초록) 국화는 전 세계적으로 중요한 화훼작물 중 하나로 다양한 품종들이 재배·육종 되고 있다. 따라서, 육종소재로서의 가치가 있는 국화 유전자원들의 보존이 필요하며, 유전자원 장기저장방법 중의 하나인 초저온저장 방법을 이용하여 국화의 효과적인 초저온 저장방법 확립과 이를 이용한 바이로이드 제거에 관한 연구를 수행하였다. 기존에 알려진 캡슐화-탈수화 방법과 캡슐화-유리화 방법의 장점만을 적용하여 캡슐화-유리화-탈수화의 새로운 방법으로 실험을 수행하였다. 국화 신초 1.0 mm 크기의 재료를 캡슐화 시켜 88 mM sucrose 가 첨가된 MS 배지에 24시간 진탕배양 후 0.3 M sucrose 가 첨가된 배지에서 16시간 진탕배양한 다음 0.7 M sucrose 가 첨가된 배지에서 6시간 동안 진탕배양한다. 전처리가 끝난 bead는 loading 용액에 180분 동안 진탕배양한 다음 PVS3 용액에 60분간 유리화 과정을 거친 후 laminar air flow cabinet 에서 4시간 동안 건조시킨다. 건조시킨 bead는 액체질소에 1시간 침지시켜 동결 후 38°C 항온수조에서 3분간 해동 시킨 다음 재생배지로 옮겨 생존율과 신초 재생율을 조사하였다. 국화 품종 보라미는 91.3 % 생존율과 80.3 % 의 신초 재생율을 보였고, 시크릿 핑크, 옐로우 캡, 화이트 엔디 역시 60.3~87.3 % 의 생존율을 나타냈으며, 신초 재생율은 55.3~70.0% 로 품종간의 차이를 보였지만 다소 높은 경향치의 생존율과 신초 재생율을 나타내었다. 이는 캡슐화-탈수화 방법과 캡슐화-유리화 방법의 장점만을 적용하여 캡슐화-유리화-탈수화 방법을 이용하여 보고한 첫번째 연구이다. 또한, 초저온저장밥법을 이용하여 바이로이드에 감염된 국화를 칠곡, 구미, 경산 등에서 수집하여 바이로이드 제거에 관한 연구의 재료로 사용하였다. 바이로이드를 제거한 결과 재료의 바이로이드 감염율이 낮았던 구미에서 수집한 재료를 사용하여 4°C에서 4주간 처리한 재료를 생장점 크기 1mm (엽원기 1-2매 포함)로 PVS2를 이용하여 유리화시킨 다음 초저온처리를 했을 때 바이로이드가 제거되었다. 하지만 바이로이드가 고농도로 감염된 식물체에서는 바이로이드가 제거되지 않았으며 이는 바이로이드 제거는 식물체의 유전형과 감염농도에 의해 그 효과의 차이가 있는 것으로 판단된다. 더불어 초저온저장시 보다 효과적인 식물체 장기저장 방법을 확립하고자 antifreeze protein (AFP) 을 이용하여 처리한 결과 AFP를 처리했을 때 동결 후 식물체의 생존율 및 신초 재생율이 앞서 확립한 방법(캡슐화-유리화-탈수화 방법) 보다 월등히 높았으며, DSC를 통해 AFP가 식물조직을 동결로부터 보호한다는 것을 추정하여 확인할 수 있었다. 이 연구 역시 화훼작물의 초저온저장에 AFP의 효과를 보고한 첫번째 연구이다.
