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Development of the permanent tetrad wall in Juncus L. (Juncaceae, Poales)

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Abstract

Juncaceae, a cosmopolitan family, belong to the cyperid clade of Poales together with Cyperaceae and Thurniaceae. Pollen grain of Juncaceae, as in Thurniaceae, is dispersed in a permanent tetrad, and knowledge about the ontogeny of its wall is still incipient, based on data from only one species. This study aims to analyze the formation of the pollen wall of seven Juncus species in order to characterize the timing and the ontogenetic events that lead to the cohesion of the four pollen grains in a permanent tetrad. Anthers at different developmental stages were submitted to techniques of light microscopy and transmission electron microscopy; dehiscent anthers with mature pollens were also analyzed in scanning electron microscopy. In all the species here studied, callose deposits around each microsporocyte, with dissolution prior to meiosis. Microspore wall starts at the end of the second meiotic division with formation of primexine. Exine comprises tectum, columellae, and foot layer. During cytokinesis, cell plates form the internal wall of the pollen tetrad. Mature permanent tetrad is enveloped externally by both the exine and intine and internally by the intine and the foot layer, which forms the continuous internal wall. Callose was detected in the early stages of microsporocytes, although reported to be absent in Juncaceae. Our data confirm the variation in Juncaceae cytokinesis and the occurrence of simple cohesion due to the presence of a continuous tectum along the pollen tetrad.

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The authors confirm that the data supporting the findings of this study are available within the manuscript.

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Acknowledgments

The authors thank Prof. Dr. Elliot Watanabe Kitajima for the permission to use the facilities of Laboratório de Microscopia Eletrônica aplicada à Pesquisa Agropecuária (NAP/MEPA - ESALQ/USP, Piracicaba, São Paulo, Brazil) and Renato Barbosa Salaroli for the technical assistance with the TEM.

Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq – Ph.D. Scholarship process number 141848/2017-0 to F.P.L. and Research Grant process numbers 307515/2015-0 and 309504/2018-0 to A.I.C.) and by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES – PNPD – Finance Code 001 to A.O.).

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The present study is part of the Ph.D. Thesis of the first author. All authors contributed to its conception and design. Material preparation and data collection were performed by Fernanda Passarini Lopes, and analysis was performed by all authors. All authors contributed and approved the final version of the present manuscript.

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Correspondence to Fernanda Passarini Lopes.

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Passarini Lopes, F., Oriani, A. & Coan, A.I. Development of the permanent tetrad wall in Juncus L. (Juncaceae, Poales). Protoplasma 258, 495–506 (2021). https://doi.org/10.1007/s00709-020-01583-0

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  • DOI: https://doi.org/10.1007/s00709-020-01583-0

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