Bulb Development in Onion (Allium cepa L.) I. Effects of Plant Density and Sowing Date in Field Conditions

Early and later maturing cultivars of both spring- and autumn-sownonions were sown on two dates at 25, 100 and400 plants m^–2.High levels of nutrients and irrigation were applied. Both high plant density and early sowing advanced the date atwhich bulb scales, rather than leaf blades, were initiated atthe shoot apex and so advanced the date of maturity by up to46 d. The later maturing spring-sown cultivar showed greaterresponses to density and sowing date than the earlier maturingspring-sown cultivar which in turn was more responsive thanthe autumn-sown cultivars. For each cultivar, maturity date increased linearly with decreasesin the percentage radiation intercepted by the leaf canopy. Onion, Allium cepa L., bulbing, competition, spacing     

C-value reassessment of plant standards: an image cytometry approach

Image cytometry (ICM) has been used to measure DNA 2C-values by evaluating the optical density of Feulgen-stained nuclei. This optical measurement is carried out using three basic tools: microscopy, digital video camera, and image analysis software. Because ICM has been applied to plants, some authors have remarked that studies should be performed before this technique can be accepted as an accurate method for determination of plant genome size. Based on this, the 2C-value of eight plants, which are widely used as standards in DNA quantifications, was reassessed in a cascade-like manner, from A. thaliana through R. sativus, S. lycopersicum, Glycine max, Z. mays, P. sativum, V. faba, to A. cepa. The mean 2C-values of all plants were statistically compared to the values reported by other authors using flow cytometry and/or ICM. These analyses demonstrated that ICM is an accurate and reliable method for 2C-value measurement, representing an attractive alternative to flow cytometry. Statistical comparison of the results also indicated Glycine max ‘Polanka’ as the most adequate primary standard. However, distinct authors have been advised that 2C DNA content of the reference standard should be close to that of the sample. As three further approaches also revisited the 2C-value of these eight plants, we have thus proposed a mean 2C-value for each eight species.     

Nuclear DNA Amounts in Roses

Nuclei isolated from young leaves were stained with propidiumiodide (PI) and their fluorescence intensities were measuredby flow cytometry. The ratio of fluorescence intensities offour calibration standards and 34 roses to an internal standard,parsley (Petroselinum crispum), provided a basis for estimatingthe DNA amounts of P. crispum and rose. The 2C DNA amount ofP. crispum(2 n = 22) was estimated as 4.46 pg (s.d. ±0.08 pg). The 2C DNA amounts of diploid roses (2n = 14) variedbetween subgenera, sections and cultivars, and ranged from 0.78pg (s.d. ± 0.08 pg) in Rosa xanthina and R. sericea(sectionPimpinellifoliae) to 1.29 pg (s.d. ± 0.08 pg) in ‘Félicitéet Perpétue’ (Hybrid Sempervirens). Within eachsection, the DNA amounts of diploid species were similar. Inthe sections Carolinae and Cinnamomeae, DNA amounts were proportionalto ploidy numbers. In the Pimpinellifoliae, DNA amounts of tetraploidswere disproportionately larger than those of diploids whichsuggests that they originated as hybrids with species of sectionswith larger DNA amounts. Ratios of the fluorescence intensitiesof nuclei of roses to P. crispum(internal standard) were alsomeasured using 4',6-diamidino-2-phenylindole (DAPI) which bindspreferentially to AT base pairs. These DAPI ratios were lowerthan, but closely correlated (r² = 0.997) with PI ratios. Fluorescenceintensities of either PI or DAPI-stained nuclei of roses canbe used as rapid indicators of ploidy if variation in the DNAamounts between different taxonomic groups is taken into account.Copyright 2000 Annals of Botany Company Flow cytometry, nuclear DNA amounts, Petroselinum crispum, phenolics, Rosa, roses     

Development of Lateral Primordia in Decapitated Adventitious Roots of Allium cepa

In decapitated adventitious roots of Allium cepa L. var. French,the time taken for lateral primordia to appear in five sectorshas been studied. This time is approx. 4–5 d after theapex of the adventitious root gave rise to the primordial initialcells. Allium cepa, adventitious root, lateral primordia     

