Growth Hormone Changes in Chrysanthemum morifolium: Effects of Environmental Factors Controlling Flowering

Simultaneous quantitative analyses have been made of the endogenouslevels of auxin- and gibberellin like substances, growth inhibitors,and auxin-oxidizing enzyme activity in the cold-requiring Chrysanthemummorifolium cv. Sunbeam subjected to different daylength, lightintensity and temperature regimes known to affect flowering.While little hormone or enzyme activity was found in extractsfrom unvernalized plants, a striking rise in auxin-oxidizingenzyme activity occurred rapidly after the end of cold treatment.Increased auxin activity was also recorded shortly after vernalization.At 28 °C both enzyme and auxin activity declined over aperiod of 3–4 weeks; at 20 °C this response was delayed.Gibberellin activity at 28 °C rose steeply about 2 weeksfrom vernalization and declined several weeks later; at 20 °Ca similar response was less marked. Low light intensity treatment,which may have increased endogenous auxin levels, or exogenousauxin application reduced gibberellin-like substance levelsand cause d devernalization.Phosphon D treatment also loweredgibberellin levels and prevented flowering. An extract fromvernalized plants containing gibberellin-like substances intensifiedthe flowering of partially vernalized test plants. Persistenceof high auxin activity in vernalized plants on long days wasassociated with failure to form normal flower buds. Stem elongationrates correlated in general with levels of endogenous auxin-and gibberellin-like substances. Significant amounts of an abscisin-likeinhibitor were found in extracts of flower buds. The mechanismof natural devernalization is discussed in relation to theseobservations.     

The Mechanism of Action of Vernalization in Lathyrus odoratus L.

In the sweet pea (Lathyrus odoratus L.) genes Dn^l andDr^h controlthe production of a graft-transmissible substance which delaysflowering and promotes outgrowth of basal laterals. Seed vernalizationpromotes flowering and reduces lateral outgrowth in intact plantsand grafted scions of genotype DnⁱDn^l, suggesting that vernalizationreduces output of the Dnⁱ system, possibly by disrupting therelationship between chronological and plastochronic age. Whenlateral outgrowth and floral abortion are used as indicatorsof inhibitor levels, it can be shown that vernalized Dnⁱ plantspossess more inhibitor but initiate flower buds at a lower nodethan unvernalized dn plants. This supports the suggestion thatin regard to floral initiation vernalization also alters thesensitivity of the shoot apex to the flowering hormone(s). InLathyrus odoratus an hormonally based vernalization responseof considerable magnitude can be shown for day-neutral (dndn)lines, supporting the suggestion that vernalization also influencesthe level of a flower promotor. Lathyrus odoratus L., sweet pea, vernalization, flowering, branching, genotype, grafting     

Influence of Genotype, Plant Growth Temperature and Anther Incubation Temperature on Microspore Embryo Production in Brassica napus ssp. oleifera

Eleven F₁ hybrid genotypes of winter rape (Brassica napus ssp.oleifera) were used in a study of induction and growth of microspore-derivedembryos. Plants of each genotype were grown in controlled environmentsat either a constant 15°C or a constant 20°C, both witha 16 h photoperiod. Equal numbers of buds, approximately 2.5mm in length, containing uninucleate microspores were harvestedfrom each genotype and either pretreated (14 d at 4°C) ordissected immediately after harvest. Anthers were cultured onliquid medium based upon that of Murashige and Skoog (1962)and containing 8% sucrose, 0.5 mg dm^–3 naphthylaceticacid and 0.05 mg dm^–3 benzylaminopurine. Anthers fromequal samples of buds were incubated at 35°C for 0, 1, 2or 3 d before transfer to 30°C (21 d) and then 25°C.After a total of 42 d incubation, cultures were scored for thepresence of macroscopic embryos (1–2 mm in length) andfor the presence of anthers containing aborted embryoids whichhad not developed further. The results showed first that bud pretreatment completely inhibitedinduction and secondly that anthers of all genotypes had anabsolute requirement for a 35°C treatment (optimal duration2 d) in order to induce embryoid formation. In the great majorityof genotypes plants grown at 15°C provided more productiveanthers than plants grown at 20°C. However, within eachtreatment there were great differences both in the frequencyof anthers showing induced embryoids and of the final yieldof embryos. There was evidence that hybrids with a common parentresponded similarly under certain treatments. This confirmedthe importance of genotypic control for some components of embryoyield. Key words: Brassica napus, Rape, Anther culture, Pollen, Haploid     

