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     

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)     

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     

Changes in the Molecular-size Distribution of Carbohydrates during Ripening in Attached and Detached Seeds of Lolium temulentum L.

Seed samples of Lolium temulentum L. were harvested at variousstages of maturity and subjected to successive cold- and hot-waterextractions. These extracts were then fractionated by gel-filtrationand the changes in the carbohydrate elution pattern with increasingseed maturity were characterized. Extracts of seeds from earlyharvests contained only free sugars, but the mean chain-lengthincreased with maturity. The hot-water fraction contained nosalient features until 17 days after anthesis but, after thispoint, a completely excluded, high-molecular-weight polysaccharideaccumulated. Infiltration studies using ^I4C-sucrose and detached seeds showedthat sugar was readily incorporated into polysaccharide, butthat the degree of uptake was directly proportional to the developmentalstage of the seed at the time of detachment. Hydrolysis dataon the various components are given and the results are discussedin terms of their practical significance.     

The typification of Lolium perenne L. and Loliutn temulentum L. (Poaceae)

LOOS, B. P. & JARVIS, C. E., 1992. The typification of Lolium perenne and Lolium temulentum (Poaceae). The typification of the Linnaean species Lolium perenne and Lolium temulentum has been studied. Lolium perenne is typified by material in LINN, as proposed by Terrell, but it has been necessary to select a lectotype for L. temulentum , and material in the Burser herbarium (UPS) has been chosen for this purpose. The study shows that although Linnaeus used awns as a diagnostic character to distinguish the two species, he was aware of the intraspecific variability in this character.     

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     

Changes in gene expression in the leaf of Lolium temulentum L. Ceres during the photoperiodic induction of flowering

Unifoliated plants of Lolium temulentum L. Ceres were induced to flower by a unique 24-h long day (LD) consisting of the extension of the regular 8-h short day (SD) (400 mol photons·m^–2·s^–1, fluorescence + incandescence) with incandescence at 10–15 mol photonsm ^–2·s^–1. The polyadenylated-RNA complement of leaf blade tissues was analysed at 4-h intervals during the photoperiod extension in LD vs. SD, by using two-dimensional polyacrylamide gel electrophoresis to resolve in-vitro-translated products. Of the 991 spots that were analysed, none appeared or disappeared during the inductive cycle, i.e. no qualitative effect of floral induction was detected, at any time. Sixty-eight spots were found whose intensity was influenced by lengthening of the photoperiod; 50 of them, i.e. ca. 5% of the population analysed, were affected before the end of the extension period and were thus potentially related to floral induction. Many of these RNAs were not quantitatively constant during a 24-h cycle in SD. Seven of them oscillated according to the light-on and the light-off signals, among which three seemed to be controlled by phytochrome since their relative amount increased under the standard light conditions but decreased under incandescence even faster than in darkness. The large majority of other RNAs varied with a timing that was not clearly driven by the alternation of light and darkness, indicating that genes related to the biological clock may be especially sensitive to the lengthening of the photoperiod. Furthermore, seven spots were observed that underwent a phase-shift in LD, which consisted, for six of them, of a phase advance of 4–8 h. The steady-state level of CAB mRNA was analysed because the CAB gene family (encoding the chlorophyll a/b-binding proteins of the light-harvesting complexes) is known to be controlled both by the biological clock and phytochrome. In SD, the level was high in the light and low in darkness; the fluctuation was conducted by a circadian rhythm. When plants were exposed to the inductive LD, the peak of mRNA accumulation that was expected according to the endogenous rhythmicity was abolished, possibly because of the change in light quality during the LD extension.Abbreviations CAB chlorophyll a/b-binding proteins of the light-harvesting complexes - 2D two-dimensional - LD(s) longday(s) - LDP(s) long day plant(s) - SD(s) short day(s) - SDP(s) short day plant(s) This work was supported by the University of Liège through the Action de Recherche Concertée (# 88/93-129). Some analyses were performed with the collaboration of Dr. H. Ougham, Institute of Grassland and Environmental Research, Aberystwyth, UK. The authors also want to thank Dr. F. Cremer (Max Planck Institute for Plant Breeding, Köln, Germany) for critical discussion of the results.     

The distribution of acid invertase in developing leaves of Lolium temulentum L.

The levels of invertase (E.C. 3.2.1.26) activity were measured throughout the development of the fourth leaf of Lolium temulentum. No neutral invertase activity was detected. Soluble acid invertase activity fell during leaf extension but rose again after ligule formation. This rise continued into senescence and was accompanied by the appearance of activity in the insoluble fraction. Evidence is presented that the insoluble activity was not an artefact of preparation, and that it represented an extracellular acid invertase. Fractionation of soluble invertase by gel filtration showed the appearance of a high molecular weight form at the time when insoluble activity was rising. The relationships between the different forms of the enzyme are discussed, together with their roles in leaf development.     

Synaptonemal complex formation in hybrids of Lolium temulentum x Lolium perenne (L.)

Comparisons were made between two kinds of tetraploids derived from the hybrid Lolium temulentum x L. perenne. One hybrid behaves like an autotetraploid with multivalents at first metaphase of meiosis in pollen mother cells. The other behaves like an allotetraploid, in which pairing at first metaphase is restricted to bivalents comprised of strictly homologous chromosomes. The diploidisation of the latter form is controlled by determinants located on both the normal, A chromosomes and on supernumary B chromosomes. Reconstruction of synaptonemal complexes and their elements, from serial sections through pollen mother cell nuclei examined under the electron microscope, reveals that at zygotene pairing in both forms results in multivalent formation involving non-homologous as well as homologous chromosomes. The mechanism responsible for the diploidisation is, therefore, not based on a restriction of pairing at early meiosis to homologous chromosomes but on a correction or transformation of the multivalent chromosome associations to bivalents subsequent to zygotene. The transformation is not completed until late pachytene. In the multivalent-forming tetraploid a maximum of four chromosomes are associated at first metaphase. Yet configurations of a higher valency are found at zygotene. There is, therefore, a partial transformation of multivalents even in this autotetraploid form which restricts configurations at metaphase I to homologous and homoeologous chromosomes only. In both hybrids some homologous bivalents are not the product of resolution of multivalents but result from two-by-two pairing from the beginning of zygotene.