Cytogenetics of Lolium perenne

Summary A number of diploid inbred lines of Lolium perenne were treated with colchicine at the early seedling stage to induce chromosome doubling. In each inbred line the colchicine-treated undoubled diploids were kept as controls, as well as the normal untreated diploids. Comparisons of vegetative growth and development, involving the three treatments within each line, revealed that colchicine treatment of seedlings has long-lasting effects upon plant growth and development independent of chromosome doubling, and that for certain characteristics the effects of chromosome doubling are confounded with other effects of the treatment used to produce tetraploids. This colchicine induced variation in the diploids is transmitted through the seed generations in at least one of the inbred lines. The variation appears to be non-random and also shows a strong genotypic component. In so far as the effects of chromosome doubling could be determined, they showed the usual gigas response but were again strongly influenced by genotype.     

Cytogenetics of Lolium perenne

Summary A number of inbred lines of Lolium perenne have been developed as far as the fifth inbred generation and are being used for basic studies on the cytogenetics of the species. An analysis on variation in the pattern of chiasma frequency and distribution, including the parent plants and all generations down to the S5, reveals that the effect of inbreeding is to reduce chiasma frequency and to increase both the cell and bivalent variances. Evidence is presented for a genetic basis of polygenic control of chiasma formation and distribution, and a model is suggested for control over the three related components of variation which involves a two-stage level of regulation.     

Primary and Secondary Induction Requirements for Flowering of Contrasting European Varieties of Lolium perenne

The flowering requirements of six European varieties of Loliumperenne L. were studied in controlled environments. In experimentson primary induction, flowering was recorded after transferto long days (LD) in a greenhouse at 12–24°C. In experimentson secondary induction, primary induction was first accomplishedat 6°C/10 h daylength for 12 weeks. When evaluated by the50% heading criterion, the requirement for duration of primaryinduction at 6°C/8 h daylength was <3 weeks in Mediterranean,5–6 weeks in Central European and 7–8 weeks in Scandinavianvarieties. While ‘Veyo’ (Italy) flowered profuselyregardless of temperature or daylength during primary induction,critical temperatures for primary induction in SD and LD were15 and 11°C in ‘Baca’ (Czech Republic) and 11and 7°C in ‘Falster’ (Denmark). The criticalphotoperiod for secondary induction at 15°C ranged from12 h in ‘Veyo’ and 14 h in ‘Baca’ to16.5 h in ‘Falster’ and 17.5 in ‘Kleppe’(Norway). The critical number of LD cycles varied correspondingly.While the Central and North European varieties required fewerLD cycles for 50% heading at 18 than at 12°C, ‘Veyo’showed the opposite response. It is concluded that the requirementsfor both primary and secondary induction of Lolium perenne increasewith increasing latitude of origin of the germplasm. In oneexperiment, 39–87% of the inflorescences came from tillersthat were not visible on transfer from primary to secondaryinduction, thus it is also concluded that there is no juvenilestage in tillers of Lolium perenne. Copyright 2000 Annals ofBotany Company Daylength, flowering, juvenility, perennial ryegrass (Lolium perenne L.), primary induction, secondary induction, temperature, varieties, vernalization     

Asynapsis in Lolium perenne

Eighteen plants displaying varying degrees of asynapsis ranging from weak to very strong were found among four out of six populations of Lolium perenne L. (2n=14) which had been subjected to three cycles of directional phenotypic selection for productivity of green material. No plants were found displaying univalents in the original generation but the incidence increased with cycles of selection, indicating the genetic control and differential distribution of asynaptic genes among these populations. — The analysis of univalents and chiasma frequency of pollen mother cells (PMC) of six partially asynaptic plants chosen for detailed study revealed that univalents occurred throughout all PMC chiasma classes irrespective of chiasma frequency, but the higher the chiasma frequency of any PMC the less the likelihood of univalents occurring. The relationship between chiasma frequency and univalent frequency per PMC per plant was negative. — Mean chiasma frequency per bivalent increased for the asynaptic cells in comparison with the normal in both the weak and medium asynaptic groups which was explained by the availability of additional chiasmata for redistribution.     

