Periodicity of Pollen Development and Quantitative Cytochemistry of Exine and Intine Enzymes in the Grasses Lolium perenne L. and Phalaris tuberosa L.

Daily analysis of anther samples during flower development hasenabled an estimation of the duration of defined developmentalperiods in pollen of the grass Phalaris tuberosa. A similarsequence of pollen development has been established for ryegrass,Lolium perenne, where changes in activity of wall enzymes havebeen followed using quantitative cytochemical methods. Acidphosphatase, an intine enzyme, showed two periods of activity:during the vacuolate period corresponding to deposition of theintine polysaccharides; and in the maturation period correspondingto cytoplasmic activity. Non-specific esterase showed greatestactivity in the parietal tapetal cells until their dissolutionearly in the vacuolate period when an increase in pollen-associatedactivity occurred. These changes provide additional evidencefor the transfer of tapetal proteins to exine sites. Lolium perenne L., Phalaris tuberosa L., ryegrass, canary grass, pollen development, quantitative cytochemistry, enzyme activities, acid phosphatase, esterase     

Pollen and Tapetum Development in Male Fertile Rosmarinus Officinalis L. (Lamiaceae)

The development of microspores/pollen grains and tapetum was studied in fertile Rosmarinus officinalis L. (Lamiaceae). Most parts of the cell walls of the secretory anther tapetum undergo modifications before and during meiosis: the inner tangential and radial cell walls, and often also the outer tangential and radial wall, acquire a fibrous appearance; these walls become later transformed into a thin poly-saccharidic film, which is finally dissolved after microspore mitosis. Electron opaque granules found within the fibrous/lamellated tapetal walls consist of sporopollenin-like material, but cannot be interpreted as Ubisch bodies. The middle lamella and the primary wall of the outer tangential and radial tapetal walls remain unmodified, but get covered by an electron opaque, sporopollenin-like layer. Pollenkitt is formed only by lipid droplets from the ground plasma and/or ER profiles, the plastids do not form pollenkitt precursor lipids. Tapetum maturation (“degeneration”) does not take place before late vacuolate stage.

The apertures are determined during meiosis by vesicles or membrane stacks on the surface of the plasma membrane. The procolumellae are conical, but at maturity the columellae are more cylindrical in shape. The columellar bases often fuse, but a genuine foot layer is lacking. The formation of the endexine starts with sporopollenin-accumulating white lines adjacent to the columellar bases. Later, the endexine grows more irregularly by the accumulation of sporopollenin globules. In mature pollen the intine is clearly bilayered.

Generative cells (GCs) and sperm cells contain a comparatively large amount of cytoplasm, and organelles like mitochondria, dictyosomes, ER, and multi-vesicular bodies, but no plastids; GCs and sperms are separated from the vegetative cell only by two plasma membranes.     

黑麦草(Lolium perenne L.)内生真菌的检测、分离及鉴定

从多年生黑麦草(LoliumperenneL.)5个品种———SR4000、Pinnacle、Topgun、CalypsoⅡ、Justus中分离出61个菌株。次培养后,所得形态稳定的菌株可分为4个形态群,依据其形态特征及APPCR的结果,确定其中的57个分离菌株为Neotyphodiumlolii。     

黑麦草内生真菌感染状况的检测及定量分析

选取内生真菌特异性引物,成功建立了利用PCR技术对黑麦草中内生真菌感染状况的检测和定量分析方法。此检测方法的准确性高于常规乳酸-苯胺蓝染色法。利用实时荧光PCR定量分析的结果表明：不同植株之间内生真菌含量差异较大,而同株植物相同龄级分蘖之间内生真菌含量无显著差异。由此可见内生真菌的含量不仅与植物种以及品种有关,也与植物的基因型密切相关。     

The genetic control of incompatibility in Lolium perenne L.

An examination of the incompatibility mechanism of Lolium perenne using the pollen stigma reaction has revealed that no precise one or two locus system is operative in this species.     

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.     

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.     

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.     

Genetic control of androgenetic response in Lolium perenne L.

