Abstract
Anthers of Poncirus tnfoliata and Citrus aurantium cultured on agar inedia were cytologically examined at three-day intervals for microspore dedifferentiation. The results proved that plantlets obtained by anther culture of these citrus originated from microspores. Microspore development in vitro followed three main routes. In route A and B, microspores ultimately lost their contents. In route C, multi-nucleate-cellular structures developed into microspore embryoids. In this route C, microspores showed abnormal nuclear division; one route (C1), produced two types of morphologically similar nuclei which were rather large or small and classified as 'vegetative-type' (C1a) or 'generative-type' nuclei (C1b) respective-ly. The other route (C2), produced 'vegetative-type' and rather small 'generative-type' nuclei. Route C2 diverged to two routes, C2a and C2b. In C\2a, only a 'vegetative-type' nucleus divided repeatedly whereas route C2b showed independent division of both 'vegeta-tive' and 'generative-type' nuclei. That is, repeated division of both 'vegetative' and 'generative-type' nuclei independently of each other contributed to the formation of microspore embryoids in citrus anther culture. Of these pathways, the route C2 may be the most responsible for the embryoid formation. Nuclear fusion occurred in route C and appeared to contribute to ploidy variation. Calli which appeared from the inside of the anthers originated from both anther wall and microspores. Embryoids derived from somatic tissue of anthers were not observed.
