Development of artificial seeds for long-term preservation of tropical medicinal plants and microalgae

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Tropical plants and microalgae are attractive resources for search of novel bioactive compounds applicable to medicines and agrichemicals. However, many species of them are on the point of extermination because of environmental deterioration such as greenhouse effect and acid rain. The aim of this research is to develop artificial seeds for long-term preservation of those valuable. Cryopreservation (preservation in liquid nitrogen) is well known as a useful method for long-term preservation of germplasm of various organisms. Therefore, an encapsulation-dehydration was employed in this study for cryopreservation of plants and microalgae, in which materials were encapsulated in Ca-alginate beads to form artificial seeds and dehydrated by air-drying before cooling in liquid nitrogen.By using this technique, hairy roots of three plant species capable of producing bioactive compounds were successfully cryopreserved. Moreover, this technique was applicable to cryopreservation of several strains of eucaryotic microalga and cyanobacterium.In case of hairy roots and eucaryotic freshwater microalgae (green algae), survival rates after dehydration were markedly increased by addition of abscisic acid (ABA) into preculture media and beads, indicating that ABA increased desiccation tolerance of these materials. Consequently, their survival rates after cooling liquid nitrogen increased to more than 70%, which is acceptable as a sufficient rate for stable long-term preservation.These results indicate that cryopreservation using encapsulation-dehydration technique is useful for long-term preservation of artificial seeds encapsulating hairy roots of medicinal plants and microalgal cells. Application of the technique developed to different species of tropical plants and microalge is in progress.