Rate of Change in Dormancy Level and Light Requirement in Weed Seeds During Stratification

The rate of change in dormancy level and light requirement,induced during stratification at 3.2 °C, was investigatedin seeds ofStellaria media, Cerastium fontanum, Veronica agrestisandTaraxacumofficinale.Two stratification environments, soil and wet filterpaper in petri-dishes, were used. On nine occasions during a6 week stratification period, germination was tested under threelight conditions at 3.5/18.5 °C: (1) darkness; (2) light;and (3) short-term light exposure followed by darkness. Priorto stratification, germination in all species was 89% in lightand 53% in darkness. Within 2 weeks of stratification, germinabilityinV. agrestisandS. mediaseeds decreased in all treatments. InC.fontanumandT. officinaleseeds, germinability also decreasedafter 2 weeks but only in the dark treatment, indicating inductionof a light requirement. After two more weeks of stratification,the induced dormancy inS. mediaseeds stratified in soil becameweaker and the light requirement inT. officinaleseeds was lost.Differences between the two stratification environments and/orinteractions between light conditions, stratification environmentsand time were found for all species. These results suggest that:(1) the dormancy level and the light requirement of seeds maychange dramatically over relatively short-time periods duringstratification; and (2) germinability depends on the stratificationenvironment experienced by the seeds. Predicting the dormancylevel or light requirement in a seed batch is difficult andrequires a thorough knowledge of the effect of the stratificationconditions used.Copyright 1997 Annals of Botany Company Burial; Cerastium fontanumBaumg.; chickweed; cold stratification; common mouse-ear; dandelion; dormancy; light requirement; seed; Stellaria media(L.) Vill.; speedwell; Taraxacum officinalegroup; Veronica agrestisL.; weed     

Biochemical Activities and Compounds in Seeds: Possible Tools for Seed Quality Evaluation

The rate and final percentage of field emergence (seed quality)was measured in 55 seed-lots of carrots (Daucus carota L.),45 seed-lots of onion (Allium cepa L.) and 32 seed-lots of cabbage(Brassica oleracea var. capitata), together with the followingbiochemical indices: rates of ATP-synthesis; reduction of tetrazoliumby seed powder; AMP and malate content. Differences in field performance of seed-lots (seed quality)showed some correlation with particular biochemical indices.Seed quality was most significantly correlated with AMP contentand ATP synthesis in carrot, with malate content, reductionof tetrazolium and ATP synthesis in onion and with malate andAMP content and reduction of tetrazolium in cabbage. Daucus carota L., Allium cepa L., Brassica oleracea var capitata, carrot, onion, seed quality, ATP, biochemical indices     

Adventitious Root Formation in Veronica Spp.

Species of the genus Veronica differ in habitat preferences,growth form and in adventitious root production. The annualspecies rarely or never produce adventitious roots in intactplants in the field but some, for example V. persica and V.arvensis will root vigorously from single node stem segmentsin culture. Others, such as V. agrestis require the presenceof IAA for substantial levels of root formation to occur incultured stem segments. Veronica hederifolia cuttings rarelyproduce roots. Stem cuttings of the perennial species, in general,rooted more vigorously than those of annual plants. Both V.fihiformis and V. serpyllifolia root very strongly. The position of root production from the stem cuttings differedfrom species to species. Roots arose either from the node, theregion of the base or at some intermediate point. Veronica arvensis,V. chamaedrys and V. persica rooted mainly from the basal regionwhereas V. filiformis rooted mainly from the node. Veronicaserpyllifolia cuttings rooted at both of these locations. Veronica filiformis, a perennial species that is infertile inBritain, produces root primordia in intact plants at nodes whichare close to the shoot apex. Thus, even very young stem segmentshave ‘preformed’ root primordia. For this reason,detached stem segments of V. filiformis root very rapidly andthis probably has been of great significance in its successfulinvasion and spread in lawns and short turf areas. Veronica spp., adventitious roots, indol-3-ylacetic acid, root primordia, vegetative reproduction     

