Floral micromorphology and microsporogenesis of gynodioecious herb Glechoma longituba (Lamiaceae)
27 May 2015
Jang, Tae-Soo; Hong , Suk-PyoGynodioecy, the phenomenon of having both hermaphrodite and female (i.e., male-sterile) individuals within the same population, is an important intermediate step in the evolution of separate sexes in flowering plants. In this study, we investigated the floral micromorphology and microsporogenesis of the gynodioecious herb Glechoma longituba from four natural populations in Korea. The floral micromorphological characters of the different sex morphs were examined and compared using scanning electron microscopy (SEM), and the ultrastructure of microspores during microsporogenesis was studied. We also examined the development of anther and pollen grains in the three sexual morphs (i.e., hermaphrodites, females, and gynomonoecious, i.e., individuals with a mixture of female and hermaphroditic flowers) based on an embryological investigation. The major difference in anther development among the three phenotypes was the early disintegration of tapetal cells in the anthers of female flowers. While mature fertile pollen grains were found in both hermaphrodite and gynomonoecious phenotypes, females did not produce any pollen grains. In addition, both fertile and sterile pollen grains in gynomonoecious phenotypes were frequently observed. The results of the present study indicate that the floral micromorphological characters of G. longituba were not distinct between morphs, except for the structure of the inner cell surfaces of the anther. The tapetum abnormalities and degeneration of pollen grains in both gynomonoecious phenotypes and females based on the embryological analysis may be the consequence of inbreeding depression of hermaphrodites.