Effects of Temperature, Photoperiod and Seed Vernalization on Flowering in Faba Bean Vicia faba

Factorial combinations of three photoperiods (10, 13 and 16h), two day temperatures (18 and 28 °C) and two night temperatures(5 and 13 °C) were imposed on nodulated plants of six diversegenotypes of faba bean (Vicia faba L.). Plants were grown inpots in growth cabinets from both vernalized (1.5±0.5°C for 30 d) and non-vernalized seeds. The times from sowingto the appearance of first open flowers (f) were recorded. Seedvernalization decreased the subsequent time taken to flowerin almost all genotype x growing environment combinations (theexceptions were plants of the cv. Maris Bead grown in threecooler, short-day regimes). The influence of temperature andphotoperiod on the rate of flowering was quantified, using amodel applied previously to other long-day species of grainlegume in which positive linear relations between both temperatureand photoperiod and the rate of progress towards flowering areassumed to apply. A significant positive linear response ofrate of progress towards flowering to limited ranges of meandiurnal temperature was detected in all six genotypes, but inthree genotypes (Syrian Local Large, Aquadulce and Maris Bead)the 28 °C day temperature reduced the rate of progress towardsflowering - suggesting that the optimum temperature for floweringin these genotypes is below 28 °C. In four genotypes (MarisBead, Giza-4, Aquadulce and BPL 1722) a significant positiveresponse to photoperiod, typical of quantitative long-day plants,was observed only in plants grown from vernalized seeds. Incontrast, plants of the genotype Zeidab Local grown from bothnon-vernalized and vernalized seeds showed the same positiveresponse to photoperiod, whereas plants of the land-race SyrianLocal Large were consistently unresponsive to photoperiod. Theimplications of this range of responses amongst diverse genotypesare discussed in relation to screening germplasm. Vicia faba, faba bean, flowering, photoperiod, temperature, seed vernalization, germplasm screening     

Interaction of vernalization, photoperiod and high temperature in flowering of Arabidopsis thaliana (L.) HEYNH.

Flowering of Arabidopsis thaliana (L.) HEYNH., var. "Stockholm",plants, raised from vernalized seeds, may be modified by thephotoperiodic conditions or a short (1 week) exposure to hightemperature (32°C) following vernalization, depending onthe duration of the cold treatment. When vernalization is partial(1 to 4 weeks at 4°C), both short days (8hr light) and hightemperature have a devernalizing effect, but when the cold requirementhas been fully satisfied, after 5 to 6 weeks at 4°C, devernalizationis no longer possible. There is no interaction between photoperiodand high temperature. Fully vernalized plant flower in bothlong and short days, although flowering is delayed in shortdays. This delay is not a photoperiodic effect, however, butmay be ascribed to the decreased radiant energy available inan 8-hr photoperiod. Thus, fully vernalized Arabidopsis plantsare day-neutral. (Received November 5, 1969; )     

Changes in nucleic acids, protein-nitrogen and amino-nitrogen of excised winter wheat embryos during vernalization

Embryos excised from winter wheat grains were vernalized for10–50 days with or without sugar (sucrose). Determinationswere made of fresh weight, protein-nitrogen, amino-nitrogen,RNA and DNA. There was no change in the contents of RNA of wheatembryos during the vernalization. The incorporation of ³²P intonucleic acid in wheat embryos during vernalization in the presenceof sugar was much higher than that of embryos vernalized withoutsugar. From these results we assumed that RNA turnover occurredduring the vernalization. There was no significant differencein the nucleotide composition of RNA extracted between the vernalizedand unvernalized embryos. The RNA of wheat embryos was separatedinto two fractions. Proportions of these two RNA fractions variedin the course of cold treatment, and similar changes were foundin developing wheat leaves. (Received July 25, 1974; )     

