Pectin: a key component deposited in the exine of Annona montana potentially associated with exine shedding.

Abstract

In angiosperms, the exine is essential for pollen‒pistil interactions and is difficult to separate from the intine. In Annona montana, however, the exine spontaneously separates from the intine during hydration, leaving the entire male gametophyte exposed and activated, which does not affect its reproduction, and fruit are produced every year. In the present study, we used light microscopy, transmission electron microscopy, immunocytochemistry, and FTIR spectroscopy to explore whether pectins located in the cavities of the exine in A. montana dissolved in water, resulting in exine shedding, and whether water was the only necessary medium for A. montana pollen exine shedding. Exine shedding has also been reported in gymnosperms (e.g., Cupressaceae, Taxaceae, and Taxodiaceae), but A. montana has been the only species with exine shedding in angiosperms. Pollen shedding exine in A. montana exhibits a special and rare reproductive characteristic in angiosperms, which will update what we have previously recognized that exine is essential in reproductive processes.