bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relation of shoot growth phases in seedling oak to development of the tap root, lateral roots and fine root tips
Authors: HARMER RALPH 
Published: April 2006

summarySeedlings of Quercus robur L. were grown in tubes containing peat and perlite and observations of the periodicity of root and shoot growth were made. Root and shoot growth were not closely coupled. The rate of elongation of the tap root was approximately constant and did not decline during periods of stem growth and leaf expansion. The complexity of the root system increased throughout growth; tap roots emerged without lateral roots but by the start of the third flush of shoot growth plants had about 10 metres of lateral root and 6500 root tips. There were about 6 first order laterals per cm of tap root but the relationships between length of the lateral root system, number of root tips and tap root length changed during growth. There was no evidence that rhythmic growth in oak is related to an unfavourable root:shoot ratio caused by rapid growth of the shoot and leaves during a flush.
The effect of soil compaction on wheat during early tillering
Authors: ATWELL B. J. 
Published: April 2006

summaryWheat (Triticum aestivum L. ev. Eradu) was grown in the field on a deep loamy sand which had either a compact soil layer (compact soil) between 10 and 55 cm depth or a deep‐tilled profile (loosened soil). Concentrations of metabolites were affected by the presence of mechanical impedance. The concentrations of soluble sugars (including glucose, fructose and sucrose), free amino acids and inorganic ions (K+, Na+, NH4+, Cl−, NO3−, H2PO4−, SO42−) in consecutive 1 cm root segments of the seminal roots are reported. When tissues equidistant from the apex were compared, the concentrations of free amino acids were greater in roots from loosened soil; soluble sugars were also more concentrated in roots from loosened soil except in the apical 1 cm of the root. However, comparing root tissues of the same age (calculated from elongation rates), showed that concentrations of soluble sugars were smaller in roots from loosened soil. Potassium, Na+, Cr and SO42 were present in fairly constant concentrations along the terminal 4 cm of the root; NO3− and H2PO4 showed more distinct gradients along the axis. Roots from loosened soil had higher NO3 and lower SO42− concentrations than those from compact soil. The total concentration of solutes assayed was 19–31 % smaller in roots growing in compact soil than in roots from loosened soil. Soluble sugar concentrations in shoots as a whole were 21 % greater in plants taken from compact soil than those from loosened soil, suggesting that the lower shoot growth rates of the former were not the result of carbohydrate shortage.
Morphological aspects of in vitro co‐cultivation of Frankia alni subsp. pommerii Lalonde (strain ACN1AG) and Frankia elaeagni (Schröter) Becking (strain EANlpec) with larch (Larix×eurolepis Henry) cells
Authors: LALIBERTÉ S. , LALONDE M. 
Published: April 2006

summaryThis study describes the establishment of in vitro co‐cultures between the microsymbiont Frankia and cells from the non‐actinorhizal plant Larix×eurolepis Henry. Co‐cultures with strains from the two host‐plant specificity groups Alnus and Elaeagnus are compared, namely Frankia alni subsp. pommerii Lalonde strain ACN1AG and Frankia elaeagni (Schroter) Becking strain EANlpec. Larch cell clumps expanded when co‐cultivated with Frankia strain ACNlAG. The actinomvcete proliferated and hyphae developed at the surface of the clumps, in intercellular spaces, in middle lamellae and, more rarely in the plant cell wall. Conversely co‐cultivation of larch cells and Frankia strain EANlpec was highly detrimental for both partners. Dual colonies became degenerate, with the appearance of necrotic plant cells and senescent Frankia structures. The plant cell wall seemed to show a hypersensitive reaction to the presence of the actinomvcete.
Stimulation of hyphal growth of the VA mycorrhizal fungus Gigaspora margarita by suspension‐cultured Pueraria phaseoloides cells and cell products
Authors: PAULA M. A. , SIQUEIRA J. O. 
Published: April 2006

