Search

Summary: Some interspecific plant hybrids show unequal transmission of chromosomes from parental genomes to the successive generations. It has been suggested that this is due to a differential behavior of parental chromosomes during meiosis. However, underlying mechanism is unknown.We analyzed chromosome composition of the F2 generation of Festuca × Lolium hybrids and reciprocal backcrosses to elucidate effects of male and female meiosis on the shift in parental genome composition. We studied male meiosis, including the attachment of chromosomes to the karyokinetic spindle and gene expression profiling of the kinetochore genes.We found that Lolium and Festuca homoeologues were transmitted differently to the F2 generation. Female meiosis led to the replacement of Festuca chromosomes by their Lolium counterparts. In male meiosis, Festuca univalents were attached less frequently to microtubules than Lolium univalents, lagged in divisions and formed micronuclei, which were subsequently eliminated.Genome sequence analysis revealed a number of non‐synonymous mutations between copies of the kinetochore genes from Festuca and Lolium genomes. Furthermore, we found that outer kinetochore proteins NDC80 and NNF1 were exclusively expressed from the Lolium allele. We hypothesize that silencing of Festuca alleles results in improper attachment of Festuca chromosomes to karyokinetic spindle and subsequently their gradual elimination. [ABSTRACT FROM AUTHOR]

This supports not only the existence of a trade-off between growth/reproduction and defence to herbivory without the participation of the plant endophytes, but also that the trade-off persists, at least in this species, in symbiotic (E+) plants (Fig. From these studies, we assume that the experimental design (E+ and E- plants) effectively disrupts any potential positive effect of the plant-microbe symbiosis in E- plants. Keywords: biological interactions; extreme environments; fungal endophytes; symbiosis; trade-off EN biological interactions extreme environments fungal endophytes symbiosis trade-off 384 387 4 06/20/22 20220715 NES 220715 Acknowledgements Our thanks to Marc-André Selosse for his constructive comments that allowed us to focus and highlight the fundamental aspects of our I Letter i . Fungal endophytes improve the performance of host plants but do not eliminate the growth/defence trade-off. [Extracted from the article]

Summary: We explored the effects of atmospheric CO2 concentration (Ca) and vapor pressure deficit (VPD) on putative mechanisms controlling leaf elongation in perennial ryegrass.Plants were grown in stands at a Ca of 200, 400 or 800 μmol mol−1 combined with high (1.17 kPa) or low (0.59 kPa) VPD during the 16 h‐day in well‐watered conditions with reduced nitrogen supply. We measured day : night‐variation of leaf elongation rate (LERday : LERnight), final leaf length and width, epidermal cell number and length, stomatal conductance, transpiration, leaf water potential and water‐soluble carbohydrates and osmotic potential in the leaf growth‐and‐differentiation zone (LGDZ).Daily mean LER or morphometric parameters did not differ between treatments, but LERnight strongly exceeded LERday, particularly at low Ca and high VPD. Across treatments LERday was negatively related to transpiration (R2 = 0.75) and leaf water potential (R2 = 0.81), while LERnight was independent of leaf water potential or turgor. Enhancement of LERnight over LERday was proportional to the turgor‐change between day and night (R2 = 0.93). LGDZ sugar concentration was high throughout diel cycles, providing no evidence of source limitation in any treatment.Our data indicate a mechanism of diel cycling between daytime hydraulic and night‐time stored‐growth controls of LER, buffering Ca and daytime VPD effects on leaf elongation. [ABSTRACT FROM AUTHOR]

Summary: Epichloë festucae is an endophytic fungus that forms a symbiotic association with Lolium perenne. Here we analysed how the metabolome of the ryegrass apoplast changed upon infection of this host with sexual and asexual isolates of E. festucae.A metabolite fingerprinting approach was used to analyse the metabolite composition of apoplastic wash fluid from uninfected and infected L. perenne. Metabolites enriched or depleted in one or both of these treatments were identified using a set of interactive tools. A genetic approach in combination with tandem MS was used to identify a novel product of a secondary metabolite gene cluster.Metabolites likely to be present in the apoplast were identified using MarVis in combination with the BioCyc and KEGG databases, and an in‐house Epichloë metabolite database. We were able to identify the known endophyte‐specific metabolites, peramine and epichloëcyclins, as well as a large number of unknown markers.To determine whether these methods can be applied to the identification of novel Epichloë‐derived metabolites, we deleted a gene encoding a NRPS (lgsA) that is highly expressed in planta. Comparative MS analysis of apoplastic wash fluid from wild‐type‐ vs mutant‐infected plants identified a novel Leu/Ile glycoside metabolite present in the former. [ABSTRACT FROM AUTHOR]

Beneficial associations between plants and microbes play an important role in both natural and agricultural ecosystems. For example, associations between fungi of the genus Epichloë, and cool-season grasses are known for their ability to increase resistance to insect pests, fungal pathogens and drought. However, little is known about the molecular changes induced by endophyte infection., To study the impact of endophyte infection, we compared the expression profiles, based on RNA sequencing, of perennial ryegrass infected with Epichloë festucae with noninfected plants., We show that infection causes dramatic changes in the expression of over one third of host genes. This is in stark contrast to mycorrhizal associations, where substantially fewer changes in host gene expression are observed, and is more similar to pathogenic interactions. We reveal that endophyte infection triggers reprogramming of host metabolism, favouring secondary metabolism at a cost to primary metabolism. Infection also induces changes in host development, particularly trichome formation and cell wall biogenesis., Importantly, this work sheds light on the mechanisms underlying enhanced resistance to drought and super-infection by fungal pathogens provided by fungal endophyte infection. Finally, our study reveals that not all beneficial plant-microbe associations behave the same in terms of their effects on the host. [ABSTRACT FROM AUTHOR]

The mechanism controlling the use of stored carbon in respiration is poorly understood. Here, we explore if the reliance on stores as respiratory substrate depends on day length. Lolium perenne (perennial ryegrass) was grown in continuous light (275 lmol photons m-2 s-1) or in a 16 : 8 h day : night regime (425 lmol m-2 s-1 during the photoperiod), with the same daily photosynthetic photon flux density (PPFD). Plants in stands were labelled with 13CO2 : 12CO2 for various time intervals. The rates and isotopic signatures of shoot- and root-respired CO2 were measured after labelling, and water-soluble carbohydrates were determined in biomass. The tracer kinetics in respired CO2 was analysed with compartmental models to infer the sizes, half-lives and contributions of respiratory substrate pools. Stores were the main source for respiration in both treatments (c. 60% of all respired carbon). But, continuous light slowed the turnover (+270%) and increased the size (+160%) of the store relative to the 16 : 8 h day : night regime. This effect corresponded with a greatly elevated fructan content. Yet, day length had no effect on sizes and half-lives of other pools serving respiration. We suggest that the residence time of respiratory carbon was strongly influenced by partitioning of carbon to fructan stores. [ABSTRACT FROM AUTHOR]

