Annals of Botany 86: 1169±1174, 2000
doi:10.1006/anbo.2000.1289, available online at http://www.idealibrary.com on
Flower Opening in Asiatic Lily is a Rapid Process Controlled by Dark-light Cycling
RO D E R I C K B I E L E S K I {, J O H N E L G A R{, JU L I A N H E Y E S * { and A L L A N WO O L F {
{The Horticulture and Food Research Institute of New Zealand Ltd., Private Bag 92 169, Auckland, New Zealand and
{New Zealand Institute for Crop and Food Research Ltd., Private Bag 11 600, Palmerston North, New Zealand
Received: 8 October 1999 Returned for revision: 22 December 1999 Accepted: 1 September 2000
In commerce, Asiatic lilies are picked in bud, each stem holding several buds. We found ¯ower opening was rapid,
taking less than 4 h both on the stem and for excised buds. Opening was also strongly synchronous. For a 12 h daynight cycle, opening began late in the dark period, reaching a mid-point after 11 h of darkness. This was equally true of
buds that were excised when nearly ready to open, and those with 3±4 d of development to complete. Reversing day
and night reversed the time of opening, and red light was as e€ective as white light in providing `day' conditions. A
15 min light break during the night did not a€ect the opening. Lengthening the night (8, 12, 16 h) and shortening the
day delayed opening from 9, to 11, to 13 h after the start of darkness, respectively. In continuous light and continuous
dark, synchronicity was lost. If opening ¯owers were held in extended darkness, two phases of opening could be
discriminated. In a `dark phase', petals opened to approx. 408, and anthers remained intact. When such ¯owers were
returned to light, there was a `light phase', where petals opened further, became more pigmented and began to recurve,
and the anthers dehisced, these events taking only 2±3 h. The net result was that ¯owers became fully open and anthers
# 2000 Annals of Botany Company
dehisced approx. 2 h after dawn, regardless of daylength.
Key words: Asiatic lily, Lilium hybrid, ¯ower opening, timing, endogenous rhythm, synchronicity.
I N T RO D U C T I O N
In earlier studies (Bieleski and Reid, 1992; Bieleski, 1993),
we explored how ephemeral daylily ¯owers open, concluding that the process was under tight physiological and
biochemical control. We have now studied the related
Asiatic lily (Lilium hybrid) ¯ower which has a much longer
¯ower life (approx. 10 d vs. 1 d). This long vase life has
allowed Asiatic lily to become an important component of
the cut-¯ower trade, being ranked fourth as a ¯ower crop in
the Netherlands (Vonk Noordegraa€, 1998). Despite such
popularity, little is known about its ¯ower physiology in
comparison with other major ¯ower crops. In a study on its
postharvest handling, we found an apparent insensitivity to
ethylene that may contribute to the good vase life (Elgar
et al., 1999). In the study, we observed that lily ¯owers open
as rapidly as those of daylily despite their very di€erent
¯ower lives.
Rapid ¯ower opening is familiar to gardeners as a cyclic
process (nyctinasty) wherein ¯owers of Compositae and
Crassulaceae species open synchronously shortly after dawn
then close again with dusk (Ewusie and Quaye, 1977).
However, other than limited study of Cestrum, where
opening occupies 4±7 h (Overland, 1960) and Oenothera
(cited in Sweeney, 1979), research on rapid nyctinastic ¯ower
movement appears con®ned to Kalanchoe blossfeldiana
(BuÈnning and Zimmer, 1962; Zimmer, 1962; Engelmann
et al., 1973), where opening takes 5±6 h.
