Physiological Research Of Peel Pitting And Isolation Of Related Genes On 'Fenjie' Navel Orange

Fenjie navel orange (Citrus sinensis Osbeck) is welcomed by consumers for its good tasty and beautiful color. But it is prone to develop peel pitting, which has been described as a severe disorder with characteristics of the extensive collapsed areas of the flavedo (outer colored part of the peel) and part of the albedo (inner part of the peel) that becomes brown with time. Peel pitting decreases the external quality and consequently the market value of the fruit.'Fenyuan 72-1'navel orange fruits were obtained from local orchards and used for the experiments shortly after harvest. Four sets of fruits, each had three replications of 30 fruits, were placed at 15℃(the control), 5℃(low temperature), waxing+ 15℃and mechanical damage+15℃respectively for ten weeks. Incidence of peel pitting and activity of peroxide (POD), Polyphenol Oxidases(PPO) Phenylalanine ammonialyase(PAL) was tested every week. The results indicated that waxing and mechanical damage could enhance development of peel pitting, whereas 5℃storage decreased. Enzyme activity of PAL, POD and PPO revealed that damaged fruits had higher enzyme activity, which exhibited more pitting, while 5℃stored fruits had lower enzyme activity and less pitting develop. The results revealed that POD, PPO and PAL are peel pitting concerned. Semi-quantitative PCR was used to study the relationship of pal genes expression with mechanical damage and pitting development. Mechanical damage induced expression of pal2 and pal6, and these genes were higher expressed in pitted fruits than un-pitted. Pal1 expression cannot be examined in damaged fruits and only expressed in pitted peel after 42 PCR cycles. Expression of pal6 was lower than pal2, which indicated that pal2 was deeper involved in pitting and damage response than pal6 and pall.Controlling technic had been set up to decrease peel pitting in navel orange. Calcium spray and bag cover after second physiological fruit drop decreased postharvest peel pitting. Waxing only before sale is another useful means.Suppression subtractive hybridization (SSH) was used to screen differentially expressed genes in navel orange peel pitting. Pitting peel and peel of no-pitting fruit were selected as the tester and the driver, respectively. Positive clones were randomly picked up and sequenced. Based on homology comparison with GenBank, six out of 50 clones haven't found homologic sequences and three were with unknown function. Five homologic genes: Ca2+ binding protein gene, cysteine proteinase gene, NAC-domain protein gene, stress and pathogenesis-related protein gene and expansin gene were examined the relationship between their expression and citrus peel pitting through semi-quantitative PCR analysis in pitting and no-pitting fruits. Results showed that the...