Circadian rhythms and the induction of flowering in the long-day grass Lolium temulentum L.

Plants of Lolium temulentum L. strain Ceres were grown in 8-h short day (SD) for 45 d before being exposed either to a single long day (LD) or to a single 8-h SD given during an extended dark period. For LD induction, the critical photoperiod was between 12 and 14 h, and more than 16 h were needed for a maximal flowering response. During exposure to a single 24-h LD, the translocation of the floral stimulus began between the fourteenth and the sixteenth hours after the start of the light period, and was completed by the twenty-fourth hour. Full flowering was also induced by one 8-h SD beginning 4 or 28 h after the start of a 40-h dark period, i.e. by shifting 12 h forward or beyond the usual SD. The effectiveness of a so-called ‘displaced short day’ (DSD) was not affected by light quality and light intensity. With a mixture of incandescent and fluorescent lights at a total photosynthetic photon flux density of 400 μmol m⁻² s⁻¹, a 4-h light exposure beginning 4 h after the start of a 40-h dark period was sufficient to induce 100% flowering. The flower-inducing effect of a single 8-h DSD was also assessed during a 64-h dark period. Results revealed two maxima at a 20-h interval. This fluctuation in light sensitivity suggests that a circadian rhythm is involved in the control of flowering of L. temulentum.     

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.     

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     

The effect of an experimental growth retardant (WL83801) on leaf growth and development in Lolium perenne L.

The experimental growth retardant WL83801, applied as a root drench, had a rapid and persistent effect in retarding the growth and development of leaves in L. perenne. Leaves of the main shoot were greatly reduced in length, were broader, and appeared faster than in control plants. The rate of extension of individual leaves was greatly reduced in retarded plants but still followed a diurnal pattern that closely corresponded with temperature. There was evidence that leaf extension was far less responsive to temperature in treated plants. At the cellular level WL83801 had no significant effect on leaf blade cell number, thus reductions in leaf length were associated with the retardation of cell elongation. Changes in leaf structure were also observed. These changes in the pattern of leaf growth and development are discussed in relation to the primary mode of action of the growth retardant in interfering with gibberellin biosynthesis.     

Analysis of the response of leaf extension to chilling temperatures in Lolium temulentum seedlings

Lolium temulentum L. plants were grown at 20°C and transferred to 2°C or 5°C at 21, 28 or 35 days after sowing, when leaves 3, 4 and 5, respectively, were at mid-expansion and leaves 4, 5 and 6 were just emerging. Leaves of plants exposed to 2°C for 7 or 14 days before their date of emergence at 20°C failed to appear at all during the course of the experiment. Transfer to 2°C at emergence resulted in a delay of about 40 days before expansion was detected and subsequent growth was extremely slow. By contrast, although leaves of seedlings exposed to 5°C at or prior to emergence were significantly smaller and slower-growing than the same leaves of plants maintained at 20°C, the difference in vegetative development and tillering between 2°C and 5°C was much less marked than between 5°C and 2°C, implying the existence of a rather sharp threshold for growth between the latter temperatures. Leaves transferred to 2°C at mid-expansion attained a final size not very different from leaves exposed to 5°C at the same time, but expension rates were only 20–30% of those at 5°C, and the time taken to achieve full expansion a corresponding 3 to 5 times longer. These responses were quantified by fitting Richards functions to measurements of leaf extension and determining, from the parameters of the curves, asymptotic maximal lengths, mean relative and absolute extension rates, inflexion points and durations of growth. The potential usefulness of Lolium temulentum as a model species for studying the relationship between temperature and growth in the Granmineae is discussed.     

Effects of sheath tube length on leaf development in perennial ryegrass (Lolium perenne L.)

Position in and contribution of leaf laminae to the canopy of forage grasses are important both in determining herbage growth rates and intake rate by grazing animals. These canopy characteristics are controlled by the way dry matter is apportioned between sheath and lamina in growing leaves. The objective of this work was to determine how the development of individual leaves is affected by altering the effective length of the psuedostem tube, on the assumption that the light environment within the tube varied. The development of a leaf from initiation at the apex to maturity was followed by successive destructive dissections of tillers. Vertical incisions were made in the pseudostem of each tiller to three different depths. The three treatments imposed were — no incision (control), moderate and severe incision of the sheath length. Destructive harvests of tillers followed 3, 6, 12 and 24 days after imposition of treatments. Incision resulted in the length of the monitored leaf being reduced significantly at all harvests, and differentiation of the sheath beginning earlier. The length reduction reflected a reduction in both cell size and cell number and the effects were evident at the earliest harvest. The data support the theory that leaf size and timing of onset of sheath development are influenced by the environment of the developing leaf. The present results indicate that sheath tube length affects leaf development and suggests that the effects are substantially explained by a direct light effect on the location and depth of the elongation zone.     

Cloning and characterization of a salt stress-inducible small GTPase gene from the model grass species Lolium temulentum

A gene encoding a small guanosine triphosphate (GTP)-binding protein (smGTP) related to the Rab2 gene family of GTPases was identified during the analysis of a salt stress suppression subtractive hybridization (SSH) expression library from the model grass species Lolium temulentum L. (Darnel ryegrass). The smGTP gene was found to have a low-level constitutive expression and was strongly induced by salt stress in root, crown and leaf tissues. The expression pattern of the smGTP gene was compared against two additional stress genes identified in the SSH expression library, the well-characterized dehydration stress tolerance gene, delta 1-pyrroline-5-carboxylate synthetase (P5CS) encoding for a key enzyme in proline biosynthesis, and the cold response gene COR413. The genes were analyzed for their response to salinity as well as their responses to 7 different forms of abiotic stress in L. temulentum plants. The smGTP gene displayed an expression pattern similar to the P5CS gene, suggesting a role in dehydration stress. In contrast, the COR413 gene was found to be up-regulated in response to all stresses tested and has utility as a general stress marker in grass plants.