bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of soil temperature on growth, biomass allocation and resource acquisition of Andropogon gerardii Vitman
Authors: DELUCIA EVAN H. , HECKATHORN SCOTT A. , DAY THOMAS A. 
Published: April 2006

summaryThe effects of root temperature on growth and resource acquisition (carbon, nitrogen and phosphorus) were examined in Andropogon gerardii, a dominant C4 grass of tallgrass prairies of the midcontinental USA. Soil temperature (5.9 to 35.5 °C) was manipulated independently from air temperature (c. 25/20 °C day/night) in a greenhouse. Total biomass at the end of the experiment and relative growth rate (RGR) were maximum at 25 °C soil temperature (Tsoil) and decreased at higher and lower temperatures. Tsoil had no effect on leaf area ratio (the ratio of leaf area to total biomass); thus the effect of Tsoil on RGR was primarily through its influence on net assimilation rate (NAR). Different mechanisms may have contributed to decreases in NAR at sub‐ and supra‐optimal Tsoil. Soil temperatures below 20 °C caused significant reductions in foliar nitrogen (N) and phosphorus (P) concentration. High concentrations of these nutrients in roots suggest that nutrient transport was more strongly inhibited than uptake, and low foliar N and P may have contributed to reduced photosynthetic rates observed at 5 and 10 °C Tsoil. Net photosynthesis was < 12 μmol m−2 s−1 at 5 and 10 °C Tsoil and > 20 °mol m−2 s−1 at 15–40 °C. Changes in net photosynthesis did not therefore contribute to the reduction in NAR at supra‐optimal Tsoil. The strong growth dependence of A. gerardii on Tsoil indicates that this abiotic factor may significantly limit productivity in tallgrass prairie, particularly early in the growing season.
Growth and biomass partitioning of populations of EuropeanPinus sylvestrisL. under simulated 50° and 60° N daylengths: evidence for photoperiodic ecotypes
Authors: OLEKSYN J. , TJOELKER M. G. , REICH P. B. 
Published: April 2006

summarySeedlings of 24 European populations of Scots pine (Pinus sylvestrisL.) were grown from seed for 4 months in controlled environments under photoperiod conditions of 50° or 60° N, but with similar temperatures and total daily quantum flux in both photoperiods. During the experiment the photoperiod was continually changed to simulate the photoperiod from 1 May to 1 September at each latitude. Secondary needle length, plant height and dry mass at harvest were greater at 60° than the 50° N photoperiod. All populations allocated significantly greater proportions of their biomass to roots at 50° than 60° N photoperiod, yet central populations allocated less to roots than northern ones in both photoperiods. Northern populations (origin > 55° N latitude) stopped height growth up to 50 d earlier than the other populations when grown under 50° N photoperiod conditions. Under the 60° N photoperiod, all populations, except the most southern one, developed terminal leader buds and ceased growth in height between 87 and 105 d after sowing. Using cluster analysis, populations with similar growth and photoperiod responses were assigned to two major groups: northern (61–56° N from Sweden and USSR), and central (55–40° N from the USSR, Poland, Germany, Belgium, France, Czechoslovakia, Yugoslavia, and Turkey). The most southern population, from Turkey, was classified independent from the central group based on growth characteristics alone. No single mechanism of height growth cessation can explain the response of all populations of 1‐yr‐old seedlings of Scots pine. Our findings support the hypothesis that northern plants respond to a combination of increasing night length and accumulated degree‐days. However, the evidence suggests that central and southern populations do not respond to increased night length as they all ceased growth earlier in the 60° than the 50° photoperiod. As hypotheses for further testing, we propose that central and southern populations are either photoperiodically insensitive or respond to short nights or to accumulated degree‐days at their native latitudes.
Tansley Review No. 36 Excited leaves
Authors: WALKER DAVID 
Published: April 2006

