Abstract
Tapetum, orbicule, and pollen grain ontogeny in Colletia paradoxa and Discaria americana were studied with transmission electron microscopy (TEM). The ultrastructural changes observed during the different stages of development in the tapetal cells and related to orbicule and pollen grain formation are described. The proorbicules have the appearance of lipid globule, and their formation is related to the endoplasmic reticulum of rough type (ERr). This is the first report on the presence of orbicules in the family Rhamnaceae. Pollen grains are shed at the bicellular stage.
Highlights
Rhamnaceae is a family of about 55 genera and 900 species, cosmopolitan in distribution, especially in warm temperate regions [1, 2]
Orbicule, and pollen grain ontogeny in Colletia paradoxa and Discaria americana were studied with transmission electron microscopy (TEM)
The proorbicules have the appearance of lipid globule, and their formation is related to the endoplasmic reticulum of rough type (ERr)
Summary
Rhamnaceae is a family of about 55 genera and 900 species, cosmopolitan in distribution, especially in warm temperate regions [1, 2]. The tribe Colletieae is a monophyletic group that comprises six genera that differ in flower and fruit traits [3,4,5,6,7]. Distribution of the tribe is associated with the Andes in South America, and usually found 30◦ South [7]. The traditional diagnostic characters of the tribe are decussate leaves, abundance of spines, and presence of serial meristems in the leaf axils [8]
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