Gametophyte morphology and development of six Chinese species of Pteris (Pteridaceae).
KEY WORDS.--Pteris. gametophyte, Vittaria-type, Ceratopteris-type, Pteris vittata, Pteris ensiformis, Pteris excelsa, Pteris fauriei, Pteris finotii, Pteris wallichiana
The genus Pteris L. (Pteridaceae) is found in the tropics and is in need of redefinition (Smith et al., 2006), however it is estimated to comprise about 250 species (Tryon et al., 1000). Differences in characteristics of fern spore germination and gametophyte development can offer compelling criteria for taxonomic and phyletic studies (Holttum, 1040; Stokey, 1951, 1060; Atldnson and Stokey, 1964; Atkinson, 1073; Raine et al., 1906; Chiou and Farrar, 1997; Chiou et al., 1008; Chandra et al., 2003). Type of spore germination, development of the prothallial plate and the meristematic regions, form of the mature and old thallus, type, position, and time of appearance of hairs when present, and form of the sex organs (especially the antheridium) may prove of value to the taxonomists. Perez-Garcia and Mendoza-Ruiz (2004) indicated that gametophytes may be useful for taxonomic and phyletic studies at the family and generic levels, as well as among species within the same genus. The combination of characters of hair type and position, margin, antheridial structure, shapes of the antheridial dehiscence, antherozoid liberation, and number of archegonial neck cells were used by Atkinson (1973), Pryer et al, (1995), and Perez-Garcia and Mendoza-Ruiz (2004) to delimit subgenera, species, or groups of species within the Thelypteridaceae.
Though the Pteridaceae is large, studies on its gametophyte morphology are limited. However, based on the limited information, the gametophytes of Pteris can be summarized as the following: germination is Vittaria-type and the prothallial development is Ceratopteris-type. The adult prothallus is cordatethalloid, with broad wings, growing very fast, with a distinct cushion. Rhizoids are nearly hyaline or pale brown, distributed in the lower surface of the cushion, with thin cell walls. The adult prothallus is naked. Gametangia are of the common leptosporangiate-type: antheridia are formed from early development stages of the prothallus. The cap cell becomes loose and is pushed off, releasing the spermatozoids. The neck of the archegonia is elongated, curving away from the apex of the prothallus (Nayar and Kaur 1971).
This study describes the gametophyte morphology and development of P. vittata L., P. ensiformis Burm, P. excelsa Gaud., P. fauriei Hieron., P. finotii Christ. and P. wallichiana Agardh.
MATERIALS AND METHODS
Spores were obtained from live plants collected from several sites in China (Table 1). Fertile pinnae were kept in clean paper bags under dry conditions until spores were shed. About one week later, the sporangia and indusia were separated from the spores by a mesh with pores 0.054 mm in diameter. Spores were cultured in plastic basins (measuring 25 cm x 20 cm x 5 cm) with a sieved mixture of black soil and sand (1:1). Thickness of the mixture was about 3 cm. The surface of the mixture was made smooth and substantial and the basins were then watered. Spores of each species were sown evenly at an average density of 250-300 spores per [cm.sup.2]. Basins were covered with transparent plastic film on which two to three small holes were made in order to avoid contamination and desiccation. They were placed in the dark at 25[degrees]C for 24 h then transferred to fluorescent light (10 000 [micro]mol x [m.sup.-2] x [sec.sup.-1]) at 25[degrees]C under a diurnal cycle of 12/12 hr. Cultures were moistened with tap water to prevent desiccation and, in the last stages, to help antheridial opening and movement of antherozoids.
Spore sizes were measured from material in water with a compound microscope (No. XTS 20130, Beijing Tech Instrument Co., LTD] equipped with an ocular micrometer. Measurements of the spore length and width were obtained from an average sample of fifty spores per species (Table 1). Spore morphology was observed under the compound microscope from material in water. All pictures of microscopic material were taken from living materials under lab conditions with a Nikon ECLIPSE E600 camera.
Spores.--Spores of all species are trilete, tetrahedral, brown and possess a distinct equatorial flange. Spores vary in size from (19) 27.4 (40) x (10) 10.3 (12) [micro]m (P.fauriei) to (92) 104 (110) x (90) 96 (100) [micro]m (P.finotii) (Figs. 1-3, see Table 2).