• Valid models are the foundation of systems biology. However, even well-established models may warrant reassessment. A testable feature of the currently accepted vacuolar model for fructan biosynthesis is its independence from metabolic energy at substrate level. The effects of limiting energy provision on fructan biosynthesis in grass leaves were determined. • It was found that, in darkness in air, the rate of fructan accumulation was reduced to half relative to a light control. In darkness under anoxia the process was immediately abolished. In the light, the leaf sucrose concentration remained high, but in darkness ± O2, 40% of this sucrose was rapidly degraded. The constant rate of dark-aerobic fructan accumulation was independent of the decrease in sucrose concentration. • Constant rates of aerobic fructan synthesis were independent of marked changes in extractable polymerase rates. In the dark under anoxia, fructan accumulation was abolished but leaves maintained ≥ 80% of the extractable polymerase. Extractable polymerase rates cannot explain the rates of fructan accumulation observed in vivo, if the process is vacuolar. • It was shown that the results were inconsistent with a vacuolar site for fructan synthesis. Six inhibitors of endomembrane function were shown to abolish fructan synthesis in vivo. [ABSTRACT FROM AUTHOR]

• Light plays an important role in two separate processes within the seeds of Lolium rigidum (annual ryegrass). Dormant seeds of L. rigidum remain dormant when imbibed in the light, but once seeds have lost dormancy through dark-stratification, light stimulates their germination. This study characterizes the light qualities and quantities which are effective in maintenance of dormancy. • Dormant seeds were stratified under narrow- and broad-waveband light to identify the potential photoreceptors involved in dormancy maintenance, and to determine whether dark-induced dormancy loss is reversible by light. • Blue and green light both mediated dormancy maintenance in a far-red-independent manner. Red light resulted in dormancy maintenance only when far-red wavelengths were excluded, suggesting a redundant function of phytochrome. At low fluence rates, white light was more effective than monochromatic light, suggesting the action of multiple photoreceptors in dormancy maintenance. By contrast, nondormant seeds did not germinate unless provided with red light. • These results indicate that seed dormancy maintenance is potentially mediated through the actions of blue and green light photoreceptors. Seed dormancy could thus be added to the growing list of plant responses that may be mediated by green light in a cryptochrome-independent manner. [ABSTRACT FROM AUTHOR]

• The role of fructan in growth and drought-stress responses of perennial ryegrass (Lolium perenne) was investigated in an F2 mapping family that segregates for carbohydrate metabolism. • A quantitative trait locus approach was used to compare the genetic control of traits. • Growth and drought-stress traits were extremely variable within the family. Most traits had high broad-sense heritability. Quantitative trait loci (QTL) were identified for most traits; the maximum number of QTL per trait was four. Between 11% and 75% of total phenotypic variation was explained. Few growth-trait QTL coincided with previously identified fructan QTL. A cluster of drought-trait QTL was close to two previously identified regions of the genome with tiller base fructan QTL in repulsion. • The high sugar parent contributed few alleles that increased ‘reserve-driven’ growth or performance during drought-stress. Correlation of growth and drought-stress traits with fructan content was low and increasing fructan content per se would not appear to improve drought resistance. Complex patterns of carbohydrate partitioning and metabolism within the cell may explain contradictory relationships between carbohydrate content and growth/stress-resistance traits. [ABSTRACT FROM AUTHOR]

• Fructan is the major nonstructural carbohydrate reserve in temperate grasses. To understand regulatory mechanisms in fructan synthesis and adaptation to cold environments, the isolation, functional characterization and genetic mapping of fructosyltransferase ( FT) genes in perennial ryegrass ( Lolium perenne) are described. • Six cDNAs ( prft1–prft6) encoding FTs were isolated from cold-treated ryegrass plants, and three were positioned on a perennial ryegrass linkage map. Recombinant proteins were produced in Pichia pastoris and enzymatic activity was characterized. Changes in carbohydrate levels and mRNA levels of FT genes during cold treatment were also analysed. • One gene encodes sucrose-sucrose 1-fructosyltransferase (1-SST), and two gene encode fructan-fructan 6G-fructosyltransferase (6G-FFT). Protein sequences for the other genes ( prfts 1, 2 and 6) were similar to sucrose-fructan 6-fructosyltransferase (6-SFT). The 1-SST and prft1 genes were colocalized with an invertase gene on the ryegrass linkage map. The mRNA levels of prft1 and prft2 increased gradually during cold treatment, while those of the 1-SST and 6G-FFT genes first increased, but then decreased before increasing again during a longer period of cold treatment. • Thus at least two different patterns of gene expression have developed during the evolution of functionally diverse FT genes, which are associated in a coordinated way with fructan synthesis in a cold environment. [ABSTRACT FROM AUTHOR]

• The molecular basis of an acetyl-CoA carboxylase (ACCase) target-based resistant Lolium rigidum population (WLR 96) was studied here. • The carboxyl-transferase domain of the plastidic ACCase gene from resistant individuals was amplified by PCR and sequenced. The DNA sequences were aligned and compared with a susceptible population. • Six amino acid substitutions were identified in the resistant population. The substitution Ile-2041-Asn, known to confer resistance to ACCase-inhibiting herbicides aryloxyphenoxypropionate (APP) in Alopecurus myosuroides, was identified in most resistant plants but it is always linked with other amino acid substitutions. This was confirmed by a cleaved amplified polymorphism (CAP) marker and an allele-specific PCR. The sole amino acid substitution Ile-2041-Asn was not found in this population. It is likely this mutation evolved later among individuals already possessing the other substitutions. Three haplotypes were identified from the resistant population based on the six amino acid combinations, and two are linked with herbicide resistance in this population. • The multiple amino acid substitutions including the Ile-2041-Asn form the molecular basis endowing a high degree of resistance to ACCase-inhibiting herbicides in this L. rigidum population. [ABSTRACT FROM AUTHOR]

• Effects of the arbuscular mycorrhizal fungus (AMF) Glomus hoi on the carbon economy of perennial ryegrass ( Lolium perenne) were investigated by comparing nonmycorrhizal and mycorrhizal plants of the same size, morphology and phosphorus status. • Plants were grown in the presence of CO2 sources with different C isotope composition (δ13C −1 or −44). Relative respiration and gross photosynthesis rates, and belowground allocation of C assimilated during one light period (‘new C’), as well as its contribution to respiration, were quantified by the concerted use of 13CO2/12CO2 steady-state labelling and 13CO2/12CO2 gas-exchange techniques. • AMF ( G. hoi) enhanced the relative respiration rate of the root + soil system by 16%, inducing an extra C flow amounting to 3% of daily gross photosynthesis. Total C flow into AMF growth and respiration was estimated at < 8% of daily gross photosynthesis. This was associated with a greater amount of new C allocated belowground and respired in mycorrhizal plants. AMF colonization affected the sources supplying belowground respiration, indicating a greater importance of plant C stores in supplying respiration and/or the participation of storage pools within fungal tissues. • When ontogenetic and nutritional effects were accounted for, AMF increased belowground C costs, which were not compensated by increased photosynthesis rates. Therefore the instantaneous relative growth rate was lower in mycorrhizal plants. [ABSTRACT FROM AUTHOR]

