Citrus Callus Browning Influences Transformation Efficiency

摘要

Our previous experiments on Agrobacterium-mediated citrus callus transformation showed that transformant regeneration is often accompanied by callus browning. To further evaluate the effect of citrus callus browning on transformation, embryogenic calli from 13 citrus species/varieties (including Citrus reticulata, C. paradisi, Fortunella crassifolia, C sinensis, etc.) were inoculated with Agrobacte-rium and assessed for their transformation potentials. Transformation results showed that all but one succeeded in regenerating kanamycin resistant tissues, and among them six produced whole transgenic plants. Histochemical P-glucuronidase (GUS) analysis and southern blot hybridization of resistant tissues confirmed transgene integration. In fact, more than 91% of transformed calli were regenerated from browning callus. Moreover, the transformation efficiency was higher in severe browning species/varieties, suggesting that callus browning was closely related to transformation efficiency. A further studyshowed that the total phenolic content of citrus callus affected callus browning and was positively correlated with transformation efficiency. Taken together, our data indicate that the effect of citrus callus browning on transformation efficiency mightcorrelate with its content of polyphenols.