Stomatal Characteristics of Four Native Herbs Following Exposure to Elevated CO2

Contrasting effects on the stomatal index (SI), stomatal density,epidermal cell size and number were observed in four chalk grasslandherbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllisvulneraria L. and Plantago media L.) following exposure to elevatedcarbon dioxide concentrations (CO₂) in controlled environmentgrowth cabinets. SI of S. minor increased for both leaf surfaces,whilst in A. vulneraria and P. media SI decreased on one surfaceonly. In L. corniculatus , no differences in SI were observedas epidermal cell density changed in parallel with stomataldensity. In L. corniculatus and S. minor stomatal density increasedon both surfaces, whereas in P. media it decreased; in A. vulnerariastomatal density decreased on the abaxial leaf surface alonefollowing exposure to elevated CO₂. In the latter three species,SI changed because stomatal density did not change in parallelwith epidermal cell density. The results suggest elevated CO₂is either directly or indirectly affecting cell differentiationand thus stomatal initiation in the meristem. In S. minor and P. media leaf growth increased in elevated CO₂,because of increased cell expansion of epidermal cells, whereasin L. corniculatus, epidermal cell size decreased and greaterleaf growth was because of an increase in epidermal cell divisions.In A. vulneraria, leaf size did not change, but increased cellexpansion on the adaxial surface suggests CO₂ affects leaf surfacesdifferently, either directly or indirectly at the cell differentiationstage or as the leaf grows. These results suggest component species of a plant communitymay differ in their response to elevated CO₂. Predicting theeffect of environmental change is therefore difficult.Copyright1994, 1999 Academic Press Elevated CO₂, Sanguisorba minor (salad burnet), Lotus corniculatus (birdsfoot trefoil), Anthyllis vulneraria (kidney vetch), Plantago media (hoary plantain), stomatal index, stomatal density, epidermal cell size     

Effects of Mecoprop (an Auxin Analogue) on Ethylene Evolution and Epinasty in Two Biotypes of Stellaria media

Petiolar epinasty and the production of ethylene (ethene) werestudied in chickweed biotypes, Stellaria media, treated withthe herbicide and auxin analogue (RS)-2-(4-chloro-o-tolyloxy)propionicacid, potassium salt, common name mecoprop. This compound causedsevere epinasty and stimulated the production of ethylene fromshoot explants. However, when intact plants were treated withethylene, the leaves became only slightly epinastic. The ethyleneprecursor, 1-aminocyclopropane-I-carboxylic acid (ACC), at concentrationswhich stimulated the release of ethylene, was equally ineffectivein causing epinasty. Furthermore, 2, 5-norbornadiene, a specific,competitive inhibitor of ethylene action, only partly alleviatedmecoprop-induced epinasty. The responses observed in chickweedwere compared with those produced in tomato plants. ACC inducedepinasty in tomato within 2 h and these symptoms were completelyinhibited by norbornadiene. However, as in chickweed, the inhibitorgave only partial reversal of mecoprop-induced epinasty, implyingthat the epinastic response caused by the herbicide was notattributable to ethylene alone. We therefore suggest that mecoprop-inducedepinasty is a result of the combined ethylene-stimulating andgrowth-promoting properties of the herbicide. Mecoprop-stimulated ethylene evolution was initially significantlygreater in a herbicide-resistant, compared with a more susceptiblebiotype of chickweed. The significance of this finding is discussedin relation to the mechanism of mecoprop resistance in chickweed. Epinasty, ethylene, (RS)-2-(4-chloro-o-tolyloxy)propionic acid, mecoprop, herbicide resistance, chickweed, Stellaria media L., tomato, Lycopersicon esculentum L.     

Low Temperature Effects on Early Vegetative Growth, Leaf Gas Exchange and Water Potential of Chilling-sensitive and Chilling-tolerant Crop Species

Two chilling-sensitive (Phaseolus vulgaris L., Zea mays L.)and two chilling-tolerant (Pisum sativum L., Spinacia oleraceaL.) species were raised in growth chambers under warm (28/18°Cday/night cycle) and cool (18/12°C) temperature regimes.Growth analysis techniques were used to evaluate leaf area andbiomass partitioning during early autotrophic growth. Plantsacclimated to both temperatures were measured for leaf gas exchangeand water potential (     

Phylloquinone (Vitamin K1) Levels in Leaves of Plant Species Differing in Susceptibility to 2,4-Dichlorophenoxyacetic Acid