Study of non-cyclic rapid and synchronous ¯ower opening, occurring at a speed comparable to nyctinastic opening
of Cestrum and Kalanchoe, is largely con®ned to behaviour
of four ephemeral ¯owers. Morning glory (Ipomoea
For correspondence. E-mail [email protected]
0305-7364/00/121169+06 $35.00/00
purpurea) ¯owers open between 0400 and 0800 h and
begin to senesce 8 h later (Kende and Hanson, 1976), as
do ¯owers of the closely-related Japanese morning glory,
Pharbitis nil (Kaihara and Takimoto, 1979, 1980). Hibiscus
(Hibiscus rosa-sinensis) ¯owers open between 0400 and
0800 h, and begin senescing 12 h later (Woodson et al.,
1985). Daylily (Hemerocallis hybrid) ¯owers open between
0000 and 0600 h and begin senescing 12 h later (Bieleski and
Reid, 1992). Only with Pharbitis nil has there been a speci®c
study on the speed of opening, and the basis of its timing.
There has been a general acceptance that opening will be
rapid in a ¯ower that will subsequently senesce rapidly, and
that the timing will be set by the requirement for opening,
pollination, and onset of senescence to be completed within
a 24 h period.
There is little information on the speed and nature of
opening processes for long-lived ¯owers of the kind used in
the cut ¯ower industry (Reid and Evans, 1986). Most study
has been on roses, where the full opening process takes in
the order of 7 d (van Doorn et al., 1991), although there is a
faster rhythmic `stepping' within the overall process, related
to the diurnal cycle (Evans and Reid, 1988). Given such
paucity of information on control of ¯ower opening, we
decided to study the process in Asiatic lily more closely. We
report phenomena that have practical implications and that
add knowledge about the action of light on plant processes.
M AT E R I A L S A N D M E T H O D S
Plant material
In commercial ¯oriculture, Asiatic lily stems are picked with
®ve±12 ¯owers still in bud, with the most mature buds 2±4 d
away from opening. We obtained our material directly from
# 2000 Annals of Botany Company
1170
Bieleski et al.ÐControl of Flower Opening in Asiatic Lily
commercial growers, using cultivars `Cordelia', `Mona',
`Elite' and `Montrose'. Most work was carried out using
`Cordelia', and the only observed di€erences in behaviour of
di€erent cultivars related to small shifts in the exact time of
opening. We did not use material harvested during midsummer (December±January) or midwinter (July±August).
Plant material from the remaining 8 months and from all
growers was consistent in behaviour. After commercial
picking and packing, stems were transported directly to the
laboratory, and received within 24 h of picking. On arrival
the stems were unpacked, leaves were removed from the
bottom 12±15 cm, and the recut bases were placed in water
in a vase life room (208C, 12 h day, 25 mmol m ÿ2 s ÿ1 cool
white ¯uorescent light at ¯ower level) until required.
approx. 358 angle (11 cm diameter). In stage 4, tepals made
an approx. 408 angle at the base, but were recurved through
another approx. 408 giving the ¯ower a ¯at appearance
(approx. 16 cm diameter), while the fully-developed anthers
were usually intact. In stage 5, tepals made an approx. 458
angle and were further recurved through 70±1008 (approx.
15 cm diameter), while the anthers were fully dehisced (see
Bieleski et al., 2000 for further details). Flowers were
recorded as open when they reached stage 4. Opening is
described in two ways. The duration (speed) of opening is
the number of hours required for the ¯ower to pass from
stage 1 to stage 4. The clock time of opening is the time
when the ¯ower reaches the midpoint between stage 1 and
stage 4. The experimental day normally started at 0700 h.
Time-lapse photography
Preparation of light ®lters
Stems of `Cordelia' were set up in a vase life room (12 h
day-night cycle at 208C), and photographed every 3 h with
an automatic time-lapse camera. During the recording
period of 4 d, ®ve ¯owers on four stems opened. Measurements of the maximum bud and ¯ower diameter were made
on the photographic images, and corrected to scale.
Additionally, stems were taken through two (`Cordelia')
or three (`Mona') day-night cycles under vase room conditions, to a point where the oldest and largest buds (based
on length and texture) were expected to open within the
next 1±2 d. Buds with pedicels attached were excised,
graded for size, and supported in 40 ml plastic centrifuge
tubes containing water. Tubes were placed in racks in front
of a ®xed camera, and photographed manually every 3 h
over 36 h (`Cordelia') or 72 h (`Mona'). Bud and ¯ower
diameters were measured as before.
