The exine ultrastructure of pollen grains in Gnetum (Gnetaceae) from China and its bearing on the relationship with the ANITA Group

Pollen grains of six species of Gnetum, G. parvifolium, G. hainanense, G. luofuense, G. pendulum, G. cleistostachyum and G. montanum, collected from China were examined using light, scanning and transmission electron microscopy. Pollen grains of Gnetum are subspheroidal or irregular-apolar, inaperturate, 11.21–22.44 µm in long axis and 9.34–20.47 µm in short axis. The exine surface is covered with spinules, 0.50(0.30–0.71) µm long spaced on average 1.12(0.81–1.46) µm apart. The exine is about 0.55 µm thick and comprises ectexine and endexine. The ectexine includes a thin tectum and an infratectal granular layer. The tectum protrudes outwards, forming the spinules. The endexine is composed of discontinuous lamellae, with lacunae between lamellae. The pollen grains of Gnetum are compared with those of Ephedra and Welwitschia, and also those of the ANITA Group of angiosperms, including Amborellaceae, Nymphaeales, Illiciales, Trimeniaceae and Austrobaileyaceae. The exine ultrastructures of Gnetum, Ephedra and Welwitschia are quite similar, consisting of tectum, granular layer and lamellated endexine. The exine ultrastructure of Gnetum is also similar to that of Nymphaea colorata (Nymphaeaceae) in the transitional region between the proximal and distal poles, but differs from that of Amborellaceae, Illicium religiosum (Illiciaceae), Schisandra (Schisandraceae), Trimeniaceae and Austrobaileyaceae. This comparison of exine ultrastructure provides new evidence for consideration of the relationship between Gnetum and the ANITA Group. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 146, 415–425.

[1]  V. Goremykin,et al.  Analysis of the Amborella trichopoda chloroplast genome sequence suggests that amborella is not a basal angiosperm. , 2003, Molecular biology and evolution.

[2]  Pamela S Soltis,et al.  Phylogeny of seed plants based on evidence from eight genes. , 2002, American journal of botany.

[3]  M. Donoghue,et al.  The root of the angiosperms revisited , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[4]  M. Källersjö,et al.  Seed Plant Relationships and the Systematic Position of Gnetales Based on Nuclear and Chloroplast DNA: Conflicting Data, Rooting Problems, and the Monophyly of Conifers , 2002, International Journal of Plant Sciences.

[5]  J. Palmer,et al.  The evolutionary split of Pinaceae from other conifers: evidence from an intron loss and a multigene phylogeny. , 2001, Molecular phylogenetics and evolution.

[6]  M. Hesse.  Pollen Characters of Amborella trichopoda (Amborellaceae): A Reinvestigation , 2001, International Journal of Plant Sciences.

[7]  F. B. Sampson.  Pollen Diversity in Some Modern Magnoliids , 2000, International Journal of Plant Sciences.

[8]  D. Soltis,et al.  Phylogeny of Basal Angiosperms: Analyses of Five Genes from Three Genomes1 , 2000, International Journal of Plant Sciences.

[9]  J. Palmer,et al.  Seed plant phylogeny inferred from all three plant genomes: monophyly of extant gymnosperms and origin of Gnetales from conifers. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[10]  C. dePamphilis,et al.  Phylogeny of seed plants based on all three genomic compartments: extant gymnosperms are monophyletic and Gnetales' closest relatives are conifers. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[11]  Michael J. Donoghue,et al.  Seed plant phylogeny: Demise of the anthophyte hypothesis? , 2000, Current Biology.

[12]  Mark W. Chase,et al.  The earliest angiosperms: evidence from mitochondrial, plastid and nuclear genomes , 1999, Nature.

[13]  W. Martin,et al.  Molecular Data from the Chloroplast rpoC1 Gene Suggest a Deep and Distinct Dichotomy of Contemporary Spermatophytes into Two Monophyla: Gymnosperms (Including Gnetales) and Angiosperms , 1999, Journal of Molecular Evolution.

[14]  W. Martin,et al.  Gnetum and the Angiosperms: Molecular Evidence that Their Shared Morphological Characters Are Convergent, Rather than Homologous , 1999 .

[15]  H. Saedler,et al.  MADS-box genes reveal that gnetophytes are more closely related to conifers than to flowering plants. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[16]  G. El-Ghazaly,et al.  Polarity, aperture condition and germination in pollen grains ofEphedra (Gnetales) , 1998, Plant Systematics and Evolution.

