| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Ecology |
2Graduate School of Agriculture, Hokkaido University, Kita-ku, Sapporo, Hokkaido 060-8589, Japan; 3Department of Biology, University of Kentucky, Lexington, Kentucky 40506-0225 USA; 4Department of Plant and Soil Sciences, University of Kentucky, Lexington, Kentucky 40546-0312 USA
Received for publication October 6, 2005. Accepted for publication March 18, 2006.
ABSTRACT
In an investigation of seed germination in Cardiocrinum cordatum var. glehnii, embryos in fresh seeds in October were underdeveloped and did not grow until September of the following year. Then, they grew rapidly and had fully elongated by early November. In the second spring after dispersal, radicles emerged under snow in late March and after snowmelt in April. Cotyledons emerged soon after radicles. In several laboratory experiments, embryos grew at 15°/5°C (light 12 h/ dark 12 h) following 25°/15°C. Radicles emerged from seeds with fully elongated embryos at 5°–15°C after cold stratification at 0°–5°C. Cotyledons emerged in 2 wk from seeds with a radicle at 15°/5°C to 30°/20°C. Although seeds require c. 18–19 mo after dispersal to germinate in nature, under controlled conditions, they required only 9 mo with a sequence of 25°/15°C 
15°/5°C 0°–5°C 15°/5°C. This is practical knowledge for propagation of plants from seeds. GA3 treatment partially substituted for the high temperature requirement. Based on dormancy-breaking requirements, the seeds have deep simple morphophysiological dormancy (MPD). A literature review of seed dormancy in taxa of Liliaceae s. str. showed that phylogenetic position in this case is not a good predictor of level of MPD.
Key Words: Cardiocrinum cordatum var. glehnii • deep simple morphophysiological dormancy • gibberellic acid • seed germination phenology • temperature requirement for dormancy break • underdeveloped embryo
Seeds that have an underdeveloped embryo at the time of dispersal and require specific temperature conditions for embryo development and radicle and cotyledon emergence have morphophysiological dormancy (MPD) (Nikolaeva, 1977
; Baskin and Baskin, 1998
, 2004
). Many species in the temperate, broadleaved, deciduous (nemoral) forests of the northern hemisphere (Breckle, 2002
) produce seeds with MPD (Baskin and Baskin, 1998
, 2003
). The majority of studies on the ecophysiology of dormancy and germination of seeds of forest herbs with MPD have been done for species of the eastern deciduous forests of North America. Recently, however, several studies also have been published on the phenology of and temperature requirements for dormancy break and germination of seeds with underdeveloped embryos in species of broadleaved, deciduous forests in Japan (Takagi, 2001a
, b; Kondo et al., 2002
, 2004
, 2005
; Nomizu et al., 2004
).
Cardiocrinum cordatum (Thunb.) Makino var. glehnii (Fr. Schmidt) Hara [Liliaceae s. str. (sensu Patterson and Givnish, 2002
)], the subject of our study, is a bulbous geophyte that inhabits the floor of broadleaved, deciduous forests in eastern Asia and ranges from central Honshu northward to Hokkaido, Japan, and to Sakhalin and the southern part of the Kurile Islands. Another taxon of Cardiocrinum, C. cordatum (Thunb.) Makino, is distributed from central Honshu southward to Shikoku and Kyushu. Cardiocrinum cordatum var. glehnii is taller and has more flowers and larger leaves than C. cordatum (Kitamura et al., 1964
; Ohwi, 1983
; Satake, 1982; Ito, 1988
). Kawano et al. (2004)
proposed that the differences between the two varieties represent geographical variation in the same taxon, and thus they should not be recognized as separate taxa.
Furuike (1958)
reported that seeds of C. cordatum var. glehnii are dispersed in October, growth of the embryo begins in early October of the following year, and germination occurs about the time of snowmelt the second spring. Following germination, plants grow vegetatively for 6–8 years before they flower (Kawano et al., 2004
). Mother bulbs form small bulblets during the vegetative stage (Tani and Takahashi, 1998
). The mother bulb decays after flowering, leaving two to several independent daughter bulbs (Kitamura et al., 1964
; Kawano, 1975
). Kawano et al. (2004)
described and illustrated the life history of C. cordatum in detail.
The specific objectives of the present study were to (1) describe the phenology of embryo growth and of radicle and cotyledon emergence outdoors under near-natural conditions, (2) experimentally define the temperature requirements for embryo growth and for radicle and cotyledon emergence, and (3) determine if GA3 can replace the temperature requirement for embryo growth and radicle emergence in this taxon. From results of these observations and experiments, we determined class and level of dormancy (sensu Baskin and Baskin, 2004
) for seeds of C. cordatum var. glehnii and compared the kind of dormancy in seeds of this taxon with that of other taxa in Liliaceae s. str.