Plant species differing in susceptibility to 2,4-dichlorophenoxyacetic acid (2,4-D) were examined as to the level of phylloquinone (K) in the leaves. The K level was found to be considerably higher in several plants resistant or moderately resistant to 2,4-D (Aegopodium podagraria L., Galium mollugo L., Lamium album L., Matricaria chamomilla L., Oxalis acetosella L., Stellaria media (L.) Vill., Viola arvensis Murr.) than in Chenopodium album L. and Sinapsis arvensis L. which are susceptible to 2,4-D. Capsella bursa-pastoris (L.) Med. and Plantago major L. (both moderately susceptible) and a few resistant or moderately resistant species (Agropyron repens (L.) PB., Anthriscus silvestris (L.) Hoffm., Triticum aestivum L.) had intermediate K levels. Cirsium arvense (L.) Scop. (susceptible) had a relatively high level of K. It is possible that a high K level in the plant can be of importance in the resistance to 2,4-D.     

Differences in Seed Production Between Stellaria media Populations from Different Habitat Types

Seed production in several populations of Stellaria media fromdifferent types of habitat was examined. Two populations, onefrom a flower garden and the other from a herring gull colonywere compared in detail by growing them at three soil fertilitylevels under similar conditions in a greenhouse. Three important differences between the two populations independentof soil fertility emerged: the garden plants flowered on averageeleven weeks earlier, they produced much smaller seeds, andthey produced more seeds per capsule. Other differences were influenced by soil fertility: at highfertility the garden plants produced about 50 per cent moreseeds than the gull colony plants, but on a seed weight basis,the gull colony plants were the more productive. However forboth populations at high fertility the proportion of shoot biomassallocated to seed production was similar. Some of these differences can be accounted for in terms of conditionsoccurring in the two habitats, in particular the relative importanceof disturbance and competition at the sites. Chickweed, Stellaria media (L.) Vill., ecotypic differentiation, time to flowering, seed production, resource allocation     

The First Appearance of Polyploid Nuclei in Primary Roots of Two Diploid Angiosperms

In Anchusa capensis, where the polyploid divisions are restrictedto a particular time and place in germination, cytophotometricanalysis showed that the polyploid cells arise at the time ofconversion of the globular-shaped embryo to the heart-shapedembryo. In Spinacia oleracea, where the divisions occur throughoutthe growth of the root, these polyploid cells do not arise duringembryogenesis but during germination and subsequent growth. Anchusa capensis Thunb., summer forget-me-not, Spinacia oleracea L., spinach, root meristem, polyploid divisions, determinate divisions, indeterminate divisions, germination, embryogenesis, cytophotometry     

A Single Equation to Quantify the Hierarchy in Plant Size Induced by Competition Within Monocultures

The following empirical model: Ra(i) = r(1+ln(w(i)/wm)Kn)(1–(w(i)/W))(1–(y/Y)) which is based on the logistic growth equation, is developedto describe the growth of differently sized individuals withinplant communities. The model is tested against extensive setsof carrot (Daucus carota L.) and red beet (Beta vulgaris L.)data and is shown to fit well. The model was used to predictindividual plant weights in independent data. The agreementsbetween observed and predicted weights were often close butsome systematic deviations did occur. Thus, a single equationdescribed most of the complex interactions that occurred withinmonocultures of annual crop plants. Carrot, Daucus carota L., red beet, Beta vulgaris L., model, growth, variation     

Acclimation of Respiratory Properties of Leaves of Spinacia oleracea L., a Sun Species, and of Alocasia macrorrhiza (L.) G. Don., a Shade Species, to Changes in Growth Irradiance