Cytomixis in Lolium perenne

Cytomixis is a spontaneous process occurring through the formation of cytoplasmic bridges between adjacent pollen mother cells. This phenomenon was observed in the pollen mother cells of 3 genotypes of Lolium perenne which had been subjected to directional selection for productivity of green material. — The process has led to the formation of up to 34.8% of PMCs with chromosome numbers deviating from the normal diploid number 2n=14. The abnormal PMCs contained chromosome numbers ranging from 2–56 as observed at first metaphase. — Abnormal PMCs were also observed with approximately the same frequency in Meiosis II. This phenomenon is under genetic control. The evolutionary significance of cytomixis and the cytological consequences are discussed.     

Photosynthesis and Photorespiration in Lolium multiflorum and Lolium perenne

The response of net photosynthesis to changing light-flux densityby leaves of Lolium multiflorum (S. 22) and L. perenne (S. 321)is more adequately described by current models when a term allowingfor photorespiration is included. The magnitude of this termwas determined from the changes in the slope of the light-responsecurves for net photosynthesis. A pseudo first-order rate-constantfor photorespiration, and a pseudo second-order rate-constantfor photosynthesis calculated by this technique for L. multiflorumwere found to be similar to corresponding parameters calculatedfrom light-compensation-point measurements using a simple modeldescribed by Brown (1969). The relative magnitudes of respirationand photosynthesis at light saturation for both Lolium specieswere similar to reported values for other temperate species(Lake, 1967). Two selection lines of L. perenne (S. 321) with contrastingdry-matter yields were found to have the same parameters forrespiration and photosynthesis.     

Flowering of the grass Lolium perenne: effects of vernalization and long days on gibberellin biosynthesis and signaling

Almost 50 years ago, it was shown that gibberellin (GA) applications caused flowering in species normally responding to cold (vernalization) and long day (LD). The implication that GAs are involved with vernalization and LD responses is examined here with the grass Lolium perenne. This species has an obligatory requirement for exposure to both vernalization and LD for its flowering (inflorescence initiation). Specific effects of vernalization or LD on GA synthesis, content, and action have been documented using four treatment pairs: nonvernalized or vernalized plants exposed to short days (SDs) or LDs. Irrespective of vernalization status, exposure to two LDs increased expression of L. perenne GA 20-oxidase-1 (LpGA20ox1), a critical GA biosynthetic gene, with endogenous GAs increasing by up to 5-fold in leaf and shoot. In parallel, LD led to degradation of a DELLA protein, SLENDER (within 48 h of LD or within 2 h of GA application). There was no effect on GA catabolism or abscisic acid content. Loss of SLENDER, which is a repressor of GA signaling, confirms the physiological relevance of increased GA content in LD. For flowering, applied GA replaced the need for LD but not that for vernalization. Thus, GAs may be an LD, leaf-sourced hormonal signal for flowering of L. perenne. By contrast, vernalization had little impact on GA or SLENDER levels or on SLENDER degradation following GA application. Thus, although vernalization and GA are both required for flowering of L. perenne, GA signaling is independent of vernalization that apparently impacts on unrelated processes.     

