Ultrastructure of hybrid callus between C₃ and C₄ species of amaranthaceae

Unlike the parent line, the hybrid calli between C₃ and C₄ species of Amaranthaceae have poor division capability. Therefore, in this study the fine structures of hybrid callus derived from protoplasts of Celosia cristata L. cv. Pink Charm (C₃ species) cell suspension and Amaranthus tricolor L. cv. Perfecta (C₄ species) cotyledon callus were investigated by light and electron microscopy, and compared with the parental. All callus lines were composed of parenchymatous cells possessing a voluminous vacuole. Parental callus lines contained organelles with a relatively normal structure. The peculiar feature characterizing the C₃/C₄ hybrid callus was the presence of highly lobed nucleus with multinucleoli and numerous small vacuoles having autophagic activity scattered in the cytoplasm. The autophagic activity is apparently related to the existence of several inclusions such as cytoplasmic organelles in the central vacuole. It might also be related to the pronounced expansion of central vacuole and the reduced cytoplasm. The failure to sustain proliferation related to some atypical features of the organelles is discussed.