Iodoacetate-treated Citrus protoplasts from embryogenic nucellar calli of Sour orange (C. aurantium) or from Rough lemon (C. jambhiri) were fused with γ-irradiated protoplasts from a related genus, Microcitrus. The fused protoplasts were cultured to obtain colonies and micro-calli. Micro-calli derived from these two fusion combinations were isolated, propagated and differentiated into embryos, which subsequently regenerated trees having the morphology of Sour orange or Rough lemon. These intergeneric fusions resulted in mitochondria with novel DNA, indicating recombination between the chondriomes of Citrus and Microcitrus. Chloroplast DNA analyses of fusion-derived embryos indicated that they contained the chloroplasts of either fusion-partner or a mix of these chloroplasts. Later plastome analyses of leaves from fully differentiated plants showed that cybrids having Rough lemon morphology had either Rough lemon or Microcitrus chloroplast DNA, indicating complete sorting out of chloroplasts. Likewise, sorting out of Microcitrus chloroplasts was detected in a cybrid plant having Sour orange morphology.
Cybrid plants having the nuclear genomes of one species and either or both plastomes and chondriomes of another species were obtained by fusing protoplasts of Nicotiana sylvestris, as "recipients", with X-irradiated protoplasts of N. rustica as "donors" of chloroplasts and mitochondria. Forty-nine flowering plants, derived from 28 calli, were analysed. As expected, they all had N. sylvestris (i.e. "recipients") morphology. Chloroplast DNA restriction patterns indicated that 8 and 41 plants had N. rustica and N. sylvestris plastomes, respectively. Some of the plants with either type of plastomes produced sterile pollen but none showed anther malformation typical to alloplasmic male sterility. Chondriome identification by mitochondrial DNA restriction analysis of cybrid plants revealed only restriction patterns which were either similar or identical to those of N. sylvestris while no cybrids with N. rustica restriction patterns were detected.
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