Regeneration of Plants from Protoplasts of Carica Species (Papaya)
The genus Carica is a native to tropical and subtropical America and comprises about 40 species, of which Carica papaya L. (papaya) is the only one being widely cultivated. Papaya is believed to have arisen from C. peltata Hook. & Arn. by natural hybr
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1 Introduction The genus Carica is a native to tropical and subtropical America and comprises about 40 species, of which Carica papaya L. (papaya) is the only one being widely cultivated. Papaya is believed to have arisen from C. peltata Hook. & Am. by natural hybridization. It is an important crop, producing edible fruit and papain-containing latex. The flavorful, melon-like fruit contains abundant vitamin A and some vitamin C. It is a popular dessert fruit used for makingjams, preserves, and iee cream ftavoring; it is also served as a vegetable. The latieifers occur in all parts of the plant. The dried latex from unripe fruit is the source of papain, a proteolytic enzyme wh ich is widely used as a me at tenderizer and in the tanning, cosmetics, and pharmaceutical industries (Litz 1984, 1986). The wild Carica species are a rieh source of germplasm for papaya genetic improvement. For instanee, resistanee to papaya ringspot virus (the most serious disease of papaya) has been found in some wild Carica species (Co no ver 1964), but is not found in papaya. Moreover, several wild speeies of Carica possess other important genetic characteristics, inc1uding cold tolerance, a pleasant fragrance, and high yield, which would be of great value if they could be transferred to papaya (Litz 1986). The ineorporation of these valuable agronomie traits into cultivated papaya is often prevented by the barrier of sexual incompatibility (Mekako and Nakasone 1975). Although culturing of embryos and ovules ean sometimes overcome the barrier of gene transfer between Carica species (Khuspe et al. 1980; Manshardt and Wenslaff 1989; Chen et al. 1991), somatic hybridization by protoplast fusion allows the exploitation of useful germplasm while avoiding the barrier of interspecific and intergeneric sexual incompatibility. Transformation of papaya by bombardment or by Agrobacterium infection (Fitch et al. 1990, 1992, 1993) has been achieved. The efficiency of these proeesses needs to be improved, however, because they are slow and have a low transformation rate. An efficient and reproducible regeneration system for protoplasts can make direct gene transformation, e.g. through mieroinjection and electroporation, feasible.
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Institute of Botany, Academia Sinica, Taipei, Taiwan 115, Republic of China
Biotechnology in Agriculture and Forestry, Vol. 29 Plant Protoplasts and Genetic Engineering V (ed. by V.P.S. Bajaj) © Springer-Verlag Berlin Heidelberg 1994
Regeneration of Plants from Protoplasts of Carica Species (Papaya)
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A brief review of the work done on Carica protoplasts is given in Table 1. Papaya protoplasts have been successfully isolated from seedling tissue or from seedling-derived callus (Litz and Conover 1979; Jordan et al. 1986; Liu et al. 1984; Litz 1986). Plant regeneration from the protoplasts, however, has not succeeded. Recently, protoplasts isolated from suspension cultures of somatic embryos of an interspecific hybrid, Carica papaya x C. caulifiora, have been successfully cultured (Chen and Chen 1992) and plants regene
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