Effect of Vernalization and Red Light Illumination of Seedlings of Bread Wheat (Triticum aestivum L.) on the Temperature Profile of cAMP Phosphodiesterase Activity

Phenotypic manifestations of Vrn(vernalization) and Ppd (photoperiod) genes responsible for transition of bread wheat Triticum aestivumL. to generative growth (flowering) are mutually related. Since the mechanism of phytochrome-induced photoperiodism involves the enzymes of cyclic adenosine monophosphate metabolism, and phosphodiesterase in particular, we tested involvement of phosphodiesterase in the process of winter wheat vernalization and formation of flowering competence in alternate wheat requiring a long photoperiod but no vernalization for its transition to flowering. We studied temperature dependence of phosphodiesterase activity in vernalized and unvernalized winter wheat on the one hand and in etiolated and red light illuminated seedlings of alternate wheat on the other hand. Short-term experiments demonstrated that red light illumination is similar to long photoperiod by the effect on the long-day plants. Both influences induced a pronounced inversion of the temperature profile of phosphodiesterase activity in the 28–45°C range. We propose that phosphodiesterase is involved in vernalization and can serve as a receptor of low temperature in winter wheat. Changed temperature profile is a radical control mechanism of phosphodiesterase activity in response to the influences (red light and vernalizing temperatures) responsible for competence of various bread wheat forms for generative growth.     

Expression of Vernalization Genes in Near-isogenic Wheat Lines: Effects of Night Temperature

Four near-isogenic lines of wheat (Triticum aestivum L.em Thell)were used to compare selected night temperatures for their effectivenessas vernalizing temperatures. All treatments (conducted withina phytotron) had a common day temperature of 20 °C for 12h and night temperatures were 4, 7, 10, 13 and 20 °C. Interpretationof results for reproductive development was confounded by threeinteracting factors, their relative importance varying withgenotype. Firstly, development rate was generally slower atlower night temperatures. Secondly, in contrast, there was atendency for lower night temperatures to hasten developmentrate if vernalization requirements were satisfied. Thirdly,the lower night temperatures provided a more favourable environmentfor leaf production such that for some genotypes, vernalizedplants had higher final leaf numbers than unvernalized plants.Only for the genotype with the strongest vernalization response(vrn1 vrn2) did hastening of development due to vernalizationoverride any delaying effects. For this genotype, 4, 7 and 10°C were vernalizing temperatures. For the other three genotypes,any hastening of development due to vernalization was outweighedby delaying effects of lower night temperatures. Spikelet numberand days to anthesis were positively correlated in three ofthe four genotypes. It appeared that differences in spikeletnumber were a direct result of night temperature influencingthe duration of the spikelet phase and/or rate of spikelet initiation.Plant size at flowering was determined by the differential effectsof night temperature on growth and development rates. Triticum aestivum L., wheat, vernalization, night temperature, isogenic lines     

Expression of Vernalization Requirement and Spikelet Number in Synthetic Hexaploid Wheats and their Triticum tauschii and Tetraploid Wheat Parents

Vernalization requirement, as measured by days from sowing toear emergence (plants grown under an 18-h photoperiod), andspikelet number per ear were recorded for 17 synthetic hexaploidwheats and the six tetraploid (Triticum durum) and the ninediploid T. tauschii parents used to synthesize them. The tetraploid parents and the synthetic hexaploids had springphenotypes (little or no vernalization requirement) whereasthe T. tauschii parents were all winter types (strong vernalizationrequirement). The tetraploid wheats and the synthetic hexaploidsreached ear emergence 50·3 to 63·8 d and 58·2to 75·3 d after sowing, respectively, while the T. tauschiilines reached ear emergence 114·3 to 179·5 d aftersowing. The spring habit of the synthetic hexaploids demonstrates theepistasis of spring over winter habit. It is considered thatwith a presumed single vrn locus in the diploid species T. tauschiithe range of ear emergence in these lines is consistent withthe action of multiple alleles at that locus. Although there was no general epistasis for spikelet number,the tetraploid parents appear to be exerting more influenceover spikelet number in the synthetic hexaploids than T. tauschii.The well established association between the duration from sowingto ear emergence and spikelet number was not evident eitherwithin each ploidy group or when the 32 lines were consideredtogether. Triticum tauschii, Triticum durum, hexaploid wheat, spikelet number, vernalization requirement     

