The Effect of Low Temperature upon Starch, Sucrose and Fructan Synthesis in Leaves

Measurements on plants in a temperature gradient tunnel showthat diurnal accumulation of starch in illuminated leaves wasgreatly reduced at temperatures below 8 °C, whereas sucrosesynthesis was less affected under similar conditions. High chillingsensitivity for leaf starch accumulation was observed in a numberof chilling resistant temperate species. Enzymes of sucroseand fructan metabolism from mature leaves of Lolium temulentumwere less strongly inhibited at low temperatures than enzymesinvolved in starch synthesis. These results are discussed inrelation to carbon partitioning in species which grow and aremetabolically active at chilling temperatures. Lolium temulentum, starch, sucrose, fructan, temperature, enzyme activity, carbon partitioning     

Leaf Development in Lolium temulentum L.: Progressive Changes in Soluble Polypeptide Complement and Isoenzymes

Ougham, Helen J., Jones, Thomas W. A. and Evans, Mair LL. 1987.Leaf development in Lolium temulentum L.: progressive changesin soluble polypeptide complement and isoenzymes.—J. exp.Bot. 38: 1689–1696. The spectrum of soluble polypeptides extracted from segmentsof the developing 4th leaf of Lolium temulentum simplified withincreasing distance from the leaf base. Most of the metabolicallyimportant isoenzymes analysed also exhibited gradients of activitywith respect to distance from the base, and in some cases twoor more contrasting gradients were observed for a given enzyme. Key words: Gradients, isoenzymes, leaves, Lolium temulentum,, soluble polypeptides     

Structure and Function in the Grass Ligule: the Newly-initiated Ligule of Lolium temulentum L., a Light and Electron Microscope Study

Initiation and early development of the membranous ligule ofLolium temulentum L. was studied by light and transmission electronmicroscopy. The ligule appeared to be derived solely from theleaf adaxial epidermis and at this stage had a structure andultrastructure typical of a meristematic tissue. Cells of thefuture collar region of the leaf appear to be initiated at thesame time as the ligule. The siting of the ligule upon the leafis briefly discussed. Darnel, ligule (initiation), Lolium temulentum L., Poaceae, ultrastructure     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. II. Anther and Pollen Development In Vivo and In Vitro

The various pathways of pollen development were investigatedin cultured anthers of Lolium temulentum, Festuca pratensisand the L. multiflorum x F. pratensis hybrid ‘Elmet’.In all three, development from the vegetative cell was the predominantpathway of pollen callus development. However, there were characteristicdifferences in the behaviour of the generative cell. In L. temulentumit remained attached to the pollen wall and degenerated, whereasin F. pratensis it divided. In ‘Elmet’ it detachedfrom the pollen wall and remained undivided. Both polarizedand unpolarized partitioned calluses were observed. Developmentof the fusion product of the vegetative and generative nucleiwere also observed in anthers of L. temulentum. Anomalous grainswere not found to be major source of pollen calluses. Sections of anthers of L. temulentum were used to investigatethe origin of S pollen grains, the small pale-staining grainswhich denote pollen dimorphism. Such grains form out of contactwith the tapetum and are therefore determined before or duringmeiosis (i.e. before harvest of anthers for culture). Sectionswere also used to demonstrate the influence of the durationof pretreatment on the development of the middle layer of theanther wall. Festuca pratensis, Lolium temulentum, Lolium x Festuca, anther culture, haploid, microspore, pollen     

Presence of Tyloses at the Blade/Sheath Junction in Senescing Leaves of Lolium temulentum L.

Aspects of age-related changes occurring in the blade/sheathjunction of leaves ofLolium temulentum L. were studied usingautoradiography, light and transmission electron microscopy.With increasing leafage the apical transport of sheath-appliedradioactive amino acids was retarded at the sheath side of theblade/sheath junction. An anatomical study revealed the presenceof tyloses in the protoxylcm lacunae of vascular bundles atthis region in senescing leaves. The possible involvement oftyloses in grass leaf senescence is discussed.     

Structure and Function in the Grass Ligule: Optical and Electron Microscopy of the Membranous Ligule of Lolium temulentum L.

