Abstract:In order to select cold-resistant lines of Morinda citrifolia for widen the range of planting, the leaf anatomic structures of eight plants growing in Yuanjiang, Yunnan, were observed by paraffin section method, and the activities of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and malondialdehyde (MDA) content were measured, and then, glycerol-3-phosphate acyltransferase (GPAT) activity and GPAT gene expression in cold-resistant lines were quantitatively analyzed. The results showed that the leaves of 4 lines (No. 5, 6, 8, 12) had high ratio of palisade tissue to spongy tissue (P/S) with compact cell structure and low porosity, showing a certain cold resistance. The activities of CAT, POD, and SOD of No. 5 leaves were high, and the content of MDA was low after treated at low temperature, indicating that No. 5 was a cold-resistant line. After low temperature treatment, the GPAT activity and GPAT gene expression in No. 5 were higher than those in other plants. Therefore, the cold resistance of M. citrifolia leaves was improved by increasing P/S and cell structure tightness, as well as the rapid response of GPAT gene.