Effect of various exogenous and endogenous factors on microspore embryogenesis in Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> (L.) Czern and Coss)

Summary The influence of donor plant growth environment, microspore development stage, culture media and incubation conditions on microspore embryogenesis was studied in three Indian B. juncea varieties. The donor plants were grown under varying environments: field conditions, controlled conditions, or a combination of the two. The correlation analysis between the bud size and microspore development stage revealed that the bud size is an accurate marker for donor plants grown under controlled conditions, however, the same does not hold true for the field-grown plants. The buds containing late uninucleate microspores collected from plants grown under normal field conditions up to bolting stage and then transferred to controlled environment were observed to be most responsive with genotypic variability ranging from 10 to 35 embryos per Petri dish, irrespective of the other factors. NLN medium containing 13% sucrose was found to be most suitable for induction of embryogenesis The fortification of this medium with activated charcoal, polyvinylpyrrolidone, colchicine, or growth regulators (6-benzylaminopurine and 1-naphthaleneacetic acid) was observed to be antagonistic for microspore embryogenesis, while silver nitrate (10 μM) had a significant synergistic effect. A post-culture high-temperature incubation of microspores at 32.5±1°C for 10–15 d was found most suitable for high-frequency production of microspore embryos. The highest frequency of microspore embryogenesis (78 embryos per Petri dish) was observed from the late uninucleate microspores (contained in bud sizes 3.1–3.5 nm irrespective of genotype) cultured on NLN medium containing 13% sucrose and silver nitrate (10 μM), and incubated at 32.5°C for 10–15 d.     

A high throughput <Emphasis Type="Italic">Brassica napus</Emphasis> microspore culture system: influence of percoll gradient separation and bud selection on embryogenesis

Microspore culture for the purpose of developing doubled haploid plants is routine for numerous plant species; however, the embryo yield is still very low compared with the total available microspore population. The ability to select and isolate highly embryogenic microspores would be desirable for high embryo yield in microspore culture. To maximize the efficiency of canola microspore culture, a combination of bud size selection and microspore fractionation using a Percoll gradient was followed. This approach has consistently given high embryo yields and uniform embryo development. Microspores isolated from buds 1.5 to 4.4 mm in length of Brassica napus genotypes Topas 4079, DH12075, Westar and 0025 formed embryos at different frequencies. The most embryogenic bud size range varied with each cultivar: Topas 4079 3.5–3.9 mm, DH12075 2.0–2.4 mm, and Westar and 0025 2.5–2.9 mm. When the microspores from 2.0 to 2.4 mm buds of DH12075 were carefully layered on top of a discontinuous Percoll gradient of 10, 20 and 40%, and subsequently spun through the Percoll layers by centrifugation, bands were formed containing populations of microspores of uniform developmental stage. The middle layer of the gradient contained the late uninucleate and early binucleate microspores that were the most embryogenic. In addition, the relationship between the bud size, developmental stage of isolated microspores, Percoll gradient concentration and the embryogenic frequency of each cultivar were studied. Optimization of these factors is required for each genotype evaluated.     

Pachytene Chromosome Pairing and Multivalent Formation in an Autotetraploid Tomato

Pachytene pairing of the nucleolus organizing chromosome wasstudied in an induced autotetraploid tomato (Lycopersicon esculentuniMill.) to elucidate the relationship of the murrence of partnerexchanges, heterochromatic fusions and centric associationsto the frequency of formation of multivalents at diakinesis.Centric and/or heterochromatic associations occurred in 93·3per cent of the cells. In 8·9 per cent of the cases,apart from such heterochromatic associations, partner exchangeswere observed in euchromatic regions of the long arm. The fourhomologues formed two pairs in 6·7 per cent of the cells.Chiasma frequency in the tetraploid is not significantly lessthan double that in the diploid. Since there is no apparentrestriction on chiasma formation, multivalent frequency is dependenton the frequency of partner exchanges. Quadrivalents were foundin only 10 per cent of the cells at diakinesis which correspondswith the frequency of partner exchanges in the euchromatic regionsimplying that heterochromatic and centric associations do notrepresent exchanges of partner. Lycopersicon esculenrum, tomato, autotetraploid chromosome pairing, heterochromatic fusion, multivalent formation     