To clarify the way in which the light available for growth affectsrespiration in leaves of sun and shade plants, we examined therespiratory properties of mature leaves of Spinacia oleraceaL., a sun species, and of Alocasia macrorrhiza (L.) G. Don.,a shade species, that had been grown at various irradiances.In leaves of S. oleracea, the respiratory rates, on a dry massbasis, decreased with time during the night, and the higherwas the growth irradiance during the day, the higher was therespiratory rate. The marked decreases in the respiratory rateduring the night were accompanied by decreases in the concentrationof carbohydrates in the leaves. By contrast, the respiratoryrates of leaves of A. macrorrhiza were virtually constant throughoutthe night and the absolute rates were lower than those of S.oleracea even though the absolute value of the concentrationof carbohydrates and its decrease at night resembled to thosein S. oleracea. The maximum activities of respiratory enzymeswere also similar to those in S. oleracea. However, the leavesof A. macrorrhiza contained less soluble protein than thoseof S. oleracea. These results suggest that, in S. oleracea,the concentration of carbohydrates might determine the respiratoryrate while such is not the case in A. macrorrhiza. The lowerrespiratory rates in A. macrorrhiza might be due to a lowerdemand for ATP. (Received November 29, 1995; Accepted February 15, 1996)     

A Model for Plant and Crop Growth, Allowing for Competition for Light by the use of Potential and Restricted Projected Crown Zone Areas

Relations for competition for light are developed and used ina plant growth model applicable to the isolated plant, to plantsin even-aged monoculture and to plants in mixed-aged monoculture.In an isolated plant, it is assumed that a leaf area, proportionalto the plant mass, is contained within a crown whose projectedzone area is proportional to plant mass to the 2/3 power. Self-shadingprogressively reduces the specific growth rate. If light werethe sole limiting resource and were constant, one can derivea growth equation, dw/dt = rw[1 - exp (-KW^1/3)]KW^1/3, which,integrated, gives w^1/3 = K^-1 ln {1 + [exp (KW^1/3₀)-1] exp (rt/3)}.It approximates, initially, to a particular case of the Richards(1959) empirical growth equation. In even-aged evenly-spaced monocrops competing only for light,it is assumed that the zone areas merge at canopy closure, andgrowth then follows the expolinear equation of Goudriaan andMonteith (1990), giving a continuous function based on groundcover. For mixed-aged monocrops, we assume a phase of canopyclosure that affects the younger plants earlier than the olderones. Under varying environmental conditions in the field, plant growthmay be affected by other factors in addition, e.g. temperature.In the growth conductance model of Aikman and Scaife (1993),the shading expressions are applied to the light-dependence. Data from two sowings of cabbage and carrot in even-aged andmixed-aged monocrops were used to test the model. The parametervalues derived from the even-aged monocultures predict the growthrates in the mixed-aged monocultures better than models whichassume uniform canopies.Copyright 1994, 1999 Academic Press Growth, model, monocrop, even-aged, mixed-aged, PAR, density, competition, light, shading, zone area, ground cover, temperature, carbon dioxide, expolinear, carrot, Daucus carota L., cabbage, Brassica oleracea L     

Predicting Growth in Stands of Mixed Species from that in Individual Species

The growth of spring cabbage (Brassica oleracea var. capitataL.) and carrot (Daucus carota L.) in mixed species stands iscompared with growth curves predicted by two forms of a dynamiccompetition model, which uses a conductance relationship (Aikmanand Scaife, 1993) to allow for the constraints on growth froma set of environmental variables. While a plant is isolated,light interception is assumed to occur within a zone whose areais a function of plant weight. Lateral foliage expansion isconstricted when the available space is filled. One form ofthe model assumes that all plants are of similar height (Aikmanand Benjamin, 1994). The second form assumes the crown zonesare in separate vertical layers, allowing greater lateral expansionin each layer but imposing shading on the underlayer. Parameter values of the model were estimated from the growthwithin even-aged monocrops. The first form of the model gavethe best prediction of growth in the intercrops, often producinga close agreement between observed and predicted weights. Onlyat the highest density used, 0·05 m spacing, did thedifferent height form of model give a better prediction of growth. Many mixed species stands may be approximated by one or otherof the forms of the model, and the relevant form can easilybe calibrated from the growth observed in monocrops. Hence,simple models may be sufficiently accurate to predict growthin mixed species systems such as intercrops, or crops and weeds.Copyright1995, 1999 Academic Press Cabbage, carrot, competition, intercrop, light, mechanistic model, temperature, canopy architecture     