Most experiments were done with wide spectrum,
photosynthetically-active `white' light. For experiments on
light quality, the treatment area needed was too great to
permit use of interference ®lters or LEDs so 25 35 cm
®lters were constructed using dyed cellophane sheets. The
`red' ®lter transmitted 51 % of incident light between
300 and 580 nm and approx. 60 % between 620 and
800 nm. The `far-red' ®lter transmitted 51.5 % of incident
light between 300 and 680 nm and approx. 60 % between
710 and 800 nm. The (600±700 nm)/(700±800 nm) ratios of
light passed by the red and far-red ®lters were approx. 0.65
and 0.055, respectively.
General protocol used in studying in¯uence of light on timing
of opening
Stems were preconditioned and buds were excised as
above. The buds were graded in order of overall development, then progressively allocated to the treatments, giving
matched sets each containing a range of bud maturities.
Experiments were carried out in a cellar lacking natural
lighting and held at 19±228C. `Day' illumination was from a
400 W mercury-vapour lamp plus a 100 W tungsten lamp,
at approx. 65 cm, such that white light intensity at ¯ower
height was 70 mmol m ÿ2 s ÿ1 (Licor, Lincoln, New England)
or 75 W m ÿ2 ( pyranometer). For red light experiments, a
250 W re¯ector tungsten lamp was substituted for the
mercury-vapour lamp, giving 25 mmol m ÿ2 s ÿ1 (Licor) or
102 W m ÿ2 ( pyranometer). `Night' treatments were carried
out by transferring the appropriate racks to adjacent lighttight 22 l containers, large enough to avoid a signi®cant
increase in CO2 concentration. For the following `day'
treatment, racks were cycled back to the light.
Changes in the bud associated with opening were
recorded on a ®ve-point system. In stage 1, sepals were
beginning to separate (cracking bud, 2±2.5 cm diameter).
In stage 2, the petals were partly separated, making an
approx. 208 angle with the axis (3.5±4 cm diameter). In
stage 3, all tepals were fully separated, straight, making an
In¯uence of day-night cycling and light quality on timing and
duration of bud opening
Six experiments were conducted, the ®rst ®ve with
`Cordelia', as follows. Except where stated there were
21 buds per treatment and the control set was kept in a
normal 12 h day-night cycle (0700±1900 h day). The
following treatments were imposed: (1) control vs.
`reversed-day' (kept in a reversed day-night cycle, 1900±
0700 h day); (2) control vs. `dark-break' (dark period interrupted halfway by 15 min of light) or `red light' (reversed
day-night cycle using red light); (3) control vs. `short-day'
(8 h day, 16 h night cycle) or `long-day' (16 h day, 8 h night
cycle); (4) control vs. `continuous-dark' (kept in a 24 h dark
cycle) or `continuous-light' (kept in a 24 h light cycle); (5)
`red/red' (a cycle of 16 h red light±8 h dark) vs. `red/far-red'
(a cycle of 8 h red light±8 h far-red light±8 dark) or `farred/red' (a cycle of 8 h far-red light±8 h red light±8 h dark);
and (6) three control sets of `Cordelia', `Elite' and
`Montrose' buds were kept in a normal 12 h day-night
cycle, while the fourth, ®fth and sixth (reversed) sets were of
the same cultivars held in a reversed day (1900±0700 h).
There were 14 buds per set.
