Serial Block-Face Scanning Electron Microscopy Reveals That Intercellular Nuclear Migration Occurs in Most Normal Tobacco Male Meiocytes.

Sergey Mursalimov,Nobuhiko Ohno,Elena Deineko,Sergey Bayborodin,Mami Matsumoto

doi:10.3389/fpls.2021.672642

Abstract

Serial block-face scanning electron microscopy (SBF-SEM) was used here to study tobacco male meiosis. Three-dimensional ultrastructural analyses revealed that intercellular nuclear migration (INM) occurs in 90–100% of tobacco meiocytes. At the very beginning of meiosis, every meiocyte connected with neighboring cells by more than 100 channels was capable of INM. At leptotene and zygotene, the nucleus in most tobacco meiocytes approached the cell wall and formed nuclear protuberances (NPs) that crossed the cell wall through the channels and extended into the cytoplasm of a neighboring cell. The separation of NPs from the migrating nuclei and micronuclei formation were not observed. In some cases, the NPs and nuclei of neighboring cells appeared apposed to each other, and the gap between their nuclear membranes became invisible. At pachytene, NPs retracted into their own cells. After that, the INM stopped. We consider INM a normal part of tobacco meiosis, but the reason for such behavior of nuclei is unclear. The results obtained by SBF-SEM suggest that there are still many unexplored features of plant meiosis hidden by limitations of common types of microscopy and that SBF-SEM can turn over a new leaf in plant meiosis research.

Highlights

Intercellular nuclear migration (INM), called cytomixis, is an enigmatic phenomenon that can be seen in plant male meiocytes
We found that 90–100% of meiocytes in a tobacco anther are involved in intercellular nuclear migration (INM) as a nuclear donor, recipient, or both
In a typical tobacco meiocyte involved in INM, a nucleus approached the cell wall and formed nuclear protuberances (NPs) that crossed the cell wall through one or a few cytomictic channel (CC) and extended into the cytoplasm of a neighboring cell

Summary

Introduction

Intercellular nuclear migration (INM), called cytomixis, is an enigmatic phenomenon that can be seen in plant male meiocytes In this process, nuclei migrate between cells through special intercellular channels called cytomictic channels (CCs), which are considerably larger than plasmodesmata (Mursalimov et al, 2010). Nuclei migrate between cells through special intercellular channels called cytomictic channels (CCs), which are considerably larger than plasmodesmata (Mursalimov et al, 2010) This unique phenomenon was discovered over a century ago in gymnosperms (Arnoldy, 1900) and was observed in angiosperms during male meiosis of Crocus vernus (Koernicke, 1901). The development of electron microscopy techniques made a significant contribution to INM investigation By these techniques, CCs were discovered, which enable the migration of such big organelles like nuclei (Heslop-Harrison, 1966)

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