The ecological distribution of C4 and C3 grasses in the Hawaiian Islands

Summary Isoenzyme analyses were carried out on the hypotetraploid Stellaria media and the diploid Stellaria pallida occurring on abandoned sandy fields in the coastal dunes of the Netherlands. Amylase isoenzymes in germinating seeds of Stellaria media showed a striking intrapopulational variability, which is in accordance with the germination behaviour of the different subpopulations. In contrast to these findings no intrapopulational variation nor developmental change in isoenzyme pattern could be detected on basis of 14 other analysed leaf enzymes. For five enzymes there was a difference in isoenzyme pattern between the species Stellaria media and Stellaria pallida. Of these five enzymes two showed an interpopulational variation in Stellaria media. The fact that there was almost no variability of the isoenzyme pattern in Stellaria pallida could be explained by the permanent autogamous (cleistogamous) state of the species. Effects of polyploidy on the isoenzyme pattern and its activity could not be demonstrated. Consequences of the extreme difference between the monomorphic pattern of the leaf enzymes as opposed to the polymorphism of the amylase are discussed in view of the difference in germination ecology and lifecycle strategy of Stellaria media subpopulations.     

The Effects of Winter Exposure to Acid Soil Conditions on the Subsequent Survival and Growth of Herbaceous, Forest Perennials: a Preliminary Investigation

For many plant species, growth is limited in acid soils, whichare characterized by high levels of potentially-toxic elementsand low nutrient availability. Although plant-soil interactionsare traditionally studied during the growing season, the highestconcentrations of toxic elements in the soil may occur duringthe winter months. The present study investigated the effectsof a 3-month exposure to either an acid or a reference soil,at temperatures fluctuating around freezing point, on subsequentsurvival and growth of eight herbs (Brachypodium sylvaticum,Carex pilulifera, Geum urbanum, Luzula pilosa, Mycelis muralis,Silene dioica, Stellaria nemorum, Veronica officinalis).Theplants were exposed to ambient weather conditions from Decemberto March, after which they were replanted in fresh referencesoil and transferred to a glasshouse. Their biomass was measured5 weeks later. The plant species differed in their responsesto the soils, in a manner reflecting their natural field distributions.All plants of the most acid-tolerant species survived in bothtreatments, whereas the more sensitive species showed lowersurvival rates after growth in the acid than in the referencesoil. Similar results were found for the regrowth:C. piluliferaandL.pilosa, the most acid-tolerant species, were unaffected by thesoil treatments (ratios between biomass in acid compared toreference soils were 0.8 and 1.1, respectively), whereasG. urbanum,M. muralis, S. nemorumandV. officinaliswere negatively affected(ratios 0.3–0.5). Effects on above- and below-ground biomasswere broadly similar. This preliminary evidence indicates thatsoil chemistry during the winter can be important for both survivaland growth during the vegetative period that follows.Copyright1998 Annals of Botany Company. Acids soils, toxicity, vascular plants, winter exposure.     

Effect of Chilling Temperatures on the Protoplasmic Streaming of Plants from Different Climates

A microscope mount was designed so that specimen temperaturescould be monitored and controlled without impairing phase contrastoptics and used to measure rates of protoplasmic streaming between0 and 25 ?C in trichome cells of Lycopersicon esculentum, Lycopersiconhirsutum, Citrullus vulgaris, Tradescantia albiflora, Digitalispurpurea, and Veronica persica. Between 10 and 20 ?C the rates of streaming varied from 2–6µm s^–1 depending on the temperature, and differencesbetween the species were small. The temperature coefficientof streaming rates was found to increase as the temperaturewas lowered so that the plot of log rate against temperaturehad a steeper slope at the lower temperatures. The largest temperature cofficients were for the warmth-requiringL. esculentum (tomato) and C. vulgaris (water melon), and thesmallest for the temperate-zone plants V. persica (speedwell)and D. purpurea (foxglove). The changes in rate always occurredover a range of temperature; no ‘critical temperature’wasobserved below which streaming abruptly stopped and above whichit was active, although the amount of streaming as well as therate decreased as the lowest temperatures were approached. The temperatures experienced by the specimens during the experimentdid not affect the recovery of normal streaming rates betweenabout 10 and 20 ?C. In a population of a wild tomato, Lycopersicon hirsutum Humb.and Bonpl., collected from different altitudes in Peru and Ecuador,i.e. from locations of different environmental temperature,the rate of protoplasmic streaming at 5 ?C was greatest in thevarieties collected from the highest altitudes. The resultssuggest that streaming rates correlate with genetic adaptationto low temperature in the species examined.     

