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Lipid‐rich tapetosomes in Brassica tapetum are composed of oleosin‐coated oil droplets and vesicles, both assembled in and then detached from the endoplasmic reticulum
Author(s) -
Hsieh Kai,
Huang Anthony H.C.
Publication year - 2005
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2005.02502.x
Subject(s) - oleosin , endoplasmic reticulum , calreticulin , tapetum , organelle , vesicle , microbiology and biotechnology , biology , golgi apparatus , kdel , calnexin , lamella (surface anatomy) , biophysics , stamen , pollen , biochemistry , botany , anatomy , membrane , microspore , gene
Summary Tapetosomes are abundant organelles in tapetum cells of floral anthers in Brassicaceae species. They contain triacylglycerols (TAGs), the amphipathic protein oleosins and putative vesicles and play a predominant role in pollen‐coat formation. Here we report the biogenesis and structures of tapetosomes in Brassica. Immunofluorescence confocal microscopy revealed that during early anther development, the endoplasmic reticulum (ER) luminal protein calreticulin existed as a network in tapetum cells, which contained no oleosins. Subsequently, oleosins appeared together with calreticulin in the ER network, which possessed centers with a higher ratio of oleosin to calreticulin. Finally, the ER network largely disappeared, and solitary tapetosomes containing oleosins and calreticulin became abundant. Transmission electron microscopy also revealed a close association between a maturing tapetosome and numerous ER cisternae. Mature, solitary tapetosomes were isolated and found to contain oleosins, calreticulin and the ER luminal binding protein (BiP). Isolated tapetosomes were treated with sodium carbonate and subfractionated by centrifugation. Two morphologically distinct constituents were isolated: low‐density oil droplets, which contained oleosins and TAGs, and relatively high‐density cisternae‐like vesicles, which possessed calreticulin and BiP. Thus, tapetosomes are composed of oleosin‐coated oil droplets and vesicles, both of which are assembled in and then detached from the ER. The structure and biogenesis of tapetosomes are unique among eukaryotic organelles. After tapetum cells lyzed, oleosins but not calreticulin and BiP of tapetosomes were transferred to the pollen surface.