Contents Summary 1 I. Background 2 II. Objectives, breeding methodologies and progress in grass breeding 4 III. Markers and their suitability for genetic analysis in grasses 5 IV. Associating markers to genes for ‘sustainability’ in the grasses 5 V. The genetic control of flowering time 8 VI. Target traits: resilience against climate change and resistance to abiotic stresses 9 VII. Target traits: carbohydrates and sustainable ruminant animal production 11 VIII. Target traits: grass biomass, climate change and energy sustainability 13 IX. Conclusions 13 References 14 Here, we review the current genetic approaches for grass improvement and their potential for the enhanced breeding of new varieties appropriate for a sustainable agriculture in a changing global climate. These generally out-breeding, perennial, self-incompatible species present unique challenges and opportunities for genetic analysis. We emphasise their distinctiveness from model species and from the in-breeding, annual cereals. We describe the modern genetic approaches appropriate for their analysis, including association mapping. Sustainability traits discussed here include stress resistance (drought, cold and pathogeneses) and favourable agronomic characters (nutrient use efficiency, carbohydrate content, fatty acid content, winter survival, flowering time and biomass yield). Global warming will predictably affect temperature-sensitive traits such as vernalisation, and these traits are under investigation. Grass biomass utilisation for carbon-neutral energy generation may contribute to reduced atmospheric carbon emissions. Because the wider potential outcomes of climate change are unpredictable, breeders must be reactive to events and have a range of well-characterised germplasm available for new applications. [ABSTRACT FROM AUTHOR]

• The aim of this work was to disentangle phosphorus status-dependent and -independent effects of arbuscular mycorrhizal fungus (AMF) on leaf morphology and carbon allocation in perennial ryegrass ( Lolium perenne). • To this end, we assessed the P-response function of morphological components in mycorrhizal and nonmycorrhizal plants of similar size. • AMF ( Glomus hoi) stimulated relative P-uptake rate, decreased leaf mass per area (LMA), and increased shoot mass ratio at low P supply. Lower LMA was caused by both decreased tissue density and thickness. Variation in tissue density was almost entirely caused by variations in soluble C, while that in thickness involved structural changes. • All effects of AMF were indistinguishable from those mediated by increases in relative P-uptake rate through higher P-supply rates. Thus the relationships between relative P-uptake rate, leaf morphology and C allocation were identical in mycorrhizal and nonmycorrhizal plants. No evidence was found for AMF effects not mediated by changes in plant P status. [ABSTRACT FROM AUTHOR]

• Costs of resistance are predicted to reduce plant productivity in herbicide-resistant weeds. • Lolium rigidum herbicide-susceptible individuals (S), individuals possessing cytochrome P450-based herbicide metabolism (P450) and multiple resistant individuals possessing a resistant ACCase and enhanced cytochrome P450 metabolism (ACCase/P450) were grown in the absence of mutual plant interaction to estimate plant growth traits. • Both P450 and ACCase/P450 resistant phenotypes produced less above-ground biomass than the S phenotype during the vegetative stage. Reduced biomass production in the resistant phenotypes corresponded to a reduced relative growth rate and a lower net assimilation rate and rate of carbon fixation. There were no significant differences between the two resistant phenotypes, suggesting that costs of resistance are associated with P450 metabolism-based resistance. There were no differences in reproductive output among the three phenotypes, indicating that the cost of P450 resistance during vegetative growth is compensated during the production of reproductive structures. • The P450-based herbicide metabolism is shown to be associated with physiological resistance costs, which may be manipulated by agronomic management to reduce the evolution of herbicide resistance. New Phytologist (2005) doi: 10.1111/j.1469-8137.2005.01465.x © New Phytologist (2005) [ABSTRACT FROM AUTHOR]

• Microsynteny with rice and comparative genetic mapping were used to identify candidate orthologous sequences to the riceHd1(Se1) gene inLolium perenneandFestuca pratensis.• AF. pratensisbacterial artificial chromosome (BAC) library was screened with a marker (S2539) physically close toHd1in rice to identify the equivalent genomic region inF. pratensis. The BAC sequence was used to identify and map the same region inL. perenne.• Predicted protein sequences forL. perenneandF. pratensisHd1 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 toL. perennechromosome 7.• The identified candidate orthologues of riceHd1and barleyHvCO1inL. perenneandF. pratensismap to chromosome 7, a region of theL. perennegenome which has a degree of conserved genetic synteny both with rice chromosome 6, which containsHd1, and barley chromosome 7H, which containsHvCO1.New Phytologist(2005)doi: 10.1111/j.1469-8137.2005.01392.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]

• Intergeneric hybrids betweenLolium multiflorumand Festuca pratensis (Lm/Fp) and their derivatives exhibit a unique combination of genetic and cytogenetic characteristics: chromosomes undergo a high frequency of homoeologous recombination at meiosis; the chromosomes of the two species can easily be discriminated by genomicin situhybridization (GISH); recombination occurs along the entire length of homoeologous bivalents; a high frequency of marker polymorphism is observed between the two species.• This combination of characters has been used to transfer and isolate aF. pratensischromosome segment carrying a mutant‘stay-green’ gene conferring a disrupted leaf senescence phenotype intoL. multiflorum.• The genetic location within the introgressedF. pratensissegment of the senescence gene has been mapped using amplified fragment length polymorphisms (AFLPs), andF. pratensis-specific AFLP markers closely flanking the green gene have been cloned.• The use of these cloned sequences as markers for the stay-green locus in marker-assisted selection programmes has been tested. The potential application ofLm/Fpintrogressions as a tool for the map-based cloning of introgressedFpgenes is discussed. [ABSTRACT FROM AUTHOR]