Increased root growth in elevated CO2: a biophysical analysis of root cell elongation

A biophysical analysis of root expansion was conducted in fourchalk downland herbs (Sanguisorba minor Scop., Lotus corniculatusL., Anthyllis vul-neraria L. and Plantago media L.) exposedto either ambient or elevated CO₂in controlled environment cabinets.Measurements of fine (F) and extra-fine (EF) root extensionrate (RER), water relations, and cell wall tensiometric extensibilityrevealed differences in the diurnal pattern of root growth betweenspecies. After 35 d of exposure to elevated CO₂, RER of bothF and EF roots increased significantly in darkness and on illuminationfor S. minor, whilst for A. vulneraria (EF roots only) and L.corniculatus a significant increase occurred at night whereasfor P. media a significant increase occurred during the day.Cells measured in the zone of elongation were longer in allspecies exposed to elevated CO₂. Water potential (     

A New Model Relating Crop Yield and Plant Arrangement

A new model is proposed which relates the weight of plants totheir spatial arrangement. The weight of each plant is calculatedas the integral of the function f(r) = L(cr² + 1)^–2 overan area allocated to it, r being distance from the plant, withL and c parameters to be specified. The model is thus concise,general, in that it can be used to describe the effects of anyspatial arrangement on plant weight, and the parameters L andc have a biological interpretation. It is also consistent withthe commonly-used relationship between plant weight (w) anddensity (p), w^–1 = a+bp. We show for carrots (Daucus carota L.) and red beet (Beta vulgarisL.), that the mean weights fitted by the model agree as wellwith the experimentally observed mean plot weight as those fittedby more complex models with more parameters, some of which arenot as general. We show also that the parameter c can be predictedfrom the time from sowing to harvest, with good results whentested on sets of data independent of those to which the modelhad been fitted. The assumptions on which the model is based,its application, and extensions to it are discussed. Crop yield, plant density, plant arrangement, carrot, Daucus carota L., red beet, Beta vulgaris L., soya bean, Glycine max L., mathematical model     

Cell Wall Degrading Enzymes in Cuscuta reflexa and Its Hosts

Pectin degrading enzymes, hemicellulose degrading enzyme andcellulose degrading enzymes were studied in Cuscuta reflexaRoxb., its susceptible hosts, Brassica campestris L., Cocciniaindica W. & A. Datura innoxia Mill, Helianthus annuus L.,Holoptelea indica Planch, Lantana camara L., Medicago sativaL., Manihot utilissima Pohl, Petunia hybrida X Hort exvilm,Pisum sativum L., Phaseolus vulgaris L. and Solanum nigrum L.and non-susceptible plants Ipomoea batata Lam. and Solanum tuberosumL. Pectin esterase and polygalacturonase were present in higheramounts in Cuscuta parasitic on P. vulgaris and S. nigrum, whichneeded more time for haustorial establishment. Exo-l, 4-ß-D-glucosidaseactivity was found in Cuscuta but could not be detected in itshosts. Xylanase and cellulase activity of host plants increasedwhile cellobiase activity decreased as a result of infectionby the parasite. Higher pectin esterase, polygalacturonase,xylanase and exo-l, 4-ß-D-glucosidase activities inthe haustorial region of the parasite is likely to bring aboutthe lysis of the cell wall of the host plant and thus facilitatethe penetration of the parasite haustoria into the host sieveelement, which is necessary for the transport of nutrients betweenthe host and the parasite. Key words: Cell wall degrading enzymes, Cuscuta reflexa     

High ice nucleating ability in plant leaves

A high ice nucleating ability in leaves of Veronica persicaand Buxus microphylla was observed on analyzing the frequencydistribution of their freezing temperatures. The most efficientice nucleators in Veronica leaves exist in structures withinthe leaf blades (mesophyll), and those of Buxus in structureswithin the midrib (vascular tissue). Dissolved or suspendedleaf structures were much less effective. (Received March 16, 1973; )