Abstract
This is the first report concerning the sequence of histological and cytological events occurring during organogenesis from cotyledon-derived meristematic nodules (MNs) in Paeonia ostii ‘Feng Dan’. Sections were made and studies were carried out with dissecting microscope, light microscope, scanning electron microscopy (SEM) and transmission electron microscopy observation. Histological studies revealed a complex developmental process of morphogenesis including five stages: (1) callus originated from cell division in both cambial and cortical regions; type I—yellow compact callus with densely arranged clumps was identified as embryogenic callus. (2) pre-nodular structure consisted of organization center (a central area of vascularization surrounded by meristematic cell layers) and an epidermis-like layer; (3) independent MNs comprised of organization center, a cortical-like area of parenchymatous cells and an epidermal-like area; (4) nodular clusters displayed vigorously internal meristematic cell division and generated a relative movement towards the nodules periphery, establishing vascular connection with primordia; (5) successive new elongated shoots with axillary bud primordia were developed. SEM observations showed three types of extracellular matrix, a smooth membranous layer, fibrillar structures and granular mucilage-like secretions on embryogenic callus, demonstrating its dynamic morphological changes. Ultrastructural analysis revealed striking changes of chloroplast morphology and starch content during MNs morphogenesis. This study allows a better understanding of in vitro regeneration via MN culture and provides references for protocol optimization and genetic transformation.
Highlights
An efficient and reproducible in vitro regeneration system via Meristematic nodules (MNs) culture have been developed, which can be a feasible system for overcoming various obstacles in the regeneration system of tree peonies published previously, such as vitrification, low multiplication, poor rooting and difficult acclimatization in micropropagation (Beruto et al 2004; Wen et al 2020), rare differentiation in callus culture (Zhu et al 2018), and high deformity rates and low germination in somatic embryogenesis (Du et al 2020)
Based on the regeneration system we obtained via MN culture, this study aims to reveal the histological and cytological pattern addressing developmental sequence for induction and differentiation process of MN in P. ostii ‘Feng Dan’, providing critical references for optimization of this system and application of gene transfer
The noticeable structure might be closely related to the origin of primordia and could be serviced as an indicator of differentiation (Brisibe et al 1992). This is the first report covering histological and cytological analyses involved in MNs morphogenesis system in P. ostii ‘Feng Dan’
Summary
Moutan) is well-known in China because of its medical, ornamental and oil value (Yu et al 2016). P. ostii is main option for oil tree peony because of the high yield and adaptability. Tissue culture is an attractive option to overcome this problem. An efficient and reproducible in vitro regeneration system via Meristematic nodules (MNs) culture (manuscript PCTO-D-21-00472) have been developed, which can be a feasible system for overcoming various obstacles in the regeneration system of tree peonies published previously, such as vitrification, low multiplication, poor rooting and difficult acclimatization in micropropagation (Beruto et al 2004; Wen et al 2020), rare differentiation in callus culture (Zhu et al 2018), and high deformity rates and low germination in somatic embryogenesis (Du et al 2020)
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