The effect of soil pH on rhizosphere carbon flow of Lolium perenne

Perennial rye-grass plants were grown at 15°C in microcosms containing soil sampled from field plots that had been maintained at constant pH for the last 30 years. Six soil pH values were tested in the experiment, with pH ranging from 4.3–6.5. After 3 weeks growth in the microcosms, plant shoots were exposed to a pulse of ¹⁴C-CO₂. The fate of this label was determined by monitoring ¹⁴C-CO₂ respired by the plant roots/soil and by the shoots. The ¹⁴C remaining in plant roots and shoots was determined when the plants were harvested 7 days after receiving the pulse label. The amount of ¹⁴C (expressed as a percentage of the total ¹⁴C fixed by the plant) lost from the plant roots increased from 12.3 to 30.6% with increasing soil pH from 4.3 to 6. Although a greater percentage of the fixed ¹⁴C was respired by the root/soil as soil pH increased, plant biomass was greater with increasing soil pH. Possible reasons for observed changes in the pattern of ¹⁴C distribution are discussed and, it is suggested that changes in the soil microbial biomass and in plant nitrogen nutrition may, in particular be key factors which led to increased loss of carbon from plant roots with increasing soil pH.     

Assessment of candidate reference genes for the expression studies with brassinosteroids in Lolium perenne and Triticum aestivum

Quantitative PCR studies need proper reference genes with expression stability exclusively validated under certain experimental conditions. The expression stability of several genes commonly used as references was tested under 24-epibrassinolide (EBR) and temperature treatment. Different statistical approaches (qBase^PLUS, BestKeeper, NormFinder) were used to prepare rankings of expression stability in two species of an economic importance: common wheat (Triticum aestivum) and perennial ryegrass (Lolium perenne). Candidate reference genes were shown to be regulated differentially in these two plant species. The maximum stability values indicated that the expression stability was higher in T. aestivum. Taking into account of all ranks it seems that TBP-1 and UBI in ryegrass and ACT, ADP and EF1A in wheat should be used as reference genes in the brassinosteroids and temperature involving studies.     

Callus Formation from Somatic Hybridization of Wheat (Triticum aestivum L.) and Ryegrass (Lolium perenne L.) by Electrofusion

Somatic hybrid calli were recovered following electrofusion of protoplasts from a chloroplast-containing cell suspension culture of wheat (Triticum aestivum L.) and a cell suspension culture of ryegrass (Lolium perenne L.). The protoplasts of wheat were inactivated by iodoacetamide; in addition morphology and colour were used as markers to aid selection of putative hybrid calli. For isozyme analysis of putative hybrids, nine isozymes were tested for differences in bands between the parental lines. Of these, three showed differences (ADH, GOT, SDH). Analysis of ADH bands of calli indicated that six lines were hybrids. These lines were analysed with the ,ther isozymes, and at the DNA level by Southern hybridisation with a wheat ribosomal DNA probe. The overall results indicated that one line was an almost complete combination of the genomes of the parental lines, but the other 5 lines were probably partial hybrids. In the latter, some loss of the wheat genome had probably occurred.     

Long-term Partitioning, Storage and Re-mobilization of 14C Assimilated by Lolium perenne (cv. Melle)

The youngest fully expanded leaves of single tillers of vegetativeperennial ryegrass plants were exposed to ¹⁴CO₂. Thereafter,quantitative and fractional analysis of the partitioning, storageand re-mobilization after defoliation of the ¹⁴C-labelled assimilatewas sequentially conducted over a 22 d period. In undefoliated plants, most ¹⁴C reached its final destinationwithin 5–6 of feeding. Forty per cent of assimilated ¹⁴Cwas subsequently lost through respiration, while 13.5, 8.5 and34 per cent remained in roots, stem bases and tops respectively.At least some ¹⁴C was distributed to tillers throughout theplant, but secondary tillers subtended by the fed tiller madethe greatest demand on ¹⁴C translocated from the fed tiller. A small, but significant portion of ¹⁴C was invested into longterm storage in undefoliated plants, four per cent of the totalassimilated still being present in a labile chemical form inroots and stem bases 22 d after feeding. In plants that wereseverely defoliated 4 d after feeding, depletion of reserve¹⁴C was observed relative to undefoliated plants. The depletiontook place from stem bases, not roots, and both low and highmolecular weight storage compounds were involved. A portionof the depleted ¹⁴C was incorporated into new growth after defoliation. Lolium perenne, perennial ryegrass, assimilate partitioning, storage, re-mobilization, defoliation     