Aspects of the structure and ultrastructure of the membranousligule of mature leaves of Lolium temulentum L. are described.In transverse section the ligule was lens-shaped and wedge-shapedin longitudinal section, 6 or 7 cells wide near the base and1 or 2 cells wide at the edges. Two uniseriate epidermes encloseda chlorenchymatous mesophyll tissue of varying thicknesses;both epidermes were continuous with the leaf adaxial epidermis.The cells comprising these three issues all appeared like typicalgrass epidermal long cells; elongate papillate cells were presentat the edges. No stomata, trichomes, intercellular spaces orvascular tissue were found in the ligule. A marked polarizationof ultrastructural complexity existed from the large-vacuolateabaxial epidermis to the ‘densely cytoplasmic’ small-vacuolateadaxial epidermis. Cells of the latter tissue contained numerousmitochondria, hypersecretory dictyosomes and abundant strandsof rough endoplasmic reticulum. Fluorescence microscopy providedevidence for the accumulation of a polysaccharide-containingmaterial within the periplasmic space next to the outer tangentialwall of adaxial epidermal cells. The ligule is considered tobe a highly organized and differentiated leaf organ with a pholosyntheticmesophyll and an adaxial epidermis active in the synthesis ofprotein and polysaccharide. Darnel, fluorescence microscopy, ligule, Lolium temulentum L., Poaceae, ultrastructure     

Vernalization in Lolium temulentum L.: Responses of In Vitro Cultures of Mature and Immature Embryos, Shoot Apices and Callus

Response of vernalization to low temperature (2C) was studiedin a winter-annual form of Lolium temulentum L., using imbibedseeds, excised mature and immature embryos, shoot apical meristemsand callus tissue. Excised embryos, as early as 5 days afteranthesis, and excised shoot apices could be vernalized as effectivelyas imbibed seeds. Cold treatment of developing embryos withinthe ear, however, appeared to have no vernalizing effect. Plantsderived from callus by somatic embryogenesis showed varyingdegrees of vernalization response. The vernalization response in L. temulentum, as in winter annualcereals, appears to be located in the shoot apical meristemand the vernalized condition can be transmitted to new axillarymeristems formed from it. Lolium temulentum L. darnel, vernalization, embryo culture, apical meristem culture, callus culture     

Early Increase in the Mitotic Index in the Shoot Apex of Lolium temulentum cv. Ceres During the Floral Transition

Six-week-old Lolium temulentum cv. Ceres plants were inducedto flower by a single long day (Day 1). Cell proliferation wasanalysed in the apex during the period extending from Day 1to Day 3. A stimulation of mitotic and DNA synthetic activitieswas observed in the apical summit at 8 h of the photoextensionperiod of the LD, i.e. before any apparent movement of the floralstimulus out of the leaves and well in advance of apex evocation. Key words: Cell cycle, flowering, Lolium, shoot apex     

Sub-cellular distribution of alanine aminotransferase in leaves of Lolium temulentum

Chloroplasts isolated from leaves of Lolium temulentum by differential centrifugation and sucrose gradient centrifugation were found to contain hig     

Structure and Function in the Grass Ligule: the Endomembrane System of the Adaxial Epidermis of the Membranous Ligule of Lolium temulentum L. (Poaceae)

The endomembrane system of the adaxial epidermal cells of themembranous ligule of the grass Lolium temulentum L. has beenstudied by conventional transmission electron microscopy, andby using zinc iodide-osmium tetroxide impregnation with examinationof thick sections at 100 kV. The components of the endomembranesystem are the nuclear membranes, rough endoplasmic reticulum(present in both cisternal and tubular forms), dictyosomes,dictyosome-derived vesicles, coated vesicles, plasma membraneand tonoplast. Direct continuity between tubular endoplasmicreticulum and the cis face of dictyosomes is demonstrated andthe applicability of the endomembrane concept to this putativesecretory tissue is discussed. The presence of vesicle-likeprofiles apparently within the outer tangential walls is reported.Copyright1995, 1999 Academic Press Ligule, Lolium temulentum L., darnel, grasses, Poaceae, Gramineae, endomembrane concept, ultrastructure, zinc-iodide-osmium tetroxide impregnation     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. I. Influence of Pretreatment, Culture Medium and Culture Incubation Conditions on Callus Production and Differentiation

This study was conducted with Lolium temulentum, Festuca pratensis,and the two hybrids L. multiflorum x F. pratensis ‘Elmet’and L. perenne x F. pratensis ‘Prior’. In a comparisonof various durations (7–42 d) of pretreatment at 4 or7 °C the highest yield of microspore-derived callus of L.temulentum was obtained after pretreatment of spikes at 7 °Cfor 28 d, conditions which also proved optimal for panicle pretreatmentwith F. pratensis. For ‘Elmet’, durations of 21–42d were optimal, and for ‘Prior’ the responses tendedto decline with increasing duration. In L. temulentum addition of charcoal (1–2 g l^–1)to medium containing 2, 4-D and KN wa     

Structure and Function of the Root Cap of Lolium temulentum L. (Poaceae): Parallels with the Ligule

