scholarly journals Inflorescence Initiation in Lolium Temulentum L. XII. an Autoradiographic Study of Evocation in the Shoot Apex

1968 ◽  
Vol 21 (6) ◽  
pp. 1083 ◽  
Author(s):  
RB Knox ◽  
LT Evans
Keyword(s):  
Shoot Apex ◽  
Autoradiographic Study ◽  
Lolium Temulentum ◽  
Long Day

Previous work has shown a rise in the incorporation of precursors of RNA and protein by the shoot apex of L. temulentum early on the day following exposure to 1 long day, which induces flowering.

The Acceleration of Primordium Initiation as a Component of Floral Evocation in Lolium temulentum L

1996 ◽  
Vol 23 (5) ◽  
pp. 569 ◽  
Author(s):  
LT Evans ◽  
C Blundell
Keyword(s):  
Shoot Apex ◽  
Floral Development ◽  
Growth Retardant ◽  
Leaf Primordium ◽  
Essential Component ◽  
Lolium Temulentum ◽  
Long Day ◽  
External Sign ◽  
Floral Evocation

An acceleration of leaf primordium initiation by the shoot apex frequently follows floral evocation, but after varying intervals. The purpose of the experiments reported here was to define more closely the relation between this reduction of the plastochron and floral evocation, using the long day (LD) plant Lolium temulentum grown under closely controlled conditions.The acceleration begins at floral evocation, on the day after the first LD exposure, and increases after exposure to additional LDs. However, plants too young to be florally evoked by one LD nevertheless manifested an acceleration of primordium initiation, so the acceleration alone is not sufficient for evocation. Single applications of highly florigenic gibberellins (GAs), such as GA5, also accelerate the initiation of primordia and floral development, more so than does the weakly florigenic GA1. By contrast, single applications of the growth retardant Trinexapac-ethyl (CGA 163'935) to plants given one LD largely prevented the acceleration of primordium initiation but without inhibiting floral development. Thus, although the acceleration of primordium initiation by LD or by GA application is the first external sign of floral evocation in L. temulentum, it is neither a sufficient nor an essential component of it.

scholarly journals Inflorescence Initiation in Lolium Temulentum L. X. Changes in 32p Incorporation into Nucleic Acids of the Shoot Apex at Induction

1967 ◽  
Vol 20 (1) ◽  
pp. 13 ◽  
Author(s):  
AHGC Rijven ◽  
LT Evans
Keyword(s):  
Nucleic Acids ◽  
Shoot Apex ◽  
Floral Induction ◽  
Transient Increase ◽  
Lolium Temulentum ◽  
Long Day ◽  
32P Incorporation ◽  
Summit Region

Previous studies have shown an increase in RNA at the shoot apex of L. temulentum following floral induction, detectable chemically 2 days after induction, and by histochemical means after 1 day. Here, a transient increase in the incorporation of 32P, applied to leaves, into nucleic acids at the apex is shown to occur at about the time when the long-day stimulus is estimated to reach the shoot apex. The increased 32p incorporation due to the long-day exposure occurs throughout the apex, and is not confined to the summit region. Most of the 32p was incorporated into RNA.

Early increased expression of a cyclin-dependant protein kinase (LtCDKA1;1) during inflorescence initiation of the long day grass Lolium temulentum

2013 ◽  
Vol 40 (10) ◽  
pp. 986 ◽  
Author(s):  
Greg F. W. Gocal ◽  
Rod W. King
Keyword(s):  
Cell Division ◽  
Shoot Apex ◽  
Target Cells ◽  
Serine Threonine Kinase ◽  
Lolium Temulentum ◽  
Apical Dome ◽  
Long Day ◽  
Vegetative Shoot Apex ◽  
Weak Expression