SUMMARYPhotosynthesis is largely to do with energy transduction; the conversion of light energy into electrical energy into chemical energy. Precisely how much light energy is needed to bring about the reduction of one molecule of carbon dioxide and the release of one molecule of oxygen (the quantum requirement) is a matter of fundamental importance and one which has attracted much past controversy. This article concludes that a minimum quantum requirement of eight, as demanded by the Z‐scheme, is obviously consistent with much contemporary work which puts the measured value for C3 leaves close to nine. Moreover, while values of less than eight (obtained in some circumstances with micro‐organisms), are a reminder that nothing is beyond challenge they are not, in the absence of confirmation and extension, sufficiently compelling to demand rejection of either the Z‐scheme or current measuring procedures. This article also shows why, even if the underlying minimum requirement was now accepted beyond all reasonable doubt, there would still be very good reasons for continuing, indefinitely, to measure actual photosynthetic efficiency in the natural environment. It discusses some of the implications of the fact that all plants, if not stressed, appear to photosynthesize at the same rate in low light. It explains the role of fluorescence in its relation to quantum yield, the possibility that the rate of photosynthesis might be determined from fluorescence measurements alone, and that a combination of fluorescence and gas exchange measurements could provide new information about the manner in which ‘dark respiration’ is affected by light. It indicates how contemporary interest in all of these matters has focused attention on the necessity for safe dissipation of excitation energy by leaves and on the manner by which this might be achieved.

CONTENTS

Summary
325

I.
Excitation
325

II.
Quantum requirement
326

III.
Learning from fluorescence
335

IV.
Safely dissipated
340

Acknowledgements
342

References
342
Root—stem junctions of a desert monocotyledon and a dicotyledon: hydraulic consequences under wet conditions and during drought
Authors: EWERS FRANK W. , NORTH GRETCHEN B. , NOBELF PARK S. 
Published: April 2006

SUMMARYJunctions between shoot‐borne main roots and stems, which are a crucial part of the water‐flow pathway in plants, were investigated for the leaf succulent Agave deserti Engelm. and the sympatric stem succulent Ferocactus acanthodes (Lem.) Britton & Rose under wet conditions and during 21 d of drying in soil. During soil drying, the hydraulic conductance per unit pressure gradient (Kh) declined dramatically in the junctions and to a lesser extent in the roots, but not in stems. The decline in junction Kh was particularly important for A. deserti, which lacks vessels in its stem, because even under wet conditions its Kh was lower in stems and junctions than in roots. For both species, the decline in Kb was due to embolism in the connective tracheary elements at the junction. Such connective elements may be particularly vulnerable to embolism due to their large areas of unlignified primary cell wall. Because the embolism is reversible, the junctions act as rectifiers. Thus, high Kh under wet conditions allows for rapid water uptake following rainfall, and low Kh during drought helps limit water loss from the succulent shoots to a dry soil.
Long‐term exposure of Norway spruce,Picea abies(L.) Karst., to ozone in open‐top chambers
Authors: WALLIN G. , OTTOSSON S. , SELLDÉN G. 
Published: April 2006

SUMMARYRates of photosynthesis at different concentrations of CO2(0–1850 μmol mol−1) were measured using one clone of Norway spruce,Picea abies(L.) Karst. exposed to three different concentrations of ozone for four seasons (1985–8) in open‐top chambers. The treatments were non‐filtered air+ozone (NF+), non‐filtered air (NF) and charcoal‐filtered air (CF). The measurements were made on shoots of four different age classes. No significant effects were found on photosynthesis or on leaf conductance to CO2in current year shoots. In 1‐ to 3‐yr‐old shoots, leaf conductance to CO2and rates of net photosynthesis at both 330 μmol mol−1CO2(Pn330), and saturating concentrations of CO2(Pnmax), decreased with increasing shoot age and ozone concentration, although this was only significant forPn330 in 3‐yr‐old shoots. In current year shoots the intercellular concentration of CO2was significantly higher in NF+‐treated shoots compared with CF‐ and NF‐treated shoots, while in the 2‐ and 3‐yr‐old shoots it was significantly higher in NF‐ and NF +‐treated shoots compared with CF‐treated shoots. The carboxylation efficiency significantly decreased in 2‐ and 3‐yr‐old shoots from the NF and NF+ treatments compared with shoots from the CF treatment. The gas phase limitation of photosynthesis decreased with increasing shoot age and ozone concentration.
The influence of CO2 and O3, singly and in combination, on gas exchange, growth and nutrient status of radish (Raphanus sativus L.)
Authors: BARNES J. D. , PFIRRMANN T. 
Published: April 2006

