Regulation Of Lignification And Quality Changes In Postharvest Loquat Fruit

Loquat (Eriobotrya japonica Lind1.) is non-climacteric fruit with short postharvest life. Biological characterization and regulations (such as LTC, 1-MCP, ASA and C2H4) of tissue lignification in relation to senescence and chilling injury was investigated in postharvest 'Luoyangqing' fruit. The objectives of present study were to have a better understanding of the biological characteristics and regulation mechanism of quality changes in postharvest loquat fruit, to provide better strategies for longer storage of loquat fruit. Results were as followings:During postharvest storage at 20 °C, a series of physiological changes occurred in loquat fruit including the increase in EC, increase in PPO activity, decrease in total phenolic content, tissue browning, decrease in soluble sugars and organic acids. As the fruit senesced, fruit firmness increased steadily and showed a significant correlation with accumulation of lignin in the flesh (r=0.95**). Among the enzymes associated with lignin biosynthesis, phenylalanine ammonia lyase (PAL) activity increased rapidly during the first three days after harvest and then declined in the fruit flesh, while cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD) activities showed a persistent rise over the whole 8 d. Accumulation of lignin in flesh tissue was also significantly correlated to the activities of CAD (r=0.97**), guaiacol-POD (G-POD) (r=0.98**) and syringaldazine-POD (S-POD) (r=0.99**). Cellulose content in flesh tissue decreased and showed a significant negative correlation with lignin content (r=-0.98**). Such results indicated that tissue lignification is a particular feature of 'Luoyangqing' loquat senescence.During postharvest storage at 0℃, chilling injury occurred with symptoms of lignification, tissue browning, and a decrease in percentage juice, increase in superoxide free radical production, electric conductivity and lignification enzyme activities. Such chilling injury symptoms developed rapidly during the first 9 d cold storage at 0 ℃ and became more severe after fruit was moved to shelf life at 20 ℃.Where fruit ripening or chilling injury were retarded by either low temperature (storage at 5 °C or conditioned at 5 °C for 6 d before 0 °C storage) or 5 \il L"1 1-MCP or an application of 1 mmol L"1 aqueous ASA or enhanced by 100 ul L"1 ethylene treatment, fruit firmness and lignification were consistently retarded or enhanced accordingly.In a conclusion, similar biological characteristics of tissue lignification were found in relations to fruit senescence and chilling injury in 'Luoyangqing' loquat fruit. Whether the same mechanism is responsible for the lignification under both situations remains unknown and a further study with the combination of histology, developmental biology and molecular biology will be carried out in our laboratory.