Abstract
Endosperm, an ephemeral and storage tissue, serves as a source of nutrition and protection during embryo development and germination. It can be used for the cultivation of polyploid plants in vitro. Here, results of plant regeneration and acclimatization from the endosperm-derived calli of four cultivars of Actinidia arguta has been presented. Seeds excised from fresh fruit and dry seeds stored for one year served as the sources of endosperm explants of selected tetraploid cultivars of A. arguta. Callus Induction Medium (CIM; containing 0.25, 0.5, or 1 mg/l of TDZ) and Actinidia Endosperm Medium (AEM; containing 2 mg/l of 2,4-D and 5 mg/l of kinetin) were used to study the organogenic responses of the calli. On AEM, the source of explant did not significantly affect the rate of callus induction for any of the tested cultivars; no organogenic events were observed. In contrast, on CIM both the source of explants and the cultivar origin caused significant differences in callus formation and subsequent organogenic events. Histological and ultrastructural analyses revealed the adventitious nature of shoot bud formation on these media. The most efficient elongation of shoot buds was achieved after transferring organogenic calli with adventitious shoot buds to a medium supplemented with zeatin or meta-topolin. Robust root induction with minimal basal callus formation occurred on the medium with indole-3-acetic acid. Flow cytometric analysis revealed that the nuclear DNA content in the leaves of some regenerants was approximately 50 % higher (4.5 pg/2C) than that in leaves from the tetraploid seedlings (3.1 pg/2C),which confirmed that those regenerants originated from the endosperm. The regeneration of such hexaploid plants was more efficient when endosperm from fresh seeds served as an explant; therefore, fresh rather than dry seeds are recommended for endosperm-derived plant production. The hexaploid plants of A. arguta can serve as an important source of breeding material.
Highlights
Due to their origin, endosperm cells usually possess a higher nuclear DNA content (3C) than the embryo (2C), which results from the doubled fertilization that occurs in flowering plants
Key message This study reveals that the genotype, thidiazuron, zeatine, meta-topolin, and age of explants affect the induction of endospermderived callus and subsequent hexaploid plant regeneration from tetraploid kiwiberry
The callus growing on the Actinidia Endosperm Medium (AEM) was soft and aqueous in appearance, while the callus from the Callus Induction Medium (CIM) was semi-compact and light-yellow, creamy
Summary
Endosperm cells usually possess a higher nuclear DNA content (3C) than the embryo (2C), which results from the doubled fertilization that occurs in flowering plants. Plant tissue culture techniques can provide a relatively faster alternative for obtaining polyploid plants (Wang et al 2016). One of such technique is culturing of isolated endosperm followed by plant regeneration. The plant growth regulators (PGRs) added to the culture medium, the sources of the explant material, and the cultivar of the donor plants all play an important role in establishing a successful regeneration protocol from endosperm explants (Wang et al 2016). The recently published protocols for endosperm-derived plant regeneration in Gomortega keule (Muñoz-Concha 2016), Melia azedazach (Thang et al 2018), Passiflora edulis (Antoniazzi et al 2018), and Passiflora cincinnata (Silva et al 2020) indicate that this technique is still attracting interest and is worth applying to economically important plant species
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