SUMMARYFive days after emergence radish (Raphanus sativus L. ev. Cherry Belle) plants were transferred to a phytotron at the GSF München, where they were exposed in four large controlled climate chambers to two atmospheric concentrations of CO2, (‘ambient’, daily means of ∼ 385 μmol−1; elevated, daily means of ∼ 765 μmol mol−1) and two O3 regimes (‘non‐polluted’ air, 24 h mean of 20 nmol mol−1; polluted air, 24 h mean of 73 nmol mol−1). Leaf gas‐exchange measurements were made at intervals, and visible O3 damage, effects on growth, dry matter partitioning and mineral composition were assessed at a final whole‐plant harvest after 27 d. In ‘non‐polluted air’ CO2 enrichment resulted in a progressive stimulation in Asat, whilst there was a decline in g which decreased E (i.e. improved WUEi). The extra carbon fixed in elevated CO2 stimulated growth of the root (+ hypocotyl) by 43 %, but there was no significant effect on shoot growth or leaf area. Moreover, a decline in SLA and LAR in CO2‐enriched plants suggested that less dry matter was invested in leaf area expansion. Tissue concentrations of N, S, P, Mg and Ca were lower (particularly in the root + hypocotyl) in elevated CO2, indicating that total uptake of these nutrients was not affected by CO2, and there was an increase in the C:N ratio in root (+ hypocotyl) tissue. In contrast, O3 depressed Asat, (∼ 26%) and induced slight stomatal closure, with the result that WUE, declined. All plants exposed to ‘polluted’ air developed typical visible symptoms of O3 injury, and effects on carbon assimilation were reflected in reduced growth, with shoot growth maintained at the expense of the root. In addition, O3 increased the P and K concentration in shoot and root (+ hypocotyl) tissue, indicating enhanced uptake of these nutrients from the growth medium. However, there was no affect of O3 on tissue concentrations of N, S, Mg and Ca. Interactions between the gases were complex, and often subtle. In general, elevated CO2 counteracted (at least in part) the detrimental effects of phytotoxic concentrations of O3, whilst conversely, O3reduced the impact of elevated CO2. Moreover, there were indications that cumulative changes in source: sink relations in O3‐exposed plants may limit plant response to CO2‐enrichment to an even greater extent in the long‐term. The future ecological significance of interactions between CO2 and O3 are discussed.
Pollination in species with dry stigmas: the nature of the early stigmatic response and the pathway taken by pollen tubes
Authors: ELLEMAN C. J. , FRANKLIN‐TONG V. , DICKINSON H. G. 
Published: April 2006

SUMMARYInteraction between the pollen grain, pollen tube and the stigma surface has been studied in five species regarded as possessing dry stigma surfaces;Brassica oleraceaL.,Arabidopsis thaliana(L.), Heynh,Papaver rhoeasL.,Cosmos bipinnatusCav. andHelianthus annuusL.InB. oleraceaandA. thaliana, stigmatic response to pollination includes events in the papillar cytoplasm and changes to the stigmatic surface beneath the grain. In particular a specialized outer element of the cell wall expands prior to pollen tube penetration. The pollen tube, which enters through a ‘foot’ of pollen coating, grows in a space generated between an inner and the outer element of the wall and extends to the base of the papilla where it enters the middle lamellae of the subjacent cell layer. However, inA. thalianatubes frequently were seen to penetrate all components of the stigmatic cell wall, an event only previously recorded in immature stigmas ofB. oleracea.In self pollinations of self‐incompatibleB. oleraceainvolving strong S (incompatibility) alleles no changes take place in the papillar cell wall.InP. rhoeasthe stigmatic surface responds to self and cross pollination by the secretion of electron‐lucent material beneath the cuticle, causing it to become detached from the outer surface of the stigmatic cell wall. The pollen tubes then penetrate the cuticle and grow towards the base of the papilla in the space thus generated. The tubes continue to grow intercellularly in the transmitting tissue which lies horizontally in rays beneath the papillae.In members of the Compositae,C. bipinnatusandH. annuus, both stigma and pollen respond to pollination by producing copious quantities of an electron‐opaque matrix, which frequently causes individual papillae to adhere together. Pollen tubes, which are formed following both compatible and incompatible intraspecific pollinations, grow into this matrix and toward the base of the papillae. There, in common with the other plants studied, they grow intercellularly and enter the transmitting tissue of the style.These findings are discussed in the light of current views of the mechanisms operating during angiosperm pollination and of the significance of the stigmatic response to the functioning of self‐incompatibility mechanisms.
The influence of medium components on secondary embryogenesis of winter oilseed rape, Brassica napus L. ssp. oleifera (Metzg.) Sink.
Authors: LOH C. S. , LIM G. K. 
Published: April 2006

