Changes Of POD Activity And Gene Expression Analysis During Litchi Pericarp Browing

In the whole world, China is the biggest yield of litchi. the sown area of litchi accounts for 90 percent of the world's total The yield of litchi accounts for 80 percent of the world's total. However, its commercial value is often reduced by the dehydration, browning, and disease developing of pericarp during postharvest storage. All of the above problem are limiting the spread of litchi on international market. The basis on developing techniques for preserving litchi should be attention to study on postharvest biology of litchi fruit. Much research focus on the physiological changes of postharvest litchi, but few reports have been searched about the postharvest molecular biology of the fruit. the molecular mechanism of pericarp browning should be explained well by cloning the differentially expressed genes and study their express patterns.Commercial maturity fruit of Feizixiao was used in this study. Some physiological changes were profiled during the browing of pericarp. and appearance changes within pericarp of none- packaged litchi stored at room temperature were studied at a 8 hours interval after havest. The results show that the browning index of pericarp obviously ascend within 48 hours ,and pericarp changed fully browning within 72 hours. Water loss of fruit , which was caused mainly by water loss of pericarp, increased during pericarp browning. Pericarp lost its water continuously during browning. stored at packaged litchi fruits of Feizixiao at hydration at a 24 hours interval after havest were studied. The results show that the browing of pericarp had no change during storage 72 hours.Otherwise, POD PPO anthocyanin flavonoid and hydroxybenzene changes within pericarp of none-packaged litchi fruits of Feizixiao stored at 25℃±1℃temperature and 70%±5% atmosphere humidity at a 8 hours interval after havest and stored at packaged litchi fruits of Feizixiao at hydration at a 24 hours interval after havest were studied. The POD and PPO activity increased during the storage. The anthocyanin, flavonoid and hydroxybenzene content decreased during the storage. During the same times the browning index POD and PPO within pericarp of litchi fruits stored at room temperature were higher than the browning index POD and PPO within pericarp of litchi fruits stored at 25℃±1℃temperature and 70%±5% atmosphere humidity. However The anthocyanin, flavonoid and hydroxybenzene content within pericarp of litchi fruits stored at room temperature were lower than the anthocyanin, flavonoid and hydroxybenzene content stored within pericarp of litchi fruits at 25℃±1℃temperature and 70%±5% atmosphere humidity. That indicate that effect of litchi fruits stored at room temperature were lower than effect of litchi fruits stored at 25℃±1℃temperature and 70%±5% atmosphere humidity.Then a CDNA library and SSH library were constructed. Four POD genes(POD1, POD2, POD3, POD4) were identified according to the hybridization results. Bioinformatics analysis of obtained POD gene.The POD1 gene is 1363 bp long . Sequence analysis in Genscan revealed it consist of a 1062 bp coding region encoding 353 bp amino acids. The POD2 gene is 1376 bp long . Sequence analysis in Genscan revealed it consist of a 990 bp coding region encoding 329 bp amino acids.But the POD3 gene and POD4 gene have no a whole open read frame. POD gene differentially express was analyzed. The results are as follow: POD1 gene up-regulated express at 8h, indifferentially express at 16h 24h 32h 40h and 48h. POD2 gene indifferentially express at 8h and 16h, but down-regulated expess at 24h,32h 40h 48h. POD3 gene indifferentially express at 8h 16h 24h 32h 40h and 48h. POD4 gene up-regulated express at 8h, indifferentially express at 16h 24h 32h 40h and 48h.