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

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. *********