Nuclear DNA Amounts in Mosses (Musci)

A comparative investigation into nuclear DNA amounts using flowcytometry and video-based Feulgen densitometry was carried outin 289 accessions of 138 different moss taxa (Bryatae), originatingfrom Austria, Switzerland, Spain, Mexico and the USA. Samplingincluded species from all major moss clades (except Sphagnum).Flow cytometry data agreed highly with the Feulgen data, whichonce again demonstrates the high reliability of both methodsfor DNA amount determination. For the first time, extensivedata on absolute C-values of mosses are available. Haploid DNAcontents (1C) ranged from 0.174 to 2.16 pg, which representsonly about a 12-fold variation. This low C-value variation isremarkable when compared to angiosperms which vary approx. 1000-fold.C-values are usually relatively constant within genera and evenfamilies; however, genera with varying C-values also exist.From the low frequency observed, secondary polyploidy playsonly a minor role in mosses. Possible reasons for the low C-valuevariation are discussed. Copyright 2000 Annals of Botany Company Mosses, Bryatae, genome size, nuclear DNA amounts, C-value variation, Feulgen, flow cytometry, densitometry, image analysis     

Genome size variation inCajanus cajan (Fabaceae): A reconsideration

A recent investigation of genome size in certain samples of the pigeonpea,Cajanus cajan, indicates values from 1.55 pg to 1.99 pg (1C level), which is 1.29-fold variation between accessions. In the present analysis those of these accessions which had particularly high or low DNA contents in that study were subjected to a reanalysis using propidium iodide and DAPI flow cytometry and Feulgen densitometry. Only minor differences in genome size, not more than 1.047-fold, were found with flow cytometry, and no significant differences were obtained with Feulgen densitometry. The previously reported genome size cannot be confirmed. It is about half as large and was determined in the present study as 0.825 pg (1C, propidium iodide flow cytometry,Glycine max as standard) and 0.853 pg (1C, Feulgen densitometry,Allium cepa andPisum sativum as standards), respectively.     

Seed Production Environment, Time of Harvest, and the Potential Longevity of Seeds of Three Cultivars of Rice (Oryza sativa L.)

Changes in seed quality (assessed by potential longevity, i.e.the value of the seed lot constant K₁ of the seed viabilityequation) in three contrasting cultivars of rice (Oryza sativaL.) were monitored during seed development and maturation intwo temperature regimes, viz 28/20°C and 32/24°C (12/12h), provided by controlled environments. Mass maturity (definedas the end of the seed-filling phase) varied only between 18and 20 d after 50% anthesis. In five of the six treatment combinationsmaximum potential longevity was not achieved until 12-19 d aftermass maturity. In contrast, the maximum potential longevityof seeds of a japonica rice cultivar produced in the warmerregime was obtained in the first harvest after mass maturity.After mass maturity, the potential longevity of the japonicarice seed lots produced in the warmer environment was much lessthan that for the cooler environments. Maximum potential longevitywas also consistently greater in the cooler than the warmerregime for the two indica cultivars, although the differencein K₁ was small (0·3-0·5). The deleterious effectof increase in temperature on seed quality development was notdetected until after mass maturity. Maximum potential longevityin the cooler regime was greatest in the glutinous indica (K₁= 3·9) and least in the japonica cultivar (K₁ = 3·1).It is concluded that the japonica cultivar is not as well adaptedto warm seed production regimes as the indica cultivars. Consequently,subject to confirmation, this research suggest that the seedproduction of japonica cultivars for long-term genetic conservationshould be undertaken, whenever possible, in warm temperate environments.Copyright1993, 1999 Academic Press Oryza sativa L., rice, genebanks, seed development, seed storage, seed longevity, temperature     

Photoperiod and Temperature Affect Sprouting of Onion bulbs (Allium cepa L.)

