关键词: 柑橘, 溃疡病, 细胞程序性死亡, 活性氧, 丙二醛, 抗氧化酶, 基因表达

Abstract: To further investigate the relationship between citrus canker disease resistance and programmed cell death（PCD），the dynamics of PCD related signals，antioxidant enzyme activities and gene expression upon Xanthomonas citri subsp. citri（Xcc）infection were studied in susceptible variety Wanjincheng orange（Citrus sinensis Osbeck）and resistant variety Jindan（Fortunella crassifolia Swingle）. Typical canker symptoms of pustule were observed in Wanjincheng orange，while hypersensitive necrosis（blown region）occurred in Jindan after inoculation with Xcc. The base level of hydrogen peroxide（H2O2）in Jindan was higher than that of in Wanjincheng orange before inoculation. After inoculation，the content of H2O2 increased in the two varieties，but the content in Jindan was always higher than that in Wanjincheng orange. Following the increase of H2O2 level，the content of malondialdehyde（MDA），which indicates the degree of membrane lipid peroxidation also increased in two varieties，but much higher in Jindan. The activity of superoxide dismutase（SOD），which is involved in scavenging reactive oxygen species decreased in the leaves of two varieties. The activity of catalase（CAT）increased in the two varieties，but no significant difference between them. Moreover，the activity of peroxidase（POD）increased in both varieties，but more rapidly in Wanjincheng orange，and the increase was lower than that of the water treatment control. The expression of CsCEP1-1，CsCEP1-2 and CsMCA1 which positively regulate the PCD were up-regulated by Xcc in two varieties，while much higher in Jindan. The transcription levels of CsDAD1-1，CsDAD1-2，CsMLO2 and CsMLO3，which negatively regulate the PCD did not significantly change in Wanjincheng orange，but gradually decreased in Jindan. The results showed that both susceptible and resistant varieties initiated the hypersensitive reaction in response to the Xcc infection. However，the reaction was more drastic in the resistant variety，which may lead to the induction of PCD and resulted to the resistance of Jindan to Xcc.

Key words: citrus, canker disease, programmed cell death, reactive oxygen species, malondialdehyde, antioxidant enzyme, gene expression