Wax-Deficient <i>Arabidopsis</i> Mutant <i>cer1-1</i> Shows Abnormal Tapetosomes, Elaioplasts, and Pollen Coat

Abstract

Normal maturation of the pollen coat is important for pollination in higher plants. The pollen coat contains abundant lipids and proteins, which are derived from tapetum cell-specific organelles, i.e., the tapetosome and elaioplast. The wax-deficient mutant eceriferum1 (cer1) shows a conditional male sterile phenotype. It is considered that this phenotype is caused by dysfunction of the pollen coat, although cer1 mutant pollen coats appear normal at a particular stage. In the present study, abnormalities in the tapetum cells and pollen coat of cer1-1 mutants were observed by scanning electron microscope and light microscopic analysis. To investigate the effect of wax composition changes on the structure of the pollen coat, tapetosome, and elaioplast in cer1-1 mutants, we observed the ultrastructure of the cer1-1 male gametophyte at various developmental stages. We observed abnormal giant aggregation of the lipids, which might be due to a fusion of the tapetosome and elaioplast in the early bicellular pollen stage tapetum cell. On the contrary, in wild-type plants, the fusion of the tapetosome and elaioplast occurred at the late bicellular pollen stage. In cer1-1, abnormalities in the tapetum cell and the pollen coat might occur because of the unusual timing of fusion of the tapetosome and the elaioplast. This is the first report showing the role of tapetum wax in the maturation of the tapetosome and elaioplast, which may affect pollen coat function.