Knowing where and when different genes express at the shoot apex during the transition to flowering will help in understanding this developmental switch. The CDKA family of serine/threonine kinase genes are appropriate candidates for such developmental switching as they are involved in the regulation of the G1/S and G2/M boundaries of the cell cycle (see review by Dudits et al. 2007) and so could regulate increases of cell division associated with flowering. Furthermore, in rice stems the gibberellin (GA) class of plant growth regulators rapidly upregulate CDKA expression and cell division. Thus, CDKA expression might be linked to the florigenic action of GA as a photoperiodically-generated, signal. For the grass Lolium temulentum L., we have isolated an LtCDKA1;1 gene, which is upregulated in shoot apices collected soon after the start of a single florally inductive long day (LD). In contrast to weak expression of LtCDKA1;1 in the vegetative shoot apex, in situ and PCR-based mRNA assays and immunological studies of its protein show very rapid increases in the apical dome at the time that florigenic signals arrive at the apex (<6 h after the end of the LD). By ~54 h LtCDKA1;1 mRNA is localised to the floral target cells, the spikelet primordia. Later both LtCDKA1;1 mRNA and protein are most evident in floret meristems. Only ~10% of cells within the apical dome are dividing at any time but the LD increase in LtCDKA1;1 may reflect an early transient increase in the mitotic index (Jacqmard et al. 1993) as well as a later increase when spikelet primordia form. Increased expression of an AP1-like gene (LtMADS2) follows that of LtCDKA1;1. Overall, LtCDKA1;1 is a useful marker of both early florigenic signalling and of later morphological/developmental aspects of the floral transition.

Shoot Apex Sugars in Relation to Long-Day Induction of Flowering in Lolium temulentum L

1991 ◽  
Vol 18 (2) ◽  
pp. 121 ◽  
Author(s):  
RW King ◽  
LT Evans
Keyword(s):  
Flux Density ◽  
Shoot Apex ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Sucrose Content ◽  
Inflorescence Development ◽  
Lolium Temulentum ◽  
Long Day ◽  
Floral Evocation

Inflorescence initiation in Lolium temulentum is induced by a single long day with a photoperiod extension of 16 h under low photon flux density (12 μmol PAR m-2 s-1) from incandescent lamps. Under these conditions the content of sucrose, the predominant free sugar in the shoot apex, fluctuates diurnally in the same way as in short day apices. There was no evidence of a greater apical sucrose content at any time during the long day or in the following period of high irradiance when floral evocation occurs. Thereafter, however, the diurnal fluctuation in apical sucrose content became more pronounced. Increasing the sugar supply to the apex by raising the photon flux density during the daily light period did not lead to flowering of non-induced plants; nor did the high contents of apical sugars reached in apices cultured in vitro on 5% sucrose medium. By contrast, when apices were excised after receipt of the floral stimulus from long day leaves, increase in the sugar content enhanced inflorescence development in vitro, this response being most pronounced after the inflorescences were initiated. Thus, floral evocation in L. temulentum does not require an increase in the content of sucrose at the apex although inflorescence development is highly responsive to it. When photoperiodic extensions with incandescent or fluorescent lamps were compared for their effects on apical sugars and flowering response, there was no interaction between light quality and photon flux density. Thus the shoot apex response to the low irradiance, photoperiodic time-measurement processes of leaves is distinct from the apical response to sugar supply. In Lolium temulentum floral evocation is controlled by the photoperiodic processes, the response to which is amplified by high sugar supplies but not replaced as it is in Sinapis alba.

scholarly journals Inflorescence Initiation in Lolium Temulentum L. IV. Translocation of the Floral Stthiulus in Relation to that of Assimilates

1964 ◽  
Vol 17 (1) ◽  
pp. 1 ◽  
Author(s):  
LT Evans ◽  
IFW ardlaw
Keyword(s):  
Shoot Apex ◽  
Small Proportion ◽  
Inhibitory Effect ◽  
Lolium Temulentum ◽  
Long Day ◽  
Short Days

Translocation of labelled assimilates to the shoot apex and other parts of the plant was followed from an upper leaf held in long-day conditions, when lower leaves in short days were either present or removed. Similarly a comparison was made of the distribution of assimilates from an upper long-day leaf and a lower leaf held in short days. The presence of lower leaves did not reduce the movement of assimilates from the upper leaf to the shoot apex, and the lower leaf supplied only a small proportion of the assimilates reaching the shoot apex, although it supplied much to the roots. It is concluded that the previously established inhibitory effect of lower leaves in short days on inflorescence initiation in L. temulentum is unlikely to be due to their interference with translocation of the long-day stimulus to the shoot apex, or to their diluting it with assimilates, but rather to their production of a transmissible inhibitor of initiation.