Cardiocrinum cordatum, including var. glehnii, is widely grown as an ornamental in temperate regions of the northern hemisphere. Thus, the results of this study, including information on reducing the time to germinate seeds of this taxon to less than half the time required under natural conditions, should be useful not only to seed ecologists and other professional botanists, but also to horticulturalists and landscape architects. Further, because the habitat of this taxon is decreasing in Japan, this information will aid in the restoration of populations in the wild.
MATERIALS AND METHODS
Seeds
Mature, brown, dehisced capsules were collected from a population of C. cordatum var. glehnii plants growing in a mesic deciduous woodland on the campus of Hokkaido University (43°04' N, 141°20' E), Sapporo, Japan, on 3 October 2001, 4 October 2002, and 2 October 2003. Seeds were removed from the fruits by hand, winnowed, then spread the same day onto stainless steel trays to dry in the laboratory for 2–4 days. Dried seeds were then put into paper envelopes and stored in a plastic container with silica gel at 5°C until used.
Definition of radicle emergence and cotyledon emergence
During germination of a C. cordatum var. glehnii seed, the radicle emerges first, then the cotyledon bows upward forming a "hairpin" loop, with the tip of the cotyledon remaining under the soil (Fig. 1). Shortly thereafter, the tip of the cotyledon emerges aboveground. In the present study, radicle emergence means the time when the radicle tip emerged 1 mm or more from the seed coat, and cotyledon emergence is when the cotyledon tip is aboveground.
|
On 6 October 2001, 10 seeds collected on 3 October 2001 were cut into thin sections using a microtome. Embryo length (initial embryo length) of each seed was measured using a dissecting microscope equipped with a micrometer. On the same day, 30 seeds were placed in each of 20 fine-mesh polyester bags and buried 3 cm deep in vermiculite in a tray in the framehouse. Thereafter, 10 seeds were removed at random from one bag about every 30 d until 3 May 2003, and embryo length was measured as described. Embryos had begun to curve by 22 October 2002 (Fig. 2). Therefore, beginning on this date, they were cut into two sections, measured, and their lengths summed to get total embryo length. On 3 March 2003, embryo length was recorded as fully elongated (5.82 ± 0.49 mm [Mean ± SD, N = 10]), i.e., embryo length just prior to radicle emergence. Thus, embryo length in a seed for which the radicle already had emerged by a given embryo-monitoring date was recorded as 5.82 mm. Embryo length was calculated as a percentage of that of a fully elongated embryo (5.82 mm).
|
On 6 October 2001, 50 seeds were sown on soil (1 : 1 v/v mixture of vermiculite and leaf mold) in each of three pots in the framehouse and covered with about 1 cm of sieved soil. Cotyledon emergence was monitored about every 30 d until 11 April 2003, when cotyledon emergence was first observed, and at 3–10 d intervals thereafter.
Laboratory experiments
In the following experiments, the daily photoperiod was 12 h in both constant and alternating temperature regimes. In the alternating regimes, the high temperature was given for 12 h in light each day and the low temperature for 12 h in darkness. The light source was white fluorescent tubes, and photon irradiance (400–700 nm) at seed level was 10–20 µmol · m–2 · s–1. In the experiments on embryo growth and radicle emergence, seeds were placed in 9-cm-diameter glass petri dishes on four layers of filter paper moistened with distilled water. Petri dishes were sealed with parafilm (Pechiney Plastic Packaging, Menasha, Wisconsin, USA) to retard evaporation. At each observation, seeds with an emerged radicle were recorded and removed from the dishes; water was added as needed to keep the filter paper moist.
Effect of temperature on embryo growth
On 25 December 2003, five petri dishes containing 40 seeds, collected on 2 October 2003, were placed at (a) constant 0°C, (b) 15°/5°C (light 12 h/ dark 12 h, alternating temperature regime), (c) 25°/15°C, (d) 15°/5°C (60 d) 0°C (90 d) 15°/5°C, (e) 25°/15°C (60 d) 0°C (90 d) 15°/5°C, or (f) 25°/15°C (60 d) 15°/5°C (60 d) 0°C (90 d) 15°/5°C. Two seeds were removed at random from each of the five dishes in each temperature treatment at approximately 30-d intervals, and the length of each embryo was measured as previously described. The mean length of fully elongated embryos in this collection of seeds was 6.29 ± 0.42 mm (±SD, N = 10).
Effect of constant and of alternating temperatures on radicle emergence
On 17 November 2003, four petri dishes containing 30 seeds each collected on 2 October 2003 were incubated at one of six constant temperatures (0°, 5°, 10°, 15°, 20°, and 25°C) or four daily alternating temperature regimes (15°/5°, 20°/10°, 25°/15°, and 30°/20°C). Observations were made at 7–14 d intervals.