summaryThe effects of suspension‐cultured Pueraria phaseoloides Benth. (pueraria) cells and cell products on growth of hyphae of the VA mycorrhizal fungus Gigaspora margarita Becker & Hall in liquid media were examined. Addition of 6‐d‐old cell cultures of pueraria cells at a concentration of 25 cells ml−1 of medium caused a 3.9‐fold increase in hyphal growth. Higher cell concentrations resulted in less growth stimulation. Cell exudates or extracts (cell products) at a concentration of 25 μl−1 of medium also stimulated hyphal growth. Successive cell additions, or transfer of the spores into fresh media containing pueraria cells, resulted in no additional hyphal growth. Spores soaked in exudates or extracts showed faster and more vigorous growth when plated on an agar medium than those soaked in a control solution. It is suggested that suspension‐cultured pueraria cells stimulate hyphal growth of VA mycorrhizal fungi by accumulating and leaking very active metabolites into the medium.
Carbon flow into soil and external hyphae from roots of mycorrhizal cucumber plants
Authors: JAKOBSEN I. , ROSENDAHL L. 
Published: April 2006

summaryCucumber (Cucumis sativus L.) plants grown in PVC tubes with a partially sterilized soil‐sand mixture were inoculated with the vesicular‐arbuscular mycorrhizal fungus Glomus fasciculatum (Thaxter) Gerdemann & Trappe emend. Walker & Koske or left uninoculated. The soil column of each PVC tube was divided into a root and a hyphal compartment by a mesh bag (60 μm), which retained the roots but allowed external hyphae to pass. Inoculated plants rapidly became infected and an extensive mycelium developed. Three weeks after seedling emergence plants were labelled with 14CO2 for 16 h. The distribution of 14C within the plants and the 14C flow into external hyphae and soil were measured during an 80 h chase period. Below‐ground respiration in mycorrhizal plants accounted for 27% of the photo assimilated 14C. Organic 14C in the soil represented 3˙1 % of the fixed 14C, and 26 % of this was located in external hyphae.Based on conservative assumptions concerning dry weight of internal mycorrhizal infection and growth yield of the fungus, it was estimated that mycorrhizal events consumed 20 % of photoassimilated 14C. The specific incorporation of C by the external mycelium in the hyphal compartment was 41 μg C mg−1 dry wt. d−1.The importance of external VA mycorrhizal hyphae for the distribution of plant‐derived C in the soil volume and as a substrate source for the soil biota is discussed.
Occurrence of unilateral genetic transfer and genomic replacement between strains of Stereum hirsutum from non‐outcrossing and outcrossing populations
Authors: AINSWORTH A. M. , RAYNER A. D. M. , BROXHOLME S. J. , BEECHING J. R. 
Published: April 2006

summaryPopulations of the wood‐decaying basidiomycete, Stereum hirsutum (Willd. ex Fr.) S. F. Gray, from different geographical regions, reproduce either by outcrossing or non‐outcrossing. Outcrossing generates variable progeny whilst non‐outcrossing results in clonal sub‐populations.Pairings between single‐basidiospore‐derived strains from non‐outcrossing and outcrossing populations commonly result in mutual rejection or mycelial invasion of the outcrosser by the non‐outcrosser. However, on the basis of both morphological evidence and studies of DNA restriction fragment length polymorphisms, some pairings result in unilateral transfer of nuclear DNA from the non‐outcrosser into the outcrosser. In some combinations the resultant putative heterokaryon may be stable and give rise to variable basidiospore progeny with unusual development and non‐self recognition responses and at least one mating‐type specificity evidently transferred from the non‐outcrosser. In other combinations, genomic takeover by the non‐outcrosser has been demonstrated, leading respectively to the emergence of mycelial sectors or production of basidiospore progeny in which solely or predominantly non‐outcrossing nuclear DNA is associated with outcrossing mitochondrial DNA.These observations add a new perspective to the selective pressures influencing sexual outcrossing and non‐outcrossing and the role and interplay of these breeding strategies in reproductive isolation and speciation.
Stump colonization byArmillaria luteobubalinaand other wood decay fungi in an age series of cut‐over stumps in karri (Eucalyptus diversicolor) regrowth forests in south‐western Australia
Authors: PEARCE M. H. , MALAJCZUK N. 
Published: April 2006