Apoplastic and bulk tissue concentrations of NH[SUB4,SUP+] and H[SUP+] were measured during senescence of intact (attached) and excised ryegrass (Lolium perenne) leaves differing in nitrogen and carbon status. The potential for NH[SUB3] emission from the senescing leaves was estimated on the basis of the ratio between NH[SUB4,SUP+] and [H+], designated the Λ-value, in apoplastic solution and bulk tissue. Attached leaves with visual symptoms of senescence showed two to three times higher NH[SUB4,SUP+] and 0.5-1 unit lower pH in both apoplastic solution and bulk tissue extracts compared with green leaves. The Λ -values were, in all cases, low in attached leaves, ranging from 20 to 300 in the apoplastic solution and 500-900 in the bulk tissue. In excised leaves with high nitrogen status and low C : N ratio (&ap;10), apoplastic NH[SUB4,SUP+] increased from around 40 μM to 2 mM after senescence in darkness for 4-9 d. Bulk tissue water NH[SUB4,SUP+] increased in the same period to > 30 mM. Apoplastic-values were in all cases < 1000, while bulk tissue Λ -values increased dramatically and reached more than 60 000 in high-nitrogen leaves. Ammonia compensation points predicted on the basis of apoplastic NH[SUB4,SUP+] and pH in senescing leaves with high-nitrogen status reached 6-8 nmol mol-1 air. Consequently, senescing leaves may constitute a significant source of atmospheric NH[SUB3]. [ABSTRACT FROM AUTHOR]

Summary • In this study, we tested the hypothesis that environmentally induced changes in the oxygen isotope ratio of leaf water are recorded in grass blade cellulose during leaf-blade expansion. • Grasses were grown hydroponically in chambers that allowed for control of relative humidity while keeping isotopic inputs (namely source water) constant. • In experiments where relative humidity was changed from 35% to 93% during grass blade expansion, a 10‰ shift in cellulose δ 18 O was observed along single grass blades of Lolium multiflorum . However, statistically significant changes were not detectable with relative humidity of 93% to 70%. • It is shown that grass blades, analogously to tree rings, record environmental change on an interseasonal basis. In light of this, care must be taken to compare leaves of the same developmental stage to avoid confusion of environmental effects with physiological effects in interpretations of leaf organic material δ 18 O. The results presented here confirm the ability of the current empirical models to predict the oxygen isotope ratio of cellulose in both grass blades that expanded in constant and variable growth conditions. [ABSTRACT FROM AUTHOR]

Experiments were set up to assess the relative impacts of grass lamina fragment density, size and quality on the activity and growth of four fungi in a particulate soil-like matrix. The fungi studied were Cladosporium cladosporioides, Fusarium lateritium, Phoma exigua and Trichoderma viride, all of which are common inhabitants of UK upland grassland soils. Resource quality was varied by using three contrasting grasses as sources of lamina fragments: Lolium perenne, Agrostis capillaris and Nardus stricta. All the fungi were able to forage effectively through the soil-like matrix (at a rate of 1-2 ml matrix d−1) and colonize and partially decompose available lamina fragments (up to 40% d. wt loss). Foraging rates (ml matrix d−1) were affected by lamina fragment species but not by fragment density or size. In general, F. lateritium and T. viride foraged at a faster rate than the other species. Mycelial activity in the soil-like matrix was directly proportional to total lamina fragment availability and was unaffected by fragment size. Biomass production on solid media was also directly related to substrate (carbohydrate) availability. The results indicate that these fungi can adjust their growth patterns in response to fragment density so as to maximize foraging efficiency (energy acquired per unit exploratory biomass production). Differences in lamina fragment species were responsible for up to 50% reduction in mycelial activity. [ABSTRACT FROM AUTHOR]

Accumulation of water-soluble carbohydrates was studied in leaf tissues of 8-wk-old plants of perennial ryegrass (Lolium perenne L. var. Bravo). The roots and leaf bases were cooled to low temperatures to reduce sink activity while source activity was enhanced by continuous illumination of the shoots. This resulted in accumulation of fructans, first in sheaths, subsequently in expanding leaves, and finally in blades. Fructan concentration increased from 6 to 23 mg g-1 f. wt in sheaths, from 8 to 30 mg g-1 f. wt in expanding leaves and from 6 to only 17 mg g-1 f. wt in mature leaf blades. Increase in concentration of low-DP fructans preceded accumulation of high-DP fructans. Expanding leaves accumulated significantly more glucose and fructose than did mature leaf tissue. Leaf blades contained a higher concentration of sucrose than either leaf sheaths or expanding leaves. Expanding leaves exhibited the greatest activity of SST (0.77 nkat g-1 f. wt), the mature leaf blades the least (0.09 nkat g-1 f. wt), whilst that of mature leaf sheaths was intermediate (0.27 nkat g-1 f. wt). In each leaf tissue, invertase activity was higher than SST activity. Under conditions of fructan accumulation, SST activity increased threefold in mature leaf sheaths and 1.2-fold in expanding leaves. In mature leaf blades, however, the activity remained constant at a low level. Invertase activity never increased. Inhibitors of protein synthesis (cycloheximide) and of RNA metabolism (actinomycin D) prevented any increase of SST activity in leaf sheaths. The results are discussed in relation to fructan metabolism in leaf tissues of Lolium perenne. [ABSTRACT FROM AUTHOR]

A partial separation of sucrose: sucrose fructosyltranferase (SST) activity from invertase activity extracted from leaves of Lolium rigidum Gaudin was achieved by gel filtration. The SST activity was purified 54-fold with a ratio of SST activity to invertase activity of 1:1:1. the partially purified SST activity eluted with an apparent molecular mass of about 68000, had an optimum pH of 5.5 and a Km of 0.12 M. When incubated with sucrose concentrations ranging from 10 to 600 mM the partially purified SST activity produced mainly 1-kestose and some 6-kestose (10-15% of trisaccharide produced). SST and invertase activities declined during storage at -25°C with invertase activity declining at a faster rate. After the loss of invertase activity in storage, the partially purified SST activity synthesized only 1-ketose. When incubated with 1-ketose the partially purified SST activity synthesized neokestose (1.9 nkat ml-1), nystose (2.2 nkat ml-1) and an unidentified tetrasaccharide (1.4 nkat ml-1) indicating that the fructosyltranferase preparation also had FFT-like activity. The partially purified invertase had significant sucrose-hydrolyzing activity (25 nkat ml-1) and contained no measurable SST activity when incubated with 10-400 mM sucrose, but produced trisaccharide (1-kestose and 6-kestose, ratio 1.5:1) when incubated with 600 mM sucrose. L. rigidum does not normally accumulate 6-ketose. The optimum pH of the sucrose-hydrolyzing activity was 4.5 and the optimum pH of the fructosyltranferase activity of the invertase preparation was 5.5. The partially purified invertase did not have significant FFT-like activity. The results support the hypothesis that SST activity synthesizes only 1-kestose, which is a key intermediate in the synthesis of fructan in L. rigidum. [ABSTRACT FROM AUTHOR]