Effect of simulated annual temperature cycle on radicle emergence
Beginning on 31 October 2002, four replications of 30 seeds collected on 4 October 2002 were subjected to the following temperature sequence: autumn (15°/5°C, 60 d) winter (0°C, 120 d) spring (15°/5°C, 30 d) summer (25°/15°C, 120 d) autumn (15°/5°C, 90 d) winter (0°C, 120 d) spring (15°/5°C, 30 d). The seeds were monitored for radicle emergence at 7–20 d intervals.
Effect of winter temperatures and length of simulated summer, autumn, winter, and spring on radicle emergence
Beginning on 16 December 2003, four replications of 30 seeds collected on 2 October 2003 were subjected to one of the following treatments: (a) 25°/15°C (60 d) 15°/5°C (60 d) 0° or 5°C (90 d) 15°/5°C (winter = 0° or 5°C), (b) 25°/15°C (0, 30, or 60 d) 15°/5°C (60 d) 0°C (90 d) 15°/5°C (different period for summer), (c) 25°/15°C (60 d) 15°/5°C (0, 30, or 60 d) 0°C (90 d) 15°/5°C (different period for autumn), and (d) 25°/15°C (60 d) 15°/5°C (60 d) 0°C (0, 60, 90, or 120 d) 15°/5°C (different period for winter). The seeds were monitored for radicle emergence at 7–20 d intervals. The same data were used in treatments that overlapped.
Radicle and cotyledon emergence during the annual temperature sequence
Beginning on 16 December 2003, four replications of 30 seeds each (in petri dishes) collected on 2 October 2003 were subjected to the temperature sequence 25°/15°C (60 d) 15°/5°C (60 d) 0°C (90 d) 15°/5°C, which simulates the annual temperature cycle. Seeds with an emerged radicle were recorded and removed from the dishes at 2- to 3-d intervals, and then they were used for observations on cotyledon emergence. For observations on cotyledon emergence, polyethylene containers (15 x 10 x 5 cm deep), each with six 5-mm-diameter drainage holes in the bottom, were filled with soil (1 : 1 v/v mixture of vermiculite and leaf mold). The soil surface was divided into 30 sections, and each section was numbered. Four containers were prepared, corresponding to four petri dishes in which radicle emergence was recorded. Seeds with an emerged radicle in petri dishes were buried about 1 cm deep in soil in each section of the container. Dates of radicle emergence and burial in soil were recorded for each seed. Because radicles emerged in the last temperature stage (15°/5°C) of the temperature sequence, the containers were kept at this stage. Containers were watered from the bottom and covered with a transparent vinyl bag with small puncture holes to reduce evaporation of water but to allow exchange of oxygen and carbon dioxide. Cotyledon emergence was recorded daily.
Effect of time at 0–5°C in the second winter and optimum temperature for radicle emergence
Seeds collected on 4 October 2002 and stored dry for 3 mo at 5°C were placed in a fine-mesh polyester bag and buried 3 cm deep in vermiculite in a tray on 6 January 2003, and the tray was placed in the framehouse. To determine if the 3-mo of dry storage at 5°C affected subsequent embryo growth, we compared the length of embryos in these seeds on 10 November 2003 to that of embryos on 5 November 2002 in 2001-collected seeds that were buried immediately after collection. Mean embryo length of 2001-collected seeds was 5.62 ± 0.44 mm (± SD, N = 10) and that of 2002-collected seeds was 5.45 ± 0.32 mm (± SD, N = 10) (t test, P > 0.05). Therefore, embryos in seeds stored for about 3 mo in this experiment developed normally.
On 14 November and 12 December 2003 and on 14 January and 13 February 2004, seeds were removed from the bag buried in vermiculite, rinsed with distilled water, and four replications of 30 seeds each were placed in petri dishes and transferred to incubators in the laboratory. Seeds transferred to incubators on 14 November and 12 December 2003 and on 14 January and 13 February 2004 had been exposed to mean temperatures of 0°–5°C for 7 d, 35 d, 68 d, and 98 d, respectively. Seeds removed from the bag on 14 November 2003 and 13 February 2004 were incubated at 5°, 10°, 15°, 20°, 25°, 15°/5°, 20°/10°, 25°/15°, and 30°/20°C, while those removed from the bag on 12 December 2003 and 14 January 2004 were incubated only at 5°, 15°/5°, 20°/10°, and 25°/15°C, because of lack of a sufficient number of seeds. Seeds with an emerged radicle were recorded at 5–14 d intervals.
Optimum temperature for cotyledon emergence
On 6 November 2003, seeds collected on 2 October 2003 were placed in a fine-mesh polyester bag and buried 3 cm deep in vermiculite in a tray, which was placed in the framehouse. On 23 March 2005, 30 seeds with an emerged radicle 2–5 mm long were buried about 1 cm deep in a 1:1 v/v mixture of vermiculite and leaf mold in 15 x 10 x 5 cm deep polyethylene containers, as previously described. Four containers with 30 seeds each were incubated at 0°, 5°, 15°/5°, 20°/10°, 25°/15°, and 30°/20°C.
