The natural hazard occurrences such as landslides, debris flows and natural/artificial slope failures were mainly caused by typhoons and extremely heavy rainfall. In order to reduce these natural hazards the efficient countermeasure methods were need to reduce the landslide and debris flow caused by variations of precipitation patterns. The positively countermeasure coping with the debris flow hazards should have to estimate mainly progress to construction of barrier facilities based on the predicted results of potential hazard types and its scales as well as establish and enforce actively maintenance of the barrier facilities. In addition we also emphasized the necessary to the types of barrier facilities and institution improvement in order to positively hazard reduction of debris flow.

Since the major important factors limiting plant growth and crop productivity are environmental stresses, of which low temperature is the most serious. It has been well known that many physiological processes are alterant in response to the environmental stress. With regard to the relationship between plant hormones and the regulation of chilling tolerance in rice seedlings, the major physiological roles of plant hormones: abscisic acid, ethylene and polyamines are evaluated and discussed in this paper. Rice seedlings were grown in culture solution to examine the effect of such plant hormones on physiological characters related to chilling tolerance and also to compare the different responses among tested cultivars. Intact seedlings about 14 day-old were chilled at conditions of 5~circC and 80% relative humidity for various period. Cis-(＋)-ABA content was measured by the indirect ELISA technique. Polyamine content and ethylene production in leaves were determined by means of HPLC and GC respectively. Chilling damage of seedlings was evaluated by electrolyte leakage, TTC viability assay or servival test. Our experiment results described here demonstrated the physiological functions of ABA, ethylene, and polyamines related to the regulation of chilling tolerance in rice seedlings. Levels of cis-(＋)-ABA in leaves or xylem sap of rice seedlings increased rapidly in response to 5~circC treatment. The tolerant cultivars had significant higher level of endogenous ABA than the sensitive ones. The (~pm )-ABA pretreatment for 48 h increased the chilling tolerance of the sensitive indica cultivar. One possible function of abscisic acid is the adjustment of plants to avoid chilling-induced water stress. Accumulation of proline and other compatible solutes is assumed to be another factor in the prevention of chilling injuies by abscisic acid. In addition, the expression of ABA-responsive gene is reported in some plants and may be involving in the acclimation to low temperature. Ethylene and its immediate precusor, 1-amincyclopropane-1-carboxylic acid(ACC) increased significantly after 5~circC treatment. The activity of ACC synthase which converts S-adenosylmethionine (SAM) to ACC enhanced earlier than the increase of ethylene and ACC. Low temperature increased ACC synthase activity, whereas prolonged chilling treatment damaged the conversion of ACC to ethylene. It was shown that application of Ethphon was beneficial to recovering from chilling injury in rice seedlings. However, the physiological functions of chilling-induced ethylene are still unclear. Polyamines are thought to be a potential plant hormone and may be involving in the regulation of chilling response. Results indicated that chilling treatment induced a remarkable increase of polyamines, especially putrescine content in rice seedlings. The relative higher putrescine content was found in chilling-tolerant cultivar and the maximal level of enhanced putrescine in shoot of chilling cultivar(TNG. 67) was about 8 folds of controls at two days after chilling. The accumulation of polyamines may protect membrane structure or buffer ionic imbalance from chilling damage. Stress physiology is a rapidly expanding field. Plant growth regulators that improve tolerance to low temperature may affect stress protein production. The molecular or gene approaches will help us to elucidate the functions of plant hormones related to the regulation of chilling tolerance in plants in the near future. Abbreviation : ABA : abscisic acid ACC : 1-aminocyclopropane-1-carboxylic acid ADC : arginine decarboxylase ELISA : enzyme-linked immunosorbent assay ODC : ornithine decarboxylase Put: putrescine SAMDC : S-adenosylmethionine decarboxylase Spd : spermidine Spm : spermine TNG 67 : Tainung 67 TCN 1 : Taichung Native 1 TTC : triphenyl tetrazolium chloride

질소수준이 높아짐에 따라서 벼 엽신에서 에칠렌 생성량이 감소하는 원인에 대하여 에칠렌생합성계에 존재하는 전구물질 메치오닌 및 직접전구물질 ACC등을 벼에 처리하여 에칠렌생성량에 미치는 영향을 검토한 결과를 요약하면 다음과 같다. 1. 벼 유묘 및 엽에 메치오닌을 처리하면 처리농도가 높을수록 에칠렌생성량은 증가하였다. 2. 직접전구물질인 ACC를 엽신에 처리하면 처리농도가 높을수록 에칠렌생성량은 직선적으로 증가하였다. 3. 질소수준이 다를 벼의 유묘 및 엽신에 메치오닌 및 ACC를 처리하면 에칠렌생성량은 증가하나 질소수준이 높아질수록 에칠렌생성량은 현저히 억제 되어진다.