Limited Genome Size Variation in Sesleria albicans

The extent and significance of intraspecific genome size variationin plants continues to be a matter of discussion: in some speciesconsiderable variation has been described, while no variationhas been detected in other taxa. In the present study, intraspecificgenome size variation was analysed in a perennial grass Sesleriaalbicans Kit. ex Schult. (Poaceae). Flow cytometry was usedfor the analysis of nuclear DNA content in ten geographicallyisolated populations ofS. albicans . Despite long-term isolationand lack of gene-flow between the populations, only negligibleinter-population differences were found. Although the differencesbetween the populations were statistically significant, themaximum inter-population difference reached only 1.6% of themean 2C value (9.78 ± 0.04 pg). The variation was notcorrelated with geographical location or with altitude of thepopulations analysed. The present study clearly demonstratesthat S. albicans belongs to the plant taxa with a highly stablegenome size. Copyright 2000 Annals of Botany Company Sesleria albicans, genome size, nuclear DNA content, intraspecific variation, flow cytometry, Europe     

Genome Size in Chinese Soybean Accessions--Stable or Variable?

Variation in genome size up to 1.12-fold has been recently reportedin 90 Chinese accessions ofGlycine max (soybean). Generallysuch results have to be viewed with reservation if rigorousinternal standardization and control tests for the repeatabilityof the results have not been done. Therefore, we reinvestigatedten accessions (five allegedly ranking high and five low) forgenome size using propidium iodide flow cytometry and Feulgendensitometry. Using flow cytometry, the maximum difference betweenaccessions was 1.018-fold (non-significant); the differencebetween the means of the high-ranking and low-ranking groupwas 1.002-fold (non-significant). With Feulgen densitometry,the maximum difference between accessions was 1.034-fold (non-significant).The present data suggest genome size constancy, in terms ofcytometric evidence, for the Chinese soybean accessions in question.Likewise, no reasonable evidence was obtained for a differencebetween Chinese and American soybeans. Copyright 1999 Annalsof Botany Company Glycine max, Chinese soybeans, U.S. soybeans, genome size variation, propidium iodide flow cytometry, Feulgen densitometry.     

Determination of Gardnerella vaginalis Genome Size by Pulsed-Field Gel Electrophoresis

The chromosomal DNA of four strains of Gardnerella vaginaliswere digested with rare cutting restriction enzymes and analyzedby pulsed-field gel electrophoresis (PFGE). The four strainsstudied were two clinical isolates (GVP 004 & GVP 007) andtwo American Type Culture Collection strains (ATCC 14018 &ATCC 14019). The restriction enzyme SfiI generated two DNA fragmentsof about 0.6 Mb and 1.1 Mb in all four strains giving a G. vaginalisgenome size of about 1.7 Mb. A similar genome size was calculatedutilizing two more GC-rich sequence specific restriction endonucleases,NotI and AscI. When digested with AscI, the chromosomal DNAof all four strains gave rise to 11 to 12 DNA fragments rangingbetween 0.01 Mb to 0.43 Mb. DNA from the two clinical isolateswere digested by NotI (yielding 7 to 9 fragments), while theDNA from the two ATCC strains were resistant to NotI digestion.In contrast to the clinical isolates, DNA from the two ATCCstrains gave an identical profile for all restriction endonucleasestested. From double digestion experiments, the two SfiI sitescould be localized on two AscI fragments. From these PFGE studies,it is concluded that the G. vaginalis genome is a circular DNAthat ranges between 1.67 Mb and 1.72 Mb in size.     

Grain Size and Seedling Growth of Wheat at Different Ploidy Levels

A study was made of the influence of grain size variation withinand between diploid, tetraploid and hexaploid wheat, on a numberof seedling growth characters. Differences in grain size within the three ploidy levels appearedto be related to total photosynthetic area and dry weight accretionin the seedling. In the diploids there was a positive correlationbetween seed size and total photosynthetic area (r = +0·99,P < 0·01) and total dry weight (r = +0·84,P < 0·05) of the seedling at 10 weeks after emergence.In the tetraploid and hexaploids, seed size was negatively correlatedwith both total photosynthetic area (r = –0·69,P < 0·05 and r = –0·33, P < 0·05for the tetraploids and hexaploids respectively) and total dryweight (r = –0·69, P < 0·05 and r = –0·59,P < 0·05 for the tetraploids and hexaploids respectively),of the seedlings 10 weeks after emergence. The main physiological distinction between the tetraploids andhexaploids appeared to be the superiority of the hexaploidsin rate of leaf appearance and the lower ratio of expanded tounexpanded leaves in the seedling 10 weeks after emergence.The tetraploids, in turn, appeared to be superior to the diploidsin these two characters. Triticum spp., wheat, polyploidy, grain size, photosynthetic area, net assimilation rate, tiller number     

