Investigation of mitosis, microsporogenesis and pollen germination in the critically endangered plant Amsonia orientalis (Apocynaceae)

摘要

Amsonia orientalis Decne. (Apocynaceae) is a medically useful and critically endangered plant which has very restricted distribution world-wide. The root tips and flower buds of A. orientalis were used as an experimental material and they were squashed in aceto-orcein. Fresh flowers and a liquid medium were used for pollen germination tests. In spite of the small size of the cells and chromosomes, all phases of mitosis and meiosis were observed. Generally the phases of mitosis were regular but there were a few abnormalities, such as laggard chromosome in metaphase and bridge formation in anaphase. There was a good relationship between the stages of pollen development and floral bud length. As a result of the cytokinesis, tetrahedral types of tetrads were occurred in microsporogenesis. The tetrad nuclei resulting from the simultaneous type of meiosis were found to be of equal size. Pollen germination had started from the first hour and pollen tube lengths and germination percentages regularly increased with increasing time. This is the first study that identifies mitotic and meiotic cycles and pollen germination in A. orientalis. Our findings about the mitosis and reproduction biology of this critically endangered plant will be useful for in vitro and in situ conservation, taxonomic and genetic studies.