[FIGURES 1-9 OMITTED]
Germination.--Spores begin to germinate between day 2 and day 13 after they are sown (Table 2). Germination is Vittaria-type in all species (Figs. 4-5). Gametophytes of all the species first develop a rhizoid. Of all species, division begins in the first prothallial cell with a transverse wall and finally forms a short germ-filament, 2-25 cells long (Figs. 6-7).
Laminar phase.--The differentiation of this phase is asynchronous in all species and the development occurs between days 6 and 40 (Fig. 8; see Table 2). In P. vittata, as the prothallial plate grows, meristematic activity gradually becomes focused on a group of marginal cells on one side of the plate, away from the apical region. This lateral meristematic region soon locates at the bottom of a notch, which increasingly becomes more obvious as growth proceeds. The position of the meristem results in the asymmetrical young prothallus with one wing larger than the other. When the meristem is formed farther away from the apex, the thallus remains distinctly lopsided longer. The thallus becomes nearly symmetrical by growth of the sides of the wings, making the meristem nearly apical. At last, the prothallial plate becomes cordate after 5-30 days, so development of the prothallial plate is Ceratopteris-type (as defined by Nayar and Kaur, 1969). Then a cushion with the gametangia forms. The adult gametophyte is cordate. The time for the first adult cordiform gametophytes of all species to differentiate ranges between days 17 and 50 (Figs. 9-11, see Table 2). The prothallial development pattern of the other species is identical to P. vittata.
Gametangia.--Once the gametophytes have reached sexual maturity (20-90 days), the gametangia differentiation and development begins. The gametangia are all of leptosporangiate, homosporous ferns. Antheridia of all species are distributed on the lower surface of the gametophyte at the basal end of the cushion. Antheridia are globose and are composed of a basal cell, a ring cell and an opercular cell (Figs. 12-13). During antheridial dehiscence the opercular cell becomes loose and is pushed off, releasing the spermatozoids.
In all species, the archegonia differentiate at about the same time as antheridia. Archegonia are distributed on the lower surface of the gametophyte at the apical end of cushion and near the meristematic region. The necks are oriented toward the basal region of the gametophytes, with 4 rows of cells, 3-5 cells per row (Figs. 14-15).
Sporophytes.--The first sporophytes were observed by about 5-8 weeks after sowing. Fertilization occurred on almost all gametophytes to produce sporophytes.
The spores of all species share features such as trilete spores with a distinct equatorial flange, however the spore sizes of the six species are different.
For all species, the germination pattern is of the Vittaria-type. It is the most common type in ferns (Nayar and Kaur, 1971). In this type, the rhizoid develops first after a wall perpendicular to the polar axis of the spores is formed. The first rhizoid of P. fauriei is chlorophyllous, but according to Nayar and Kaur (1971), the rhizoids of Pteris are nonchlorophyllous. The first prothallial cell divides and then the apical cell continues to divide, producing a short filament 2-25 cells long. Germination time differs among all species; spores of P. vittata germinate faster than the other species.
[FIGURES 10-15 OMITTED]
Prothallial development in all species is of the Ceratopteris-type in which the prothallial plate is nonmeristic at the beginning. With its growth, a multicellular meristem emerges on one side of the plate. Cell divisions in the meristem make the young thallus asymmetrical. With the growth of the smaller wing of the thallus, it becomes symmetrical. The adult gametophyte develops faster in P. vittata than the other species.
Sex organs are of the common leptosporangiate type. The dehiscence type in antheridia is consistent with the description given by Nayar and Kaur (1971). The uniform development of the gametophyte in all species has been mentioned above. Distinguishing characteristics among the six species such as size of the spores, germination time, time of formation of the gametangia, thallus margin shape, number of archegonial neck cells was also observed.
This work was supported by the Project of the Ministry of Science and Technology of the People's Republic of China (2005DKA21006, 2006GH559901) and the Project of Chinese Academy of Sciences (KSCX2-YW-N-52). We thank Aniceto Medoza-Ruiz and Dr. Blanca Perez-Garcia for valuable comments on the manuscript.
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K. M. ZHANG
Institute of Botany, the Chinese Academy of Sciences, Beijing, 100093, China
Graduate University of Chinese Academy of Sciences, Beijing, 100040, China
L. SHI *, X. C. ZHANG, and C. D. JIANG
Institute of Botany, the Chinese Academy of Sciences, Beijing, 100093, China
W. L. TIM-CHUN
Kadoorie Farm & Botanic Garden Corporation, Hong Kong, China
* Corresponding author (telephone: 01062836270, fax number: 01082593616, e-mail: shilei67@ 263.net).