Genome Size inAllium: In Quest of Reproducible Data

ComparingAlliumgenome size measurements of different authors,we noticed that the estimates for certain species diverge morestrongly than one would have expected in view of the methodologicaladvantages of the material. As the matter has theoretical significancefor explaining the biological role of genome size variation,we measured, by Feulgen densitometry, 28 species and altogether57 accessions or cultivars. Flow cytometric measurements supplementedthese data. The current hypothesis of a discontinuous and step-wisedistribution of DNA amounts inAlliumseems questionable, as mostof our DNA values did not appear in the corresponding DNA groupas proposed previously. On the other hand, we can confirm thatthere is a significant negative correlation between genome sizeof a species and its first month of flowering, but only in diploids,or in diploids and polyploids if only the basic genome size(2Cxlevel) is considered. We compared our results with thoseof nine other publications. Only 29 of 60 2C values publishedpreviously deviate less than 10% from our data, the others deviatemore strongly, from 0.44- to 1.44-fold. The more comprehensivedata sets of various authors were compared by correlation analysiswith our data. Positive and mostly significant correlationswere seen in all tests, but nevertheless the degree of incongruencebetween studies was unsatisfactory in view of the much betterintra-laboratory reproducibility of the present data. The presentwork highlights the need for generally agreed improvements instandardization and preparative procedures of cytophotometricgenome size determination.Copyright 1999 Annals of Botany Company Allium, genome size, Feulgen densitometry, flow cytometry, discontinuous DNA content variation, nucleotype hypothesis, flowering time, data reproducibility, correlation analysis.     

On the Supposed Changes in Stomatal Frequency and Size with Height of Leaf Insertion

The hypotheses put forward by Meidner and Mansfield (1968. Physiologyof stomata. London: McGraw Hill), that stomatal frequency (stomataper unit area) increases with height of insertion of leaveswhile stomatal size decreases, are examined using material ofeuropean trees cultivated in Canberra, Australia. The data obtaineddo not support the hypotheses. Measurements were also made onspecies of Eucalyptus native to the Canberra area or cultivatedthere, but again no support was offered to the hypotheses. Neitherstomatal size nor frequency changed appreciably and size mayeven increase with height of leaf insertion. Some evidence wasobtained in one species of a possible increase in size withposition along the annual shoot, but this would require furtherwork to be fully established. Copyright 2000 Annals of BotanyCompany Stomata, stomatal frequency, trees, Eucalyptus     

Size structure of plankton in a temporary, saline inland lake

The study of the size structure of a planktonic community ina relatively extensive (1350 ha), very shallow (0.46 m maximumdepth), temporary inland saline lake during a relatively rainyyear (1987–88) showed an average biomass-size spectrumwith four clear modes at nano-, micro-, meso- and macroplanktonsize ranges. The size-abundance distribution was dominated bymedium-sized phytoplankton cells (Gymnodinium cf. excavatum,Tetraselmis apiculata, Dunaliella spp. and several diatom species),large ciliates (Fabrea salina) and a few zooplankton speciesadapted to changing temporary environments within a wide sizerange (Cletocamptus retrogressus, Moina salina, Branchinellaspinosa). This polymodal size distribution is compared withresults obtained in other systems, including small physicallycontrolled lakes, large lakes, oceans and marine benthos. Considerationof the size structure within homogeneous groups of organismsshows slopes less negative than the average for the whole sizerange analysed, a feature which is common in small and physicallycontrolled ecosystems. A seasonal study of the size structurerevealed uneven distributions throughout the year, resultingin discontinuities in the size spectra as well as in differencesof total size range. There were noticeable differences amongthe size spectra at each particular time, showing phases ofprimary producer predominance and phases with a marked predominanceof consumers. The time-integrated size spectrum did not exhibitany distinct discontinuity. The influence of extreme shallownessand resuspension on the shape and dynamics of the size spectrumis examined and discussed compared to deeper aquatic systems.     