Structure of the root cap ofLolium temulentum L. and of thechemistry of its secretory product were investigated with conventionaltransmission electron microscopy, zinc iodide–osmium tetroxideimpregnation, and use of protein and polysaccharide localizationtechniques at the ultrastructural level. Structural and functionalinformation concerning the root cap is compared with that previouslyobtained for the membranous ligule of this species. Similaritiesbetween root cap cells and adaxial epidermal cells of the liguleare described and discussed. It is concluded that both systemsare secretory and represent a similar response to the commonproblem of easing the passage of growing organs against thesoil or other plant parts. Darnel; Gramineae; grasses; ligule; Lolium temulentum L.; Poaceae; root cap; secretion; ultracytochemistry; ultrastructure; zinc iodide-osmium tetroxide impregnation     

The Effects of Leaf Age and Senescence on the Distribution of Carbon in Lolium temulentum

Assimilate distribution in leaves of Lolium temulentum was establishedby root absorption of [¹⁴C]sucrose and after exposure to ¹⁴CO₂.Age determined the amount of carbon assimilated, with more labelbeing incorporated during expansion than at maturity. Duringsenescence ¹⁴C assimilation was much lower. Ethanol-solubleextracts from various tissues of root-labelled plants containedmost of the radioactivity chiefly in basic and acidic compounds.The neutral fraction was composed predominantly of sucrose. Sucrose was comparably labelled in leaves from plants fed equalamounts of either [¹⁴C]sucrose, glucose, or fructose and onlytraces of labelled monosaccharides appeared in extracts. Radioactive sucrose was translocated rapidly from mature leaveswhereas, in the expanding leaf, carbon incorporation was directedtowards growth and the greater proportion of label present atligule formation was in ethanol-insoluble material. Induced senescence, of a mature leaf fed during expansion, produceda rapid loss from the pool of insoluble ¹⁴C. This was accompaniedby a reduction in the contents of chlorophyll and soluble proteinand an accumulation of amino acids. The onset of senescencecaused changes in leaf sugar levels which were correlated withincreased rates of respiration.     

Darkness promotes flowering in the absolute long-day requiring plant, Lolium temulentum L. Ceres

Vegetative plants of the long-day grass Lolium temulentum L.Ceres were exposed to threshold long days or light breaks. Protracteddarkness given just afterwards clearly promoted flowering andwas weakly inductive on its own. The promotive effect of darknesswas restricted to floral induction since further apical developmentwas weak. Key words: Lolium temulentum, flowering, photoperiodism, darkness     

Reproductive Development in Lolium temulentum L.: Spike Morphogenesis and Grain Set Limitations

Reproductive development in cereals is not easy to investigatebecause their quantitative response to environmental factorsmakes it difficult to synchronize the plants. In this paper,one of our aims was to assess whether Lolium temulentum strainCeres, a qualitative long-day grass, could serve as a modelof reproductive development for cereals. The morphological patternsfrom floral transition to seed set were studied. A flowering scale was established to evaluate developmentalrate during spike morphogenesis. Apex growth was found to increaseaccording to biphasic kinetics; double ridge appearance markedthe beginning of an exponential phase. Developmental progression and apical growth rate were both increasedby giving repeated long days. In contrast, the final numberof lateral spikelets (20–25) could not be manipulatedafter the beginning of long-day treatment. When plants were kept in continuous light from the beginningof induction, double ridges appeared on the fifth 24 h cycle.Spikelet initiation began in the upper mid-part of the spike,and then extended acro- and basipetally. The phase of spikeletinitiation lasted 6 d, with l?5 to 1?9 spikelets being produceddaily. Within each spikelet, florets were initiated at an averagerate of l?3 primordia per day and developed acropetally. Thefirst signs of apical site degeneration were observed in themost developed upper spikelets just before heading. Ear emergenceoccurred between the 20th and 25th cycles of continuous light;anthesis was observed 6 or 7 d later. The proportion of floretssetting grain averaged about 40%. Grains were produced mainlyin the lower spikelets while the upper mid-part of the inflorescenceshowed a much lower fertility rate. Complex developmental gradients described in this paper suggestthat L. temulentum could serve as a model of reproductive developmentin cereals, with the added advantage of flowering in responseto a single long-day. Key words: Lolium temulentum L., spike morphogenesis, spikelet number, floret number, grain set     

Structure and Function in the Grass Ligule: Mitochondria and Microbodies in the Membranous Ligule of Lolium temulentum L., an Ultrastructural and Cytochemical Study

