Partitioning of sugars in Lolium perenne (perennial ryegrass) during drought and on rewatering

Simulated swards of perennial ryegrass ( Lolium perenne ) growing in 1-m³ soil blocks in the glasshouse were either well watered or deprived of water for 57 d and then rewatered. The first aim was to measure effects of drought on sugar (water-soluble carbohydrate) composition of laminae and sheaths of mature laminae, and bases and laminae of young (growing) leaves. The second aim was to use pulse labelling with ¹⁴CO₂ to follow the partitioning of recently-fixed assimilates, and the assembly and consumption of reserve sugars (fructans). Over the last 7 d of drought growth almost stopped, old leaves died faster than they were replaced, and total sugar (which had doubled in concentration during drought) was rapidly consumed. Leaf laminae had lower content of total sugars and of large fructan (DP>5) than did growing bases and sheaths. Drought greatly reduced the rate at which sugar was exported from the laminae to the sheaths and growing leaf bases, and the rate at which it was converted to fructan. Nevertheless, fructan accumulated over the first 50 d of drought. Rewatering did not result in depolymerization and remobilization of sugars that had been formed during the last 7 d of drought, but stimulated their further assembly into high-DP fructans. Our hypothesis, that accumulation of neo-kestose (a DP-3 fructan) in droughted laminae was a symptom of sugar remobilization just before death, was disproved. It is concluded that sugar reserves contribute to drought resistance only under extreme conditions. The specific role of fructan in dry environments might be to improve regrowth when drought is relieved, rather than to enhance growth during drought.     

Regeneration from leaf-base explants of <Emphasis Type="Italic">Lolium perenne</Emphasis> L. and <Emphasis Type="Italic">Lolium multiflorum</Emphasis> L.

The regenerability of Lolium perenne and Lolium multiflorum was investigated using leaf-base sections excised from plantlets grown in vitro. Young leaf bases were cut into three sections each 2 mm in length, the lowest 0–2 mm section adjacent to, but not including, the apical meristem. Callus development followed by embryogenesis occurred only in the lowest 2 mm leaf-base sections of L. perenne cv. Limes, whereas L. multiflorum leaf bases showed an embryogenic response along the entire 6 mm section. Rooted, green plantlets were obtained from 100% of the 0–2 mm sections of L. perenne cv. Limes and from 91%, 65% and 26% of leaf-base sections at 0–2, 2–4 and 4–6 mm respectively from L. multiflorum. Microprojectile bombardment of leaf-base explants resulted in transient expression of the -glucuronidase gene.     

Dissecting the regulation of fructan metabolism in perennial ryegrass (Lolium perenne) with quantitative trait locus mapping

Quantitative trait locus (QTL) mapping, which can be a useful tool for dissecting complex traits, has been used here to study the regulation of fructan metabolism in temperate forage grasses. An F2 mapping family, derived from a high water-soluble carbohydrate (WSC) x low WSC cross, was used to map fructans and the other components of WSC (sucrose, glucose and fructose) in leaves and tiller bases of perennial ryegrass (Lolium perenne) in spring and autumn. To characterize regions of the genome that control basic carbohydrate metabolism, a strategy to minimize the impact of genotype (G) x environment (E), and E-effects on the characterization of G-effects, was adopted. Most traits were highly variable within the family. There was also considerable year-to-year environmental variation. However, significant genetic effects were detected, and several traits had high broad-sense heritability. QTL were identified on chromosomes 1, 2, 5 and 6. Leaf and tiller base QTL did not coincide. Individual QTL explained between 8 and 59% of the total phenotypic variation in the traits. Fructan turnover, metabolism and their genetic control, and the effect of environment, are discussed in the context of the results.     

Lolium multiflorum density responses under ozone and herbicide stress

Adaptations to overcrowding of individual plants result in density dependant control of growth and development. There is little information on how anthropogenic stresses modify these responses. We investigated whether combinations of diclofop‐methyl herbicide and tropospheric ozone alter the pattern of expected growth compensation with density changes resulting from intraspecific competition in Lolium multiforum Lam (Poacea) plants. Individual plant vegetative parameters and total seed production were assessed for plants growing under various densities and different herbicide rates and ozone treatments. The stressors differently changed the frequency distribution for average individual plant weight resulting from increasing densities. Only herbicide affected seedling mortality. Plants were able to compensate during grain filling maintaining similar seed production – density relationships in all treatments. Our findings contribute to the understanding of the impact of stress factors on the demographic changes in plant populations. Important ecological implications arise: (i) contrasting responses to ozone and herbicide, alone and in combination of individual plants resulted in different biomass – density relationships; (ii) stress effects on plant populations could not be predicted from individual responses; and (iii) changes in competitive outcome by single or combined stress factors may alter the expected genotype frequency in a crowded population with few dominant individuals.     

Identification of perennial ryegrass (Lolium perenne (L.)) and meadow fescue (Festuca pratensis (Huds.)) candidate orthologous sequences to the rice Hd1(Se1) and barley HvCO1 CONSTANS-like genes through comparative mapping and microsynteny

Microsynteny with rice and comparative genetic mapping were used to identify candidate orthologous sequences to the rice Hd1(Se1) gene in Lolium perenne and Festuca pratensis. A F. pratensis bacterial artificial chromosome (BAC) library was screened with a marker (S2539) physically close to Hd1 in rice to identify the equivalent genomic region in F. pratensis. The BAC sequence was used to identify and map the same region in L. perenne. Predicted protein sequences for L. perenne and F. pratensis Hd1 candidates (LpHd1 and FpHd1) indicated they were CONSTANS-like zinc finger proteins with 61-62% sequence identity with rice Hd1 and 72% identity with barley HvCO1. LpHd1 and FpHd1 were physically linked in their respective genomes (< 4 kb) to marker S2539, which was mapped to L. perenne chromosome 7. The identified candidate orthologues of rice Hd1 and barley HvCO1 in L. perenne and F. pratensis map to chromosome 7, a region of the L. perenne genome which has a degree of conserved genetic synteny both with rice chromosome 6, which contains Hd1, and barley chromosome 7H, which contains HvCO1.     