Size of the Chrysanthemum Shoot Apex in Relation to Inflorescence Initiation and Development

The size of the apical dome of Chrysanthemum morifolium Ramat.at the transition to inflorescence initiation in continuouslight (long days) was not systematically influenced by eitherthe temperature or the irradiance under which the plants weregrown. It was generally 0.26 mm in diameter and c. 3.6 x 10^–3mm³ in volume when the first bract was initiated. The dimensionsof the apical dome of plants in short days were only slightlysmaller at this stage. Similarly, each step in the further developmentof the chrysanthemum inflorescence was associated with a narrowrange of apex sizes, indicating that inflorescence initiationand development are closely related to apex size. Chrysanthemum morifolium Ramat, shoot apex, inflorescence initiation     

Effects of the Mode of Competition on Stationary Size Distribution in Plant Populations

The effects of the mode of between-individual competition onthe stationary size distribution in uneven-aged and continuallyreproducing tree populations were investigated theoretically,based on the diffusion and continuity equation models. The B(t,x) function, which gives a measure proportional to total leafarea of individual trees larger than dbh (trunk diameter atbreast height) x at time t, expresses the effect of one-sidedcompetition on the subject individual of dbh x. The effect oftwo-sided competition on individuals of any size is equallygiven by B(t, x₀), i.e. total leaf area of the stand (or LAI),where x₀ is the minimum dbh. The following two points, whichwere shown by Kohyama (1991) from results of model simulation,were theoretically derived: (1) the effect of the diffusionterm [D(t, x) function] of the diffusion model on the stationarysize distribution is small for the range of parameter valuesobtained empirically for the warm-temperate and tropical rainforests; (2) the shape of the stationary size distribution underone-sided competition is less changed by a change in the seedlingsupply rate than under two-sided competition. The followingtwo points were further shown theoretically: (3) one-sided competitionis likely to lead to a monotonically decreasing size distributionof dbh with the peak at x = x₀, which is a characteristic ofthe rain forest; (4) the slope of size distribution of dbh steepensas one-sided competition intensifies. Relationships betweenthe mode of competition and the stability of population structure,and general functional forms of one-sided and two-sided competitionare discussed. Diffusion model, one-sided competition, stability of population structure, stationary size distribution, two-sided competition     

Influence of Gibberellic Acid on Nucleolar Size Changes in Storage-tissue 3

The nucleoli of tissue discs cut from stem tubers of Helianthustuberosus L. or roots of Daucus carota L. increase in size whenthe discs are shaken in aerated distilled water. The size increaseof up to several hundred per cent which occurs within 24 h isfollowed by a significant decrease in size within the next 24h. Addition of 10^-5M gibberellic acid to the system acceleratesthe beginning of the size increase and finally results in alarger nucleolus.     

A Canopy Photosynthesis Model for the Dynamics of Size Structure and Self-thinning in Plant Populations

A dynamic model for growth and mortality of individual plantsin a stand was developed, based on the process of canopy photosynthesis,and assuming an allometric relationship between plant heightand weight, i.e. allocation growth pattern of plant height andstem diameter. Functions G(t, x), for the mean growth rate ofindividuals of size x at time t, and M(t,x), for the mortalityrate of individuals of size x at time t, were developed fromthis model and used in simulations. The dynamics of size structurewere simulated, combining the continuity equation model, a simpleversion of the diffusion model, with these functions. Simulationsreproduced several well-documented phenomena: (1) size variabilityin terms of coefficient of variation and skewness of plant weightincreases at first with stand development and then stabilisesor decreases with an onset of intensive self-thinning; (2) duringthe course of self-thinning, there is a power relationship betweendensity and biomass per unit ground area, irrespective of theinitial density and of the allocation-growth pattern in termsof the allometric parameter relating plant height and weight.The following were further shown by simulation: (a) competitionbetween individuals in a crowded stand is never completely one-sidedbut always asymmetrically two-sided, even though competitionis only for light; (b) plants of ‘height-growth’type exhibit a greater asymmetry in competition than plantsof ‘diameter-growth’ type, (c) the effect of competitionon the growth of individuals in a crowded stand converges toa stationary state, even when the stand structure still changesgreatly. All of these theoretical results can explain recentempirical results obtained from several natural plant communities.Finally, a new, general functional form for G(t, x) in a crowdedstand is proposed based on these theoretical results, insteadof a priori or empirical growth and competition functions. Canopy photosynthesis, competition mode, continuity equation, self-thinning, simulation, size distribution     