The effects of photoperiod and temperature on sprouting wereinvestigated using three cultivars of onion which exhibit differentresponses to daylength during bulb growth. Two photoperiods(8 h and 14 h) and two constant temperatures (15 C and 20 C)were used. Two cultivars showed enhanced sprouting and leafemergence in short days, and one sprouted poorly in all conditions.In long days, some plants showed growth of new bulbs withinthe old one, without sprouting. Photomorphogenesis, photoperiodism, Allium cepa L, onion, dormancy, bulb sprouting     

Plant Chromatin Replicated in the Absence of Protein Synthesis

The aim of the present work is to detect possible differencesin the chromatin of plants replicated in the absence of proteinsynthesis. The kinetics of nuclease digestion in Allium cepa L., evaluatedafter making the cells permeable, was faster for the chromatinof meristem cells replicated in the presence of 1.0 µgml^–1 cycloheximide than in control cells. In order to have a synchronous population in the meristems,cells were labelled as binucleate by a short treatment with5.0 mM caffeine. Treated cells failed to increase both theircontent in dense chromatin and intranuclear histones. Thesefacts suggest that chromatin replicated in the presence of cycloheximidedid not incorporate histones and was unable to be integratedinto dense chromatin patches. Key words: Allium cepa L., Chromatin replication, Protein synthesis     

Reference standards for determination of DNA content of plant nuclei

Flow cytometry was used to compare 14 potential reference standards for plant DNA content determination. Both chicken and plant internal standards were used, as were propidium iodide (PI) and 4'-6-diamidino-2-phenylindole (DAPI) as fluorochromes. Means and standard errors of the means are presented for the 14 potential reference standards, and the means are compared to those obtained by Feulgen densitometry. Five species are recommended as an initial set of international standards for future plant DNA content determinations: Sorghum bicolor cv. Pioneer 8695 (2C = 1.74 pg), Pisum sativum cv. Minerva Maple (2C = 9.56 pg), Hordeum vulgare cv. Sultan (2C = 11.12 pg), Vicia faba (2C = 26.66 pg), and Allium cepa cv. Ailsa Craig (2C = 33.55 pg). It is recommended that the reference standard of choice be one with 2C and 4C nuclear DNA content peaks similar to, but not overlapping, the 2C and 4C peaks of the target species. We recommend PI as the fluorochrome of choice for flow cytometric determination of plant DNA content. DAPI should be used only if the estimated DNA value is corroborated by using a second stain that has no bias for AT- or GC-rich sequences within genomes.     

The Effects of Priming and 'Natural' Differences in Quality amongst Onion Seed Lots on the Response of the Rate of Germination to Temperature and the Identification of the Characteristics under Genotypic Control

Ellis, R. H. and Butcher, P. D. 1988. The effects of primingand ‘natural’ differences in quality amongst onionseed lots on the response of the rate of germination to temperatureand the identification of the characteristics under genotypiccontrol —J. exp. Bot. 39: 935–950. A screening procedure was applied to define the response ofthe rate of seed germination to sub-and supra-optimal temperaturesfor different lots or sub-lots of two onion (Allium cepa L.)cultivars.Three sub-lots of the cultivar White Lisbon were derived froma control lot by osmotic priming (–1.4 MPa, 20 °C.7 d) alone, by priming and drying and by priming, drying andsubsequently storing the seeds for 7 weeks at 2–5 °C.The major effect of priming was to reduce the thermal time forgermination at both sub- and supra-optimal temperatures. Primingalone also altered the distribution of thermal times at sub-optimaltemperatures. A new equation is presented to describe this variation.In contrast, priming had no consistent effect on base temperature(T_b and little effect on the distribution of ceiling temperatures[T_e(G)]. For the control lot of White Lisbon T_b was 4°C,whilst the best common estimate of T_b for all four sub-lotswas 3.5°C. The mean estimate of T_c(50) for the control,primed and primed and dried sub-lots was 35.5°C.Comparisonof three lots of the cultivar Senshyu Semi Globe Yellow of widely-differingviability showed substantial differences in the thermal timefor germination at sub-optimal temperatures, but no significantdifferences in T_b (P>0.10), the common estimate being 4°C.There was a significant negative correlation between probitpercentage viability and the logarithm of the thermal time for50% germination at sub-optimal temperatures amongst the threelots (P<0.05). The work suggests that base temperature forgermination is a genotypic characteristic which is unaffectedby differences in seed quality. It also shows that the effectof priming, quantified as a reduction in thermal time requirementsfor germination, varies amongst the seeds within a lot. Key words: -Onion, seed germination rate, temperature, priming     

