Pollen Viability and Male and Female Gametophyte Development in Houttuynia cordata Thunb.

The aim of this study was to understand the characteristics of sexual reproduction in Houttuynia cordata and provide a theoretical basis for cross breeding. Using a population of H. cordata with three years of cultivation, pollen viability was determined by I₂-KI staining, Brewbaker & Kwack culture medium and fluorescence microscopy observation, respectively; the developmental course of male and female gametophytes was observed using paraffin sections. Results showed that H. cordata pollen viability was extremely low, with I₂-KI staining showing pollen viability of 3.18%, and culture and fluorescence microscopy observation unable to measure pollen viability at all. The male gametophyte was normal in early development, but in the dyad period the tapetum cell was disintegrated. The cytoplasm of free microspores gradually disappeared and showed an empty flat shape, the microspore shape changed from suborbicular to irregular. Finally, microspore abortion occurred before pollen sac cracking. A pistil was composed of three united carpels and connated into one locular, parietal placentation. The ovule was atropous, double integument and tenuinucellus. Sporogenous cells originated from the nucellar cells immediately beneath the epidermis, and developed into macrosporal mother cells. Macrosporal mother cell meiosis formed linear or T-shaped megaspore tetrads. The large one at the chalazal end was a functional megaspore. The functional megaspore developed into a polygonum type embryo sac, which contained seven cells containing eight nuclei after three times consecutive mitosis. Male sterility may be due to the premature disintegration of the tapetum, and the seed may come from apomixis.