Degeneration pattern in somatic embryos of Pinus sylvestris L.

Malin Abrahamsson,Sara Von Arnold,Emma Larsson,Silvia Valladares,Irene Merino

doi:10.1007/s11627-016-9797-y

Malin Abrahamsson, Sara Von Arnold + Show 3 more

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https://doi.org/10.1007/s11627-016-9797-y

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Abstract

Somatic embryos can be used for propagating forest trees vegetatively, which is of great importance for capturing the genetic gain in breeding programs. However, many economically important Pinus species are difficult or impossible to propagate via somatic embryogenesis. In order to get a better understanding of the difficulties to propagate Pinus species via somatic embryogenesis, we are studying the developmental pathway of somatic embryos in different cell lines. In a previous study, we showed that the morphology of early somatic embryos in Scots pine (Pinus sylvestris) differs between cell lines giving rise to normal or abnormal cotyledonary embryos. In this study, we have compared the proliferation and degeneration pattern of early and late embryos in a normal and abnormal cell line. In both cell lines, a high frequency of the embryos degenerated. Among the degenerating embryos, two main degeneration patterns could be distinguished. In the normal cell line, the embryos degenerated similar to how the subordinate embryos are degraded in the seed. In the abnormal cell line, the degeneration of the embryos resulted in a continuous loop of embryo degeneration and differentiation of new embryos. We observed a similar degeneration pattern when embryogenic tissue was initiated from megagametophytes containing zygotic embryos at the stage of cleavage polyembryony. Based on our results, we suggest that the degeneration pattern in abnormal cell lines starts during initiation of embryogenic cultures.

Highlights

Vegetative propagation of the economically important conifers makes it possible to capture the genetic gain obtained in the breeding program
In the normal cell line, the degenerated embryos were degraded, while in the abnormal cell line, the degenerated embryos started to differentiate new abnormal early embryos. This is the first report that describes degeneration patterns of somatic embryos in Scots pine, and the results suggest that when embryogenic cultures are established from immature zygotic embryos, there is a risk that the cell lines will be abnormal and give rise to abnormal cotyledonary embryos
A large proportion of early somatic embryos degenerate We have previously described the general developmental pathway of somatic embryos in cell lines yielding normal cotyledonary embryos and cell lines yielding a large proportion of abnormal cotyledonary embryos in Scots pine (Abrahamsson et al 2012; Fig. 1)

Summary

Introduction

Vegetative propagation of the economically important conifers makes it possible to capture the genetic gain obtained in the breeding program. For many Pinus species, several problems remain to be solved before somatic embryogenesis can be used as a reliable propagation tool (Klimaszewska et al 2007; Bonga et al 2010). In most Pinus species, embryogenic cultures are initiated from immature zygotic embryos (Klimazewska et al 2007, with ref.). In these species, the apical cells in the zygotic proembryo cleave and develop into four separate embryos. When using immature zygotic embryos at the stage of cleavage polyembryony as primary explants, the embryogenic tissue might be initiated by a continuation of the cleavage process (Bozhkov et al 1997; Park et al 2006). Polyembryony can be a potential problem in somatic embryogenesis in Pinus (Klimaszewska et al 2007)

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