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.

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. 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.

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 Timing of Evocation and Development of Flowers in Pharbitis Nil

1969 ◽  
Vol 22 (3) ◽  
pp. 559 ◽  
Author(s):  
RW King ◽  
LT Evans
Keyword(s):  
Shoot Apex ◽  
Dark Period ◽  
Leaf Primordium ◽  
Axillary Buds ◽  
Axillary Bud ◽  
Pharbitis Nil ◽  
Main Shoot ◽  
Floral Evocation

When P. nil seedlings were exposed to a single inductive dark period, the main shoot apex and the lowest axillary bud which had not differentiated more than one leaf primordium underwent floral evocation within about 12 hr of the end of the dark period. The higher axillary buds appeared to be evoked in acropetal sequence over the following 2 days at 28�C, or 4 days at 21�C.

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.

Disruption by Temperature of Floral Evocation and Cell-Cycling in the Shoot Apical Meristem of Helipterum roseum

1990 ◽  
Vol 17 (6) ◽  
pp. 629 ◽  
Author(s):  
KV Sharman ◽  
M Sedgley ◽  
D Aspinall
Keyword(s):  
Cell Cycle ◽  
Steady State ◽  
Shoot Apex ◽  
Apical Meristem ◽  
Shoot Meristem ◽  
Cycle Duration ◽  
Floral Initiation ◽  
H 41 ◽  
Cell Cycling ◽  
Floral Evocation

Flowering is inhibited in plants of Helipterum roseum grown under constant 25°C temperature conditions with a 12 h photoperiod and irradiance of 250 W m-2, but not at a constant temperature of 20°C. Floral inhibition was investigated by transferring plants between the two temperature con- ditions at different times to determine the morphological stage of inhibition, and by investigating cell-cycling at the shoot apex at the two temperatures. Floral initiation in Helipterum roseum was inhibited if the temperature increase from 20 to 25°C occurred at the doming of the apical meristem, and was delayed when the increase occurred at the initiation of involucral bracts. Steady-state cell-cycling was observed in the shoot meristem at 20°C and the cell-cycle duration was estimated at the morphological stages of large vegetative meristem, doming of the meristem and initiation of the involucral bracts. The length of the cell-cycle at these stages was 64 h, 41 h and 47 h respectively. Steady-state cell-cycling was not observed in shoot apical meristems at 25°C, and the meristem did not undergo the floral transition. It is concluded that the stage of commitment to flower is the initiation of involucral bracts, and that floral initiation is inhibited at 25°C by the loss of steady-state cell-cycling at the shoot apex.

Regulation in Lolium temulentum of the Metabolism of Gibberellin A20 and Gibberellin A1 by 16,17-Dihydro GA5 and by the Growth Retardant, LAB 198 999

1997 ◽  
Vol 24 (3) ◽  
pp. 359 ◽  
Author(s):  
O. Junttila ◽  
R.W. King ◽  
A. Poole ◽  
G. Kretschmer ◽  
R.P. Pharis ◽  
...  
Keyword(s):  
Growth Retardation ◽  
Higher Plants ◽  
Shoot Elongation ◽  
Stem Growth ◽  
Growth Retardant ◽  
Shoot Tips ◽  
Stem Tissue ◽  
Lolium Temulentum ◽  
Gibberellin A1 ◽  
Excised Tissue

The ring D-modified gibberellin [GA], 16,17-dihydro GA5, can retard stem growth in Lolium temulentum L. while promoting flowering (Evans et al., 1994, Planta193, 107–114). Using [1,2,3-3 H]GA20 to study the final biosynthetic step to GA1 (a known effector of shoot elongation in higher plants), it was shown that C-3b-hydroxylation of GA20 to GA1 is blocked by 16,17-dihydro GA5 but is little affected by GA5. Another late-stage biosynthetic inhibitor, the acylcyclohexanedione, LAB 198 999, also blocked GA1 formation. Furthermore, endogenous levels of GA20 built up after application of 16,17-dihydro GA5. Consequently, growth retardation by 16,17-dihydro GA5 and LAB 198 999 is likely to be the result of their inhibition of GA20 3b-hydroxylation to GA1. Another fate for GA20 in Lolium is its C-2b-hydroxylation to growth-inactive GA29. This conversion was also inhibited by 16,17-dihydro GA5 but less so by LAB 198 999. The analogous step involving 2b-hydroxylation of GA1 to GA8 appeared to be insensitive to either growth retardant. When [3H]GA20 was injected into the cavity within the young intact sheathing leaves, there was an appreciable metabolism of this GA20 to GA1 and thence to GA8 (ca 10% and 30% respectively within 5 h). For excised shoot tips, however, [3H]GA20 was converted rapidly and virtually completely to GA29 in 3–5 h. Interestingly, with these excised shoot tips, GA3 and GA5 as well as 16,17-dihydro GA5 when applied via the agar strongly inhibited 2b-hydroxylation of GA20 to GA29. In contrast, while 16,17-dihydro GA5 blocked GA20 metabolism to GA29 in intact sheath/stem tissue, this conversion was not inhibited by GA5. These differences in structural specificity for GAs which inhibit 2b-hydroxylation as opposed to 3b-hydroxylation are in accordance with these two Ring-A hydroxylation steps being catalysed by different enzymes. Finally, the differences in GA20 metabolism between intact versus excised tissue raise the possibility that tissue wounding with excision enhanced the activity of the GA20 2b-hydroxylase(s).

Inhibition of Flowering in Lolium temulentum L. By Water Stress: a Role for Abscisic Acid

1977 ◽  
Vol 4 (2) ◽  
pp. 225 ◽  
Author(s):  
RW King ◽  
LT Evans
Keyword(s):  
Abscisic Acid ◽  
Water Stress ◽  
Long Day ◽  
Relative Water ◽  
The One ◽  
Floral Evocation ◽  
Leaf Photosynthetic Rate ◽  
Response To Water ◽  
Aba Content ◽  
High Intensity Light

A brief, 8-h water stress during the induction of flowering in L. temulentum reduces the flowering response, the more so the greater the stress. Water stress also affected leaf photosynthetic rate, relative water content of leaves and leaf elongation. Water stress was most inhibitory to flowering when applied during the period of high-intensity light at the beginning of the one long day. The abscisic acid (ABA) content of leaves increased up to 30-fold during the imposition of water stress and fell rapidly after stress was relieved, regardless of when the stress was imposed. The greater the stress, the higher was the level of ABA in leaves and the greater was the inhibition of flowering. The ABA content of apices also rose in response to water stress, in some cases during the stress treatment but usually 8-22 h later. Flowering was inhibited when apical ABA contents were high at the end of the long day. Although water stress may influence the flowering of plants in several ways, these experiments suggest that water stress during the long day induction of L. temulentum inhibits flowering by raising the content of ABA at the shoot apex during floral evocation.

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