Abstract
A ploidy chimera of the Meiwa kumquat (Fortunella crassifolia Swingle), which had been induced by treating the nucellar embryos with colchicine, and had diploid (2n = 2x = 18) and tetraploid (2n = 4x = 36) cells, was examined for its ploidy level, morphological characteristics, and sizes of its cells in its leaves, flowers, and fruits to reveal the ploidy level of each histogenic layer. Furthermore, the chimera was crossed with the diploid kumquat to evaluate the ploidy level of its reproductive organs. The morphological characteristics and the sizes of the cells in the leaves, flowers, and fruits of the chimera were similar to those of the tetraploid Meiwa kumquat and the ploidy periclinal chimera known as “Yubeni,” with diploids in the histogenic layer I (L1) and tetraploids in the histogenic layer II (L2) and III (L3). However, the epidermis derived from the L1 of the chimera showed the same result as the diploid Meiwa kumquat in all organs and cells. The sexual organs derived from the L2 of the chimera were significantly larger than those of the diploid. Moreover, the ploidy level of the seedlings obtained from the chimera was mostly tetraploid. In the midrib derived from the L3, the chimera displayed the fluorescence intensity of a tetraploid by flow cytometric analysis and had the same size of the cells as the tetraploid and the Yubeni. According to these results, the chimera is thought to be a ploidy periclinal chimera with diploid cells in the outermost layer (L1) and tetraploid cells in the inner layers (L2 and L3) of the shoot apical meristem. The chimera had desirable fruit traits for a kumquat such as a thick pericarp, a high sugar content, and a small number of developed seeds. Furthermore, triploid progenies were obtained from reciprocal crosses between the chimera and diploid kumquat.
Highlights
The shoot apical meristem of higher plants consists of three histogenic layers [1]
The original diploid Meiwa kumquat, the tetraploid induced by treating nucellar embryos of the Meiwa kumquat with colchicine, and the ploidy periclinal chimera mutant Yubeni, which originated from the Meiwa kumquat and has diploids in L1 and tetraploids in L2 and L3, were used as the control
An aliquot (550 μL) of each sample was filtered through Miracloth (Merck KGaA, Drarmstadt, Germany), and the filtrate was stained with 50 μL of 0.5 g L−1 propidium iodide (PI)
Summary
The shoot apical meristem of higher plants consists of three histogenic layers [1]. This is known as the “Tunica-Corpus” theory; i.e., the shoot apical meristem consists of L1 (Tunica) and L2/L3 (Corpus).In the genus Citrus and its related genera, the histogenic layers are differentiated by their parts: the dermal system (guard cell and juice sac) in L1, parenchyma and reproductive organs (mesophyll cell, pollen and seed) in L2, and the vascular bundle (cambium and pith) in L3, respectively [2]. The shoot apical meristem of higher plants consists of three histogenic layers [1]. This is known as the “Tunica-Corpus” theory; i.e., the shoot apical meristem consists of L1 (Tunica) and L2/L3 (Corpus). Agronomy 2019, 9, 562 is considered to be a chimera if it has two or more genetic constitutions in its shoot apical meristem, and chimeras are classified into three types: sectorial, periclinal, and mericlinal [3,4]. Sectorial chimeras have a sector of all cell layers that is genetically different. Periclinal chimeras are chimeras in which one or more entire cell layer(s) is genetically distinct from another cell layer. Mericlinal chimeras have part of one or more layers that is genetically different
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
