Chin Bull Bot ›› 2019, Vol. 54 ›› Issue (5): 596-605.doi: 10.11983/CBB18261

• EXPERIMENTAL COMMUNICATIONS • Previous Articles     Next Articles

Megasporogenesis, Microsporogenesis and Development of Male and Female Gametophytes of Clematis heracleifolia

Yang Yi1,Wang Na1,Wang Kuiling1,Liu Qinghua1,Li Wei1,Guo Xiao1,Ma Yingjie2,Liu Qingchao1,*()   

  1. 1. College of Landscape Architecture and Forestry, Qingdao Agricultural University, Qingdao 266109, China
    2. Weihai Shuimuyuan Design Co. Lid, Weihai 264205, China
  • Received:2018-12-05 Accepted:2019-06-18 Online:2020-03-10 Published:2019-09-01
  • Contact: Liu Qingchao


In Clematis (Ranunculaceae) species show significant differences in floral morphology and structures, consistent with their complex genetic background. Thus, it is important to study the embryological characteristics prior to any attempts of breeding by hybridization. Here, we report the characterization of microsporogenesis, microgametogenesis, megasporogenesis and macrogametogenesis of Clematis heracleifolia by floral dissection. We show that C. heracleifolia is androdioecy. Aborted microgametophyte cells are observed in the majority of bisexual flowers but occasionally found in male flowers, which results in the formation of functional female flowers. However, in a small number of normal bisexual flowers, male gametophytes mature faster than that of female gametophytes. During microsporogenesis, the tetrasporangiate anther is formed, followed by simultaneous microsporocyte cytokinesis, and the formation of glandular tapetum, occasionally with amoeboid tapetum. After meiosis, the microspores tetrads are mostly tetrahedral, and occasionally symmetrical. The wall of mature anther contains fibrous thickening epidermis and endothecium. Pollen grains are spheroidal, pantocolpate, and 2-celled. The ovary has one chamber with a normal and a few degraded ovules, which contains a anatropous, unitegmic, tenuinucellate, and Polygonum-type embryo-sac. A linear tetrad of megaspores and dikaryocyte antipodal cells can be observed. This species may belong to a transitional clade within Clematis. In breeding practice for C. heracleifolia, it is advised to use plants bearing male flowers and hermaphrodite flowers as male and female parents, respectivley, with the bisexual flowers of 0.5-0.8-cm-long to be emasculated.

Key words: Clematis heracleifolia, Clematis, gametophyte, Ranunculaceae, sporophyte

Figure 1

The floral structure of Clematis heracleifolia Staminate flower; (B) Bisexual flower. Bars=5 mm"

Figure 2

Microspore development in staminat e flower of Clematis heracleifolia (A) Archesporial cell (arrow, up), primary parietal cell (arrow, up) and primary sporogenous cell (arrow, down); (B) Anther wall; (C1) A row of secondary sporogenous cells; (C2) Prophase (arrow); (C3) Metaphase (arrow, right) and anaphase (arrow, left); (C4) Telophase (arrow); (D) Microspore mother cells; (E1) Microspore mother cells at prophase of prophase I of meiosis; (E2) Microspore mother cells at metaphase of meiosis I (arrow); (E3) Microspore mother cells at anaphase (arrow, right) and telophase (arrow, left) of meiosis I; (F1) Microspore mother cells at anaphase of meiosis II (arrow, left) and amoeboid tapetum (arrow, right); (F2) Microspore mother cells at telophase of meiosis II (arrow) and symmetrical microspore tetrads; (G) Degrading tetrahedral tetrad; (H) The asynchronous phases; (I1)-(I4) Aborted microspores. Bars=50 μm"

Figure 3

Microgametophyte development in staminate flower of Clematis heracleifolia (A) Microspore at monokaryotic stage; (B) Microspore at monokaryotic side stage; (C1) Microspore at prophase (arrow); (C2) Microspore at metaphase (arrow, down) and anaphase (arrow, up); (C3) Microspore at anaphase (arrow); (C4) Microspore at telophase, vegetative cell and germ cell are formed (arrow); (D) The dehiscent anther, and the 2-celled mature pollen grains. (A), (B), (C1), (D) Bars=50 μm; (C2)-(C4) Bars=20 μm"

Figure 4

Microspore and pollen grain development in bisexual flower of Clematis heracleifolia (A)-(D) Aborted microspore mother cells; (E), (F) Some aborted microspore mother cells; (G), (H) Normal pollen grains. an: Anther; ov: Ovary. (A), (C), (G) Bars=500 μm; (B), (F) Bars=50 μm; (D), (E), (H) Bars=200 μm"

Table 1

Pollen characteristics of Clematis heracleifolia"

Characters State
Shape Spheroidal
Type of aperture Pantocolpate
Diameter (μm) 16.09±0.88
Spinule height (μm) 0.46±0.09
Number of spinules (3×3 μm2) 3.80±1.08

Figure 5

Scanning electron microscopy views of pollen grains of Clematis heracleifolia (A) Bar=10 μm; (B)-(D) Bars=1 μm"

Figure 6

Megaspore and megagametophyte development in bisexual flower of Clematis heracleifolia (A), (B) The ovary and ovule; (C) Archesporial cells (arrow); (D) Megaspore mother cells (arrow); (E) A linear tetrad of megaspores (arrows); (F) The three endostome megaspores were degenerated and the chalazal one was a functional megaspore (arrows); (G) Binucleate embryo sac; (H) Tetranucleate embryo sac; (I) Embryo sac with 8 nuclei; (J)-(L) Mature embryo sac of seven-cell with eight nuclei. ac: Antipodal cell; cc: Central nucleus; ec: Egg cell; sy: Synergids. (A), (B) Bars=200 μm; (C)-(L) Bars=50 μm"

Table 2

Relationship between gametophytes development and flower bud morphology in staminate flower of Clematis heracleifolia"

Bud length (cm) Stamen length (cm) Male gametophyte
0.22-0.40 0.15-0.31 Microsporocyte, meiosis
0.40-0.85 0.31-0.51 Meiosis, microspore
0.85-1.09 0.51-0.86 Microspore, monokaryotic side stage, mitosis
1.09-1.39 0.86-1.12 Mitosis, 2-celled pollen
1.39-2.14 1.12-1.32 2-celled pollen

Table 3

Relationship between gametophytes development and flower bud morphology in bisexual flower of Clematis heracleifolia"

Bud length (cm) Stamen length (cm) Pistil length (cm) Male gametophyte Female gametophyte
0.16-0.36 0.10-0.14 0.05-0.11 Microsporocyte, meiosis, microspore -
0.36-0.50 0.14-0.34 0.10-0.18 Microspore monokaryotic side stage, mitosis Archesporium, megasporocyte
0.50-0.88 0.34-0.48 0.18-0.21 Mitosis, 2-celled pollen Megasporocyte, uninucleate embryo sac
0.88-0.95 0.48-0.52 0.21-0.30 2-celled pollen Uninucleate embryo sac, 2-nucleate or 4-nucleate embryo sac
0.95-1.42 0.52-0.60 0.30-0.42 2-celled pollen 4-nucleate or 8-nucleate embryo sac, mature embryo sac
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