TABLE 1. Collection data for materials used in current study. Collection No. Scientific name Collector name and date P. vittata W. L. Tim-Chun 141 04/2004 P. finotii W. L. Tim-Chun 1894 04/2004 P. fauriei W. L. Tim-Chun 1941 04/2004 P. excelsa B. D. Liu 151 07/2004 P. wallichiana B. D. Liu 192 07/2004 P. ensiformis X. C. Zhang 172 06/2004 Scientific name Site location Deposit herbarium P. vittata Hongkong, terraces Herbarium of KFBG near herbarium of Kadoorie Farm & Botanic Garden (KFBG) P. finotii Fern Walk at KFBG Herbarium of KFBG P. fauriei Orchid Fall at KFBG Herbarium of KFBG P. excelsa Yunnan, Kunming Herbarium of Harbin Normal University P. wallichiana Yunnan, Kunming Herbarium of Harbin Normal University P. ensiformis Institute of Botany, Herbarium of the Chinese Academy Chinese National of Sciences (IBCAS) Herbarium, IBCAS (PE) Spore Scientific name numbers P. vittata 50 P. finotii 51 P. fauriei 50 P. excelsa 50 P. wallichiana 49 P. ensiformis 50 TABLE 2. Developmental stages of the gametophytes of the six species of Pteris. Scientific name Spores Germination P. vittata Trilete, tetrahedral, Vittaria-type, day brown and possess a 2-3, a rhizoid first distinct equatorial develops and the flange, (90) 95 (100) first prothallial cell X (80) 87.5 (90) divides with a trans- [micro]m verse wall P. finotii Trilete, tetrahedral, Vittaria-type, day brown and possess a 4-6, a rhizoid first distinct equatorial develops and the first flange, (92) 104 (110) prothallial cell di- X (90) 96 (100) vides with a trans- [micro]m verse wall P. fauriei Trilete, tetrahedral, Vittaria-type, about brown and possess a one week, a rhizoid distinct equatorial first develops and the flange, (19) 27.4 (40) first prothallial cell X (10) 10.3 (12) divides with a trans- [micro]m verse wall P. excelsa Trilete, tetrahedral, Vittaria-type, day brown and possess a 7-11, a rhizoid first distinct equatorial develops and the first flange, (29) 31 (34) prothallial cell di- X (20) 24 (29) vides with a trans- [micro]m verse wall P. wallichiana Trilete, tetrahedral, Vittaria-type, about brown and possess a day 13, a rhizoid first distinct equatorial develops and the first flange, (44) 50 (56) prothallial cell di- X (40) 46 (51) vides with a trans- [micro]m verse wall P. ensiformis Trilete, tetrahedral, Vittaria-type, about brown and possess a one week, a rhizoid distinct equatorial first develops and the flange, (27) 30 (32) first prothallial cell X (23) 28 (29) divides with a trans- [micro]m verse wall Scientific name Filamentous phase Plate phase P. vittata Germinal filaments Ceratopteris-type, 2-19 cells long, about one week spore coat remains attached P. finotii Germinal filaments Ceratopteris-type, 2-12 cells long, spore 10-40 days coat remains attached P. fauriei Germinal filaments Ceratopteris-type, 2-7 cells long, spore 7-14 days coat remains attached P. excelsa Germinal filaments Ceratopteris-type, 2-22 cells long, spore about 20 days coat remains attached P. wallichiana Germinal filaments Ceratopteris-type, 2-7 cells long, spore about 36 days coat remains attached P. ensiformis Germinal filaments Ceratopteris-type, 2-25 cells long, spore about 25 days coat remains attached Scientific name Adult phase Gametangia P. vittata 17-50 days, asym- [female] [male] metrical spatulate to cordiform 20-40 days P. finotii about 26 days, [female] [male] asymmetrical spatulate to cordiform 26-60 days P. fauriei about 24 days, [female] [male] asymmetrical spatulate to cordiform 28-80 days P. excelsa about 25 days, [female] [male] asymmetrical spatulate to cordiform about 25 days P. wallichiana about 43 days, [female] [male] asymmetrical spatulate to cordiform about 36 days P. ensiformis about 50 days, [female] [male] asymmetrical spatulate to cordiform about 90 days
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|Author:||Zhang, K.M.; Shi, L.; Zhang, X.C.; Jiang, C.D.; Tim-Chun, W.L.|
|Publication:||American Fern Journal|
|Date:||Jan 1, 2008|
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