Akitoshi Iwamoto1, Ryoko Izumidate2, Louis P Ronse De Craene3. 1. Department of Biology, Tokyo Gakugei University, 4-1-1 Nukui Kita-machi, Koganei-shi, Tokyo 184-8501, Japan akitoshi@u-gakugei.ac.jp. 2. Department of Biology, Tokyo Gakugei University, 4-1-1 Nukui Kita-machi, Koganei-shi, Tokyo 184-8501, Japan. 3. Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, UK.
Abstract
PREMISE OF THE STUDY: The phylogenetic position of Ceratophyllum is still controversial in recent molecular analyses of angiosperms, with various suggestions of a sister group relation to all other angiosperms, eudicots, monocots, eudicots + monocots, and magnoliids. Therefore, the morphological characters of Ceratophyllum are important for resolving the phylogeny of angiosperms. In this study, we observed the detailed developmental anatomy of all lateral organs and their configurations to elucidate the floral development and phyllotactic pattern of Ceratophyllum demersum. METHODS: We observed fixed shoots of C. demersum with scanning electron microscopy and serial sections of the samples with light microscopy. KEY RESULTS: Bract primordia arise first, followed by the stamen primordia in staminate flowers. Both bracts and stamens initiate unidirectionally, first on the abaxial side of the floral apex and later on the adaxial side, most likely due to the contact pressure imposed by the leaf primordium at the superior node. In pistillate flowers, bract primordia on the abaxial side were also initiated first. The configuration of buds at one node showed six patterns and each pattern included at least one vegetative bud, and flower buds were always accompanied by vegetative buds at the same node. CONCLUSIONS: The initiation pattern of organs in the outer whorls of C. demersum flowers is distorted by mechanical pressure, resulting in the phyllotactic variation of staminate flowers. Vegetative buds are the main axillary buds with floral buds as accessory buds, which suggests that the shoot of C. demersum has been modified from a decussate phyllotaxis.
PREMISE OF THE STUDY: The phylogenetic position of Ceratophyllum is still controversial in recent molecular analyses of angiosperms, with various suggestions of a sister group relation to all other angiosperms, eudicots, monocots, eudicots + monocots, and magnoliids. Therefore, the morphological characters of Ceratophyllum are important for resolving the phylogeny of angiosperms. In this study, we observed the detailed developmental anatomy of all lateral organs and their configurations to elucidate the floral development and phyllotactic pattern of Ceratophyllum demersum. METHODS: We observed fixed shoots of C. demersum with scanning electron microscopy and serial sections of the samples with light microscopy. KEY RESULTS: Bract primordia arise first, followed by the stamen primordia in staminate flowers. Both bracts and stamens initiate unidirectionally, first on the abaxial side of the floral apex and later on the adaxial side, most likely due to the contact pressure imposed by the leaf primordium at the superior node. In pistillate flowers, bract primordia on the abaxial side were also initiated first. The configuration of buds at one node showed six patterns and each pattern included at least one vegetative bud, and flower buds were always accompanied by vegetative buds at the same node. CONCLUSIONS: The initiation pattern of organs in the outer whorls of C. demersum flowers is distorted by mechanical pressure, resulting in the phyllotactic variation of staminate flowers. Vegetative buds are the main axillary buds with floral buds as accessory buds, which suggests that the shoot of C. demersum has been modified from a decussate phyllotaxis.
Authors: Dmitry D Sokoloff; Elena S El; Elena V Pechenyuk; Laetitia Carrive; Sophie Nadot; Paula J Rudall; Margarita V Remizowa Journal: Front Cell Dev Biol Date: 2022-04-28
Authors: Kester Bull-Hereñu; Patricia Dos Santos; João Felipe Ginefra Toni; Juliana Hanna Leite El Ottra; Pakkapol Thaowetsuwan; Julius Jeiter; Louis Philippe Ronse De Craene; Akitoshi Iwamoto Journal: Plants (Basel) Date: 2022-02-28