summaryAs part of a study of interactions betweenArmillaria luteobubalinaWatling and Kile and other wood decay fungi, we conducted a three‐year floristic survey of fungal colonization of 150 eucalypt stumps (left after clearfelling of mature forest) in a series of karri (Eucalyptus diversicolorF. Muell.) regrowth stands of different ages. Certain fungi showed preferences for different eucalypt species or parts of stumps in their choice of food base. A successional trend of fungal species was evident in the age series of stumps (0–16 yr after logging). There was no significant relationship between the absence ofA. luteobubalinaand the presence of other fungal species on stumps, but there was a significant correlation between the percent stump base colonized byA. luteobubalinaand presence of other fungi, indicating some degree of natural suppression ofA. luteobubalina.More than 80 wood decay fungi were observed on stumps, some of which are cosmopolitan, such asCoriolus versicolor(L. ex Fr.) Quel. andStereum hirsutum(Wild, ex Fr.) S.F. Gray, but a number of which are yet undescribed.
Effects of water on the decomposition and release of nutrients from cow pats
Authors: DICKINSON C. H. , CRAIG G. 
Published: April 2006

summaryDecomposition of cow pats was studied using artificially placed pats which were either covered, uncovered or irrigated with additional water. Weight losses were recorded and these showed that there was little difference between the irrigated and uncovered treatments whereas the covered dung decayed extremely slowly. These dung pats were also analysed for their nutrient content, as was the surface horizon of the underlying soil. The results showed that nutrient losses from the dung were not paralleled by a concomitant increase in the soil, which implies that considerable quantities of nutrients were removed from the soil almost as quickly as they left the dung. It is suggested that this implies considerable root activity under the cow pats, perhaps commencing almost as soon as they are laid.
The influence of ozone, acid mist and soil nutrient status on Norway spruce [Picea abies(L.) Karst.]
Authors: BARNES J. D. , EAMUS D. , BROWN K. A. 
Published: April 2006

summaryThree‐year old Norway spruce [Picea abies(L.) Karst.] trees of clonal stock originating from medium altitude in southern Germany were transplanted in May 1986 into two acid brown‐earth soils which differed particularly in the amounts of exchangeable Ca2+and Mg2+. During the summers of 1987 and 1988 trees were exposed in large‐scale fumigation chambers (solardomes) to ozone at 200 or 40 (control) μg m−3Acid (pH 3˙6) or control mist (pH 5˙5) solution was applied daily to trees in each half of the solardomes. In late autumn (1988) the light response of CO2exchange, and the chlorophyll and soluble carbohydrate contents of needles were determined. Ozone and/or acid mist treatment had only minor (< 10%) effects on the light‐saturated rate of photosynthesis which were not statistically significant in plants from either soil. Needles from trees raised on the richer soil and exposed to a combination of ozone and acid mist showed a significant increase in the apparent quantum yield of photosynthesis which was associated with an increase in chlorophyll content. Ozone (alone) stimulated the rate of dark respiration by 40 and 58 % for trees grown in richer and poorer soils, respectively, and this was associated with a decrease in ethanol‐soluble carbohydrate content of needles. Where significant interactions between ozone and acid mist were found, they were generally antagonistic. The reduction in the ethanol‐soluble carbohydrates would be expected to reduce frost hardiness, and may contribute to the increased sensitivity of ozone‐treated needles to freezing, which has been reported in previous studies.
Cation‐exchange properties and adaptation to soil acidity in bryophytes
Authors: BÜSCHER P. , KOEDAM N. , VAN SPEYBROECK D. 
Published: April 2006