Bulb Development in Onion (Allium cepa L.) II. The Influence of Red: Far-red Spectral Ratio and of Photon Flux Density

Bulb development was followed in four onion cultivars growingin controlled environments under 17 h days in factorial combinationsof photon-flux densities (PFD) of 111 and 333 µmol m^–2s^–1 with red: far-red spectral ratios (R : FR) of 2.88and 1.41. A PFD of 111with R : FR of 0.86 was used in a secondexperiment. The lower the R : FR or the higher the PFD the higherthe mean bulbing ratio and the ratio of bulb plus sheath toleaf blade dry weight and the earlier the bulb swelling. LowerR : FR accelerated scale initiation as did the higher PFD underR : FR 2.88 but not under R : FR 1.41. In high PFD bulb swellingoccurred before scale initiation because many sheaths of bladedleaves thickened, but in low PFD and low R : FR bulb swellingand scale initiation were concurrent. In the low PFD a low R: FR increased soluble carbohydrate concentrations in sheathsand scales compared to high R : FR. In high PFD, soluble carbohydrateconcentrations did not vary with R : FR and were higher thanunder low PFD. Onion, Allium cepa L., bulb, photon flux density, red: far-red ratio, light spectral quality, soluble carbohydrate     

Growth, Dry Matter Partition and Radiation Interception in an Overwintered Bulb Onion (Allium cepa L.) Crop

Growth, bulb development, partition of dry weight between leafblades and bulbs, and the interception of solar radiation weremeasured in overwintered crops of five cultivars of bulb onionwith different maturity dates sown on successive dates in threeseasons. The onset of bulbing was later the later maturity ofthe cultivar. Later sowing did not delay the onset of bulbingbut it did delay maturity. There was little mean differencebetween cultivars in the duration of bulb growth defined asthe interval between onset of bulbing and maturity, but therewere considerable differences between cultivars within a season,and between seasons for a given cultivar. Duration of bulb growthranged from 11 to 46 days with a mean of 35 days. Increases in total shoot dry weight during bulb developmentand, in the absence of much bolting, bulb dry-matter yieldswere linearly related to the total radiation intercepted duringbulb growth. These relationships were similar to those reportedfor other crops in Britain. Radiation interception during thephase of bulb growth was low compared with other crops, witha mean value of 49 per cent and a maximum of 65 per cent. Thepercentage of solar radiation intercepted during bulb developmentwas higher from early sowings than from later ones, particularlyin early maturing cultivars. The harvest index was high, withtypically more than 80 per cent of the shoot dry weight in bulbsat maturity. Allium cepa L., onion, blub, growth, partition of dry matter, radiation interception     

Inhibitory effect of fusicoccin on cell division

Rapid interactions in cell division and cytodifferentiationare induced by hormone treatments in dark-cultured explantsof Jerusalem artichoke. Fusicoccin, at concentrations between10^–6 and 10^–5 M, markedly inhibited the division-promotingactivity induced by plant hormones. Further, fusicoccin-treatedmeristematic root tips of Vicia faba and Allium cepa showeda rapid decrease in the mitotic index. Fusicoccin seems to inhibitsome hormone-sensitive processes required during the inductionand regulation of cell division. (Received March 28, 1979; )     

The Relationship Between Lateral-Root Distribution and Endodermis and Pericycle Cell Length in Allium cepa L. Adventitious Roots

Endodermis and pericycle cell lengths were measured in intactand decapitated adventitious roots of Allium cepa L. Decapitationhad no effect on cell length in mature portions of the root,although it affected more immature cells, impeding normal elongation.Cell length shows a characteristic pattern in different zonesof the adventitious root: cells in the medial region were moremarkedly elongated. The number of lateral root primordia wasalso determined in different zones of the adventitious root.The possible relationship between lateral root distributionpattern and cell length in the endodermis and pericycle is discussed. Allium cepa, onion, endodermis, pericycle, lateral root, cell length     