Effects of Density and Extinction Coefficient on Size Variability in Plant Populations

The effects of density and extinction coefficient on size variability,as measured by the coefficient of variation of plant weightin even-aged monocultures, were investigated theoretically usinga diffusion model of growth and size distribution and a canopyphotosynthesis model over the range of densities at which self-thinning(size-dependent mortality) does not occur. Size inequality (thecoefficient of variation of plant weight) increases with increasingdensity or leaf area index at each growth stage. Plants witherect leaves are prone to lower size inequality than plantswith horizontal leaves. These results agree well with existingobservations on even-aged plant monocultures and suggest thatcompetition between plants is mainly one-sided (competitionfor light). One sided competition affects size variability througha G(t, x) function (mean growth of plants of size x at timet per unit time). Two-sided competition (including competitionfor nutrients) affects size variability through a D(t, x) function(variance of growth of plants of size x at time t per unit time).In this case, size inequality decreases with increasing density.The importance of studying size variability is emphasized. Helianthus annus L., size variability, size inequality, coefficient of variation, competition, density effect, extinction coefficient, diffusion model, canopy photosynthesis model     

Effects of Constant and Variable Nitrogen Supply on Sunflower (Helianthus annuus L.) Leaf Cell Number and Size

The effects of nitrogen (N) availability on cell number andcell size, and the contribution of these determinants to thefinal area of fully expanded leaves of sunflower (Helianthusannuus L.) were investigated in glasshouse experiments. Plantswere given a high (N =315 ppm) or low (N=21 ppm) N supply andwere transferred between N levels at different developmentalstages (5 to 60% of final size) of target leaves. The dynamicsof cell number in unemerged (< 0.01 m in length) leaves ofplants growing at high and low levels of N supply were alsofollowed. Maximum leaf area (LA_max) was strongly (up to two-fold)and significantly modified by N availability and the timingof transfer between N supplies, through effects on leaf expansionrate. Rate of cell production was significantly (P<0.05)reduced in unemerged target leaves under N stress, but therewas no evidence of a change in primordium size or in the durationof the leaf differentiation–emergence phase. In fullyexpanded leaves, number of cells per leaf (N_cell), leaf areaper cell (LA_cell) and cell area (A_cell) were significantly reducedby N stress. WhileLA_cell and A_cellresponded to changeover treatmentsirrespective of leaf size, significant (P<0.05) changes inN_cellonly occurred when the changeover occurred before the leafreached approx. 10% of LA_max. There were no differential effectsof N on numbers of epidermal vs. mesophyll cells. The resultsshow that the effects of N on leaf size are largely due to effectson cell production in the unemerged leaf and on both cell productionand expansion during the first phase of expansion of the emergedleaf. During the rest of the expansion period N mainly affectsthe expansion of existing cells. Cell area plasticity permitteda response to changes in N supply even at advanced stages ofleaf expansion. Increased cell expansion can compensate forlow N_cellif N stress is relieved early in the expansion of emergedleaves, but in later phases N_cellsets a limit to this response.Copyright 1999 Annals of Botany Company Helianthus annuus, leaf expansion, leaf cell number, leaf cell size, nitrogen, leaf growth, sunflower.     

A Modified Self-thinning Equation to Describe Size/Density Relationships for Defoliated Swards

Use of the self-thinning rule to describe size/density compensation(SDC) in defoliated swards is examined. It is shown that defoliationrelated variation in leaf area and associated morphogeneticchanges in plant structure necessitate slope corrections, designatedC_a and C_r , respectively. The theory predicts that reduced leafarea in more heavily defoliated swards will result in SDC atslopes more negative than -3/2 (variable leaf area SDC), andthat there will be a transition to -3/2 (constant leaf area)SDC at higher herbage mass. Empirical data from previous experiments with Lolium perenneL. and Medicago sativa L. are examined, and appear to confirmthe theoretical predictions, including the slope change at thepoint of transition from variable to constant leaf area SDC.This transition point, designated d_i , is subject to interspecificvariation and is related to the mature shoot size of a particularspecies. Some applications of this theory are discussed, andin particular a sward productivity index is proposed.Copyright1995, 1999 Academic Press Variable leaf area self-thinning, size/density compensation, Lolium perenne, Medicago sativa, sward productivity index     