[17]  J. Doyle.  Molecules, morphology, fossils, and the relationship of angiosperms and Gnetales. , 1998, Molecular phylogenetics and evolution.

[18]  W. Friedman,et al.  Double Fertilization in Gnetales: Implications for Understanding Reproductive Diversification among Seed Plants , 1996, International Journal of Plant Sciences.

[19]  S. Carlquist.  Wood, Bark, and Stem Anatomy of Gnetales: A Summary , 1996, International Journal of Plant Sciences.

[20]  W. Friedman,et al.  Double fertilization in Gnetum gnemon (Gnetaceae): its bearing on the evolution of sexual reproduction within the Gnetales and the anthophyte clade , 1996 .

[21]  W. Friedman,et al.  Double Fertilization in Gnetum gnemon: The Relationship between the Cell Cycle and Sexual Reproduction. , 1995, The Plant cell.

[22]  J. Fisher,et al.  Vessel dimensions in liana and tree species of Gnetum (Gnetales) , 1995 .

[23]  Masamichi Takahashi.  Exine Development in Illicium Religiosum Sieb. et Zucc. (Illiciaceae) , 1994 .

[24]  N. Gabarayeva,et al.  Exine development in Nymphaea colorata (Nymphaeaceae) , 1994 .

[25]  T. Taylor,et al.  The ultrastructure of fossil ephedroid pollen with gnetalean affinities from the Lower Cretaceous of Brazil , 1993 .

[26]  M. Zavada,et al.  Comparative pollen wall development of Welwitschia mirabilis and selected primitive angiosperms , 1991 .

[27]  R. Schmid,et al.  The Families and Genera of Vascular Plants. Vol. 1. Pteridophytes and Gymnosperms , 1991 .

[28]  P. K. Endress,et al.  Pollen morphology in the trimeniaceae , 1984 .

[29]  M. Hesse.  Pollenkitt is lacking inGnetatae:Ephedra andWelwitschia; further proof for its restriction to the angiosperms , 1984, Plant Systematics and Evolution.

[30]  M. Zavada.  Pollen Wall Development of Austrobaileya maculata , 1984, Botanical Gazette.

[31]  R. Sattler,et al.  VESSEL STRUCTURE OF GNETUM AND THE ORIGIN OF ANGIOSPERMS , 1982 .

[32]  R. Honegger,et al.  The Pollen of the Austrobaileyaceae and its Phylogenetic Significance , 1980 .

[33]  M. Hesse.  Pollenkitt is lacking inGnetum gnemon (Gnetaceae) , 1980, Plant Systematics and Evolution.

[34]  James W. Walker.  EVOLUTION OF EXINE STRUCTURE IN THE POLLEN OF PRIMITIVE ANGIOSPERMS , 1974 .

[35]  H. Godwin,et al.  Pollen Morphology and Plant Taxonomy: Angiosperms , 1967 .

[36]  C. Wan-chun.  A New Name for a Species of Gnetum L. , 1964 .

[37]  A. Love.  Pollen and Spore Morphology, Plant Taxonomy. Gymnospermae, Pteridophyta, Bryophyta. (An Introduction to Palynology, II). G. Erdtman , 1958 .

[38]  G. Erdtman.  Pollen Morphology and Plant Taxonomy , 1953 .

[39]  R. P. Wodehouse.  Pollen grains : their structure, indentification and significance in science and medicine , 1937 .

[40]  T. Just,et al.  Pollen Grains, Their Structure, Identification and Significance in Science and Medicine. , 1936 .

[41]  A. Zharkikh,et al.  Molecular phylogeny of extant gymnosperms and seed plant evolution: analysis of nuclear 18S rRNA sequences. , 1997, Molecular biology and evolution.

[42]  L. Gillespie,et al.  Systematic implications of pollen morphology in Gnetum , 1994 .

[43]  Kevin C. Nixon,et al.  A Reevaluation of Seed Plant Phylogeny , 1994 .

[44]  F. B. Sampson.  Pollen morphology of the Amborellaceae and Hortoniaceae (Hortonioideae: Monimiaceae) , 1993 .

[45]  Peter R. Crane,et al.  Phylogenetic analysis of seed plants and the origin of angiosperms , 1985 .

[46]  B. Gullvåg.  The Fine Structure of Some Gymnosperm Pollen Walls , 1966 .

[47]  Plunt Sv.stemutits,et al.  Pollenkitt is Lacking in Gnetatae : Ephedra and Welwitschia ; Further Proof for its Restriction to the Angiosperms , 2022 .