SUMMARYThe secondary embryogenic potential of Brassica napus L. ssp. oleifera (Metzg.) Sink. ev. Primor could be maintained for many years on complete Murashige and Skoog's medium without diminution. Experiments were conducted to investigate the effects of reducing or deleting certain components of the medium on secondary embryogenesis. Secondary embryogenesis was found to be significantly suppressed when strength of iron in the medium was reduced. Secondary embryogenesis, completely suppressed in ‘iron‐free’ medium, could be regained when iron was incorporated into the medium. Micronutrients and organic nutrients in the medium had no effect on secondary embryogenesis. A reduction in the strength of the medium or its macronutrients decreased secondary embryogenesis significantly.
Effects of dichlorobenzonitrile on the formation of cell wall appositions (plugs) in internodal cells of Chara corallina Klein ex. Willd, em. R.D.W. and Nitella flexilis (L.) Ag.
Authors: FOISSNER ILSE 
Published: April 2006

SUMMARYThe effect of dichlorobenzonitrile (DCB), an inhibitor of cellulose synthesis, on the formation of local cell wall appositions (plugs) was studied in internodal cells of the characeae Chara corallina Klein ex. Wild, em. R.D.W. and Nitella Flexilis (L.) Ag. DCB Significantly reduces size and number of fibrillar, membrane‐free plugs induced by 6 × 10−2 M Cacl2. Formation of these plugs leads to an increase in the cellulose content which is abolished in the presence of DCB. Plugs formed during treatment with DCB have a less regular structure, but membrane recycling appears not to be disturbed. Cells are able to recover from DCB treatment and normal plugs are then formed. DCB has only minor effects on size, number and structure of amorphous, membrane‐containing plugs induced by chlortetracycline (CTC) although their callose content is significantly enhanced. The data confirm that fibrillar plugs consist mainly of crystalline cellulose and that this polysaccharide does not play any role in the formation of amorphous plugs.
Microscopic evidence on how iron deficiency limits nodule initiation in Lupinus angustifolius L.
Authors: TANG CAIXIAN , ROBSON A. D. , DILWORTH M. J. , KUO J. 
Published: April 2006

SUMMARYLupins (Lupinus angustifolius L. ev. Yandee), grown in solution culture, have been used to study the sites and process of infection by Bradyrhizobium sp. (Lupinus) and the impairment of nodulation by iron deficiency.Infection leading to nodulation occurred in an area of epidermal cells either lacking root hairs or with very young root hairs at the time of inoculation. Cells aged 13 h or over appeared not to be infected. Infection was initiated in the outer cortex. Rare, short infection threads were evident on day 4 after inoculation, 2 d after the initial division of cortical cells resulting from the bradyrhizobial inoculation. Bacteria had been released into the cytoplasm of cortical cells within 5 d after inoculation. Bacteroids multiplied in the cytoplasm, segregated passively and spread in the infection zones by repeated division of the invaded cells.Under iron deficiency, initial cell division occurred in the outer cortex of host roots, as in iron‐sufficient plants after inoculation. Iron deficiency then limited further division of cortical cells. Only a few surviving infection sites developed nodules with normal structure but development was much slower than in iron‐sufficient plants.
Vesicular‐arbuscular mycorrhizal infection of grass seedlings in a degraded semi‐arid savanna in Botswana
Authors: VEENENDAAL E. M. , MONNAAPULA S. C. , GILIKA T. , MAGOLE I. L. 
Published: April 2006

SUMMARYInfection of eight indigenous grasses with vesicular‐arbuscular mycorrhizal (VAM) fungi was studied in a savanna in South‐eastern Botswana. Infection of seedlings with VAM fungi was rapid just after germination at the onset of the rainfall season. Particularly high infection levels were found in the primary roots of seedlings but levels temporarily dropped with the development of the secondary roots. In 30 % of all cases germinating spores were found to be the source of infection, suggesting an important role for them in semi‐arid grasslands. The inoculum potential of soils from eroded and non‐eroded sites in the study area was compared. Subsoil was found to have a lower inoculum potential than topsoil. Topsoil from an eroded site without vegetation showed a lowered inoculum potential compared to sites with vegetation present. Topsoil from unvegetated sites where soil material was deposited however, did not always show a lower inoculum potential. This indicates that the transport and redistribution of water and soil material does not automatically result in lower infection levels.
Developmental biology of legume nodulation
Authors: HIRSCH ANN M. 
Published: April 2006