Size, Age and Demography of Metamorphosis and Sexual Maturation in Fishes

Understanding what determines the timing of transitions betweenlife-history stages in fishes is crucial to an understandingof their demography. Most theoretical treatments assume thatthese transitions are age dependent, but evidence accumulatingfrom a variety of organisms indicates that size is an importantvariable also. In the starry flounder, Platichthys slellatus(Pallas),the onset of metamorphosis is more closely related to size thanage. In the platyfish, Xiphophorus maculatus (Günther),the onset of sexual maturation depends on both size and age.I compare these results with those reported for other organisms,and outline the expected ecological correlates of age- and sizedependenttransitions between life history stages in general.     

Indirect Measurement of Pore Size and Permeability in Scots Pine and Norway Spruce

Five experiments to investigate the water relationships of Scotspine and Norway spruce sapwood are described. Field exposureof stakes, and their moisture characteristic relating wood moisturecontent to the water potential of the surroundings showed thatspruce had a lower moisture content than pine under the sameconditions. A pore size distribution derived from the characteristicsshowed more large pores in spruce than in pine, but in sprucethere were also more small pores. The inference was that thelarge pores of spruce were readily accessible to water, allowinga fast rate of water uptake, as found in the wick action andswelling investigations, while the small pores were not accessible,resulting in a low rate of water uptake and a low rate of swelling.The possibility is briefly discussed that it is the pore sizedistribution of the two woods which determines their water relationships,and the difference in pore size which determines their treatability. Key words: Pinus sylvestris L, Picea abies (L) Karst, Pore size, Water uptake     

Cell Number and Cell Size in Parthenocarpicvs. Pollinated Blueberry (Vaccinium ashei) Fruits

Gibberellic acid (GA₃) promotes parthenocarpic fruit developmentand is used commercially to increase fruit set in many crops.However, fruit size is usually smaller than that of pollinatedfruit. The purpose of this work was to determine the anatomicalbasis for differences in fruit size between pollinated and GA₃-inducedparthenocarpic blueberry (Vaccinium asheiReade) fruits. Freshweights at ripening averaged 1.6 and 2.5 g for GA₃-treatedvs.pollinated fruits, respectively. In both pollinated and GA₃-treatedfruits, mesocarp cell number comprised about 75% of the totalpericarp cell number, and increased from     

The Relationship Between Size of Shoot Apices and Morphological Features of Mature Leaves and Stems of Four Species of Angiosperm Trees

Shoot apex, leaf and stem growth parameters for four speciesof deciduous trees were measured. Only in elm was there a correlationbetween the size of shoot apical meristems and mature leaves.In ash, basswood and cottonwood there was no significant differencebetween size of shoot apices of sucker and canopy branches,despite significant differences in lamina size. In the suckerbranches of all species studied there occurred an early, lateralexpansion of the subapical region of the shoot apical meristem.This correlated well with the greater diameter of stem and pithregions of sucker branches. In addition, the season's annualring of xylem was greater in basswood, cottonwood and elm. Diametersof vessel elements were greater in sucker than canopy branchesin three of the four species. Total branch and internode andnumber of nodes per branch were significantly greater for suckerbranches than canopy growth of all species studied. A hypothesis is proposed to explain the development of the verylarge surface area of leaves on sucker branches. This hypothesisis based on the position of sucker branches in relation to theroot system and involves differences in water stress known tobe present in all plants.Copyright 1993, 1999 Academic Press Sucker leaves, canopy leaves, Fraxìnus pennsylvanica Marsh, green ash, Ulmus amerìcana L., American elm, Populus deltoides Marsh, cottonwood, Tilia americana, basswood     

Electronic Measurement of Plant Cell Number and Size in Suspension Culture

The rapid and accurate determination of cell number and sizeis very desirable for obtaining data on growth kinetics andchanges in the physiological state of a culture. The CoulterCounter has been widely applied to bacterial and animal cellsuspension cultures to determine electronically cell numberand cell size. The application of such techniques to plant cellsuspension cultures is discussed in the following paper anddemonstrated for cultures of Pauls Scarlet Rose (Rosa sp.) andsoybean (Glycine max L.). A new formula for coincidence correctionsis suggested.