Clade classification of monolignol biosynthesis gene family members reveals target genes to decrease lignin in Lolium perenne

In monocots, lignin content has a strong impact on the digestibility of the cell wall fraction. Engineering lignin biosynthesis requires a profound knowledge of the role of paralogues in the multigene families that constitute the monolignol biosynthesis pathway. We applied a bioinformatics approach for genome‐wide identification of candidate genes in Lolium perenne that are likely to be involved in the biosynthesis of monolignols. More specifically, we performed functional subtyping of phylogenetic clades in four multigene families: 4CL, COMT, CAD and CCR. Essential residues were considered for functional clade delineation within these families. This classification was complemented with previously published experimental evidence on gene expression, gene function and enzymatic activity in closely related crops and model species. This allowed us to assign functions to novel identified L. perenne genes, and to assess functional redundancy among paralogues. We found that two 4CL paralogues, two COMT paralogues, three CCR paralogues and one CAD gene are prime targets for genetic studies to engineer developmentally regulated lignin in this species. Based on the delineation of sequence conservation between paralogues and a first analysis of allelic diversity, we discuss possibilities to further study the roles of these paralogues in lignin biosynthesis, including expression analysis, reverse genetics and forward genetics, such as association mapping. We propose criteria to prioritise paralogues within multigene families and certain SNPs within these genes for developing genotyping assays or increasing power in association mapping studies. Although L. perenne was the target of the analyses presented here, this functional subtyping of phylogenetic clades represents a valuable tool for studies investigating monolignol biosynthesis genes in other monocot species.     

Flowering of S. 24 Perennial Ryegrass (Lolium perenne L.) in Short Days at Low Temperature

The flowering of the quantitative long-day plant perennial ryegrass(Lolium perenne L.) in short days (8 h), when grown at low temperature(9/4 °C) and under natural summer daylight, is presentedas evidence for the replacement of specific environmental requirementsfor flowering by alternative stimuli in a grass.     

Uptake of glycine by non-mycorrhizal Lolium perenne.

Plants of Lolium perenne were grown in sterile solution culture. 15N-labelled glycine (Gly) coupled with gas chromatograph mass spectrometry was used to prove that non-mycorrhizal plants of L. perenne are capable of acquiring N in the form of intact Gly. It was estimated that a minimum of 80% of Gly-N uptake, over a 3 h period, was as intact Gly, though possible processes resulting in deviation from this estimate are discussed. The relative incorporation of 15N derived from Gly uptake into serine (Ser) compared with other amino acids in the root amino acid pool suggested the enzyme serine:glyoxylate aminotransferase was at least partly responsible for the synthesis of Ser from Gly. Defoliation was shown to reduce Gly uptake by L. perenne. The addition of either 25 mol x m(-3) sucrose or 50 mol x m(-3) glucose to the uptake solution of defoliated plants increased Gly-N uptake compared with both defoliated plants without sugars and with undefoliated plants. Addition of a glucose analogue, 3-O-methyl-D-glucopyranose, that is absorbed but not metabolized by plants, did not affect Gly uptake by defoliated plants. Increasing pH from 3.5 to 9.2 caused a reduction in Gly uptake. Results of the effects of defoliation and pH are consistent with Gly uptake by L. perenne being by an energy-dependent proton symport. When either or Gly were supplied to plants at equimolar concentrations, uptake was five times greater than that of Gly at pH 6 and 13 times greater at pH 9.     

多年生黑麦草的组织培养和植株再生

1植物名称多年生黑麦草(Lolium perenne)栽培品种"德比"(Derbv). 2材料类别成熟种子. 3培养条件(1)愈伤组织诱导培养基:N6 2,4-D10.0 mg·L-1(单位下同) 6-BA 0.5 NAA 0.5 CH(水解酪蛋白)500;(2)继代培养基:N6 2,4-D 5.0 NAA 0.5 6-BA 0.5 CH 300;(3)分化培养基:N6 6-BA 1.0 KT 0.5;(4)壮苗培养基:N6;(5)生根培养基:1/2N6 NAA 0.2.以上培养基中除生根培养基蔗糖含量为3%以外,其余均为5%.pH 5.8,琼脂含量为6.5%.愈伤组织诱导及继代为暗培养;分化培养及生根培养的光照度均为1800 1x,光照时间12 h·d-1,培养温度(25 2)℃.     