Fructan- and sucrose-hydrolyzing activity was extracted from plants of Lolium rigidum Gaudin. Sucrose-hydrolyzing activity varied 30-fold between different plant parts and parts of different ages. In contrast, fructan-hydrolyzing activity only varied two-fold. At least four β-fructofuranosidase activities were partially purified from mature vegetative tissues of Lolium rigidum. The β-fructofuranosidases were characterized by their different elution patterns on various chromatographic media and their relative rates of hydrolysis of sucrose and fructan extracted from different sources. Fructan-hydrolyzing activities were partially purified that hydrolyzed fructan containing predominantly 2-1 glycosidic linkages relatively more rapidly than fructan containing predominantly 2-6 glycosidic linkages. β-fructofuranosidases that were relatively more active against fructan than sucrose when compared with activity present in the crude extract, were inhibited by sucrose. It is concluded that it is necessary to use appropriate fructan substrates and to consider the possible involvement of all β-fructofuranosidase activities in hydrolysis of fructans in grasses. [ABSTRACT FROM AUTHOR]

Selected populations of Lolium perenne have previously been shown to have contrasting rates of mature leaf dark respiration and yield. Plants were now grown in high-and in low-density stands. We were able to reproduce the differences in yield for the high-density-grown plants. However the low-density-grown plants did not different in yield and so the correlation between respiration and yield is no apparent. It is concluded that the difference in respiration rate is not the most important factor determining yield with these populations. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of osmotic stress on metabolism of NO3- in Lolium perenne L. cv. Réveille, plants were exposed to NaCl or polyethylene glycol 6000 in the culture medium. Four-week-old plants were kept in the dark for 36 h in order to decrease nitrate reductase activity (NRA). Afterwards, they were placed in a greenhouse for 27 h under continuous illumination with a nutrient solution containing 1 mM 14NH4 16NO3. To induce osmotic stress, the solution wits supplemented with either NaCl or PEG 6000 to give an osmotic potential of --0.335 MPa in the medium. Osmotic adjustment in PEG treated plants was strongly limited, because PEG could not be absorbed. Over 7(1 not of the osmoregulation in NaCI treated plants resulted from chloride uptake. Compared to control plants, PEG 6000 treatment decreased absorption (by 40%) and reduction (by 60%) of NO3- in the leaves, leading to NO3- storage in the vacuolar pool. In contrast, addition of NaCI in the medium did not significantly affect either uptake or reduction of NO3-. The proportion of NO3- translocated to the leaves was unaffected by osmotic stress and represented about 76% of consumed NO3-. Nitrate reductase activity, measured in vivo with exogenously supplied NO3-, was not significantly different between treatments. Compared to reduction of P15NO3 in control plants, it appeared that reduction of NO3- in leaves of PEG-treated plants was not limited by enzyme activity or by the amount of reducing power. Availability of NO3- at the site of reduction therefore seems to be limiting when PEG 6000 is added to the medium. [ABSTRACT FROM AUTHOR]

This paper reports the conditions for the assay of sucrose-sucrose fructosyltransferase (SST); fructan-fructan fructosyltransferase (FFT), invertase and fructan hydrolase (FH) in extracts of leaves of Lolium rigidum Gaudin. Invertase had a temperature optimum between 30 and 35 °C and a pH optimum between 4.5 and 5.0 whereas the enzymes of fructan metabolism had temperature optima at 25 °C and pH optima at about 5.5. Analysis of the products of enzyme assays showed that crude SST activity produced mainly 1-kestose from 100 mM sucrose and when incubated with 500 mM sucrose, neokestose and possibly 6-kestose were also formed in low concentrations. FFT produced two tetrasaccharides and neokestose after incubation with 100 mM 1-kestose and FH produced fructose exclusively after incubation with high-molecular-weight fructan extracted from Lolium rigidum and Helianthus tuberosus L. and with a commercial preparation of bacterial levan. Enzyme activities were also measured during a phase of fructan accumulation. FH activity declined by 50% but SST and FFT activities increased about 2.5-fold during this period. The data supported the proposed synthetic pathway of fructan accumulation from sucrose via 1-kestose into high-molecular-weight fructan and indicated that fructan synthesis may occur at low substrate concentrations. Extracts from leaves which had not accumulated fructans contained measurable activities of SST and FFT. [ABSTRACT FROM AUTHOR]

Accumulation of water-soluble carbohydrates (WSC) in leaves of intact seedlings of annual ryegrass (Lolium rigidum Gaudin cv. Wimmera) was studied using a novel model system. The roots and leaf bases of intact seedlings, grown in nutrient solution, were cooled to 5 °C to reduce sink activity and the production of photosynthates was enhanced by continuous illumination of the plants. This resulted in accumulation of WSC in the shoots. Thin-layer chromatography showed the presence of a complex series of fructans, distinct from those found in tubers of Helianthus tuberosus. Two trisaccharides, 1-kestose and neokestuse, were present in various proportions, but no 6-kestose was detected in the shoots. After feeding 14CO2 to the seedlings in a pulse-chase experiment, high specific radioactivity was measured in monosaccharides, sucrose and fructan oligosaccharide fractions to DP 5 within 1 hr. These fructan pools were rapidly turned over without significant accumulation of fructans during the first 16 h of the accumulation phase. Neokestose and 1-kestose contained equally high specific radioactivity, 1 h after feeding. These results indicated that neokestose was possibly as important as 1-kestose as a possible precursor for synthesis of fructan. Concentrations of WSC increased linearly from 2 to 14 mg g-1f. wt of the leaves after 16 h and reached a concentration of 30 mg g-1f. wt after 64 h. Sucrose, glucose and fructose were the first sugars to be accumulated and reached concentrations of 10, 3.5 and 2.5 mg g-1 f. wt, respectively. Tri- and tetrasaccharide accumulated to measurable concentrations after approximately 16 h of treatment and reached concentrations of 2.5 and 2.0 mg g-1. wt, respectively. The appearance of these oligosaccharides occurred when sucrose and monosaccharides reached stable concentrations in the leaves. [ABSTRACT FROM AUTHOR]

Lolium multiflorum Lam. plants were used to investigate whether phytochrome-mediated tillering responses, anticipatory to competition: (a), are potentially disturbed by the twilight drop in the red to far-red ratio (R: FR) of sunlight (caused by atmospheric factors), and (b), occur in densely-sown (> 280 plants m-2) grass canopies, where competition is quickly established. Isolated plants grown under sunlight received natural low R: FR during twilight, but supplementary R provided simultaneously did not increase tillering. When a wide range of R: FR was provided at the end of natural or fluorescent light photoperiods, tillering was reduced only by very low R: FR (lower than natural twilight R: FR). Leaf sheath length followed a similar pattern of response. Single plants were grown in pots placed at various densities. High densities reduced the R: FR at plant bases and the number of tillers per plant before changes in dry weight and leaf number were found. Both very low R: FR provided at the end of the photoperiod, and increasing plant densities, caused more erectophile shoots. In densely-sown canopies of Lolium multiflorum both R: FR signals caused by neighbours, and tillering responses occur well before strong competition is established. Tillering is not obviously affected by the twilight drop in R:FR. [ABSTRACT FROM AUTHOR]