In a study of androgenesis in 90 Norwegian genotypes of perennial ryegrass (Lolium perenne L.), heritabilities ranged from h _b ² =0.46 to 0.80. Very high or completely positive genotypic correlations were found between most characters of androgenetic response (e.g. embryo-like structures per 100 anthers, plants per 100 embryo-like structures, albino plants per 100 anthers, green plants per 100 anthers). Three genotypes, 2 Norwegian (7-5 and 9-5) and 1 Danish (245), which had significantly different androgenetic responses were selected to study the genetic control of the processes. Genotypes 7-5 and 9-5 were highly embryogenie, 7–5 and 245 were relatively high producers of green plants, while 9-5 was unable to produce green plants. The six possible reciprocal crosses between these three genotypes were made, and 10 or 11 F₁ plants from each cross were used for anther culture experiments. The cross 7-5 x 245 showed average superiority over both parents for total plant regeneration and green plant production, results not previously reported. The phenotypic correlations estimated among progenies from the crosses ranged from r=-0.99^*** to 0.81^***. These considerable changes, relative to the results of the screening experiment, are most likely the result of changed allele frequencies caused by the strong selection of parents in these crosses, and a relatively simple genetical control. This is also inferred from the large transgressive segregation observed.Abbreviations ANT anthers - ELS embryo-like structures - ALB albino plants - GRP green plants - DH doubled haploid plants     

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.     

Development and mapping of a public reference set of SSR markers in Lolium perenne L.

We report on the characterization and mapping of 76 simple sequence repeat (SSR) markers for Lolium perenne. These markers are publicly available or obtained either from genomic libraries enriched for SSR motifs or L. perenne expressed sequence tag (EST) clones. Four L. perenne mapping populations were used to map the SSR markers. A consensus linkage map of the four mapping populations containing 65 of the SSR markers is presented, together with primer information and a quality score indicating the usefulness of the SSR marker in different populations. The SSR markers identified all seven L. perenne linkage groups.     

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.     

Identification and mode of action of self-compatibility loci in Lolium perenne L

The two-locus gametophytic incompatibility system in perennial ryegrass (Lolium perenne L.) is not always fully effective: obligate selfing of plants sieves self-compatible pollen mutants, and self-fertility becomes fixed in subsequent generations. Self-compatibility (SC) was investigated in an F2 family. In vitro self-pollinations were analysed and recorded and plants were classified as being either partially or fully compatible. Distorted segregation ratios of markers on linkage group (LG) 5 were found, which indicate the possible presence of a gametophytic SC locus. Interval linkage analysis of pollen compatibility after selfing confirmed that this distortion was due to a locus (T) analogous to the S5 locus of rye. However, even though markers in this region were, on average, less than 1 cM apart, the minimum number of plants possessing the unfavoured allele was never less than 6% for any marker locus. We proved that this was because of the presence of another SC locus, exhibiting gametophytic selection, segregating in this population and identified by interval mapping analysis of compatibility classes of in vitro self-pollinations. This locus was located on LG1, and probably corresponds to the S locus. We show that the T locus, a relic of a multilocus system, functions through interaction with the S locus: F2 segregation of incompatibility phenotypes and linked markers demonstrated that the S/t pollen genotype combination, expected to be compatible on selfing, was sometimes incompatible. Further evidence is presented to show that this interaction must be dependent on yet another locus located on LG2. A prime candidate would be the Z incompatibility locus.     

The Growth and Survival of Severely-shaded Tillers in Lolium perenne L.

The effect of shading a single tiller to below its compensationpoint for a period of 5 weeks in vegetative plants of Loliumperenne L. cv. S23, was studied in two different experimentseach employing two light regimes, one of which was common toboth experiments. In the first experiment tillers in the axils of the first leafwere shaded three weeks from appearance at both 40 and 70 Wm^–2. None of the shaded tillers died and they continuedto produce new leaves and increase in dry weight but at a reducedrate. In the second experiment, tillers with one emerged leafin any leaf axil position were shaded at 70 W m^–2 andin a treatment in which light was reduced to 13 W m^–2after initial growth at 70 W m^–2. As in the first experimentall shaded tillers survived at 70 W m^–2 but in the 70 13 W m^–2 transfer regime all shaded tillers died. In the second experiment shaded tillers in both light regimeswere supplied with ¹⁴C-assimilate by translocation from theremainder of the plant but in the 70 13 W m^–2 the initialsupport was withdrawn within 5 weeks of shading. The results are discussed in terms of the physiological relationshipsbetween the tillers of the grass plant. Lolium perenne L., growth of tillers, survival of tillers, effect of light     

Development of novel microsatellite markers for the grassland species Lolium multiflorum,Lolium perenne and Festuca pratensis

Twelve microsatellite markers were isolated from Lolium multiflorum. Allelic variability and cross‐species amplification were assessed on 16 individuals of each of the three grassland species L. multiflorum, Lolium perenne and Festuca pratensis. Cross‐species amplification success was 100% for L. perenne and 83% for F. pratensis. The number of alleles detected ranged from one to 14 with an average of 3.4. While three microsatellite loci were polymorphic in all three species, one marker produced species‐specific alleles in all three species. These microsatellite markers provide a valuable tool for population genetic studies within and among species of the Festuca–Lolium complex.