Abstract
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.
Highlights
The development of male gametophyte in vascular plants is a complex process that requires coordinated action and participation of numerous cells and both sporophyte and gametophyte tissues
Taking advantage of advanced high-performance liquid chromatography tandem mass spectrometry, we provide a detailed analysis of endogenous phytohormones during pollen ontogeny in four tobacco species differing in their phylogenetic position within the genus Nicotiana, the model plant N. tabacum and three other species (Nicotiana alata, Nicotiana langsdorffii, and Nicotiana mutabilis; all section Alatae)
The profiles and dynamics of phytohormones were characterized during the process of microgametogenesis in four Nicotiana species (N. tabacum, N. alata, N. langsdorffii, and N. mutabilis)
Summary
The development of male gametophyte in vascular plants is a complex process that requires coordinated action and participation of numerous cells and both sporophyte and gametophyte tissues. The life cycle of the male gametophyte can be divided into a developmental phase leading to the formation of mature pollen grains and a functional (progamic) phase beginning. The pollen grain of angiosperms is formed within the anthers of the flower via two successive developmental programs: microsporogenesis and microgametogenesis. The diploid pollen mother cells will undergo meiosis and form tetrads of haploid microspores encased by a callose layer. Microgametogenesis comprises events that lead to the progressive development of the unicellular microspores into mature pollen. Thereafter, the microspores undergo highly asymmetric pollen mitosis I (PMI), leading to a large vegetative cell and a small generative cell. In Nicotiana, the generative cell undergoes one more cell division, pollen mitosis II (PMII), which occurs before pollen maturation in bi-cellular pollen. The endosperm and double fertilization are unique and are often used as defining features of angiosperms
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