Spatial distribution of bacterial communities and phenanthrene degradation in the rhizosphere of Lolium perenne L

Rhizodegradation of organic pollutants, such as polycyclic aromatic hydrocarbons, is based on the effect of root-produced compounds, known as exudates. These exudates constitute an important and constant carbon source that selects microbial populations in the plant rhizosphere, modifying global as well as specific microbial activities. We conducted an experiment in two-compartment devices to show the selection of bacterial communities by root exudates and phenanthrene as a function of distance to roots. Using direct DNA extraction, PCR amplification, and thermal gradient gel electrophoresis screening, bacterial population profiles were analyzed in parallel to bacterial counts and quantification of phenanthrene biodegradation in three layers (0 to 3, 3 to 6, and 6 to 9 mm from root mat) of unplanted-polluted (phenanthrene), planted-polluted, and planted-unpolluted treatments. Bacterial community differed as a function of the distance to roots, in both the presence and the absence of phenanthrene. In the planted and polluted treatment, biodegradation rates showed a strong gradient with higher values near the roots. In the nonplanted treatment, bacterial communities were comparable in the three layers and phenanthrene biodegradation was high. Surprisingly, no biodegradation was detected in the section of planted polluted treatment farthest from the roots, where the bacterial community structure was similar to those of the nonplanted treatment. We conclude that root exudates and phenanthrene induce modifications of bacterial communities in polluted environments and spatially modify the activity of degrading bacteria.     

Bacterial diversity in the bulk soil and rhizosphere fractions of Lolium perenne and Trifolium repens as revealed by PCR restriction analysis of 16S rDNA

The rhizosphere of Trifolium repens and Lolium perenne was divided into three fractions: the bulk soil, the soil adhering to the roots and the washed roots (rhizoplane and endorhizosphere). After isolation and purification of DNA from these fractions, 16S rDNA was amplified by PCR and cloned to obtain a collection of 16S rRNA genes representative of the bacterial communities of these three fractions. The genes were then characterized by PCR restriction analysis. Each different profile was used to define an operational taxonomic unit (OTU). The numbers of OTUs and the numbers of clones among these OTUs allowed to calculate a diversity index. The number of OTUs decreased as root proximity increased and a few OTUs became dominant, resulting in a lower diversity index. In the root fraction of T. repens, the restriction profile of the dominant OTU matched the theoretical profile of the 16S rRNA gene of Rhizobium leguminosarum. This study showed that plant roots create a selective environment for microbial populations.     

Effects of photon flux density on carbon partitioning and rhizosphere carbon flow of Lolium perenne

The distribution and partitioning of dry matter and photoassimilateof Lolium perenne was investigated under two light regimes providingphotosynthetically active radiation of 350 µmol m^–2s^–1 (low light treatment) or 1000 µmol m^–2s^–1 (high light treatment). Plants were grown at specificgrowth conditions in either soil or sand microcosm units tofollow the subsequent release of carbon into the rhizosphereand its consequent incorporation into the microbial biomass(soil system) or recovery as exudates (sand system). The distributionof recent assimilate between the plant and root released carbonpools was determined using ¹⁴CO₂ pulse-chase methodology atboth light treatments and for both sand- and soil-grown seedlings.A significant (P     

Characterization of bacterial community structure in the rhizosphere of Triticum aestivum L.

The plant microbiome influence plant health, yield and vigor and has attained a considerable attention in the present era. In the current study, native bacterial community composition and diversity colonizing Triticum aestivum L. rhizosphere at two distant geographical locations including Mirpur Azad Kashmir and Islamabad was elucidated. Based on IonS5™XL platform sequencing of respective samples targeting 16S rRNA gene that harbor V3-V4 conserved region revealed 1364 and 1254 microbial operational taxonomic units (OTUs) at ≥97% similarity and were classified into 23, 20 phyla; 70, 65 classes; 101, 87 orders; 189,180 families; 275, 271 genera and 94, 95 species. Respective predominant phyla accounting for 97.90% and 98.60% of bacterial community were Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidetes, Firmicutes, Chloroflexi and Gemmatimonadetes. Diversity indices revealed variations in relative abundance of bacterial taxa owing to distant geographical locations however predominant bacterial taxa at both locations were similar. These findings paved a way to dissect consequence of associated microbiota on future wheat production system.     

Assimilation of 14CO2 by the Inflorescence of Poa annua L. and Lolium perenne L.