R E S U LT S
Time-lapse photography
Measurements on photographic images of ¯owering
`Cordelia' stems and excised buds of `Cordelia' and
`Mona' showed that the full process of bud opening was
70
160
60
140
50
Diameter (mm)
Diameter (mm)
Bieleski et al.ÐControl of Flower Opening in Asiatic Lily
40
30
20
A
120
100
80
60
40
10
20
0
24
48
72
Time (h)
96
0
120
F I G . 1. Change with time in the maximum diameter of Asiatic lily
¯ower buds `Cordelia' on ¯owering stems during ¯ower opening. d and
m, Behaviour of two buds on two stems in the ®rst run. s, n and h,
Behaviour of three buds on two stems in the second run. Horizontal
bars denote the dark periods, and show that opening was 50 %
complete approx. 9 h after the start of the dark period.
always completed in less than 6 h and in general took only
2±3 h. All buds opened at the same time of day in each
experiment, passing through stage 3 and reaching maximum diameter 9 h after the start of the dark period (Fig. 1,
attached buds) and approx. 10±11 h after the start of the
dark period (Fig. 2A, detached `Cordelia' buds and Fig. 2B,
`Mona' buds), regardless of whether opening took place on
the ®rst, second or third day. Thus, detached buds showed
the same behaviour as buds on the harvested ¯ower stem.
E€ect of reversing day and night
Opening was rapid (44 h) and synchronous within both
control and `reversed day' treatments (Fig. 3A). When data
were expressed by plotting the midpoint of opening against
time of day, control buds all opened between 0500 and
0900 h and `reversed-day' buds opened between 1700 and
2100 h (Fig. 3B), regardless of whether opening occurred on
the ®rst, second, third or fourth day after excision. Hence
the midpoint of opening was approx. 10±11 h after the start
of the dark period in each treatment.
E€ect of red light and a night break on opening of isolated
buds
Neither the night break nor red light had any e€ect on
the speed of opening, and opening was both rapid (44 h)
and synchronous (Fig. 4A). Imposing a night break had no
e€ect on the time of day when opening occurred (Fig. 4B).
Reversing the day with red light resulted in a complete
reversal of the opening time so that it occurred between
1700 and 2100 h (Fig. 4B), again 10±11 h after the start of
the dark period. That is, red light was as e€ective as white
light (Fig. 3B) in setting the day-night cycle.
E€ect of short and long days on opening of isolated buds
Opening was both rapid (44 h) and synchronous across
all treatments. Long day buds all opened approx. 9 h after
onset of darkness and mostly during the following light
0
160
12
24
36
Time (h)
48
60
72
B
140
Diameter (mm)
0
1171
120
100
80
60
40
20
0
0
12
24
36
60
48
Time (h)
72
84
96
F I G . 2. Change with time in the maximum diameter of excised Asiatic
lily ¯ower buds during ¯ower opening. Black horizontal bars denote
the dark periods. A, `Cordelia' cultivar, The eight separate curves
indicate the course of events in eight separate buds. B, `Mona' cultivar:
d, Values for the single bud which opened on day 1; m, mean values
(‡s.d., vertical bars) for 11 buds which opened on day 2; j, mean
values (ÿs.d.) of the four buds which opened on day 3.
period (Fig. 5). Short day buds opened approx. 13 h after
the start of the night period, well before the start of the
following day. They did not open past stage 4 but remained
in that state until returned to the light. If such short-day
stage 4 ¯owers were held in darkness for a further 12±24 h
after the start of the normal experimental day, they still
remained at stage 4, and did not develop the orange
`eyespot' characteristic of fully-open yellow `Cordelia'
¯owers. However, once such ¯owers were returned to the
light, three processes occurred within the next 2 h: the ¯ower
®nished opening to stage 5; the anthers completed dehiscence; and the eyespot developed to its normal intensity. If
petals were excised from short-day stage 4 ¯owers at the end
of the dark period and ¯oated on water in Petri dishes
(+light), only petals in the light developed orange eyespots
(data not shown).
