Histocytological Study of Somatic Embryogenesis in the Tree Cinnamomum camphora L. (Lauraceae)

Ruyue Jing,Peilan Wang,Zhen Huang,Zhihui Li

doi:10.15835/nbha47411655

Abstract

Histocytological studies were conducted on primary, secondary, and malformed embryos produced during somatic embryogenesis of Cinnamomum camphora L. to better understand its development. Exploring its callus types and structures provided a theoretical basis for clarifying the mechanism of somatic embryogenesis, which may shed light on the mechanism of zygotic embryogenesis. We used immature zygotic embryos as explants to induce somatic embryos, forming many embryogenic calli that differentiated into mature somatic embryos. Our results showed that somatic embryogenesis of C. camphora was similar to that of zygotic embryos. We have been dedifferentiated four types of callus. Compared with non-embryogenic cells, embryogenic cells had a closer arrangement, larger nucleus, thicker cytoplasm, more starch granules and easier to stain into black. Somatic embryogenesis had two pathways: direct (predominate) and indirect (rare). Embryogenic cells of C. camphora could have either an internal or external origin, the latter being primary, for which occurrence sites include epidermis and near-epidermis (little internally). Mostly arising from single cells, C. camphora follows two developmental pathways: single-cell equal as opposed to unequal, wherein both divide to form multi-cell proembryos. However, multicellular origins can occasionally occur and feature physiological isolation during somatic embryo development. This development has four embryo stages: globular, heart-shaped, torpedo, and cotyledon, with procambium cells apparent in globular embryos and late cotyledons forming “Y-shaped” vascular bundles. Secondary embryos were present in all stages, directly occurring on primary embryo’s germ and radicle end surfaces. We conclude that secondary and primary embryos of C. camphora undergo similar developmental processes. At the same time, conjoined cotyledon embryos and morphological abnormal embryos were found, with an internal origin more likely to generate abnormal embryos.  ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********

Highlights

The tree Cinnamomum camphora L., belonging to the order Laurales (Lauraceae), is a representative species of subtropical evergreen broad-leaved forest and provides dense canopy shade (Zhang, 2009)
The second type was direct generation, which could occur via two modes: (1) hypocotyl of the zygotic embryo directly induced the pale-yellow somatic cells, the germ end, and the radicle end, which took roots to produce regenerated plants (Fig. 1-B); and (2) cotyledon embryos were first induced at the hypocotyl of the zygotic embryos (Fig. 1-C), which turned into regenerated plants through tissue budding (Fig. 1-D)
Somatic embryogenesis of C. camphora was studied from five aspects: modes of occurrence, calli types and histocytological observations, differences between embryogenic and non-embryogenic cells, histological and cytological process of origin and development, and location and characteristics

Summary

Introduction

The tree Cinnamomum camphora L., belonging to the order Laurales (Lauraceae), is a representative species of subtropical evergreen broad-leaved forest and provides dense canopy shade (Zhang, 2009). In China, it is a precious native tree found at the south of the Yangtze River and is a national second-class wild protected plant species (Zou et al, 2009). This species may serve as a landscape plant and as a natural spice resource for aromatic camphor (Guo et al, 2016). Studies of somatic embryogenesis of more tree species are occurring, including that of broad-leaved (Capuana, 1997; Corredoira, 2008; Martínez, 2019) and coniferous trees (Kim, 1999; Salajová, 2005; Maruyama, 2019), in addition to some shrubs (Shekhawat, 2016), ferns (Grzyb, 2019), crops (Gamborg, 1968; Hayta-Smedley, 2018) and Received: 05 Sep 2019.

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Conclusion