Resistance Evaluation Of The Transgenic Sweet Orange Plants Overexpression PtADC Gene

Citrus production is seriously destroyed by a variety of biotic or abiotic stresses, and enormous work has shown that polyamines play important roles in stress resistance. Previously, PtADC cloned from Poncirus trifoliata L. Raf. was introduced into sweet orange(Citrus sinensis Osbeck'Bingtangcheng') in our laboratory, but the resistance to transgenic plants was not analyzed. In this study, the resistant to biotic and abiotic stresses was evaluated in three selected transgenic lines (517,533 and 576) and untransformed plants (WT). The main results are as follows:1. Polyamine content and expression of the transgene:HPLC analysis showed that the content of putrescine, spermidine and total polyamines in the three transgenic lines was higher than that in the WT. Moreover, the three transgenic lines had higher ratios of putrescine/total polyamines but lower ratios of sperdimine/total polyamines when compared with the WT, while spermine level is undetectable.2. Canker resistance analysis:Inoculation with canker bacteria (Xanthomonas axonopodis pv. citri) showed that the canker occurrence was delayed in the transgenic plants, and the transgenic lines had lower disease incidence than the WT, This data indicating that the transgenic plants should enhance canker resistance.3. Analysis of resistance to oxidative stress:The leaf discs of the WT and transgenic plants were treated with 2% of (v/v) H2O2. After 12 h of treatment, the WT leaf discs began to bleach, and completey became white after 36 h. After treating for 36 h, the transgenic plants still remained green color. Determination of chlorophyll content indicated that the chlorophyll level in the leaf discs of transgenic plants was significantly higher than that of the WT. Treatment with 200μmol/L of methyl viologen(MV) showed that the transgenic lines could maintain green for long time than the WT, along with higher chlorophyll content. These data suggest that the oxidative stress resistance was enhanced in the transgenic plants.4. Activity of antioxidant enzymes:The activity of 517,533 and 576 was higher than that of WT. The CAT activity of all three lines was significantly higher than that of WT, whereas only significance difference in POD activity was detected between 517 and the WT. These results suggest that antioxidant capacity of the transgenic plants may have been enhanced as compares with WT.