Changes in carbohydrate content and composition of ryegrass (Lolium perenne L.) cv. Réveille field-grown in Normandy were investigated from May 1987 to May 1988. During the winter period, the concentrations of high DP (degree of polymerization) fructan were the lowest whilst those of ethanol-soluble carbohydrates were the highest. Ethanol-soluble carbohydrates also accounted for most of the non-structural carbohydrates of four cultivars of Lolium perenne field-grown in central France in January 1989. The accumulation of osmotically active carbohydrates during winter leads only to a small depression of freezing point and consequently, these sugars cannot be considered as efficient cryoprotectants in ryegrass. [ABSTRACT FROM AUTHOR]

The pyenidium of a Stagonospora sp. observed in degenerating leaf sheath and blade tissues of Lolium perenne L. contained concentric bodies similar to those found in the mycobiont of several lichens and a few other free-living ascomycetes. These bodies occurred in vegetative hyphae, hyphae of the pycnidial wall, in conidiogenous cells and in conidia and comprised a central electron-translucent core surrounded by a granular zone and an outer radially orientated fibrillar or lamellar zone. In some cases the entire body was surrounded by a translucent halo. A second feature of the interwoven hyphae of the pycnidial wall was the occurrence of pores connecting adjacent hyphae. These lateral pores appeared identical to pores in septa between cells of individual hyphae, and like them, were associated with Woronin bodies. [ABSTRACT FROM AUTHOR]

summary Analyses of the kinetic properties and products of fructosyl transferases from Lolium temulentum L. suggest that these enzymes are artifacts of conventional extinction and/or assay methods. An alternative approach to the investigation of fructan biosynthesis in cell-free extracts has been developed. This approach employs the Sensitivity of radiotraeers to overcome the limitations of conventional quantitative methods for the analysis of fructan. Homogenates of leaves were prepared, which contained enzyme protein, endogenous sucrose and fructan. These extracts catalysed the rapid and efficient incorporation of radioactivity from [U-14C]sucrose into material with a decree of polymerization greater than 2. The chromatographic pattern of these labelled products was identical to the pattern of native leaf fructan. Kestose, which does not accumulate to high concentrations in vivo but was a major product of our previous enzyme assay procedures, was not a product of these homogenates. The flux of radioactivity into oligofructan was sufficient to account for observed rates of fructan accumulation in the leaf And fructosyl transfer was observed at sucrose concentrations between 15 and 30 mol m−3, which is within the probable physiological range of substrate concentration for L. temulentum leaf cells. Extracts derived from leaves which were not actively accumulating fructan were unable to label oligofructan. Labelling of fructan was not due to non-enzymic isotope exchange. Leal homogenates contained invertase and fructan hydrolase activities. Invertase activity was inhibited by pyridoxal HCl and pyridoxine MCI when these compounds were included in reactions at 20 mol m−3. Inhibition of invertase activity was correlated with a marked stimulation of fructosyl transfer, suggesting competition for substrate. Because this system functions at physiologically relevant sucrose concentrations and produces a pattern of labelled products identical to native leaf fructan, we suggest that it represents a more convincing starting point for studies of the enzymology of fructan biosynthesis than previous cell-free extracts. [ABSTRACT FROM AUTHOR]

The isotope 15N was used to estimate N2-fixation by white clover, and N-transfer from clover to perennial ryegrass. Pure stands of each of these pasture plants and a mixed sward of both were established in a field soil in which it had been demonstrated that vesicular arbuscular mycorrhizal inoculation was necessary for suitable development of the clover. All plants, whether clover or ryegrass, received the same amount of a selected mycorrhizal inoculum. The 15N/11N ratio of the grass in pure stands was used to evaluate N2-fixation by clover growing alone, and that of the grass in the mixture to estimate that by the companion clover. Tentative evidence of N-transfer was obtained by comparing the 15/11N ratio in the grass growing alone with that when mixed with the legume. In spite of a decline with time in 15N enrichment, the N2-fixation rates were about the same throughout the growing season and for the two cropping systems. The total N, P and dry matter yields in the grass/clover mixture were greater than in monocultures. A lower 15N enrichment of the grass growing mixed compared to that growing alone, suggesting N-transfer, was only obtained at the second harvest. The mycorrhizal colonization of the grass in the mixed grass/clover sward was significantly enhanced, as compared with that of the grass in pure stands. Mycorrhizal hyphae are known to be involved in NH4+ uptake, translocation and transfer to the host plants, and this may partly explain the improvement of pasture productivity when grass and mycotropic legumes are grown together. [ABSTRACT FROM AUTHOR]

The induction of fructan biosynthesis in excised, illuminated leaves of Lolium temulentum L. is accompanied by a concomitant increase in extractable sucrose: sucrose fructosyl transferase (SST) activity. In leaves treated with the L-isomer of 2-(4,methyl-2,6,-dinitroanilino)-N-methyl propionamide (L-MDMP) fructan biosynthesis in vivo occurs in the absence of such an increase in extractable SST, suggesting that the activity measured in vitro is not an obligatory component of fructan biosynthesis in vivo. Sucrose : sucrose fructosyl transferase preparations from L. temulentum catalyse the formation of isokestose and kestose from sucrose. The rates of synthesis of these trisaccharides were determined in the range of sucrose concentration 10-700 mol m-3. Increase in total trisaccharide synthesis was linear with respect to substrate concentration. Isokestose was formed over the entire range whilst kestose synthesis was inactive below 80 mol m-3. Neither isokestose nor kestose synthesis was saturated at 700 mol m-3. The Km for isokestose synthesis was high at 380 mol m-3. Conventional kinetic analysis of kestose data failed, indicating that this activity does not obey classical Michaelis-Menten kinetics. The intracellular sucrose concentration in leaf tissue was estimated to be 100 mol m-3. At this substrate concentration, isokestose synthesis would be functioning well below the measured Km and kestose synthesis would be operating at the extreme lower limit of its activity range. Higher oligosaccharide products of fructosyl transferase incubations were not representative of the oligofructans which accumulate in the leaf. This data casts further doubt on the physiological significance of the measured fructosyl transferase activities. Isokestose synthesis was localized in vacuoles derived from leaf mesophyll protoplasts, con... [ABSTRACT FROM AUTHOR]

Leaf growth rate and the turgor pressure of cells in the expanding zone of leaves of Lolium temulentum were measured simultaneously. Growth rate was reduced over a range from 30 μm min to zero by reducing the temperature of the expanding zone from 20 to 2 °C. Turgor pressure remained constant at 0.5 MPa. This implies that growth reduction by low temperature is due to changes in cell wall rheology. Cell membrane hydraulic conductivity (LP) was reduced with temperature as expected, but this was not sufficient to influence growth rate detectably. [ABSTRACT FROM AUTHOR]