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     

Nuclear DNA C-values Complete Familial Representation in Gymnosperms

The gymnosperms are a monophyletic yet diverse group of woodytrees with approx. 730 extant species in 17 families. A recentsurvey showed that DNA C-values were available for approx. 16%of species, but for only 12 of the 17 families. This paper completesfamilial representation reporting first C-values for the fiveremaining families: Boweniaceae, Stangeriaceae, Welwitschiaceae,Cephalotaxaceae and Sciadopityaceae. C-values for nine Ephedraand two Gnetum species are also reported. C-values are now availablefor 152 (21%) species. Analysis confirms that gymnosperms arecharacterized by larger C-values than angiosperms (modal 1Cof gymnosperms = 15.8 pg compared with 0.6 pg in angiosperms)although the range (1C = 2.25–32.20 pg) is smaller thanthat in angiosperms (1C = 0.05–127.4 pg). Given completefamilial coverage for C-values and increasing consensus in gymnospermphylogeny, the phylogenetic component of C-value variation wasalso investigated by comparing the two datasets. This analysisrevealed that ancestral gymnosperms (represented by cycads and/orGinkgo; mean genome size = 14.71 pg) probably had larger genomes thanancestral angiosperms. Copyright 2001 Annals of Botany Company Gymnosperm DNA amounts, C-values, phylogeny, ancestral genome size, Cycadales, Ginkgo, Gnetales, conifers, Pinaceae     

Measurements of 14C Incorporation by Illuminated Intact Leaves of Coffee Plants from Gas Mixtures Containing 14CO2

A study was made of the incorporation of ¹⁴C by intact leavesof Coffea arabica (cultivars Mundo Novo, Catuai, 1130–13,and H 6586–2) and Coffea canephora (cultivar Guarini)supplied with gas mixtures containing ¹⁴CO₂ under controlledconditions. Samples of the leaves were combusted and the ¹⁴Cin the CO₂ produced measured using a liquid scintillation counter.The results were used to estimate photosynthetic rates. Theeffects of changing the partial pressures of O₂ and CO₂ on thephotosynthetic rate were studied and estimates made of the CO₂compensation point and photorespiration. The data obtained show differences between the mean net photosyntheticrates of the C. arabica cultivars (6·14 mg CO₂ dm^–2h^–1) and the mean rate for the C. canephora cultivar (3·96mg CO₂ dm^–2 h^–1). The cultivar of the latter speciesphotorespired more rapidly than the cultivar Catuai of C. arabica.Rates of photosynthesis in coffee measured using the ¹⁴CO₂ methodwere similar to rates obtained by others using an infrared gasanalyser. The ¹⁴CO₂ method proved to be reliable for photosyntheticmeasurements and the apparatus is suitable for use in fieldconditions.     

Characterization of the Germination Responses to Temperature of Lettuce (Lactuca sativa L.) Achenes

Germination tests were done on 23 cultivars of lettuce (Lactucasativa L.) comprising a variety of different morphological formsselected for cultivation at various seasons. Significant differences at the upper limit of temperature tolerancewere found between different cultivars: maximum temperaturesfor 50 per cent germination ranged from 23 to 32 °C, andsusceptibility to the induction of secondary dormancy by hightemperatures varied widely from one cultivar to another. Nocorrelations were established between germination responsesand heading type, achene colour or growing season The germination responses of all cultivars at temperatures fromjust above 0 to 20 °C were closely similar and results froma large number of experiments were used to produce a standardgermination reference curve foti culvars of L. sativa. Departfuresrom this curve were found to arise predominantly from variationsin seed quality or test conditions rather than from the genotypeof the cultivar. Detailed comparisons of germination at all possible combinationsof alternate and constant day/night temperatures are presentedfor two cultivars. One with relatively high tolerance to high-temperatureinducedinhibition, the other with low tolerance. The results are discussed in relation to the original distributionof the species as a wild plant and its history of cultivationby man. Lactuca sativa L., Lettuce, achene germination, temperature response