The ultrastructure and distribution of the mitochondria andmicrobodies within the tissues of the ligule of mature leavesof Lolium temulentum L. are described. Staining of the mitochondriaand microbodies with diaminobenzidine (DAB) was observed. Mitochondrialstaining was totally inhibited by potassium cyanide and sodiumazide but not by aminotriazole, and did not occur in the presenceof added hydrogen peroxide; it was concluded that cytochromec oxidase (EC 1.9.1.3 [EC] ) was responsible. In the microbodies stainingwas reduced in the absence of added hydrogen peroxide and eliminatedin the presence of aminotriazole; it was concluded that catalase(EC 1.11.1.6 [EC] ) was responsible. Presence of succinic dehydrogenase(EC 1.3.99.1 [EC] ) activity was demonstrated in the mitochondriausing the copper-ferricyanide reaction; presence of sodium malonateand absence of sodium succinate greatly reduced mitochondrialdeposition of reaction product. The results are discussed inrelation to possible functions of these organelles in the ligule. Key words: Ligule, Lolium temulentum L., Enzyme ultracytochemistry     

Kinetics of Leaf Growth in Lolium temulentum at Optimal and Chilling Temperatures

Lolium temulentum plants were grown at 20 °C, under an 8-hdaylength, in a controlled-environment chamber, and the kineticsof leaf expansion were observed by measuring the movement ofan optical grid attached to the fourth leaf. The leaf emerged23–24 d after sowing and was fully expanded 9–10d later. Extension rate was maximal between the second and fifthdays after emergence and declined markedly thereafter. Duringthe rapid growth phase the rate of elongation exhibited a distinctdiurnal rhythm, fluctuating between 1.9 to 2.3 mm h^–1in the light period, and 1.3 to 1.7 mm h^–1 in the dark.A circadian oscillation with a period of about 27 h was observedin leaves elongating in continuous darkness. When plants weretransferred to 5 °C soon after emergence of the fourth leafthere was an immediate reduction in rate of growth to about22 per cent of the rate at 20 °C: the Q₁₀ for the mean elongationrate in the range 20–5 °C was 3.7. When plants weretransferred from 20 to 2 °C at fourth leaf emergence, meanextension rate declined to less than 5 per cent, correspondingto a Q₁₀ in the range 5–2 °C of more than 300. Furthermore,growth at 2 °C was confined almost entirely to the darkphase of the photoperiod cycle. The responsive tissue was shownto be a small area of expanding leafless than 1.5 cm above theshoot apex and the possible mechanisms underlying low temperatureeffects in this region are discussed. Lolium temulentum L., leaf growth, auxanometer, low temperature, diurnal rhythm     

Leaf Development in Lolium temulentum: Photosynthesis and Photosynthetic Proteins in Leaves Senescing under Different Irradiances

Changes in carbon fixation rate and the levels of photosyntheticproteins were measured in fourth leaves of Lolium temulentumgrown until full expansion at 360 µmol quanta m^–2s^–1 and subsequently at the same irradiance or shadedto 90 µmol m^–2 s^–1. Ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco), light-harvesting chlorophylla/b protein of photosystem II (LHCII), 65 kDa protein of photosystemI (PSI), cytochrome f (Cytf) and coupling factor 1 (CF₁) declinedsteadily in amount throughout senescence in unshaded leaves.In shaded leaves, however, the decrease in LHCII and the 65kDa protein was delayed until later in senescence whereas theamount of Cyt f protein decreased rapidly following transferto shade and was lower than that of unshaded leaves at the earlyand middle stages of senescence. Decreases in the Rubisco andCF₁ of shaded leaves occurred at slightly reduced rates comparedwith unshaded leaves. These results indicate that chloroplastproteins in fully-expanded leaves are controlled individually,in a direction appropriate to acclimate photosynthesis to agiven irradiance during senescence. (Received August 20, 1992; Accepted January 5, 1993)     

Analysis of the Nitrogen Response of Leaf Extension in Lolium temulentum Seedlings

Lolium temulentum seedlings were grown on a nutrient mediumcontaining NH₄NO₂ at 0, 0·1, 0·5, 1·0 and4·3 mmoll^–1 as the sole N source. Relative andabsolute extension rates, maximal leaf size, duration of extensiongrowth, rate of leaf appearance and plastochron index were determinedfrom the parameters of Richards functions fitted to lengthsof laminae measured at intervals after sowing. The final lengthof leaf I was relatively insensitive to N whereas mean relativeextension rate was increased and duration of growth decreasedwith increasing NH₄NO₂ concentration. Leaves 2 and 3 enlargedprogressively with N at concentrations up to 1·0 mmoll^–1but were unresponsive thereafter. There was no significant correlationbetween final length and mean relative extension rate for leaves1 to 3. Leaves 4 to 6 continued to show increasing length beyond1·0 mmoll^–1 N and final length was significantlycorrelated with mean relative extension rate. Increasing N increasedthe rate of leaf appearance by decreasing the duration of leafextension and plastochron. These results are discussed in relationto the control of leaf and N turnover. Lolium temulentum, rye grass, leaf extension, nitrogen, Richards function, growth analysis