Microbiological Synthesis of Fat: THE FORMATION OF FAT FROM SUCROSE

1. Forty-three strains of moulds, selected from ten species,were examined to ascertain their capabilities as producers offat, when grown in four different solutions of nutrient inorganicsalts together with sucrose. The three highest yields of feltwere given by Penicillium javanicum van Beyma, P. Soppi Zaleski,and Aspergillus nidulans Eidam, in that order. The fat contenton felt weight was maximal at 34·8 per cent, with P.Soppi, at 28·4 per cent. with Fusarium lini(1), and at25·8 per cent. with A. nidulans; on sugar utilized itwas maximal at 11·4 per cent. with P. Soppi, at 7·9per cent, with A. nidulans, and at 5·6 per cent. withF. lini(1). 2. Other moulds considered worthy of further trial were P. spinulosum,P. aurantiobrunneum, F. graminearum, A. flavus, F. oxysporum,A. clavatus, and P. oxalicum.     

Influence of Preculture Variables on Microspore Embryo Production in Brassica napus ssp. oleifera cv. Duplo

The effect of four preculture variables on microspore embryoinduction and growth were examined: (1) the source of the budselected for culture (apical or axillary inflorescence; (2)the method of harvest (single harvest of whole inflorescenceor sequential harvest of individual buds; (3) the length ofthe bud (2, 3 or 4 mm); and (4) the application of a 4 ^°Cpretreatment to the bud after harvest. Microscopic and macroscopicanalysis of every anther used for culture permitted an assessmentof the following parameters: (1) the percentage of induced buds;(2) the number of induced anthers per induced bud; (3) the numberof productive buds (with macroscopic embryos) as a percentageof the induced buds; (4) the degree of induction per inducedanther (an estimate of the number of microspores in which initialembryogenic divisions had commenced); and (5) embryoid survival(the number of embryos as a proportion of the degree of induction). The product of parameters 1 and 2 gave the number of inducedanthers and all five parameters were components of the finalyield - the number of embryos produced per bud cultured. It was found that the maximum number of induced buds (67·0per cent) occurred with 2 mm sequentially harvested non-pretreatedbuds. Overall, the values decreased with increasing bud lengthand were lower for pretreated and axillary buds. In contrast,the two other estimates of induction - number of induced anthersper induced bud and degree of induction per induced anther -both had maximum values from 3 mm sequentially harvested, pretreatedbuds from apical inflorescences. The highest final yield ofembryos per cultured bud (44·9) was found with 2 mm non-pretreatedbuds taken from a single harvest of the apical inflorescence.The study therefore confirmed that the different componentsof the final embryo yield are differentially affected by thefour preculture variables tested. These variables must be controlledif reproducible results are to be achieved. Brassica napus, tape, anther culture, pollen, microspore, haploid     

Effects of Temperature and Photoperiod on Phenological Development in Three Genotypes of Bambara Groundnut (Vigna subterranea)

Factorial combinations of four photoperiods (10, 11·33,12·66 and 16 h d^-1) and three mean diurnal temperatures(20·2, 24·1 and 28·1°C) were imposedon nodulated plants of three Nigerian bambara groundnut genotypes[Vigna subterranea (L.) Verdc., syn. Voandzeia subterranea (L.)Thouars] grown in glasshouses in The Netherlands. The photothermalresponse of the onset of flowering and the onset of poddingwere determined. The time from sowing to first flower (f) wasdetermined by noting the day on which the first open flowerappeared. The time from sowing to the onset of podding (p) wasestimated from linear regressions of pod dry weight againsttime from sowing. Developmental rates were derived from thereciprocals of f and p. In two genotypes, 'Ankpa 2' and 'Yola',flowering occurred irrespective of photoperiod and 1/f was controlledby temperature only, occurring sooner at 28·1 than at20·2°C. The third genotype, 'Ankpa 4', was sensitiveto temperature and photoperiod and f was increased by coolertemperatures and photoperiods > 12·66 h d^-1 at 20·2°Cand > 11·33 h d^-1 at 24·1 and 28·1°C.In contrast, p was affected by temperature and photoperiod inall three genotypes. In bambara groundnut photoperiod-sensitivitytherefore increases between the onset of flowering and the onsetof podding. The most photoperiod-sensitive genotype with respectto p was 'Ankpa 4', followed by 'Yola' and 'Ankpa 2'. Therewas also variation in temperature-sensitivity between the genotypesinvestigated. Evaluation of bambara groundnut genotypes foradaptation to different photothermal environments will thereforerequire screening for flowering and podding responses.Copyright1994, 1999 Academic Press Vigna subterranea (L.) Verdc., Voandzeia subterranea (L.) Thouars, bambara groundnut, phenology, photoperiod, daylength, temperature, flowering, podding     