summaryCation‐exchange processes of plant tissue are often hypothesized to affect ion uptake. Fixation of cations on exchange sites could either withdraw cations from further uptake, or concentrate them for the absorption sites. For a number of bryophyte taxa (Atrichum undulatum(Hedw.) P. Beauv.,Homalothecium sericeum(Hedw.) B.S.&G.,Leucobryum glaucum(Hedw.) Angstr.,Mnium hornumHedw.,Plagiomnium undulatum(Hedw.) T. Kop.,Polytrichum formosumHedw.), these contrasting hypotheses were tested by studying cation‐exchange properties and soil preference of populations with respect to soil acidity and soil exchangeable cations (Al, H, Fe, Mn, Ca, Mg, K). Acidiphilous and acidicline taxa (preference for soils with pH < 5) with relatively lower cation‐exchange capacities tolerate high exchangeable aluminium levels and low calcium levels. Neutrocline taxa (preference for soils with pH > 5) with higher cation‐exchange capacity avoid aluminium in the substrate and thrive on calcium‐rich substrates. Cation‐exchange properties therefore do not protect mosses against potentially toxic cations such as aluminium through a sequestration mechanism. However cation exchange sites may increase the availability of cations. High cation‐exchange capacity was indeed shown to favour fixation of aluminium over calcium ions and hence a low capacity is a prerequisite for taxa adapted to acid soils.
Proteolytic activity during senescence of plants
Authors: HUFFAKER R. C. 
Published: April 2006

summaryAlthough information has rapidly developed concerning the intracellular localization of plant proteins, relatively few reports concern the intracellular location of endo‐ and exo‐proteolytic activities. Relatively few proteases have been purified, characterized, and associated with a specific cellular location. With the exception of the processing proteases involved in transport of proteins across membranes, little progress has yet been made concerning determination of in vivo products of specific proteases.Information on the turnover of individual proteins and the assessment of rate‐limiting steps in pathways as proteins are turned over is steadily appearing. Since chloroplasts are the major site of both protein synthesis and, during senescence, degradation, it was important to show unambiguously that chloroplasts can degrade their own constituents. Another important contribution was to obtain evidence that the chloroplasts contain proteases capable of degrading their constituents. This work has been more tenuous because of the low activities found and the possibility of contamination by vacuolar enzymes during the isolation of organelles.The possible targeting of cytoplasmic proteins for degradation by facilitating their transport into vacuoles is a field which hopefully will develop more rapidly in the future.Information on targeting of proteins for degradation via the ubiquitin (Ub) degradation pathway is developing rapidly. Future research must determine how much unity exists across the different eukaryotic systems. At present, it has important implications for protein turnover in plants, since apparently Ub is involved in the degradation of phytochrome.Little information has been developed regarding what triggers increased proteolysis with the onset of senescence, although it appears to involve protein synthesis. Thus far, the evidence indicates that the complement of proteases prior to senescence is sufficient to carry out the observed protein degradation. This field of study has great practical implications, e.g. maintaining photosynthesis during seed‐fill in order to obtain greater crop yields. The current use of ‘stay green’ variants in the populations of several crop plants to produce increased yields shows the potential for future development.The near future should see exciting discoveries in these areas of research that will have far reaching effects on the construction of transgenic plants for future research accomplishments and agricultural use.

CONTENTS

Summary
200

I.
Introduction
200

II.
Protein turnover
201

III.
Proteases
201

IV.
Plant proteases
202

V.
Senescence
203

VI.
Proteolytic activity during senescence
205

VII.
Chloroplasts
207

VIII.
Proteolytic activities associated with chloroplasts
209

IX.
Proteolytic activities associated with stromal fractions
210

X.
Thylakoid proteins
211

XI.
Proteolytic activities associated with thylakoid fractions
214

XII.
Targeting proteins for degradation
215

References
223
Spectral properties and net photosynthesis of Aster tripolium L. and Halimione portulacoides (L.) Aellen leaves under saline and hypoxic conditions
Authors: LORENZEN BENT , SKOVHUS KARIN , JENSEN ARNE 
Published: April 2006