Effects of GA3 on embryo growth and radicle emergence
Beginning on 30 April 2004, seeds collected on 2 October 2003 were subjected to the following treatments: control, 25°/15°C (60 d) 15°/5°C (60 d) 0°C (90 d) 15°/5°C (to confirm when radicle emergence occurs), (a) 25°/15°C (60 d) 15°/5°C + GA3 (90 d) 15°/5°C (to test whether GA3 substitutes for the low temperature of 0°C), (b) 15°/5°C + GA3 (90 d) 0°C (90 d) 15°/5°C (to test whether GA3 substitutes for the high temperature of 25°/15°C, (c) 25°/15°C + GA3 (90 d) 15°/5°C (to test whether GA3 substitutes for the cool temperatures of 15°/5°C and for the low temperature of 0°C, and (d) 0°C + GA3 (90 d) 15°/5°C (to test whether GA3 substitutes for the high temperature of 25°/15°C and for the cool temperature of 15°/5°C).
Nine-cm-diameter glass petri dishes with four layers of filter paper were moistened with 10 ml of distilled water (0 mg/l of GA3) or with a solution of 100 or 1000 mg/l of GA3 dissolved in distilled water by adding a bit of ethyl alcohol. Forty seeds were placed in each dish, which was sealed with parafilm, and five dishes were used per treatment. After treatment with GA3 for 90 d, seeds were rinsed with distilled water to remove GA3, transferred to new filter paper moistened with distilled water, and returned to the four temperature-sequence treatments described previously. Two seeds were removed at random from each of five dishes in each treatment and control every 60 or 90 d after sowing them, and lengths of embryos were measured as described previously.
The effect of GA3 on radicle emergence was investigated in a second experiment, using the procedures described. Four replications of 30 seeds each were used for each treatment, and seeds with an emerged radicle were recorded about once a week.
RESULTS
Phenology of embryo growth and of radicle and cotyledon emergence
Embryo length on 6 October 2001 was 0.66 ± 0.07 mm, which was 11.3% of the length of fully elongated embryos (Figs. 2 and 3). Embryos hardly grew at all until after 13 June 2002, and they grew only a little during summer 2002. Mean embryo length on 9 September 2002 was 21.9% of that of fully elongated embryos (Fig. 3, Table 1). However, between 9 September and 5 November 2002 embryos grew rapidly to 97% of the length of fully elongated embryos. Embryos grew only slightly after 5 November 2002.
|
|
On 11 April 2003, about 1 week after snowmelt, cotyledons had emerged from 1.3% of the seeds sown on 6 October 2001, but on 28 April cotyledons had emerged from 86.7% of the seeds (Fig. 3, Table 1).
Laboratory experiments
Effect of temperature on embryo growth
Embryos did not grow at 0°C, and they grew to only 21.5% full length at 25°/15°C (Fig. 4a). At 15°/5°C, embryo growth began between days 82 and 123, by which time they had more than doubled in length. By 300 d after sowing, embryo length was 101% of that of fully elongated embryos; however, no radicles had emerged. In the temperature-sequence treatments 15°/5°C (60 d) 0°C (90 d) 15°/5°C and 25°/15°C (60 d) 0°C (90 d) 15°/5°C, embryos began to grow rapidly 60 d after they were transferred to the third stage in the sequence (15°/5°C) (Fig. 4b). Final embryo length in these two treatments was 83.3% and 76.1%, respectively, of that of fully elongated embryos; however, no radicles had emerged. In the 25°/15°C (60 d) 15°/5°C (60 d) 0°C (90 d) 15°/5°C temperature-sequence treatment, embryos grew little at 25°/15°C (60 d), but they grew rapidly at the second stage in the sequence (15°/5°C), reaching 83.5% of the length of fully elongated embryos. Embryos grew slowly at 0°C, but they became fully elongated 29 d after transfer to the fourth stage (15°/5°C) in the temperature sequence, by which time radicles had emerged from 24.0% of the seeds. By 50 d after transfer to the fourth stage, they had emerged from about 90% of the seeds.
|
Effect of simulated annual temperature cycle on radicle emergence
In the annual temperature sequence that simulates autumn—(15°/5°C, 60 d) winter (0°C, 120 d) spring (15°/5°C, 30 d) summer (25°/15°C, 120 d) autumn (15°/5°C, 90 d) winter (0°C, 120 d) spring (15°/5°C, 30 d), radicles had emerged from 50.8% of the seeds 103 d after they were transferred to 0°C, corresponding to the second winter (Fig. 5). Radicles had emerged from 100% of the seeds 11 d after transfer from 0°C to 15°/5°C (second spring).