Changes in nucleic acid metabolism in barley seedlings during vernalization

Changes in nucleic acid metabolism of barley seedlings duringvernalization were investigated using thymidine-³H and uridine-³H. DNA content increased in the early germination stage from the1st to 3rd week in vernalized seedlings. In unvernalized seedlings,the most rapid increase was found in the late germination stage.RNA content in the vernalized seedlings increased after 1 weekand reached maximum level after 3 weeks of vernalization treatment.The unvernalized seedlings had a comparatively high contentat 2 days' germination which then gradually increased. Much thymidine-³H was incorporated into DNA and uridine-³H intoRNA fractions in the seedlings during early vernalization. Onthe contrary, without vernalization, heavy incorporation ofthymidine-³H was delayed during the late germination stage.Incorporation of uridine-³H showed a linear increase. A more detailed distribution of thymidine-³H and uridine-³Hin the nucleic acids was examined by methylated albumin-coatedkieselguhr column chromatography. A considerable amount of theincorporated uridine-³H was found in the tenaciouslybound ribonucleicacid (TB-RNA) in the vernalized seedlings. (Received January 18, 1973; )     

Loss of Viability in Lettuce Seeds and the Accumulation of Chromosome Damage under Different Storage Conditions

Loss of seed viability in lettuce (Lactuca sativa L.) duringstorage is associated with an increase in the frequency of cellsin the surviving seeds showing chromosome damage during firstmitoses. The relation is linear when probit of the frequencyof aberrant cells is plotted as a function of probit percentagenormal germination. The slope of the relation, however, variesaccording to moisture content so that the proportion of aberrantcells for any given loss of germination increases with decreasein moisture content over the range 13.0–5.5 per cent.At 3.3 per cent moisture content, however, the proportion ofaberrations was no greater than at 5.5 per cent moisture content;and at 18.1 per cent moisture content the proportion was noless than at 13.0 per cent moisture content. Despite these differences,the increase in chromosomal aberrations per unit time for agiven temperature was always less the lower the moisture content.Diplontic selection markedly reduced the frequency of chromosomalaberrations and eliminated the differences in these frequenciesbetween the different storage treatments. But even after fiveweeks' growth, root tips from aged seed still contained abouttwice as many aberrant cells as compared with similar root tipsderived from the original seed stock. Studies on the frequencyof recessive mutations indicated that excessive amounts of heritablemutations were not present in the progenies of aged seed, evenwhen stored at moisture contents as low as 5.5 per cent. Allthis and other evidence reinforces the view that orthodox seedsfor genetic conservation should be stored at not more than about5 per cent moisture content, and that even lower moisture contentsare worth considering. The results also emphasise the need formaintaining a high regeneration standard, i.e. the percentageto which seed viability is allowed to fall during storage beforethe seed stock is regenerated. Lactuca sativa, lettuce, seed storage, seed viability, chromosomal aberrations, phenotypic mutations     

Influence of Vernalization and Photoperiod on Supernumerary Spikelet Expression in Wheat