The relative assimilatory activity of the inflorescence, itsindividual components, and the leaves of flowering tillers ofPoa annua L. and Lolium perenneL. was determined over the periodfrom inflorescence emergence to seed shedding. The pattern of¹⁴CO₂ fixation was similar for both species and the inflorescencewas by far the most important assimilatory organ of the reproductivetiller, particularly over the latter period of seed developmentas leaf senescence progressed. With the exception of the seedsall parts of the inflorescence showed significant assimilatoryactivity and the lemmas and paleas accounted for 40–50per cent of the total ¹⁴C fixed by the inflorescence in bothspecies. The importance of the grass inflorescence as a photosyntheticstructure is discussed in relation to similar studies on cereals. Poa annua, Lolium perenne, carbon dioxide assimilation, inflorescence     

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.     

黑麦草根系分泌物剂量对污染土壤芘降解和土壤微生物的影响

模拟根际根系分泌物梯度递减效应,研究了黑麦草根系分泌物剂量对污染土壤中芘降解特征和土壤微生物生态特征的影响.结果表明:污染土壤中芘残留量随根系分泌物添加剂量的增加呈现先下降后上升的非线性变化,达到最低芘残留量的添加剂量是总有机碳(TOC) 32.75 mg·kg-1,说明此浓度下根系分泌物显著促进了芘的降解;土壤微生物生物量碳和微生物熵的变化趋势与污染土壤中芘残留量变化趋势相反,表明土壤微生物与污染土壤 中芘残留量存在密切关系.芘污染土壤中微生物群落以细菌占主导地位,且细菌变化趋势与芘降解变化一致,表明芘以细菌降解为主,根系分泌物主要通过影响细菌数量,进而影响芘的降解.能催化有机物质脱氢反应的土壤微生物胞内酶——脱氢酶活性的变化与土壤微生物变化趋势一致,进一步证明微生物及其生物化学特性变化是污染土壤中芘残留量随根系分泌物添加剂量变化的生态机制.     

Carbon partitioning and rhizosphere C-flow in Lolium perenne as affected by CO2 concentration, irradiance and below-ground conditions

Plant responses to increasing atmospheric CO₂ concentrations have received considerable interest. However, major uncertainties in relation to interactive effects of CO₂ with above- and below-ground conditions remain. This microcosm study investigated the impacts of CO₂ concentration on plant growth, dry matter partitioning and rhizodeposition as affected by: (i) photon flux density (PFD), and (ii) growth matrix. Plants were grown in a sandy loam soil for 28 d under two photon flux densities: 350 (low PFD) and 1000 μmol m^–2 s^–1 (high PFD) and two CO₂ concentrations: 450 (low CO₂) and 720 μmol mol^–1 (high CO₂). Partitioning of recent assimilate amongst plant and rhizosphere C-pools was determined by use of ¹⁴CO₂ pulse-labelling. In treatments with high PFD and/or high CO₂, significant (P < 0.05) increases in dry matter production were found in comparison with the low PFD/low CO₂ treatment. In addition, significant (P < 0.05) reductions in shoot %N and SLA were found in treatments imposing high PFD and/or high CO₂. Root weight ratio (RWR) was unaffected by CO₂ concentration, however, partitioning of ¹⁴C to below ground pools was significantly (P < 0.05) increased. In a separate study, L. perenne was grown for 28 d in microcosms percolated with nutrient solution, in either a sterile sand matrix or nonsterile soil, under high or low CO₂. Dry matter production was significantly (P < 0.01) increased for both sand and soil grown seedlings. Dry matter partitioning was affected by matrix type. ¹⁴C-allocation below ground was increased for sand grown plants. Rhizodeposition was affected by CO₂ concentration for growth in each matrix, but was increased for plants grown in the soil matrix, and decreased for those in sand. The results illustrate that plant responses to CO₂ are potentially affected by (i) PFD, and (ii) by feedbacks from the growth matrix. Such feedbacks are discussed in relation to soil nutrient status and interactions with the rhizosphere microbial biomass.     

