Comparative microsporangium development in male‐fertile and male‐sterile flowers of Consolea (Cactaceae): When and how does pollen abortion occur

Abstract

Anther development, microsporogenesis, and microgametogenesis were studied using both light and TEM microscopy in the six accessible subdioecious/cryptically dioecious species of Consolea (Cactaceae). Anther wall development, microsporogenesis, and microgametogenesis are uniform in staminate flowers of all six species, and are typical for Cactaceae. Breakdown of microsporogenesis in male‐sterile anthers occurs early, at the onset of meiosis, and results in anthers bearing no pollen grains. The abortive process follows a common pattern in all investigated species. The tapetum is the first layer to deviate from normal male‐fertile anther development. Tapetal cells in male‐sterile anthers elongate at an early stage and have abundant rER with atypical configurations. Ultimately, the tapetum becomes hypertrophied and non‐functional. Male‐sterility in pistillate flowers appears to be directly related to these anomalies. In addition, other anther layers and tissues are affected, and normal patterns of programmed cell death (PCD) are disrupted. The relationship between these patterns and the pattern of PCD in normal male‐fertile anthers is discussed. We hypothesize a single origin for the cryptically dioecious/subdioecious breeding system of Consolea based on the uniformity of the anther's abortive processes in pistillate flowers.

Keywords:

• Male‐sterility
• programmed cell death
• cryptic dioecy
• tapetum ultrastructure

Acknowledgements

The authors thank Ethan Fried, Laurel Richey, Nathan Sammons, and Joel Timyan for invaluable help with fieldwork. We also thank the Jardín Botánico Nacional, Dr. Rafael M. Moscoso (Dominican Republic) and the Bahamas National Herbarium for their assistance with collecting permits. We also thank Dr. Beatriz G. Galati for reviewing this manuscript and for assistance in pollen descriptions used in this work, an anonymous reviewer for the useful comments to improve the manuscript, and the EM facility at Miami University for their helpful assistance. The Botany Department of Miami University, its Academic Challenge program, and the W. S. Turrell Herbarium Fund supported this dissertation research.