Pure stands of Trifolium repens L. N.Z. Huia and Lolium perenne L. S32 and mixtures of various densities and frequencies were treated with sulphuric acid solutions of pH 2.5, 3.5 and 5.6. The species yield was recorded over live sequential harvests. Multifactorial response equations were used to describe the behavior of the species yield as a function of acidity and the density of both species. Predictions, made through these models, showed that the response of yield of these species to simulated acid rain treatments varied greatly depending on the planting density, the time of harvesting and on whether the plants were growing in monoculture or in mixture. This suggests that it is not sufficient to consider the effects of experimentally applied acid rain on single individuals or low density stands, since the results obtained will not reflect the response in a close canopy sward. [ABSTRACT FROM AUTHOR]

Leaves of Lolium multiflorum Lam. and Zea mays L. of different ages were prepared for TEM by a number of cytochemical methods. After post-fixation in potassium ferricyanide with osmium tetroxide the peripheral reticulum in both mesophyll and bundle sheath chloroplasts of maize stain very clearly. Post-fixation with uranyl acetate, copper and lead stilts also stains the chloroplast envelope rather than the internal thylakoid system. Differences between the mesophyll and bundle sheath chloroplasts of maize and between those of ryegrass are revealed after post-fixation in zinc iodide with osmium tetroxide. After post-fixation in potassium iodide with osmium tetroxide the loculi stain less intensely than in zinc iodide. Malachite green added to glutaraldehyde at pH 7.0 enhances membrane staining in general and reveals large lipid drops in the stroma. At pH below 6.0 only the 'A' space is stained. The 'A' space and the loculus are stained when ethidium bromide is added to glutaraldehyde. The different reactions of the chloroplast membranes probably reflect differences in chemical composition. [ABSTRACT FROM AUTHOR]

Three experiments using soil-grown Lolium perenne plants were performed in order to investigate the effects of a gradually increasing drought stress on the death of root cells and the growth of lateral roots. Water potentials of -2 to -10 MPa caused death of the root cortex, but death of root tips occurred only at soil water potentials below -10 MPa. Low soil water potentials promoted lateral root initiation and elongation, the total length of lateral roots being between three and five times that of control plants. On rewetting severely droughted plants, root growth continued by elongation of existing, previously initiated, lateral roots. [ABSTRACT FROM AUTHOR]

Sample sub-populations, each of six plants, were chosen for high, mid and low tolerance of copper from each of two naturally-occurring copper tolerant populations and from tolerant individuals selected from a cultivar of Agrostis capillaris L. The naturally-occurring ecotypes came from a closed sward community at Drws y Coed, and from an open community at Parys Mountain, both copper mines in North Wales. Clonal replicates of all plants were introduced into swards of perennial ryegrass cvs. S23 or S24, growing on normal soil at the University of Liverpool Botanic Gardens. S23 plots were cut eight times between June 1977 and July 1978, whilst S24 plots were cut 3 times during the same period. Half the experimental plots received N, P, K, fertilizer; the rest received none. Plants selected from the cultivar (selected) produced most dry matter, and with infrequent defoliation flowered freely in competition with ryegrass. Those taken from Parys Mountain mine spoil produced least dry matter and no inflorescences. Drws y Coed plants were intermediate in dry matter and inflorescence production. These results may reflect differences in population density in the habitats from which the populations were sampled. Sub-populations chosen for high, mid or low copper tolerance within the selected and Drws y Coed populations did not differ significantly in dry matter yield. By contrast under certain circumstances Parys Mountain plants with low tolerance outyielded other more tolerant plants. These results are considered with respect to growth strategies adopted by plants growing on and off copper mine sites. [ABSTRACT FROM AUTHOR]

The lateral spread in a steamed lateritic podsol of Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. and Trappe from localized inoculum was examined in two pasture species: Trifoliumsubterraneum L. (subterranean clover) and Lolium rigidum Gaud. (Wimmera ryegrass). Mycorrhizal infection was estimated 21, 28, 38 and 59 d after sowing at points 2,4,6,8,10, 14, 20 and 26 cm from the inoculum. The proportion of root length infected by G. fasciculatum at increasing distances from the inoculum could be best described by a Gompertz curve in both plant species at all harvests. Thus the curve had an upper plateau of the maximum percentage of infection. It is suggested that the pattern of spread of G. fasciculatum through roots of subterranean clover and ryegrass is related to changes in the amount of inoculum with distance from the point of inoculation, as well as over time. The rate of spread of the infection front was not constant. Thus it may not be appropriate to calculate mean rates of spread of mycorrhizal fungi over long time periods. [ABSTRACT FROM AUTHOR]

The number and spatial distribution of perennial ryegrass (Lolium perenne L.) genotypes in 4 pastures were estimated by sampling single tillers from points 5 cm apart on an 11 7times; 11 grid. Three electrophoretic loci were used initially to determine the genotype of each tiller. Three 10-year-old sown swards contained at least 36--43 different genotypes per 0·25 m2 quadrat (10% of the number sown) while a 40-year-old pasture contained only 5 genotypes per 0·25 m2 quadrat. The cut sward had a greater proportion of its area occupied by a few large genotypes than the swards grazed by sheep or cattle. The importance of age, management, and other factors influencing genotypic diversity in swards is discussed. [ABSTRACT FROM AUTHOR]

Shoot concentrations of Se associated with a 10% reduction in dry matter yield were established for perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) grown in sand culture. Selenite-treated plants had lower shoot concentrations of Se than those treated with selenate; the critical toxic values associated with a 10% reduction in growth were 48 and 320 µg Se g-1 dry matter shoots for ryegrass plants, and 160 and 330 µ Se g-1 dry matter shoots for white clover plants, respectively. Differences in the mode of absorption of selenite and selenate, and in the distribution and chemical form of Sc found in the plant after absorption, probably account for this disparity in toxicity. While both selenate and selenite increased the Se concentration in the tissues of the plants to high levels, a greater proportion of the absorbed Se was transported to the shoots of the selenate-treated plants than of those treated with selenite. Increasing supplies of selenate were associated with a reduction in chlorophyll content. Contrary to the concept of a common uptake mechanism in the roots for selenate and sulphate, increasing supplies of selenate had a synergistic effect on S concentrations in the shoots rather than the expected antagonistic effect. [ABSTRACT FROM AUTHOR]

In two pot experiments with a soil deficient in P and N, vesicular-arbuscular mycorrhizas stimulated the shoot growth of Lolium perenne L. greatest (24%) with the highest levels of applied P and/or N, and where the shoot N and P concentrations approached the normal agronomic range. It is suggested that applied N, and possibly P, resulted in mycorrhizas making a more important contribution to the plant's P or Cu status. Previous experiments purporting to show the mycorrhizal dependency of species are criticized if the levels of nutrients in the soil (other than P) which might have been limiting were not considered. Mycorrhizas reduced root/shoot ratios even in those treatments where a growth response was not detected. There was a negative relationship within treatments between responsiveness to mycorrhizas and the size of the non-mycorrhizal plant. This may have relevance in plant breeding. [ABSTRACT FROM AUTHOR]

