[The relationship between activity and gene expression of phenylalanine ammonia-lyase and peel pitting in 'Fengjie' navel orange fruits].

Citrus fruit is prone to develop peel pitting during development and storage, which greatly decreases its fresh market value because of the deterioration of the peel. In the present study, we have examined the effect of different temperatures (15 degrees C and 4 degrees C), waxing and mechanical damage on the changes in the activity of phenylalanine ammonia-lyase (PAL) and the incidence of peel pitting in 'Fengjie' navel orange (Citrus sinensis Osbeck) fruits. The expression levels of PAL2, PAL6 genes in the peel during the development of peel pitting have been investigated through semi-quantitative PCR method. The incidence of peel pitting was greatly enhanced by waxing and mechanical damage and was decreased in lower temperature storage (4 degrees C) (Fig.1). Waxing and mechanical damage might be the important factors inducing peel pitting and suitable low temperature could decrease the incidence of this disease. The PAL activity increased during the whole storage period in accordance with the development of this pitting (Fig.2). The expression levels of PAL2 and PAL6 genes in damaged peel were higher than those in healthy peel and the expression of PAL2 is much more higher than that of PAL6 (Figs.4 and 5). The results suggested that the enzyme activity of PAL, along with the expression of PAL2 gene is highly related to this peel pitting occurred on 'Fengjie' navel orange fruits.