Hormonome Dynamics During Microgametogenesis in Different Nicotiana Species

Plant microgametogenesis involves stages leading to the progressive development of unicellular microspores into mature pollen. Despite the active and continuing interest in the study of male reproductive development, little is still known about the hormonomics at each ontogenetic stage. In this work, we characterized the profiles and dynamics of phytohormones during the process of microgametogenesis in four Nicotiana species (Nicotiana tabacum, Nicotiana alata, Nicotiana langsdorffii, and Nicotiana mutabilis). Taking advantage of advanced HPLC-ESI-MS/MS, twenty to thirty endogenous hormone derivatives were identified throughout pollen ontogenesis, including cytokinins, auxins, ABA and its derivatives, jasmonates, and phenolic compounds. The spectra of endogenous phytohormones changed dynamically during tobacco pollen ontogeny, indicating their important role in pollen growth and development. The different dynamics in the accumulation of endogenous phytohormones during pollen ontogenesis between N. tabacum (section Nicotiana) and the other three species (section Alatae) reflects their different phylogenetic positions and origin within the genus Nicotiana. We demonstrated the involvement of certain phytohormone forms, such as cis-zeatin- and methylthiol-type CKs, some derivatives of abscisic acid, phenylacetic and benzoic acids, in pollen development for the first time here. Our results suggest that unequal levels of endogenous hormones and the presence of specific derivatives may be characteristic for pollen development in different phylogenetic plant groups. These results represent the currently most comprehensive study of plant hormones during the process of pollen development.

Pollen Ontogeny Comparison of Natural Male-Fertile Diploid and Male-Sterile Triploid Lilium lancifolium in Korea

Lilium lancifolium (syn. L. tigrinum) is the only polyploidy-complex species involving both diploid (2n = 2x = 24) and triploid (2n = 3x = 36) plants in the genus. The origin of natural triploid remains a mystery and research has been limited mainly to chromosomal studies that have overlooked research on pollen ontogeny. By spatiotemporal comparison of the development and morphology of diploid and triploid pollen grains, we study the correlations between pollen fertility and morphological development in diploid and triploid plants and propose the necessity and importance of further research on natural polyploid-ontogenetic diversity. In this comparative investigation, we used various microscopy techniques including histological analyses, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The main morphological differences between triploid and diploid pollen grains started with abnormal tetrad formation of triploid, followed by inadequate amylogenesis and amylolysis in young microspores, and finished with the formation of an abnormal structure of pollen surface layers in maturing pollen grains, which finally resulted in pollen grain unfolding and male sterility. From observing the series of morphological events that induced male-sterile pathway in natural triploid pollens, this study showed a variety of correlations between pollen development and fertility, which differed from male sterility resulting from gene mutation, indicating that there exists greater variability in pollen male-sterile ontogeny. Our results suggest that multilateral research is required for understanding the fickle ontogeny of natural male-sterile polyploid.