|
15°/5°C (60 d) 0° or 5°C (90 d) 15°/5°C treatment (Fig. 6a), radicles emerged in the fourth stage (15°/5°C) of the sequence following 0° or 5°C (winter). Final percentages of radicle emergence in seeds exposed to winter temperatures of 0° and 5°C were 92.5% and 85.8%, respectively (t test, P > 0.05). At the temperature sequence 25°/15°C (0, 30, or 60 d) 15°/5°C (60 d) 0°C (90 d) 15°/5°C (Fig. 6b), no radicles emerged from the seeds unless they were exposed to the summer temperature regime. Percentage of radicle emergence increased with time seeds were exposed to 25°/15°C, and seeds kept at this part of the sequence for 60 d germinated to 92.5%. At the temperature sequence 25°/15°C (60 d) 15°/5°C (0, 30, or 60 d) 0°C (90 d) 15°/5°C (Fig. 6c), radicles emerged from only 5.0% of the seeds when the second stage of 15°/5°C was eliminated. On the other hand, radicles emerged from 91.7% and 92.5% of the seeds when the second stage of 15°/5°C was 30 d and 60 d, respectively. At the temperature sequence 25°/15°C (60 d) 15°/5°C (60 d) 0°C (0, 60, 90, or 120 d) 15°/5°C (Fig. 6d), percentage of radicle emergence increased with time at 0°C, and radicles emerged from >90% of the seeds kept at this portion of the cycle for 90 d or 120 d.
|
15°/5°C [60 d] 0°C [90 d] 15°/5°C) in Effect of temperature on embryo growth. About 80% of the embryo growth occurred at the simulated autumn temperature regime (15°/5°C) following 60 d at the simulated summer temperature (25°/15°C). Embryos continued to grow slowly at the simulated winter temperature (0°C) and reached their full length at the simulated spring temperature (15°/5°C) (Fig. 7). Both radicles and cotyledons emerged after seeds were transferred to the simulated spring temperature regime (15°/5°C). Cotyledons emerged in about 17 d from seeds with an emerged radicle.
|
|
|
15°/5°C (60 d) 0°C (90 d) 15°/5°C temperature sequence control (Fig. 10a–d), embryos did not grow at 25°/15°C, then grew rapidly at the first regime of 15°/5°C and continued to grow slowly at 0°C, reaching their full length by the end of this period. Further, radicles had emerged from about 10% of seeds 33 d after transfer to the second 15°/5°C regime and from 100% of the seeds at the end of experiment (300 d). In the 25°/15°C (60 d) 15°/5°C + GA3 (90 d) 15°/5°C (Fig. 10a), 25°/15°C + GA3 (90 d) 15°/5°C (Fig. 10c), and 0°C + GA3 (90 d) 15°/5°C temperature sequences (Fig. 10d), embryos in seeds with and without exposure to GA3 grew to full length at 15°/5°C, but no radicles emerged. In the 15°/5°C + GA3 (90 d) 0°C (90 d) 15°/5°C sequence (Fig. 10b), embryos in seeds treated with 0 or 1000 ppm GA3 grew to about 50% of their full length at the second 15°/5°C regime, but no radicles emerged. On the other hand, embryos in seeds treated with 100 ppm GA3 grew to 66% of their full length, and radicles emerged from 43% of the seeds. Thus, 100 ppm GA3 somewhat replaced the requirement for the 25°/15°C portions of this temperature sequence.
|
The phenology of embryo growth and of radicle and cotyledon emergence in seeds of C. cordatum var. glehnii in Hokkaido, Japan, are summarized in Table 1. Seeds of this species are dispersed in early October, when the embryos are underdeveloped. Embryos had grown only a little by mid-June of the following year, and they grew slowly from mid-June to early September. Between early September and early November, embryos grew rapidly and reached their full length. They remained in this condition under snow from early November to early March. Radicle emergence in the seed population under snow began in March and continued after snowmelt until mid-April, about 18 mo after seed dispersal. Cotyledons emerged in April, soon after radicle emergence. Thus, under near-natural conditions in a framehouse, embryos in seeds of C. cordatum var. glehnii complete growth at moderate temperatures in the second autumn after seed dispersal, and radicles and cotyledons emerge in spring after the second winter.
In laboratory experiments, radicles emerged from a high percentage of seeds of C. cordatum var. glehnii at the temperature sequence simulating autumn winter spring summer autumn winter spring outdoors in Hokkaido (Fig. 5). However, only the summer autumn temperature sequence was required for embryo growth (Figs. 4 and 7), and the winter spring temperature sequence was required for emergence of radicles and cotyledons from seeds with fully elongated embryos (Figs. 6–9). Therefore, only the sequence of high moderate low moderate temperatures is required for embryo growth and germination. Thus, although in nature seeds of C. cordatum var. glehnii require about 18–19 mo from dispersal to germination, seeds in the laboratory germinate after about 9 mo in the 25°/15°C (60 d) 15°/5°C (60 d) 0°C (120 d) 15°/5°C temperature sequence. This means that seeds in nature are spending several months after they are dispersed "waiting" for the appropriate sequence of dormancy-breaking temperature regimes to begin. Thus, from the time of seed dispersal in autumn to the following spring or summer, in the field seeds are exposed to mortality-causing factors without any physiological progression toward dormancy break/germination. As such, theoretically it would seem that this stage of the reproductive biology of C. cordatum var. glehnii would be less than optimal with regard to fitness of this species. The practical implication of this research for horticulturalists, gardeners, and restoration ecologists intending to propagate C. cordatum var. glehnii from seeds is that seedlings can be obtained in about 8–9 mo under controlled temperature conditions vs. 18–19 mo if fresh seeds are sown under natural conditions following dispersal in October.