E€ect of continuous dark and continuous light on opening of
isolated buds
The speed of opening was markedly reduced by continuous day and continuous night conditions (Fig. 6A). All
20
18
16
14
12
10
8
6
4
2
0
Bieleski et al.ÐControl of Flower Opening in Asiatic Lily
A
Control
25
Reverse Day
Number of buds
Number of buds
1172
2–4
4–6
6–8
8–10
10–12
5
12–14
Normal Day
0–2
2–4
Number of buds
0100– 0300– 0500–
0300h 0500h 0700h
0700– 0900– 1100–
0900h 1100h 1300h
1300– 1500– 1700– 1900– 2100– 2300–
1500h 1700h 1900h 2100h 2300h 0100h
18
16
14
12
10
8
6
4
2
0
B
Interaction of red and far-red light on opening of isolated
buds
Opening was both rapid (44 h) and synchronous in all
three treatments. The red/red buds all opened with a
midpoint at approx. 9 h after the start of the night period,
as previously found in a long-day treatment with white
light. Red/far-red and far-red/red treatments gave results
identical to the red/red controls (Fig. 7). Thus far-red light
was as e€ective as white light in setting the day-night cycle
(cf. Fig. 5), and no red/far-red interaction could be detected
within equipment limits.
Comparative e€ects of day-night cycling on bud opening in
three Asiatic lily cultivars
In all three cultivars, normal opening was completed
within approx. 4 h (data not shown). In all three cultivars,
8–10
10–12
12–14
0100– 0300– 0500–
0300h 0500h 0700h
Night break
0700– 0900– 1100–
0900h 1100h 1300h
Red-reversed
1300– 1500– 1700– 1900– 2100– 2300–
1500h 1700h 1900h 2100h 2300h 0100h
Time of day
F I G . 4. Duration (A) and clock time (B) of opening of excised Asiatic
lily ¯ower buds, `Cordelia', held under a normal day-night cycle, a daynight cycle broken by an interval of light midway through the night
cycle, and a day-night cycle reversed with red light. x-axes as in Fig. 3.
Black horizontal bars show dark periods for normal day.
20
Number of buds
buds in continuous light and continuous dark opened
eventually, but much of the normal synchronicity was lost
(Fig. 6B). It was observed that the most-developed buds that
opened in the ®rst 1±2 d did so near their `normal' time,
between 0300 and 0900 h. That is, there was a degree of
memory in the system, but buds opening 3±4 d after excision
had lost nearly all of their synchronicity.
6–8
Normal day
Time of day
F I G . 3. Opening of excised Asiatic lily ¯ower buds, `Cordelia', held
under a normal day-night cycle and under a reversed day-night cycle.
A, Duration (speed) of opening, where the number of buds which
completed opening is shown in 2-h categories. B, Clock time of
opening where the number of ¯owers reaching their midpoint in
opening is shown for each successive 2-h time period. Black horizontal
bars show dark periods for normal day.
4–6
Duration of opening (h)
Reversed Day
Number of buds
B
Red-reversed
10
Duration of opening (h)
20
18
16
14
12
10
8
6
4
2
0
Night break
15
0
0–2
Normal day
A
20
Normal day
SD
ND
LD
Short day Long day
15
10
5
0
0100– 0300– 0500–
0300h 0500h 0700h
0700– 0900– 1100–
0900h 1100h 1300h
1300– 1500– 1700– 1900– 2100– 2300–
1500h 1700h 1900h 2100h 2300h 0100h
Time of day
F I G . 5. Clock time of opening of excised Asiatic lily ¯ower buds
`Cordelia', held under a normal day-night cycle, a short day-long night
cycle, and a long day-short night cycle. x-axis as in Fig. 3B. Horizontal
bars show dark periods; arrows indicate the onset of night for shortday (SD), normal day (ND) and long-day (LD), respectively.
synchronous opening occurred at a ®xed time of day. In all,
reversing the day-night cycle with red light gave a complete
reversal of opening behaviour: that is, opening occurred
after the same length of darkness rather than at the same
clock time (Fig. 8). Day reversal with white light gave the
same e€ect (data not shown). There were small but
signi®cant cultivar di€erences in the peak time of opening:
approx. 12 h after the start of the dark period for `Cordelia',
14.5 h for `Elite', and 12.5 h for `Montrose' (Fig. 8).
