Pollen and microsporangium development in Ziziphus jujuba, Z. mucronata, Paliurus spina-christi and Gouania ulmifolia (Rhamnaceae).

Marina M Gotelli,Elsa C Lattar,Gabriela Zarvlasky,Beatriz G Galati

doi:10.1590/0001-3765202020181382

Abstract

The aim of this paper is to investigate the ultrastructural events that occur during pollen grains development, with emphasis in pollen grain wall and tapetum ontogeny in Ziziphus jujuba, Z. mucronata, Paliurus spina-christi (Paliureae) and Gouania ulmifolia (Gouanieae). Anthers at different developmental stages were processed according to classic techniques for transmission electron microscopy. Differences in the number of endothecium layers and in the number of tapetal cell nuclei were found. Tapetal cells present an anastomosing tubular network and large vesicles with fibrillar content in the cytoplasm. Pollen grain development and ontogeny of pollen grain wall are similar in the four species. The number of endothecium layers, the number of nuclei of the tapetal cells and tapetal cells ultrastructure of the four species support the phylogenetic relationships previously published for the Rhamnaceae family. Tapetal vesicles with fibrillar or polysaccharide content seem to be an exclusive characteristic of the tribes Paliureae and Gouanieae. Some ultrastructural characters of the pollen grain wall development are common to other species of Rhamnaceae, such as the primexine matrix present at the microspore mother cell stage, the aperture entirely built up during the tetrad stage, the thick and fibrillar intine, and the granular infractectum.

Highlights

Rhamnaceae is a family with a cosmopolitan distribution that includes 55 genera and 900 species (Medan & Schirarend 2004, Perveen & Qaiser 2005). Richardson et al (2000a, b) proposed a classification with 11 tribes, which is strongly supported in three clades: Rhamnoid, Ziziphoid and Ampelozizyphoid
The aim of this paper is to describe the ultrastructure of pollen grains and microsporangium development with special attention to tapetum and pollen grain wall ontogeny in species from the Paliureae and Gouanieae tribes, in order to broaden the embryological knowledge of family and to evaluate the characters of reproductive sporophytic structures that support the current classification for Rhamnaceae
Tapetal cells are uninucleate in G. ulmifolia, P. spina-christi, and binucleate in both species of Ziziphus

Summary

Introduction

Rhamnaceae is a family with a cosmopolitan distribution that includes 55 genera and 900 species (Medan & Schirarend 2004, Perveen & Qaiser 2005). Richardson et al (2000a, b) proposed a classification with 11 tribes, which is strongly supported in three clades: Rhamnoid, Ziziphoid and Ampelozizyphoid. Hauenschild et al (2016) claimed that there are some notable uncertainties and that the morphological characters known until now do not support a formal taxonomic description of these three clades as subfamilies. According to Gotelli et al (2016a), the morphology and the ultrastructure of the nectaries of Rhamnaceae underpin the plastid DNA-based phylogenetic analysis made by Richardson et al (2000a). In this family, the anatomic data of the reproductive sporophytic structures show more systematic value than the gametophytic structures (Gotelli et al 2016b).

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