초록 : This study was undertaken to identify the region of cucumber (Cucumis sativus) root tips that display the greatest sensitivity to low temperature stress and the factor that mediates the response. Cucumber seedlings grown for 4 days in darkness in an incubator were exposed to 8℃ for 15 min, 1 h, and 24 h. The sequential sections taken through 4 ㎜ segments of untreated and low temperature-treated root tips, which had been fixed in glutaraldehyde and embedded in a resin, were examined by using a light microscopy. H₂O₂ content was determined and cytochemically localized by the cerium chloride method. The observations indicated the rapid response of cucumber to low temperature stress to be localized to a region of root tip approximately 0.5 ㎜ behind the root apex and mediated by the accumulation of significant amounts of H₂O₂. The sensitivity of this region, referred to here as the transition zone (TZ), in cucumber roots to low temperature is discussed in relation to the features described, as well as the information available from other recent studies to suggest that TZ may be selectively responsive also to other abiotic factors. 키워드 : cytochemistry, hydrogen peroxide, root tips