖM B. 
Published: April 2006

summaryThe uptake and assimilation of 16N‐labelled ammonium was followed in Pinus sylvestris L. plants infected with four different ectomycorrhizal fungi, Rhizopogon roseolus Fr. Suillus bovinus (Fr.) O. Kuntze, Pisolithus tinctorius (Fr.) Fr. and Paxillus involutus (Mich, ex Pers.) Cohen & Couch. Plants were grown in flat perspex observation chambers or in Petri dishes containing non‐sterile peat; in each case the fungal mycelium growing from a host plant was allowed to cross a barrier and to colonize an area of peat from which roots had been excluded. Labelled ammonium was fed to the mycelium, and the shoot, root and mycelial tissues analysed for total and 15N‐labelled free amino acid contents after a feeding period of 72 h. High proportions of 15N‐labelled glutamate/glutamine, aspartate/asparagine, and alanine were found in the fungal mycelia of all species except Pax. involutus where labelled aspartate/asparagine was not found. Lower proportions of labelled serine, threonine, tyrosine, lysine, ornithine and arginine were also found in the mycelium. The degree of 15N enrichment declined throughout the transport pathway but between 5 and 50% of the amino acids were 15N‐labelled in the plant shoots. In total, at least 2–3 % of the nitrogen supplied was assimilated as labelled amino acid during the 3 day feeding period, the largest amounts of labelling occurred in glutamic acid/gultamine and aspartic acid/asparagine.
Vesicular–arbuscular mycorrhizas and the soil‐disturbance‐induced reduction of nutrient absorption in maize
Authors: EVANS D. G. , MILLER M. H. 
Published: April 2006

summaryThis study was designed to test the hypothesis that disruption of the macrostructure of a previously zero‐tilled soil is capable of reducing vesicular‐arbuscular (VA) mycorrhizal infection to a degree such that phosphorus (P) absorption is reduced. Undisturbed soil cores (within plastic cylinders) were excavated from long‐term, zero‐tilled plots. Soil removed from these plots, which was first subjected to structurally disruptive forces and then packed into identical cylinders, formed the disturbed comparisons. Maize(Zea mays L.), wheat(Triticum aestivum L.), spinach(Spinacea oleracea L.)or rape(Brassia napus L.)were grown in the cores and P and zinc (Zn) absorption patterns monitored.Soil disturbance significantly reduced P and Zn absorption by maize grown in soil originating from three sites differing in local geography and/or texture. Disturbance also reduced mycorrhizal infection in the three soils.A significant effect of disturbance upon the VA mycorrhizal infection of both maize and wheat roots (both mycorrhizal) and also upon the P absorption by these species was observed. None was found with respect to spinach and rape comparisons (non‐mycorrhizal).Injection of benomyl, a potent inhibitor of mycorrhizal fungi, into the soil surface significantly reduced the influence of soil disturbance upon P absorption. No significant differences were found in VA mycorrhizal infection within fungicide‐treated cores.We accepted our hypothesis based upon the above evidence.
Physical and topological assessment of effects of a vesicular–arbuscular mycorrhizal fungus on root architecture of big bluestem
Authors: HETRICK B. A. DANIELS , LESLIE J. F. , WILSON G. THOMPSON , KITT D. GERSCHEFSKE 
Published: April 2006

summaryThe influence of a vesicular‐arbuscular (VA) mycorrhizal fungus, phosphorus (P) fertilization, and soil microorganisms on growth and root architecture of big bluestem (Andropogon gerardii Vitroari) was investigated. In pasteurized soil, mycorrhizal inoculation significantly improved plant growth and increased root length and the number and the diameter of the primary, secondary and tertiary roots. These differences between mycorrhizal and non‐mycorrhizal plants diminished with added P. In pasteurized soil amended with non‐sterile soil sievate, differences between mycorrhizal and non‐mycorrhizal plants were still obvious, but in many treatments these plants grew more poorly (had less dry weight, root length, number or diameter) than their counterparts in unamended pasteurized soil. Growth in non‐sterile soil was also suppressed, and mycorrhizal responses were not detected since all of the plants in non‐sterile soil became mycorrhizal whether or not they were inoculated. Two analyses of calculated parameters which describe root‐system architecture were conducted. The first, specific root length (SRL), revealed that mycorrhizal symbiosis dramatically alters root morphology in soils of low fertility. These changes were similar to the changes evoked by added P. The second, path length (Pe) revealed that mycorrhizal fungi (and to some degree other soil microbes) significantly alter root architecture by reducing the relative amount of root branching. Apparently, mycorrhizal plants develop a more elongate, exploratory growth pattern which permits the fungal hyphae to extract nutrients from a larger volume of soil. In contrast roots of non‐mycorrhizal plants maintain a more highly branched pattern of root growth, and the roots themselves play a more critical role in the direct extraction of nutrients from the soil. These differences in root topology were not directly associated with the concentration of exogenous P, but instead appeared to be controlled by the mycorrhizal fungi themselves. Thus, while internal P content of plants mediates the establishment of the mycorrhizal symbiosis, the fungi can alter the root architecture of the plant to a form which best accommodates the symbiosis under the prevailing fertility and rhizosphere conditions in the soil. By altering root‐system architecture in this manner, the mycorrhizal fungi can control, at least to some degree, the dependence of the host on the symbiosis. Thus, the topology of the root system is contingent upon the microflora in the rhizosphere. The topological analysis revealed differences in root architecture not detected by any of the other measures of root morphology. These differences suggest that mycorrhizal fungi affect root architecture and plant growth in ways not directly associated with phosphorus uptake.