Detection of brassinosteroids in pollen of Lolium perenne L. by immunocytochemistry

Bioactive brassinosteroids have been localized in developing and mature pollen of anhydrously fixed rye-grass (Lolium perenne) by immunocytochemistry using polyclonal antibodies to castasterone generated in rabbits. Tricellular pollen fixed by freeze-substitution was also labelled in the starch granules. Study of the developmental sequence of the pollen through the microsporocyte, microspore, bicellular and tricellular stages showed that the brassinosteroids were increasingly sequestered in starch granules as the amyloplasts matured, supporting the view that these are storage organelles for these potent plant growth promoters. In bicellular pollen, heavy labelling was seen in the zone within 0.5 m of the starch granule, where stromal tissue remains. Thus, the stroma may be the site of synthesis of these compounds. During aqueous fixation, the brassinosteroids leached from the starch granules of tricellular pollen, indicating that they would be quickly available after imbibition to influence the physiology of germinating pollen. The results from high-performance liquid chromatography of dansylaminophenylboronates from partially purified extracts of freshly dehisced tricellular pollen of rye-grass showed 25-methylcastasterone may be a minor component, together with two unknown peaks. No specific binding of brassinolide to any soluble proteins extracted from tricellular rye-grass pollen was observed using the antibodies in gel electrophoresis or enzyme-linked immunosorbent assays.Abbreviations HPLC high-performance liquid chromatography - R_t retention time - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis We thank the Australian Research Council for support, the N.S.W. Department of Agriculture for rice seed, Professor K. Mori and the Zen-Noh Corporation for authentic brassinosteroid samples, Dr. I. Hudson for statistical advice, Dr. A. Bacic and Ms. I. Bonig for helpful discussion, and J.M.S. thanks Professor R.B. Knox for laboratory facilities.     

Effects of nutrient supply and competition from other species on root growth of Lolium perenne in soil

Summary In competition experiments with Lolium perenne and Agrostis tenuis on sandy soil with nitrogen supplied and therefore not limiting, it was found that the competitive interactions could be explained in terms of phosphate uptake, and that the ratio of root weight: length was proportional to root density. The effects of competition were then investigated in an experimental system that enabled them to be distinguished from those of nutrient supply. High levels of nutrients specifically stimulated the production of fine laterals whereas competition affected length and weight of the root system of Lolium equally. The ecological implications are discussed in the light of recent physiological work on root responses to nutrient supply. re]19750324     

Detection of fungal infection in Lolium perenne by Fourier transform infrared spectroscopy

Aims The goal of the study was to apply Fourier transform infrared (FTIR) spectroscopy followed by chemometrical data treatment for the differentiation of fungi-infected perennial ryegrass (Lolium perenne) from uninfected grass.Methods FTIR was used to rapidly discriminate between leaves of perennial ryegrass (L. perenne) infected by a fungal endophyte (Epichlo?; asexual forms: Neotyphodium) and uninfected leaves. Besides drying and grinding of the sampled leaves, no other preparation steps were needed. FTIR measurements were performed in the attenuated total reflection (ATR) mode. Aliquots of powdered leaf samples were placed on a ZnSe crystal and the spectra were collected, followed by chemometrical analysis (multidimensional factor analysis, hierarchical cluster analysis).Important findings ATR-FTIR allowed a rapid detection of fungal infections in the plant material and proved to be a fast and reliable tool for the differentiation of plant biomass without the need of time-consuming sample preparation.     

Comparative characteristic of Triticum aestivum/Triticum durum and Triticum aestivum/Triticum dicoccum hybrid lines by genomic composition and resistance to fungal diseases under different environmental conditions

The genetic diversity of common wheat hybrid lines Triticum aestivum/Triticum durum and Triticum aestivum/Triticum dicoccum (2n = 42, F_6–7) using chromosome-specific microsatellite (SSR) markers and C-banding of chromosomes was studied. Cluster analysis of data obtained by 42 SSR markers indicated that the hybrid lines can be broken into three groups according to their origin. There were two cases of complete genetic similarity between lines 183₂-2/184₁-6 and 208-3/213-1, which were obtained using common wheat as the parental plants. In cross combinations, when the stabilization of the nuclear genome of hexaploid lines occurred against a background of the cytoplasmic genome of tetraploid wheats, there was a high level of divergence between sister lines, in some cases exceeding 50%. The evaluation of the degree of susceptibility of the lines to powdery mildew, leaf and stem rust, and septoria leaf blotch was performed under different environmental conditions. It was shown that resistance to powdery mildew and leaf rust significantly depended on the region where assays were conducted. An evaluation of the field data showed that the lines 195-3, 196-1, and 221-1 with T. durum genetic material displayed complex resistance to fungal pathogens in Western Siberia and the Republic of Belarus. For lines 195-3 and 196-1, one shows a possible contribution of chromosomes 4B and 5B in the formation of complex resistance to diseases. Hybrid lines with complex resistance can be used to expand the genetic diversity of modern common wheat cultivars for genes of immunity.