summarySpectral properties of leaves of Aster tripolium L. and Halimione portulacoides (L.) Aellen grown under saline and hypoxic conditions were studied in relation to the net photosynthesis (Pn) of the leaves. Cuttings of A. tripolium and of H. portulacoides were grown in aerated or nitrogen flushed nutrient solution under glasshouse conditions. During a 13 d period both Pn and the directional spectral reflectance and transmittance of the adaxial surface of marked leaves was recorded. At the end of the experiment the water content and total chlorophyll content of the leaves was determined. The chlorophyll content and Pn of the leaves were highly correlated. Between 56 and 67 % of the variation in Pn could be accounted for by changes in chlorophyll content. Light absorption by the plant pigment was negatively correlated to the reflectivity. More than 91 % of the variation in reflectivity could be accounted for by changes in absorption. However, Pn of the two species grown under saline and hypoxic conditions was poorly or not correlated to spectral reflectance (r2= 0.07–0.14), and only 12–14% of the variation in absorptance could be accounted for by changes in Pn. The low correlation between Pn and spectral properties may be due to asymptotic spectral characteristics when chlorophyll content exceeded 2 mg g−1 d. wt and to changes in respiration and stomatal conductance that may influence Pn independent of reflectance.
Rates of apoplastic diffusion in wheat leaves
Authors: CANNY M. J. 
Published: April 2006

summarySince the movement of water in leaves beyond the veins is not apoplastic, solutes excluded from the symplast move in the apoplast by diffusion. Estimates of the diffusivities (D) of sulphorhodamine G (SR) in the apoplast of wheat leaves are presented, measured by the analysis of advancing profiles of fluorescence of SR over a range of times from 7 to 90 min. The greatest values of D were found from vein sheaths, over the surface of fibre extensions where present, to and along the inner periclinal walls of the epidermises. The value along the lower epidermis (D = 8 × 1(T8 cm2 s1) was consistently twice that in the upper epidermis. SR diffused radially into the fibre walls of the vein extensions at a much lower rate (D= 10−10 cm2 s−1). At these rates the visible fluorescence occupied much of the apoplast between the veins after about 1 h. These findings suggest that useful generalizations may be gained from investigations of the spread of natural solutes of the transpiration stream in cell wall material.
Studies on the tolerance to sulphur dioxide of grass populations in polluted areas
Authors: WILSON G. B. , BELL J. N. B. 
Published: April 2006

summaryClones of Lolium perenne L., chosen as sensitive or tolerant to sulphur dioxide (SO2) injury, were employed in a half‐dialled crossing programme to carry out an analysis of the genetic basis of tolerance to acute SO2 concentrations. Their progeny were fumigated with SO2 and the percentage injury on the foliage scored and subjected to an analysis of variance designed to test an additive dominance model. The genetic analysis indicated that dominance was towards SO2 susceptibility. Further analysis of the relationship between variance and covariance of members of the same parental array supported this finding and suggested that only a few genes were involved. The results show clearly that the relative sensitivity of L. perenne to acute SO2 concentrations is heritable, with significant additive and non‐additive components. A comparison with the very limited number of other studies on the genetic basis of SO2 tolerance, suggests that it is highly variable between species.
Explant cultures of maize (Zea mays L.) raised under water‐deficit and waterlogged conditions
Authors: DHINGRA JYOTI H. R. , VARGHESE T. M. 
Published: April 2006

summaryRoot‐tip segments excised from plants grown under conditions of water deficit and waterlogging did not exhibit any significant change in the extent of callus induction over controls when cultured on Murashige and Skoog's (MS) medium supplemented with 2,4–D alone or in combination with L‐proline. On the other hand, the mesocotyls cultured on medium with 2,4–D showed an increase in the extent of callus induction which was further improved by the addition of L‐proline. The root tip callus from plants grown under water deficit conditions showed increases in both fresh and dry weight over controls on MS medium supplemented with 2 mg 1–1 2,4‐D while mesocotyl segments from plants grown in the presence of 5 % polythylene glycol‐6000 produced heavier calli on 2,4‐D supplemented media. The addition of L‐proline to the medium favoured an increase in both fresh and dry weights of root tip callus but failed to bring about a similar change in mesocotyl callus.Waterlogging pre‐treatment resulted in an increase in fresh weight of root tip callus over control on 2,4‐D supplemented medium but not with the mesocotyl callus. Further, addition of proline to the medium enhanced both fresh and dry weights of root tip callus but did not affect the weights of the callus of mesocotyl origin. The pre‐conditioning treatment did not modify the regeneration potential of the explants. The biochemical basis of such a differential behaviour of the two explant types is discussed in the light of available information.