Mechanical Pressure, Not Genes, Makes Ovulate Parts Leaf-Like in Cycas


The so-called “megasporophylls” of Ginkgoales, Coniferales, and Gnetales have been proven metamorphosed shoots, making “megasporophyll” of Cycas the last one resembling a leaf. Why and how it is so in Cycas (the most ancient seed plant dated back to the Palaeozoic) become key questions because their answers are hinged with the fates of several hypotheses in botany. Here, we performed a controlled developmental experiment on the ovulate parts (megasporophylls) in a single strobilus of Cycas sexseminifera. By removing the neighboring ones, two of the ovulate parts were left isolated spatially from others, in contrast to others left intact. A half-year-long continuous observation indicates that the isolated ovulate parts change their ovule arrangement from initial pinnate into helical pattern, while the intact ones in the same strobilus remain pinnate as usual. Since all ovulate parts are in the same strobilus and controlled by the same genome in this case and the only difference is lack of pressure from neighbors for the isolated ones, the changes in ovule orientation and ovulate part morphology can only be attributed to the lack of mechanical pressure among the ovulate parts. Therefore, we conclude that mechanical pressure, not genes, controls the morphology of ovulate parts and contributes to the leaf-like ovulate part morphology in Cycas. This conclusion cautions previous superficial interpretations of plant morphology.

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X. Wang and B. Luo, "Mechanical Pressure, Not Genes, Makes Ovulate Parts Leaf-Like in Cycas," American Journal of Plant Sciences, Vol. 4 No. 12A, 2013, pp. 53-57. doi: 10.4236/ajps.2013.412A1008.

Conflicts of Interest

The authors declare no conflicts of interest.


[1] J. W. V. Goethe, “Versuch die Metamorphose der Pflanzen zu Erklären,” Carl Wilhelm Ettinger, Gotha, 1790.
[2] D. R. Kaplan, “The Science of Plant Morphology: Definition, History, and Role in Modern Biology,” American Journal of Botany, Vol. 88, No. 10, 2001, pp. 1711-1741.
[3] R. Classen-Bockhoff, “Plant Morphology: The Historic Concepts of Wilhelm Troll, Walter Zimmermann and Agnes Arber,” Annals of Botany, Vol. 88, No. 6, 2001, pp. 1153-1172.
[4] M. C. Dornelas and O. Dornelas, “From Leaf to Flower: Revisiting Goethe’s Concepts on the ‘Metamorphosis’ of Plants,” Brazilian Journal of Plant Physiology, Vol. 17, No. 4, 2005, pp. 335-344.
[5] Z. Zhou, S. Zheng and L. Zhang, “Morphology and Age of Yimaia (Ginkgoales) from Daohugou Village, Ningcheng, Inner Mongolia, China,” Cretaceous Research, Vol. 28, No. 2, 2007, pp. 348-362.
[6] E. D. Brenner, D. W. Stevenson and R. W. Twigg, “Cycads: Evolutionary Innovations and the Role of Plant-Derived Neurotoxins,” Trends in Plant Science, Vol. 8, No. 2003, pp. 446-452.
[7] P. Martens, “Les Gnetophytes,” Gebrueder Borntraeger, Berlin, 1971.
[8] R. Florin, “The Morphology of Trichopitys heteromorpha Saporta, a Seed Plant of Palaeozoic Age, and the Evolution of the Female Flowers in the Ginkgoinae,” Acta Horti Bergiani, Vol. 15, No. 5, 1949, pp. 79-109.
[9] S. Zheng and Z. Zhou, “A New Mesozoic Ginkgo from Western Liaoning, China and Its Evolutionary Significance,” Review of Palaeobotany and Palynology, Vol. 131, No. 1-2, 2004, pp. 91-103.
[10] Z. Zhou and S. Zheng, “The Missing Link in Ginkgo Evolution,” Nature, Vol. 423, No. 6942, 2003, pp. 821822.
[11] F. J. F. Shaw, “A Contribution to the Anatomy of Ginkgo biloba,” New Phytologist, Vol. 7, No. 4-5, 1908, pp. 85-93.
[12] G. W. Rothwell and R. A. Stockey, “Evolution and Phylogeny of Gnetophytes: Evidence from the Anatomically Preserved Seed Cone Protoephedrites eamesii gen. et sp. nov. and the Seeds of Several Bennettitalean Species,” International Journal of Plant Sciences, Vol. 174, No. 3, 2013, pp. 511-529.
[13] A. J. Eames, “The Relationships of Ephedrales,” Phytomorphology, Vol. 2, No. 1, 1952, pp. 79-100.
[14] A. Carlsbecker, J. F. Sundström, M. Englund, D. Uddenberg, L. Izquierdo, A. Kvarnheden, F. Vergara-Silva and P. Engström, “Molecular Control of Normal and Acrocona Mutant Seed Cone Development in Norway Spruce (Picea abies) and the Evolution of Conifer Ovule-Bearing Organs,” New Phytologist, Vol. 200, No. 1, 2013, pp. 261-275.
[15] D. W. Stevenson, “Morphology and Systematics of the Cycadales,” Memoirs of the New York Botanical Garden, Vol. 57, No. 1, 1990, pp. 8-55.
[16] R. Melville, “A New Theory of the Angiosperm Flower: I. The Gynoecium,” Kew Bulletin, Vol. 16, No. 1, 1962, pp. 1-50.
[17] A. D. J. Meeuse, “From Ovule to Ovary: A Contribution to the Phylogeny of the Megasporangium,” Acta Biotheoretica, Vol. XVI, No. 3-4, 1963, pp. 127-182.
[18] E. J. Hermsen, T. N. Taylor, E. L. Taylor and D. W. Stevenson, “Cataphylls of the Middle Triassic Cycad Antarcticycas schopfii and New Insights into Cycad Evolution,” Americna Journal of Botany, Vol. 93, No. 5, 2006, pp. 724-738.
[19] A. M. F. Tomescu, “Megaphylls, Microphylls and the Evolution of Leaf Development,” Trends in Plant Science, Vol. 14, No. 1, 2008, pp. 5-12.
[20] S. Hao and J. Xue, “Earliest Record of Megaphylls and Leafy Structures, and Their Initial Diversification,” Chinese Science Bulletin, Vol. 58, No. 23, 2013, pp. 2784-2793.
[21] X. Wang, D. Stevenson and N. Li, “Doubt on the Foliar Nature of Cycad Megasporophylls,” Botanical Society of America Annual Meeting, Columbus, 10 July 2012, ID: 841.
[22] Z.-T. Guan and L. Zhou, “Cycads of China,” Sichuan Science and Technology Press, Chengdu, 1996.
[23] F. Wang, H. Liang, T. Chen and D. Wang, “Cycads in China,” Guangdong Science & Technology Press, Guangzhou, 1996.
[24] D.-X. Xiao, “Anatomy of the Vegetative Organs of Cycas szechuanensis,” Journal of Zhongkai University of Agriculture and Technology, Vol. 18, No. 3, 2005, pp. 1-5.
[25] Y.-J. Tang and J.-P. Liao, “Studies on Comparative Anatomy of the Pinnae of Six Species of Cycas,” Chinese Bulletin of Botany, Vol. 18, No. 5, 2001, pp. 615-622.
[26] W. C. Worsdell, “The Vascular Structure of the Sporophylls of the Cycadaceae,” Annals of Botany, Vol. os-12, No. 2, 1898, pp. 203-241.

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