One hundred ppm GA3 substituted in part for 25°/15°C in the 15°/5°C + GA3 (90 d) 0°C (90 d) 15°/5°C (Fig. 10b). Embryos in seeds treated with 100 ppm GA3 grew to an average of 66% of their full length, and radicles had emerged from 43% of the seeds. The seed populations treated with 100 ppm GA3 in the temperature sequence described consisted of seeds in which embryos grew, but not enough for radicle emergence, and for those in which embryos grew to full length and their radicles emerged. GA3 did not substitute for low temperature.
Seeds of C. cordatum var. glehnii have an underdeveloped embryo that is physiologically dormant at the time of seed dispersal, thus they have morphophysiological dormancy (MPD) (Nikolaeva, 1977
; Baskin and Baskin, 1998
; Baskin and Baskin, 2004
). There are eight levels of MPD, distinguished on the basis of (1) the temperature regime(s) that seeds must be exposed to before they complete germination, (2) temperatures required at time of embryo growth, and (3) response of seeds to gibberellic acid (Baskin and Baskin, 1998
, 2004
; Baskin et al., 2002
). The eight levels of MPD are divided into two categories: simple and complex. In seeds with simple MPD, high (usually 10°C or above) temperatures are required for embryo growth, and in those with complex MPD low (c. 0–10°C) temperatures are required for embryo growth. The various levels of simple and complex MPD are based on the effects of GA3 on germination and time of radicle and shoot emergence.
Panax ginseng C. A. Meyer is a classic example of a species whose seeds have deep simple MPD (Nikolaeva, 1977
; Baskin and Baskin, 1998
). The phenology and temperature requirements for embryo growth and seed dormancy break in C. cordatum var. glehnii are similar to those of P. ginseng. Seeds of P. ginseng usually mature in late summer (Kuribayashi et al., 1971
; Choi and Takahashi, 1977
), and they germinate in the second spring after dispersal, i.e. , 18–20 months following maturity (Grushvitzky, 1967
; Kuribayashi et al., 1971
; Choi and Takahashi, 1977
). Seeds of P. ginseng require moderate temperatures (e.g., 20°C) for embryo growth followed by cold stratification (e.g., 2°–6°C) to break physiological dormancy of the fully developed embryo (Grushvitzky, 1967
). Further, GA3 promoted embryo growth (Grushvitzky, 1967
; Kuribayashi et al., 1971
; Choi, 1977
), but it did not break physiological dormancy in seeds with a fully elongated embryo (Choi, 1977
).
Jeffersonia diphylla (L.) Pers. is another example of a species whose seeds have deep simple MPD, requiring high (e.g., 30°/15°C) followed by moderate (e.g., 20°/10° or 15°/6°C) temperatures for embryo growth (Baskin and Baskin, 1989
). Seeds with fully elongated embryos require pretreatment at low temperature (e.g., 5°C) for radicle emergence. Further, GA3 can substitute for warm but not for cold stratification in seeds in this species. Thus, the temperature requirements from embryo growth to radicle emergence and effects of GA3 in J. diphylla seeds correspond well with those of C. cordatum var. glehnii. However, seeds of J. diphylla are dispersed in late spring, whereas those of C. cordatum var. glehnii are dispersed in autumn. Therefore, in J. diphylla embryo growth occurs in the first autumn and germination in the first spring following seed dispersal, whereas in C. cordatum var. glehnii these events in the life cycle occur in the second autumn and second spring, respectively. Thus, although the kind of seed dormancy in C. cordatum var. glehnii and J. diphylla is the same, the phenology of embryo growth and germination differs due to temporal difference in seed maturation/dispersal.
Thus, we conclude that seeds of C. cordatum var. glehnii have deep simple MPD, i.e., C1bB-C3 in the Nikolaeva (2001)
formula system for the kinds of seed dormancy. This conclusion differs from that of Nikolaeva et al. (1985)
who reported [under Lilium glehnii Fr. Schmidt, a synonym for C. cordatum Fr. Schmidt var. glehnii (Fr. Schmidt) Hara] that this taxon has deep simple epicotyl MPD, i.e., C1bB(root)-C3(epicotyl) (Nikolaeva, 2001
).