Abscisic Acid and Xanthoxin Contents in the Long-Day Plant Lolium temulentum L. In Relation to Daylength

1977 ◽  
Vol 4 (2) ◽  
pp. 217 ◽  
Author(s):  
RW King ◽  
LT Evans ◽  
RD Firn
Keyword(s):  
Abscisic Acid ◽  
Liquid Chromatography ◽  
Shoot Apex ◽  
Gas Liquid Chromatography ◽  
Consistent Effect ◽  
Lolium Temulentum ◽  
Long Day ◽  
Inductive Photoperiod ◽  
Endogenous Aba

In L. temulentum L., flowering can be inhibited by application of abscisic acid (ABA) close to the shoot apex towards the end of an exposure to a single inductive long day. However, analysis by gas-liquid chromatography showed that the contents of endogenous ABA and xanthoxin in L. temulentum leaves are not consistently changed after an inductive photoperiod. Apex extractions carried out when (�)-ABA application near the apex is most inhibitory to flowering also showed no consistent effect of daylength on the content of ABA which was, however, much higher than in leaves. Thus it is unlikely that induction of flowering in L. temulentum by exposure to long days is due to changes in the endogenous levels of ABA and xanthoxin in the leaves or of ABA in the shoot apex.

scholarly journals Inflorescence Initiation in Lolium Temulentum l. II. Evidence for Inhibitory and Promotive Photoperiodic Processes Involving Transmissible Products

1960 ◽  
Vol 13 (4) ◽  
pp. 429 ◽  
Author(s):  
LT Evans
Keyword(s):  
Leaf Blade ◽  
Light Period ◽  
Continuous Illumination ◽  
Rate Of Development ◽  
Lolium Temulentum ◽  
Short Day ◽  
Long Day ◽  
Inductive Treatment ◽  
Short Days

Plants of Lolium temulentum, raised in short days, were given an inductive treatment by exposure of one leaf blade to a 32-hr period of continuous illumination. Then either the leaf exposed to this one long light period or varying areas of lower leaves which were simultaneously in short-day conditions were removed at intervals after the long-day exposure. The longer the long-day leaves remained on the plants, the greater was the proportion of plants which initiated inflorescences and the greater the rate of development of their inflorescences. This was so even when short-day leaves were present above the long-day ones. The longer the short-day leaves remained, and the greater their area, the lower was the proportion of plants which initiated inflorescences.

scholarly journals Gibberellins and flowering in long day plants, with special reference to Lolium temulentum

1999 ◽  
Vol 26 (1) ◽  
pp. 1 ◽  
Author(s):  
L. T. Evans
Keyword(s):  
Environmental Control ◽  
Control Points ◽  
Subsequent Work ◽  
Feedback Effects ◽  
Factors Affecting ◽  
Lolium Temulentum ◽  
Long Day ◽  
Precise Role ◽  
Flowering Process

The relation between gibberellins (GAs) and flowering in some long day (LD) plants is reviewed, with particular emphasis on Lolium temulentum. Lang’s early experiments with rosette plants established the effectiveness of several GAs in replacing the need for LD. Subsequent work with mutants, especially of Arabidopsis, has clarified genetic and environmental control points in GA synthesis, various feedback effects and some of the factors affecting responsiveness to, as well as synthesis of, GAs in the flowering process. Further complexities are revealed in the experiments with Lolium temulentum, which have clearly shown that the structural requirements for effectiveness of GAs in the flowering process are quite different from those for elongation growth. The precise role of GAs in the long day induction of flowering remains unclear.

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