The order of toxicity of different metals affecting root growth of seedlings of rye grass (Lolium perenne S24) was: copper> nickel > manganese> lead> cadmium> zinc > aluminium> mercury> chromium > iron. With the sole exception of manganese,these results confirm those of other studies and the order follows that of the stability of the metallic-organic complexes. The results are of value in predicting the toxicity of heavy metals in plant growth on contaminated soils. [ABSTRACT FROM AUTHOR]

Monocultures of Lolium perenne were grown at high densities under various shade regimes to investigate the effects of shade on self-thinning. Unshaded populations conformed to the minus 3/2 power law when dead matter was taken into account in the calculation of mean weight per plant. In a plot of live weight per plant, populations reached a common minus 3/2 line but then deflected from it. Adherence to the minus 3/2 power law is a characteristic of shoots but not of whole plants of L. perenne. Populations increased in shoot:root ratio as they developed so that the thinning line for shoot plus root weight per plant was shallower than the thinning line for shoot weight per plant. Shoot: root ratios were generally higher in shaded than in unshaded populations. Tiller weights and numbers in experimental populations of L. perenne also conformed to the minus 3/2 power law. Populations grown in deep shade thinned along a line of slope minus 1 when sown at 'low' densities but those sown at very high densities underwent an initial period of thinning along a slope of minus 3/2, followed by a switch to a slope of minus 1. Populations at intermediate levels of shade showed a decrease in the intercept of the thinning line with increasing shade but no change in gradient. A schematic diagram is presented to help explain the effects of shade on self-thinning. [ABSTRACT FROM AUTHOR]

Nitrate utilization, as judged by dry matter production and nitrate reductase activity, was examined in species of the genus Agrostis and compared with species of Lolium and Poa. A. setacea had the lowest ability to utilize nitrate which correlated with its restricted ecological distribution in areas of low nitrate availability. In contrast, A. tenuis which may also be found in low nitrate sites, exhibited a higher nitrate reductase activity but lower dry matter production than the species A. stolonzfera and L. multiflorum, both of which are characteristic of sites with higher nitrate availability. A high potential to utilize nitrate may be important in low nitrate areas subjected to marked fluctuations in supply. Correlations between nitrate utilization and growth were, in general, non-significant and often negative. The results suggest that the efficiency of incorporation of reduced nitrogen into plant structure may bring about differences between species in the production of dry matter. Significant variations between species and response to nitrate were found in relation to the time of year. Maximum enzyme activities were found during the winter months with little change, after a drop in activity in the early spring, during the growth period. The peaks in activity found may not represent nitrate utilization but rather the induction of high levels of enzyme with little subsequent reduction of nitrate. Variation in soil pH did not modify the seasonal pattern and had little overall effect on either nitrate utilization or dry matter production although significant differences were found between species in both of these factors. [ABSTRACT FROM AUTHOR]

The growth of perennial ryegrass and lucerne was inhibited by D-threo-Chloramphenicol at concentrations generally considered safe for preventing bacterial contamination. Inhibition of growth was the result more of a reduction in photosynthetic activity than of a specific effect on ion absorption. Young plants were more susceptible to chloramphenicol than older plants and the cumulative effect of repeated applications of the bactericide at low concentrations depressed growth and chlorophyll content to the same extent as a single concentrated application. The present results have been related to known effects of chloramphenicol on protein synthesis, leading to the conclusion that its use to prevent bacterial contamination in studies on the growth of green plants is inadvisabIe. Recognition of this fact makes suspect much published work where chloramphenicol has been used for this purposes. [ABSTRACT FROM AUTHOR]

In six experiments Lolium perenne L. and Plantago lanceolata L. were grown together in pots. Two experiments also included L. perenne alone, P. lanceolata alone, or L. perenne + Trifolium repens L. In five of the experiments prior sterilization of the soil followed by reinoculation was used to obtain two treatments, one having plants infected with vesicular-arbuscular mycorrhiza, the other non-mycorrhizal. The shoots of some plants in each pot ('donors') were injected with 32P. After a week these shoots were removed, and after a further week the remaining plants ('receivers') were harvested and their 32P content determined. In all experiments and species-combinations there was some 32P transfer to the shoots of both mycorrhizal and non-mycorrhizal receiver plants. The amount of transfer in mycorrhizal treatments was 2 to 8-fold greater than in non-mycorrhizal treatments, except in one experiment where mycorrhizal infection was very low. There was no clear difference between the different species combinations in the amount by which phosphorus transfer was enhanced by mycorrhizas. These results show that mycorrhizas can increase phosphorus transport between plants, but do not show whether there is direct transport from one root to another via interconnecting hyphae or whether the phosphorus must leave the donor root before being taken up by mycorrhizal hyphae. [ABSTRACT FROM AUTHOR]

Using a buried slide technique, hyphal connections are shown to exist between different roots on one plant, Lolium perenne L., and also between two roots of different species L. perenne and Plantago lanceolata L. These two species are commonly found together in permanent pasture. [ABSTRACT FROM AUTHOR]

The effect of increasing concentrations of sodium chloride in the root zone on growth, chemical composition and nitrate reductase activity of perennial ryegrass and timothy was investigated in a glasahouse pot experiment. For ryegrass, a natrophile, sodium chloride had little effect on growth, whereas for timothy, a natrophobe, growth was severely depressed by comparatively low concentrations of salt. The result also indicate that translocation of sodium into the leaves of timothy took place readily only after the accumulation sites in the roots and lower stems had been saturated with this element. This means that relatively large quantities of sodium chloride were needed to produce concentrations of sodium in the leaves of timothy as high as those normally found in the leaves of ryegrass. Sodium chloride increased the uptake of total and nitrate-nitrogen but, in contrast, depressed the uptake of potassium by ryegrass and timothy It was therefore concluded that the marked stimulation by sodium chloride of nitrate reductase activity in both species was more the result of the increased uptake of nitrates than a specific effect of this salt on the enzyme. The practical implications of these results are discussed. [ABSTRACT FROM AUTHOR]

The seed weight of individual perennial ryegrass seeds was measured prior to recording their date of emergence and subsequent growth in experimental populations raised in the glasshouse and sown at different initial densities. Seed size did not correlate with time to emergence although lighter individuals had a slightly lower probability of emergence. Seed size had no statistically significant effect on subsequent tillering up to 27 weeks, or on the dry wt attained by this time. The time from sowing to emergence was significantly related to subsequent tillering of the grass plants for a number of weeks in populations sown at different densities. After some 20 weeks the effect of emergence time became non-significant. This coincided with the onset of tiller mortality in the population. Even after 27 weeks individual emergence time was inversely related to dry wt but was not related to mean tiller weight. [ABSTRACT FROM AUTHOR]