Liliaceae s. str. (Patterson and Givnish, 2002
) contains nine genera: Fritillaria, Lilium, Nomocharis, Cardiocrinum, Notholirion, Gagea, Lloydia, Erythronium, and Tulipa. Information on the kind of dormancy for seeds of species in seven of these nine genera is presented in Table 2. Takhtajan (1997)
indicates the embryo of Lloydia is underdeveloped, and Bonde (1965)
obtained high germination percentages for seeds of Lloydia serotina (Linn.) Reichenb. at 18°C in darkness in less than 30 d. Taken together, available evidence suggests that L. serotina seeds have morphological dormancy (sensu Baskin and Baskin, 2004
). However, more detailed studies may prove that they have MPD, e.g., nondeep simple MPD. Six of the seven genera listed in Table 2 clearly have MPD with the level varying between genera and tribes and even within a genus. Thus, phylogenetic position of a taxon in the Liliaceae s. str. clade is not a good predictor of level of MPD.
|
FOOTNOTES
1 This work was partially supported by a Grant-in-Aid for Scientific Research (C) (10153727) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology. 
5 Author for correspondence (kondo{at}res.agr.hokudai.ac.jp
), fax: +81–11–706-2805
LITERATURE CITED
Barton L. V.. 1936. Germination and seedling production in Lilium sp[p]. Contributions from Boyce Thompson Institute 8: 297-309.
Baskin C. C. Baskin J. M.. 1998. Seeds: ecology, biogeography, and evolution of dormancy and germination Academic Press, San Diego, California, USA.
Baskin C. C. Meyer S. E. Baskin J. M.. 1995. Two types of morphophysiological dormancy in seeds of two genera (Osmorhiza and Erythronium) with an Arcto-Tertiary distribution pattern. American Journal of Botany 82: 293-298.[CrossRef][ISI]
Baskin C. C. Milberg P. Andersson L. Baskin J. M.. 2002. Non-deep simple morphophysiological dormancy in seeds of the weedy facultative winter annual Papaver rhoeas. Weed Research 42: 194-202.[CrossRef][ISI]
Baskin J. M. Baskin C. C.. 1985. Seed germination ecophysiology of the woodland spring geophyte Erythronium albidum. Botanical Gazette 146: 130-136.[CrossRef]
Baskin J. M. Baskin C. C.. 1989. Seed germination ecophysiology of Jeffersonia diphylla, a perennial herb of mesic deciduous forests. American Journal of Botany 76: 1073-1080.[CrossRef][ISI]
Baskin J. M. Baskin C. C.. 2003. Classification, biogeography, and phylogenetic relationships of seed dormancy. In R. D. Smith, J. B. Dickie, S. H. Linington, H. W. Pritchard, and R. J. Probert [eds.] Seed conservation: turning science into practice 518-544 Royal Botanic Gardens, Kew, UK.
Baskin J. M. Baskin C.C.. 2004. A classification system for seed dormancy. Seed Science Research 14: 1-16.
Bonde E. K.. 1965. Further studies on the germination of seeds of Colorado alpine plants. University of Colorado Studies Series in Biology 18: 1-30.
Breckle S.-W.. 2002. Walter's vegetation of the earth: the ecological systems of the geo-biosphere, 4th ed Springer-Verlag, Berlin, Germany.
Choi K. G.. 1977. Studies of seed germination in Panax ginseng C. A. Meyer. 2. The effect of growth regulators on the dormancy breaking. Bulletin of the Institute for Agricultural Research, Tohoku University 28: 159-170 (in Japanese with English summary).
Choi K. G. Takahashi N.. 1977. Studies of seed germination in Panax ginseng C. A. Meyer. 1. The effect of germination inhibitors in fruits on dormancy breaking. Bulletin of the Institute for Agricultural Research, Tohoku University 28: 145-157 (in Japanese with English summary).
Crocker W. Barton L. V.. 1957. Physiology of seeds Chronica Botanica, Waltham, Massachusetts, USA.
Furuike H.. 1958. On the floral construction of the Cardiocrinum in Japan (2). The Journal of Geobotany 7: 23-26 (in Japanese).
Grushvitzky I. V.. 1967. After-ripening of seeds of primitive tribes of angiosperms, conditions and peculiarities. In H. Borriss [ed.] Physiologie, Ökologie und Biochemie der Keimung 329-336 figs. 1–8. Ernst-Moritz-Arndt-Universitat, Griefswald, Germany.
Ito K.. 1988. Cardiocrinum Endl. ex Lindl. In Y. Tsukamoto [ed.] The grand dictionary of horticulture, vol. 1, 287–288 Shyogakukan, Tokyo, Japan (in Japanese).
Kawano S.. 1975. The productive and reproductive biology of flowering plants. II. The concept of life history strategy in plants. Journal of the College of Liberal Arts, Toyama University, Japan (Natural Science) 8: 51-86.
