Germination and the Early Stages of Seedling Development in Brachypodium distachyon.

Elzbieta Wolny,Agnieszka Braszewska-Zalewska,Joanna Lusinska,Magdalena Rojek,Alexander Betekhtin,Robert Hasterok

doi:10.3390/ijms19102916

Elzbieta Wolny, Agnieszka Braszewska-Zalewska + Show 4 more

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https://doi.org/10.3390/ijms19102916

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Abstract

Successful germination and seedling development are crucial steps in the growth of a new plant. In this study, we investigated the course of the cell cycle during germination in relation to grain hydration in the model grass Brachypodium distachyon (Brachypodium) for the first time. Flow cytometry was performed to monitor the cell cycle progression during germination and to estimate DNA content in embryo tissues. The analyses of whole zygotic embryos revealed that the relative DNA content was 2C, 4C, 8C, and 16C. Endoreplicated nuclei were detected in the scutellum and coleorhiza cells, whereas the rest of the embryo tissues only had nuclei with a 2C and 4C DNA content. This study was accompanied by a spatiotemporal profile analysis of the DNA synthetic activity in the organs of Brachypodium embryos during germination using EdU labelling. Upon imbibition, nuclear DNA replication was initiated in the radicle within 11 h and subsequently spread towards the plumule. The first EdU-labelled prophases were observed after 14 h of imbibition. Analysis of selected genes that are involved in the regulation of the cell cycle, such as those encoding cyclin-dependent kinases and cyclins, demonstrated an increase in their expression profiles.

Highlights

Seed germination is considered to be the initiation of the first developmental phase in the lifecycle of higher plants and is followed by the postgerminative growth of the seedling [1]
We describe the early events of cell cycle activation during the germination and early stages of seedling development in the monocotyledonous model plant Brachypodium, which has been proposed as a model to study grain dormancy in grasses
Brachypodium embryos exhibit polysomaty, and nuclei with 2C, 4C, 8C, and 16C have been detected among embryo tissues

Summary

Introduction

Seed germination is considered to be the initiation of the first developmental phase in the lifecycle of higher plants and is followed by the postgerminative growth of the seedling [1]. In the case of the germination of a monocotyledonous plant seed, the coleorhiza is the first part to grow out of the seed coat, whereas during the germination of a dicotyledonous plant seed, the radicle grows out of the seed coat first [5] In both groups, the progress of germination is strictly related with the water uptake rate. There is a rapid imbibition of water by a dry seed (phase I) until the seed tissues are fully hydrated. This is followed by a limited water uptake during phase II, whereas in phase III, there is an increase of water uptake that is related to the completion of germination. The protrusion of the radicle does not require mitotic activity [8], in tomato, the activation of cell division has been found to occur before the protrusion of the radicle [9]

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