20
18
16
14
12
10
8
6
4
2
0
A
24-hour day
Normal day
12
10
10–12
12–14
B
14
Number of buds
0
0300–
0500h
16
Normal day
24-hour day
24-hour night
12
Time of day
10
8
M (rev)
E (rev)
C (rev)
M
E
C
F I G . 8. Clock time of opening of excised buds from three cultivars (C,
`Cordelia'; E, `Elite'; and M, `Montrose') of Asiatic lily, held under
either a normal day-night cycle or under a dark-light cycle reversed
with red light (`rev'). x-axis as in Fig. 3B.
6
4
2
0100– 0300– 0500–
0300h 0500h 0700h
0700– 0900– 1100–
0900h 1100h 1300h
1300– 1500– 1700– 1900– 2100– 2300–
1500h 1700h 1900h 2100h 2300h 0100h
Time of day
F I G . 6. Duration (A) and clock time (B) of opening of excised Asiatic
lily ¯ower buds `Cordelia' held under a normal day-night cycle,
continuous day conditions, and continuous night conditions. x-axes as
in Fig. 3. Black horizontal bars show dark periods for normal day.
25
Number of buds
2
2300–
0100h
8–10
1900–
2100h
6–8
4
1500–
1700h
4–6
6
1100–
1300h
2–4
8
0700–
0900h
0–2
Duration of opening (h)
0
1173
24-hour night
Number of buds
Number of buds
Bieleski et al.ÐControl of Flower Opening in Asiatic Lily
20
Red-Red
Red-FRed
FRed-Red
15
10
5
0
0100– 0300– 0500– 0700– 0900– 1100– 1300– 1500– 1700– 1900– 2100– 2300–
0300h 0500h 0700h 0900h 1100h 1300h 1500h 1700h 1900h 2100h 2300h 0100h
Time of day
F I G . 7. Clock time of opening of excised Asiatic lily ¯ower buds
`Cordelia', held under a red light-red light-darkness lighting cycle (8 h
each); a red light-far-red light-darkness lighting cycle (8 h each); and a
far-red light-red light-darkness lighting cycle (8 h each). x-axis as in
Fig. 3B. Black horizontal bars show dark periods and arrows mark
points at which the light environments were changed.
DISCUSSION
Flower opening in Asiatic lily appears to have two
novel features. First is the remarkable speed of opening.
Regardless of whether buds were on the ¯owering stem or
were excised and held in water, opening rarely took more
than 4 h, with most of the process frequently occurring in
90 min. The second feature concerns the strong synchrony
of the process, and its strong diurnal character. There are
several observations leading us to conclude that these events
in Asiatic lily are controlled by the cycle of light and dark,
but not as a photosynthetic response or as a direct response
to the presence or absence of light (as in nyctinastic ¯owers).
Timing was set just as e€ectively in the absence of photosynthetic organs (leaves) as in their presence (compare
Figs 1 and 2), and although the ¯ower has a small amount
of functional chlorophyll it is only 1 % of leaf content
(Laing, pers. comm.). Also, the cycle was completely set by
photosynthetically-insigni®cant light levels (25 mmol m ÿ2
s ÿ1 in a vase life room). The joint constraints of very low
chlorophyll content and low light intensity mean that
photosynthetic activity would have been well below
compensation point. In addition, the light should not have
been sensed through the chlorophyll mechanism because
light of non-photosynthetic wavelengths (4620 nm,
Figs 4B, 8 and 4710 nm, Fig. 7) was as e€ective as white
light in determining the cycle.