Kawano S. Ohara M. Masuda J.. 2004. Cardiocrinum cordatum (Thunb.) Makino (Liliaceae). In S. Kawano [ed.] Life history monographs of Japanese plants, vol. I, Spring plants no. 1 49-56 Hokkaido University Press, Sapporo, Japan (in Japanese with English summary).
Kitamura S. Murata G. Koyama T.. 1964. Coloured illustrations of herbaceous plants of Japan (monocotyledoneae) Hoikusha, Osaka, Japan (in Japanese).
Kondo T. Okubo N. Miura T. Honda K. Ishikawa Y.. 2002. Ecophysiology of seed germination in Erythronium japonicum (Liliaceae) with underdeveloped embryos. American Journal of Botany 89: 1779-1784.
Kondo T. Miura T. Okubo N. Shimada M. Baskin C. C. Baskin J. M.. 2004. Ecophysiology of deep simple epicotyl morphophysiological dormancy in seeds of Gagea lutea (Liliaceae). Seed Science Research 14: 371-378.[CrossRef][ISI]
Kondo T. Okubo N. Miura T. Baskin C. C. Baskin J. M.. 2005. Ecophysiology of seed dormancy and germination in the mesic woodland herbaceous perennial Corydalis ambigua (Fumariaceae) in Japan. Canadian Journal of Botany 83: 571-578.[ISI]
Kuribayashi T. Okamura M. Ohashi H.. 1971. Physiological and ecological studies in Panax ginseng. I. Effects of various temperature and chemical control substances on the dehiscence of seed. Syoyakugaku Zasshi 25: 87-94 (in Japanese with English summary).
Liu M. Li R.-J. Liu M.-Y.. 1993. Adaptive responses of roots and root systems to seasonal changes. Environmental and Experimental Botany 33: 175-188.[CrossRef][ISI]
Nikolaeva M. G.. 1977. Factors controlling the seed dormancy pattern. In A. A. Khan [ed.] The physiology and biochemistry of seed dormancy and germination 51-74 North-Holland, Amsterdam, Netherlands.
Nikolaeva M. G.. 2001. Ekologo-fiziologicheskie osobennosti pokoya i prorastaniya semyan (itogi issledovantii zaistekshee stoletie) [Ecological and physiological aspects of seed dormancy and germination (review of investigations for the last century)]. Botanicheskii Zhurnal 86: 1-14 (in Russian, for English translation see http://www.usd./isss/Nikolaeva-manuscript-web.doc.).
Nikolaeva M. G. Rasumova M. V. Gladkova V. N.. 1985. Reference book on dormant seed germination. M. F. Danilova [ed.], ‘Nauka' Publishers, Leningrad, Russia (in Russian).
Nomizu T. Niimi Y. Watanabe E.. 2004. Embryo development and seed germination of Hepatica nobilis Schreber var. japonica as affected by temperature after sowing. Scientia Horticulturae 99: 345-352.[CrossRef]
Ohwi J. [revised by M. Kitagawa]. 1983. New flora of Japan. Shibundo, Tokyo, Japan (in Japanese).
Patterson T. B. Givnish T. J.. 2002. Phylogeny, concerted convergence, and phylogenetic niche conservatism in the core Liliales: insights from rbcL and ndhF sequence data. Evolution 56: 233-252.[CrossRef][ISI][Medline]
Satake Y.. 1982. Cardiocrinum Endl. In Y. Satake, I. Ohwi, S. Kitamura, S. Watari, and T. Tominari [eds.] Wild flowers of Japan, vol. I, Herbaceous plants: monocotyledoneae Heibonsya, Tokyo, Japan (in Japanese).
Takagi H.. 2001a. Breaking of two types of dormancy in seeds of Polygonatum odoratum used as vegetables. Journal of the Japanese Society for Horticultural Science 70: 416-423.[ISI]
Takagi H.. 2001b. Breaking of two types of dormancy in seeds of edible Polygonatum macranthum. Journal of the Japanese Society for Horticultural Science 70: 424-430.[ISI]
Takhtajan A.. 1997. Diversity and classification of flowering plants. Columbia University Press, New York, New York, USA.
Tamura M. N.. 1998. Liliaceae. In Kubitzki K. The families and genera of vascular plants. Vol. III, Flowering plants: monocotyledons, Lilianae (except Orchidaceae) 343-353 Springer-Verlag, Berlin, Germany.
Tani T. Takahashi H.. 1998. Bulb and shoot architecture of Cardiocrinum cordatum var. glehnii (Liliaceae). Journal of Phytogeography and Taxonomy 46: 109-112 (in Japanese).
This article has been cited by other articles:
|
|
 |
|
  F. Vandelook and J. A. Van Assche Temperature Requirements for Seed Germination and Seedling Development Determine Timing of Seedling Emergence of Three Monocotyledonous Temperate Forest Spring Geophytes Ann. Bot., August 30, 2008; (2008) mcn165v1. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
