ON THE STABILITY OF SYNERGID APOGAMY IN RICE OVARY CULTURE AND ITS DEVELOPMENTAL CONDITIONS

Synergid apogamy has been found out to be the main origin of haploid plants induced by unpollinated ovary culture in rice(Tian and Yang, 1983; Li and Yang, 1986). However, it was not clear whether it was a result of the given conditions or a common phenomenon induced in vitro in this species. Therefore we designed a series of experiments to clarify this problem. These include various modifications of factors involved in the culture, i e. exclusion of exogenous hormone MCPA, supplementation of Iactoalbumin, substitution of MCPA with picloram, supplementation of ABA, high density culture, vertical culture on solid medium, alteration of basic medium components, and culture in light instead of dark condition. Ovaries were sampled at definite intervals after inoculation and sectioned by paraffin method. Microscopical observations confirmed that in all these cases the proembryos were derived from the synergids (Plate:1—9). So we concludcd that cmbryoids originated from synergid apogamy is a stable character in rice ovary culture, not to be easily changed by culture conditions.Although hormon-free culture, vertical culture(ovary free of the medium)and culture under light could induce synergid apogamy, it resulted only in small proembryos. Further growth of cmbryoids should be supported by exogenous hormone supply, direct contact of ovary with the medium and culture in darkness. It indicates that the conditions for triggering apogamous program and those for promoting subsequent development of the apogamous embryoids are different, a case similar to that as have been found in rice anther culture (Yang and Zhou, 1983).