Glucose utilization by 6pgd genotypes in Lolium perenne

To gain a deeper understanding of the mechanisms underlying associations between allozyme genotypes and rates of respiration in Lolium perenne, V_max K_m and rates of glucose flux through glycolysis and the pentose phosphate pathway were estimated for the three genotypes of the 6pgd locus. K_m V_max and V_max/K_m differed significantly among genotypes. Values of K_m for the 11, 12, and 22 genotypes were 0.29, 0.25, 0.13, while the values of V_max/K_m for die 11, 12, and 22 genotypes were 3.79, 3.85, 6.70. Flux through the pentose shunt did not differ among genotypes at 20 °C, but at 35 °C the rates of flux for the 11, 12, and 22 genotypes were 0.15, 0.25 and 0.42, respectively. Thus, the 6PGD allozyme genotypes differ markedly in both enzyme kinetic characteristics and in flux through a metabolic pathway. These associations reveal potentially causal relationships between allozyme genotypes and rates of respiration.     

黄土性土壤固化对黑麦草生长和根系活力的影响

采用盆栽试验,研究了安塞黄绵土不同容重、不同固化剂(路邦EN-1固化剂)掺量对黑麦草生长和根系活力的影响.结果表明:黄绵土容重在1.2～1.4 9·cm-3范围内,随土壤容重的增加,黑麦草叶绿素含量、根系活力、根冠比、根生物量和植株生物量均降低;各土壤容重条件下,黑麦草叶绿素含量、根系活力、根冠比、根生物量和植株生物量均高于对照,且随着固化剂掺量的增加均呈先增加后降低的趋势.土壤容重和固化剂掺量交互作用对根生物量和总生物量的影响均显著(P＜0.05).总体来看,土壤容重1.3 g·cm-3、固化剂掺量0.15％处理下,各指标值均最高.     

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.     

Physicochemical characterization of cellulose from perennial ryegrass leaves (Lolium perenne)

In this study, we investigated the physicochemical properties of the cellulosic preparations obtained from both untreated perennial ryegrass leaves and de-juiced leaves. It was found that treatment at 22 degrees C with 18% NaOH and 18% KOH for 2h, and 10% NaOH and 10% KOH for 16 h yielded 28.2%, 28.8%, 22.7%, 23.4%, respectively, of 'cellulose' residue from untreated ryegrass leaves and 35.7%, 36.8%, 32.8% and 34.6%, respectively, from the de-juiced leaves. For each cellulosic fraction, the glucose content was 71.6%, 69.6%, 67.8%, 66.7%, 69.7%, 68.6%, 63.9% and 61.7%, respectively. The structure of the cellulose samples was examined using FTIR and CP/MAS (13)C NMR spectroscopy and X-ray diffraction. The cellulosic preparations were free of bound lignin except for noticeable amounts of residual hemicelluloses (28.4-38.3%), and had intrinsic viscosities between 275.1 and 361.0 mL/g, along with molecular weights from 144,130 to 194,930 g/mol. This study found that the cellulose samples isolated from both de-juiced ryegrass leaves and the untreated leaves had a much lower percent crystallinity (33.0-38.6%) than that from wood-based fibres (60-70%) and had much shorter fibres (0.35-0.49 mm) than those of either cereal straws, bagasse or wood. In addition, a partial disruption of the hydrogen bonds and microfibrils may occur during the de-juicing process by mechanical activity, which results in a decreased cellulose crystallinity and fibre length. These findings are significant in relation to hydrolysing ryegrass cellulose for bio-ethanol production.     

Improvement of persistence and yield of Italian ryegrass (Lolium multiflorum) through pesticide use

The present two field experiments, involving plots of Italian ryegrass sown in 1976, 1980 and 1984 confirmed results of earlier work in which the yield and persistence of Italian ryegrass was greatly increased by the application of pesticide. A range of pesticide treatments were used. The responses to application of permethrin applied three times per year average 8% for the three years of the first experiment and 5% for the five years of the second experiment. Such responses appeared cost-effective, but the overall environmental impact of such applications is not known.     

多年生黑麦草成熟胚再生体系的建立及基因枪转化

目的:建立以多年生黑麦草成熟胚为起始材料的再生体系,用于基因枪转化。方法:多年生黑麦草成熟种子在附加 5mg L 2,4 D的MS培养基上诱导愈伤组织,转至新继代培养基上产生胚性愈伤组织。分化培养基为无激素MS培养基。再生植株在培养基成分减半的无激素MS培养基生根,之后移栽至土壤。基于这一再生体系,用含有水稻几丁质酶基因RC2 4的质粒pARN6和含有草丁膦乙酰转移酶基因Bar的质粒pDB1,通过基因枪轰击胚性愈伤组织。用附加PPT的继代培养基进行转化植株的抗性筛选。结果:共获得 2 4 3株再生植株。通过PCR进行检测,获得1 8株整合有RC2 4基因的植株,1 5株整合有Bar基因的植株,同时转入 2个基因的植株 2株。