Chrysanthemum is one of the globally important ornamental plant and therefore grown worldwide. In this study, an efficient encapsulation-vitrification- dehydration protocol was reported for cryopreservation of Chrysanthemum morifolium shoot tips. Shoot tips of 1.0 mm size that were encapsulated, and pre-cultured in liquid MS medium containing 88 mM sucrose for 24 h followed by in containing 0.3 M sucrose for 16 h and in 0.7 M sucrose for 6 h, treated with loading solution for 180 min, dehydrated with PVS3 for 60 min, and sequentially air dried for 4 h (33.0% water content) in laminar air flow cabinet prior to exposure with liquid nitrogen (LN) for 1 h was found to be the most suitable regime for cryopreservation of Chrysanthemum shoot tips. Under the optimal conditions, the highest survival rate of 91.3%, and shoot regrowth rate of 80.3% was obtained using cultivar ‘Borami’. The method developed was successfully adapted to three more cultivars, ‘Secret pink’, ‘Yellow cap’, and ‘White ND’ which showed a survival rate of 60.3?87.3%, and shoot regrowth rate of 55.3?70.0%. This could be the first report combining the advantage of encapsulation-vitrification and encapsulation- dehydration in cryopreservation. This developed protocol will be a great tool to conserve chrysanthemum germplasm. Chrysanthemum morifolium ‘Borami’ and ‘Secret Pink’ showing symptoms of stunt disease caused by chrysanthemum stunt viroid (CSVd) and the cultivar Yellow Cap showing chlorotic mottle disease caused by chrysanthemum chlorotic mottle viroid (CChMVd) were confirmed to be infected by the respective viroids by using reverse transcription polymerase chain reaction (RT-PCR). Real-time PCR results showed that the viroid concentrations in the infected cultivars varied between the different regions of origin (Chilgok, Gumi, and Gyeongsan). We applied a cryopreservation protocol for elimination of CSVd from naturally infected Borami cultivars collected from Gumi, which showed the lowest concentration of CSVd, by varying several factors such as plant vitrification solutions (PVS2 and PVS3), duration of exposure to liquid nitrogen, shoot-tip size, and low-temperature treatment. The vitrification solution (PVS2) and low-temperature treatment were found to be critical factors determining the efficacy of viroid elimination. We optimized the protocol by combining of all resulted optimal factors and tested the applicability of the optimized protocol in Borami collected from Chilgok and Gyeongsan and in Secret Pink from Chilgok, Gumi, and Gyeongsan, which displayed different viroid concentrations. The elimination rates varied depending on the cultivar and origin of region. Similar results were observed when the protocol was applied to eliminate chrysanthemum chloric mottle viroid (CChMVd) from the Yellow Cap cultivar collected from the same regions. Finally, this finds that nested PCR is more reliable for viroid detection than RT-PCR. Overall, these results suggested that cryopreservation can be used to eliminate viroids from infected chrysanthemums; however, the efficacy depends on the plant genotype and initial viroid concentration. This is the first study to show the application of antifreeze protein (AFP) in cryopreservation of ornamental plants. In this study, the effects of AFP on cryopreservation of Chrysanthemum morifolium ‘Borami’, ‘Secret Pink’, and ‘Yellow Cap’ were investigated. For all cultivars, lower survival and regrowth rates were observed in shoot tips vitrified with plant vitrification solution 3 (PVS3) than in those vitrified with PVS3 containing various concentrations of AFP. The optimal concentration of AFP was found to be genotype-dependent. Results of scanning electron microscopy revealed that shoot tips vitrified with PVS3 containing AFP had less freezing injury than those treated with PVS3 alone. Analysis of the enthalpy in each sample by differential scanning calorimetry supported the finding that AFP is a potent cryoprotectant that can readily reduce the freezing point of water in plant tissues. These findings will facilitate successful application of AFPs in cryopreservation of rare and commercially important plant germplasm.
LIST OF TABLES ············································································ iLIST OF FIGURES ·········································································· iiiGENERAL INTRODUCTION ························································· 1LITERATURE REVIEW ··································································· 5CHAPTER I ······················································································ 12Application of encapsulation-vitrification in combination with air dehydration enhances cryo-tolerance of Chrysanthemum morifolium shoots tipsCHAPTER II ····················································································· 47Attempts to eliminate chrysanthemum stunt viroid (CSVd) and chrysanthemum chlorotic mottle viroid (CChMVd) from infected chrysanthemums by cryopreservationCHAPTER III ···················································································· 71The benefit of antifreeze proteins for cryopreservation of chrysanthemumGENERAL DISCUSSION ······························································ 85Summary ························································································· 96REFERENCE ··················································································· 99ABSTRACT (KOREAN) ······························································ 120