SUMMARYMany legumes respond to Rhizobium inoculation by developing unique structures known as nodules on their roots. The development of a legume nodule in which rhizobia convert atmospheric N2 into ammonia is a finely tuned process. Gene expression from both partners of the symbiosis must be temporally and spatially coordinated. Exactly how this coordination takes place is an area of intense study. Nodule morphogenesis appears to be elicited by at least two distinct signals: one from Rhizobium, a product of the nod genes (Nod factor), and a second signal, which is generated within plant tissues after treatment with Nod factor. The identity of the second signal is unknown but changes in the balance of endogenous plant hormones or the sensitivity of plant tissues to these hormones are likely to be involved. These hormonal changes may be triggered by endogenous flavonoids produced by the root in response to inoculation with Rhizobium. There is some controversy as to whether the legume nodule is an organ sui generis or a highly derived lateral root. A resolution of this question may become more critical as attempts to induce nodules on non‐legume hosts, such as rice or maize, increase in number and scope.

CONTENTS

Summary
211

I.
Introduction
211

II.
Nodule development
213

III.
Nodule initiation
220

IV.
The second signal for nodule morphogenesis: role for the plant hormones ?
225

V.
Lateral root development
229

VI.
Are nodules modified lateral roots ?
229

VII.
Conclusions and future prospects
231

Acknowledgements and dedication
232

References
232
Leaf development inLolium temulentumL.: characterization of aslow‐to‐greenmutant
Authors: OUGHAM HELEN J. , THOMAS ANN M. , THOMAS BARRY J. , ROBERTS PETER C. , MUTINDA CHARLES , HAYWARD MICHAEL D. , DALTON SUSAN J. 
Published: April 2006

SUMMARYA nuclear‐gene mutation of the C3 grassLolium temulentumL., which arose following cell suspension culture and plant regeneration, is manifested as delayed and incomplete greening, which occurs from the leaf tip downwards. Many plastids in the mutant exhibit abnormal morphology when examined by transmission electron microscopy; the plastid outer envelope lacks integrity and thylakoids, while still stacked, are spread over a wide area surrounded by diffuse stromal contents. These aberrant plastids can coexist with apparently normal chloroplasts in the same cell of mutant plants. Levels of chlorophyllaandb, and carotenoids, are all lower in the mutants than in normalLolium temulentum.Leaf length, absolute growth rate, and number of cells per unit length at the leaf base, are greatly reduced (20‐30% the normal values) inslow‐to‐greenplants, but relative growth rate, duration of leaf growth, length of cell division zone and proportion of cells dividing are little affected. This novel mutant is a potentially valuable resource for studying interrelationships between photosynthetic function and leaf extension growth in grasses.
Free radical processes and loss of seed viability during desiccation in the recalcitrant species Quercus robur L.
Authors: HENDRY GEORGE A. F. , FINCH‐SAVAGE WILLIAM E. , THORPE P. CHRISTOPHER , ATHERTON NEIL M. , BUCKLAND SARAH M. , NILSSON KATRINA A. , SEEL WENDY E. 
Published: April 2006

SUMMARYLoss of moisture in mature seeds of Quercus robur L. was associated with loss of viability, a rise in lipid peroxidation and build‐up of free radicals. Radical‐initiated damage was largely confined to the embryonic axes as their moisture contents declined to below 47 %. The accumulation of a stable free radical in axial tissue, detected by electron para‐magnetic resonance (EPR), was indistinguishable from the EPR response previously shown in a moss on droughting and maize roots on desiccation. A minor higher‐field component appeared to represent an intermediate stage in the sequence of free radical reactions associated with loss of water. Using seeds from freshly abscised fruits dried to different moisture contents, protective mechanisms against activated forms of oxygen were monitored in cotyledons and in embryonic axes. The two tissues exhibit distinctly different molecular defences against oxidative attack; that in the cotyledons being predominantly enzymatic, with relatively high and increasing activities of superoxide dismutase and glutathione reductase; that in the axes being largely through the anti‐oxidants, ascorbic acid and alpha‐tocopherol. We conclude that a decrease in enzymic protection against oxidative attack in the axes, associated with diminishing concentrations of alpha‐tocopherol (and depletion of the precursor gamma‐tocopherol) as moisture was lost, was directly linked with lipid peroxidation and free radical formation in the axes and that these events taken together may contribute to loss of viability in these recalcitrant seeds.