The genetics of meiotic chromosome pairing in Lolium temulentum x Lolium perenne tetraploids

Summary The degree of preferential pairing of homologous chromosomes was estimated in a series of tetraploid hybrids of Lolium temulentum x Lolium perenne by means of cytological and genetic analyses. The correlations between the frequency of bivalents at first metaphase of meiosis in the hybrid tetraploids and the degree of preferential pairing calculated from the segregation pattern of isozyme alleles in a test cross was extremely high. The results showed clearly that suppression of heterogenetic pairing in these Lolium tetraploids is achieved by a genetic system involving the A chromosomes as well as the B chromosome system which has been known for some time. Certain similarities with the genetic system controlling pairing in polyploid wheats are discussed.     

Temperature-induced alteration to root longevity in Lolium perenne

The production and mortality of roots is an important factor determining nutrient and carbon fluxes in terrestrial ecosystems. However, the effect of temperature on the longevity of roots is not understood. In this study the impact of changes in temperature on the longevity of Lolium perenne roots was determined.Plants were grown at 15 °C, 21 °C and 27 °C and their roots observed using a minirhizotron system. Major effects of temperature were measured with large reductions in root longevity occurring at higher temperatures. The implications of these data are discussed.     

Selection and stability of synthetic varieties of Lolium perenne

Summary The performance of three experimental cultivars of Lolium perenne selected for yield or water soluble carbohydrate content was monitored over four generations of seed multiplication under relaxed selection. In each variety the selected trait regressed towards that of the base population from which the selection line derived. This could be accounted for by residual genetic variation within the lines for the selected trait, and in some instances, by association of this variation with the fitness character, seed numbers produced. These results emphasize the need for practical breeding programmes to consider the nature of the gene action controlling the selected trait, if additive, directional selection should be effective in increasing the expression of the character. Where ambidirectional dominance and epistasis are important, consideration should be given to means of achieving reassortment of the controlling genes prior to selection.     

Synaptonemal complex formation in hybrids of Lolium temulentum x Lolium perenne (L.)

Comparisons were made between two kinds of tetraploids derived from the hybrid Lolium temulentum x L. perenne. One hybrid behaves like an autotetraploid with multivalents at first metaphase of meiosis in pollen mother cells. The other behaves like an allotetraploid, in which pairing at first metaphase is restricted to bivalents comprised of strictly homologous chromosomes. The diploidisation of the latter form is controlled by determinants located on both the normal, A chromosomes and on supernumary B chromosomes. Reconstruction of synaptonemal complexes and their elements, from serial sections through pollen mother cell nuclei examined under the electron microscope, reveals that at zygotene pairing in both forms results in multivalent formation involving non-homologous as well as homologous chromosomes. The mechanism responsible for the diploidisation is, therefore, not based on a restriction of pairing at early meiosis to homologous chromosomes but on a correction or transformation of the multivalent chromosome associations to bivalents subsequent to zygotene. The transformation is not completed until late pachytene. In the multivalent-forming tetraploid a maximum of four chromosomes are associated at first metaphase. Yet configurations of a higher valency are found at zygotene. There is, therefore, a partial transformation of multivalents even in this autotetraploid form which restricts configurations at metaphase I to homologous and homoeologous chromosomes only. In both hybrids some homologous bivalents are not the product of resolution of multivalents but result from two-by-two pairing from the beginning of zygotene.     

Efficacy of Selective Gametocides on Lolium perenne L.

The efficacy of six chemicals as selective male gametocideson perennial ryegrass plants was studied by making use of agenetic marker technique. In a preliminary screening experimenteach of the chemicals was used in five concentrations and infive treatments at several stages of development at or nearear emergence. Promising treatments from within this experimentwere assessed in more detail subsequently. In most treatmentsfemale fertility was impaired more than male fertility. In thetreatments in which the desired effect was found, i.e. malefertility was depressed appreciably more than female fertility,the differential gametocidal selectivity of the chemicals couldnot be considered distinct enough to merit application on afield scale.