Morphogenetic status of somatic embryos of Citrus sinensis from mature polyembryonic seeds and those produced in vitro | Морфогенетический статус соматических зародышей Citrus sinensis, содержащихся в зрелых многозародышевых семенах и полученных в культуре in vitro
2010
Moiseeva, N.A. | Serebryakova,V.N. | Nosov, A.M., Russian Academy of Sciences, Moscow (Russian Federation). The K.A. Timiryazev Institute of Plant Physiology | Nardi, L. | Lucretti, S., Italian National Agency for New Technologies, Energy and the Environment, Rome (Italy)
In tissue culture of sweet orange (Citrus sinensis (L.) Osbeck, cv. Tarocco), we obtained mass regeneration of somatic embryos (SE) with two morphologically distinct cotyledons (CT) about 3 mm in length, their numbers amounting to 110-150 embryos per Petri dish and 60 to 80% of the population. The morphogenetic state of SE was compared using the embryos with the CT of different size (from 3 to 10 mm) from mature polyembryonic seeds as a test system and the cell number, size, and ultrastructural organization, and the number of protein bodies in the cotyledon cells as morphological and biochemical criteria. Cell number in the CT of different size was related to the content of protein bodies therein. Typical protein bodies where 33 kD polypeptide of storage proteins was identified were detected only in the CT, which size was identical to that of embryonic CT from monoembryonic seeds of citrus plants. In the cells of smaller CT, we detected protein-accumulating vacuoles with electron-dense inclusions that irrespective of their size, shape and structure accumulated the gold label. The number of the cells with protein depositions in vacuoles decreased when the CT became smaller. Irrespective of the origin of embryos (in vivo or in vitro), lipids were the major storage metabolites in the cells of 3-mm CT. As the cotyledon-forming cells became smaller and less numerous, their metabolic activity tended to decrease in line with the fragmentation of endoplasmic reticulum, the absence of polysomic complexes, and indistinct inner organization of mitochondria and plastids. It was concluded that SE developing in vivo and in vitro were physiological dwarfs, that is, the structures with diminutive storage organ with characteristically incomplete cell differentiation. Apparently such forms emerged due to the suppression of cotyledon growth at the initial stages of organogenesis; as a result, the cell population could not properly realize both organo- and histogenesis
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