Morphology and cytology of three flower phenotypes in a duodichogamous tree species, Acer mono

doi:10.3724/SP.J.1003.2011.07035

Abstract

Abstract:

Duodichogamy, where individual plants produce two batches of male flowers that are temporally separated by a batch of female flowers, is the rarest temporal sexual system in flowering plants. Duodichogamy is present in some species of Acer, whose flowers of the first (male I) and second male phases (male II) differ morphologically. To explore the influence of floral development on flower morphology and phenology, we used paraffin methods and light microscopy to compare morphological and cytological differences among male (I and II) and female flowers at different developmental stages. Our main results were as follows: the ovary of male I degenerated and disappeared quickly upon megaspore tetrad degeneration, and developed into macrosporocytes; while the ovary of male II degenerated gradually during this period and only traces of residual ovule remained in the fully-developed ovary; the failure of anthers of female flowers to dehisce might be caused by retardant degeneration of tapetum tissue and loss of lip cells, i.e. formation sterility. In conclusion, both pistil and stamen primordial could be found in male (I and II) and female flower buds at early phases of sex differentiation, but selective abortion occurred in later developmental phases.

Key words: Acer mono, duodichogamy, functional male and female flowers, morphology, cytology

Lingzhi Zhang, Hui Shang, Yibo Luo, Xin Cheng, Weining Bai. Morphology and cytology of three flower phenotypes in a duodichogamous tree species, Acer mono[J]. Biodiv Sci, 2011, 19(5): 551-557.

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URL: https://www.biodiversity-science.net/EN/10.3724/SP.J.1003.2011.07035

https://www.biodiversity-science.net/EN/Y2011/V19/I5/551

Figures/Tables 3

Fig. 1 Male and female flowers of Acer monoat anthesis. (A) Male I flower, showing eight stamens; (B) Male II, showing small ovary and style; (C) Female flower, showing no-dehiscent stamens and normal pistil. St, Stamen; Pi, Pistil.

Fig. 2 The process of stamen development in Acer mono. (A) The early development of flowers, both male (I and II) and female flowers are in the bisexual stage; (B) The tetrahedral tetrads are formed; (C) The microspores are released from the tetrad; (D) Formation of a large vacuole pushes the single nucleus towards the wall; (E), (F) and (I) are showing the process of formation, maturation and dehiscence of two-celled pollens in male I and II, respectively; (G) and (H) are the formation and maturation of two-celled pollens in female flowers, respectively; (J) and (K) are showing SEM micrographs for mature pollen grains in A.mono, and (J) for male I and II, (K) for female flowers, respectively. Lc, Lip cell; Ta, Tapetum; An, Anther; Ov, Ovary; Fl, Fibrous layer; Mmc, Microspore mother cell; Ms, microspore; Gc, Generative cell; Vc, Vegetative cell. Scale bars = 50 µm for A, 20 µm for B to K.

Fig. 3 The process of pistil development in Acer mono. (A) Longitudinal section of ovary and ovule, showing the bisexual stage of male flowers; (B) Both integuments arise from the ovule primordium, and the megaspore mother cell is formed; (C) Linear megaspore tetrad is formed as result of meiosis of the megaspore mother cell; (D) to (G) The process of pistil abortion in male I and II; (D)The marginal cells of ovule are obscure; (E) The whole ovule cells become unclear; (F) The mushroom cloud abortive ovule; (G) The depauperate ovary with the wholly abortive ovule; (H) to (N) The process of perfect pistil development in female flowers: (H) Chalazal megaspore is functional, while the other three megaspores have degenerated; (I) Two-nucleate embryo sac; (J) to (K) Fournucleate embryo sac; (L) to (N) 8-nucleate embryo. Mmc, Megaspore mother cell; Mt, Megaspore tetrad; Fm, Functional megaspore; Ec, Egg cell; Art, Antipodal cell; Pn, Polar nucleus; Sy, Synergid. Scale bars = 20 µm for A, F,G; 10 µm for B to E, and H to N.

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