Development of the permanent tetrad wall in Juncus L. (Juncaceae, Poales)
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ORIGINAL ARTICLE
Development of the permanent tetrad wall in Juncus L. (Juncaceae, Poales) Fernanda Passarini Lopes 1
&
Aline Oriani 1,2
&
Alessandra Ike Coan 1,2
Received: 11 July 2020 / Accepted: 30 October 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
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. Keywords Cyperids . Callose . Primexine . Exine . Intine
Introduction The pollen grain wall in angiosperms usually consists of exine and intine formed after microsporocyte meiosis (HeslopHarrison 1968, 1971; Stanley and Linskens 1974; Bhojwani and Bhatnagar 1978). The beginning is marked by the deposition of a callose wall around each newly formed microspore (Heslop-Harrison 1963, 1964, 1968, 1971; Stanley and Linskens 1974; Bhojwani and Bhatnagar 1978; Knox 1984), with subsequent deposition of primexine between the callose wall and the plasma membrane of each microspore (HeslopHandling Editor: Benedikt Kost * Fernanda Passarini Lopes [email protected] 1
Programa de Pós-Graduação em Ciências Biológicas (Biologia Vegetal), Universidade Estadual Paulista “Júlio de Mesquita Filho” (Unesp), Instituto de Biociências, Rio Claro, São Paulo, Brazil
2
Departamento de Biodiversidade, Universidade Estadual Paulista “Júlio de Mesquita Filho” (Unesp), Instituto de Biociências, Rio Claro, São Paulo, Brazil
Harrison 1963, 1971; Bhojwani and Bhatnagar 1978; Knox 1984). Primexine is the precursor of exine (Heslop-Harrison 1971) and the matrix in which the polymerization of sporopollenin will occur (Knox 1984). After the enzymatic dissolution of
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