Two tetraploid (Triticum turgidum L.emend gr. turgidum and gr.durum) and five hexaploid wheats (Triticum x aestivum L. emendgr. aestivum) with reported tendencies for ‘branched heads’(supernurnerary spikelets) exhibited variation in its expressionunder different vernalization photoperiod and temperature regimes. Two main types of supernumerary spikelets were identified, multiplesessile spikelets (MSS) with two or more complete spikeletsat a rachis node and indeterminate rachilla spikelets (IRS)with two to 13 spikelets on an extended rachilla. The degree of supernumerary spikelet expression in wheats withvernalization response differed from those without. Short photoperiods(9–14 h) both outdoors and in a glasshouse environment,were more conducive to supernumerary spikelet expression than24 h photoperiod in both environments. The 24 h photoperiodglasshouse environment (higher mean temperatures) was leastconducive to its expression except in lines with a strong vernalizationresponse. The high stability of supernumerary spikelet expression in certaingenotypes in the different environments indicated the feasibilityof incorporating this character in breeding and selecting commercialwheats to increase grain number per head. Triticum, wheat, ear-branching, supernumerary spikelets, vernalization, photoperiod, temperature     

Effect of Severity of Defoliation on the Viability of Reproductive and Vegetative Axillary Buds of Trifolium repens L.

This glasshouse experiment was performed to assess the effectsof a range of constant defoliation regimes applied to cuttingsof a single large-leaved genotype ofTrifolium repens L. on theviability of its axillary buds. Plants were established to comprisea single main stolon (axillary branches were removed) and defoliationtreatments were applied by removing the older (basal) leavesuntil leaf complements of 1·0, 1·5, 2·0,2·5, 3·0 or all leaves (control) remained. Basalleaves were subsequently removed as necessary to maintain thetarget leaf complements. Only severe defoliation (leaf complements of 1·0 and1·5) induced a loss of viability in axillary buds. Lossof viability was greatest in reproductive buds present withinthe apical bud when the treatments were first imposed. Althoughthe most severe treatment (leaf complement 1·0) resultedin death of half the plants, in plants surviving that treatment,death of vegetative axillary buds was restricted to 21% of thevegetative buds at the three youngest node positions withinthe apical bud at the time of treatment application. No othertreatment induced any loss of viability of vegetative buds.There was no loss of viability of axillary buds at nodes formedafter the treatments were imposed. The frequency of initiationof inflorescences at nodes formed after treatments were imposeddecreased as defoliation severity increased. Severe defoliation resulted in marked changes in plant morphologyindicative of a sharp decrease in availability of intraplantresources. It was concluded that under severe defoliation: (1)the potential for vegetative growth (as represented by viablevegetative axillary buds) was maintained at the expense of reproductivegrowth; and (2) that the loss of viability of axillary budswas associated with the sudden changes in physiological processesinduced by defoliation as there was no loss of viability inbuds formed after plants had adjusted their phenotype to oneof smaller size. Trifolium repens L.; white clover; defoliation; axillary buds; viability; inflorescences     

Development of asparagus microspores in vivo and in vitro is influenced by gametogenic stage and cold treatment

Summary Development of asparagus microspores in cold-treated buds of varying sizes and shed microspores from these buds in in vitro culture were observed cytologically for the G459 genotype. Before cold pretreatment, more than 75% of the microspores in flower buds of the 1.4–1.6, 1.7–1.9, 2.0–2.2, 2.3–2.5, and 2.6–2.8 mm size classes were at the early-, mid-, late-uninucleate, early-, and late-binucleate stages, respectively. After 7 d in cold treatment, percentages of microspores at different stages changed in all flower buds. Most notable was the appearance of binucleate microspores resulting from symmetric rather than asymmetric division. For flower buds of 1.7–1.9, 2.0–2.2, and 2.3–2.5 mm size classes, 4.9%, 27.2%, and 11.4% of the microspores had divided symmetrically, respectively. When microspores from buds of each size category were cultured in androgenesis induction medium, only microspores completing symmetric pollen mitosis I during cold treatment were observed to divide further, and calluses were only obtained from microspores of flower bud size classes where symmetric divisions were observed after several days of cold treatment. Significant correlations existed among microspore callus yield, the percentage of late-uninucleate microspores in vivo before cold treatment, and the frequency of symmetric pollen mitosis I after 7 d of cold treatment. Consequently, asparagus microspore androgenesis may occur through one developmental pathway, where a symmetric first mitotic division is a prerequisite for continued development.