Instead, the characteristics observed showed some
similarities to processes controlled by phytochrome. The
timing of opening was completely set by the day-night
cycle. Even after only one cycle of reversed day, the clock
time of opening was mostly dictated by the new cycle, and
after two cycles of reversed day, resetting of the opening
time was complete (Figs 3B, 4B and 8). However, opening
was not a simple response to turning on or turning o€ the
light. In a 12 h day/12 h night cycle, a long period of
darkness was needed before opening started, opening was
initiated in the dark, and it was almost complete before the
light was turned on (Figs 1 and 2). Changing the ratio of
day to night from 8 : 16 h to 12 : 12 h to 16 : 8 h caused a
shift in opening time approximately half that of the shift in
daylength (i.e. a 2 h shift in opening for a 4 h shift in
nightfall; Fig. 5), an indirect relationship analogous to that
seen in Mimosa leaves (Toriyama and Komada, 1971).
Abolishing the day-night cycle by imposing either a 24 h
day or a 24 h night both had the e€ect of greatly slowing
1174
Bieleski et al.ÐControl of Flower Opening in Asiatic Lily
the speed of opening and weakening the synchronicity
(Fig. 6A and B). The phenomena we observed were highly
repeatable over time using `Cordelia' ¯owers taken from
di€erent growers during di€erent seasons. They were also
consistent over the four cultivars tested, other than for
small di€erences in the time of ¯ower opening (Fig. 8). Such
consistency suggests that the phenomena have a robust,
fundamental and well-conserved control system.
Because of the implications that a system resembling
phytochrome was active in controlling the opening of lily
¯owers, we carried out two of the customary tests for
phytochrome involvement. A light break during the night
did not reset timing of the night response (Fig. 4), and
neither did we detect any red/far-red interaction (Fig. 7). If
far-red light had simply not been sensed by the sensor
system, ¯owers in the red/far-red treatment should have
opened 8 h earlier than those in the far-red/red treatment.
The closeness of opening times in all three treatments does
not provide any evidence for a red/far-red interaction of the
kind observed for Pharbitis (Kaihara and Takimoto, 1980),
but it does suggest that whatever the nature of the sensor, it
is primarily driven by far-red light (4700 nm), in that
timing was set as e€ectively by far-red light as by the red
and white light supplied (which both contained signi®cant
amounts of far-red light).
The control process we have observed resembles the lightsensing mechanisms controlling nyctinastic leaf movements
where phytochrome is thought to be involved (Satter, 1979;
Lumsden, 1991). It has been assumed that nyctinastic
movement of Kalanchoe ¯owers has the same physiological
basis as leaf nyctinasty (Sweeney, 1979). However, the only
®ndings with ¯owers that are directly comparable to our
results for Asiatic lily are those obtained with the ephemeral
Japanese morning glory, Pharbitis nil (Kaihara and
Takimoto, 1979, 1980), where it has been proposed that
phytochrome sets the time of opening. Asiatic lily responds
to variations in daylength and complete day-night reversal,
but not to night-breaks, which suggests the onset of some
irreversible processes at the onset of night once the ¯ower is
mature enough to open. Our data show the photosensor
is not chlorophyll but is responsive to far-red light. If it is
phytochrome, Asiatic lily ¯ower opening would seem to be
a separate phenomenon to the well-known involvement of
phytochrome in ¯ower induction and to be an extreme
example of an `acute response', where night phase-speci®c
genes are expressed (Anderson et al., 1997).
Finally the results suggest that complete opening of
Asiatic lily ¯owers to anthesis takes place in two stages. The
®rst stage, opening of the bud through to stage 4, takes
place in the dark. We see the further opening to stage 5
coupled with enhanced formation of petal pigments and
rapid anthesis as a direct response to light mediated by a
separate system, and where a photosynthetic response is not
excluded. In Asiatic lily, the end result of the two processes
acting in tandem is that regardless of the time of year and
changing daylengths, anthesis occurs approx. 2 h after
daybreak, optimizing pollen protection until required by
pollinators.
AC K N OW L E D G E M E N T S
This study was carried out with funding from the New Zealand
Foundation of Research, Science and Technology (FRST
Programme CO6625). We acknowledge help from commercial
lily growers (B. & P. Kay, R. & A. Kopse, and D. &
A. Blewden), and pro®table discussions with Professors M.S.
Reid and W.G. van Doorn.
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