The Effects Of1-MCP On Activities Related With Softening Of Postharvested Papaya Fruits And The Analysis In Transcription Levels Of Key Enzyme Genes

Papaya is a kind of typical climacteric fruit,which is extremely easily to rot and mature to soft after postharvest.l-MCP is a new type of preservation which could kee-p fruit and vegetable fresh by the mean of competition with ethylene receptor. After1-MCP treatment, papaya fruit would loss the normal ability to soften （accompanying w ith poor flavor, like carrot）, it is called "rubbery" phenomenon because of lacking of normal taste and flavor. There is closely relationship between fruit softening and cell wall degradation enzymes.Domestic and foreign research show that the cell wall degr adation enzymes include PG, CX, PME, endoglucanase, endo-xylanase, β-galactosidase et al.In this paper, the effects of1-MCP（1.0μl·L-1） on enzyme activities related with cell wall metabolism of papaya fruit （80%maturity,CV.’RI SHENG’）, and the change s in gene transcription levels of the key enzymes related with softening..Followings ar e the main results:（1）The firmness of papaya fruit presented a slow tendency of decrease after1-M CP treatment,when fruit firmness of the early stage of the harvest （0days） and the lat e stage （35days） were0.91Kg·cm-2and0.78Kg·cm-2respectively and storage period of fruit firmness fell by only14.29%.1-MCP had an important effect on related enzy-mes about metabolism in cell wall,but there was a diversity between different kinds o f enzyme activity:an increasing growth taking place in the activity of PG,PME,CX en-zymes with a peak changing trend.The peak of enzyme activity of PG enzyme、PME enzyme and CX enzyme appeared after harvesting5、25and5days.The activity value-s were35.64『mol·h-1·g-1、39.67U·h-1·g-1and18.71μmol·h-1·g-1respectively.However, tre-atment of1-MCP greatly inhibited the activity of endoglucanase and P-galactosidase. T he figures were lower than the fruit of CK6.35μmol·h-1·g-1and28.46·mol·h-1·g-1（P≤0.01） respectively in the fifth day of storage period.The activity of endoglucanase was at its lowest level throughout the storage period and its activity value remained4.49μ mol·h-1·g-1which was below6.08μmol·h-1·g-1（the fruit of CK） and4.80μmol·h-1·g-1（eth ephon treatment）in the late storage period （30days）.There was a significant difference between the processing （P≤0.01）. The possible reason of why papaya fruit of higher fruit firmness and the abnormal of fruit softening was that the activity of endoglucana se and β-galactosidase is rather low.This was also crucial related to maintain he integ-rity of the cell wall structure and inhibit the degradation of cell wall.（2）Biological information analysis showed that there was an obvious difference at the gene transcription level between PG, PME, endoglucanase and β-galactosidase after the treatment of1-MCP.1-MCP treatment significantly inhibited the transcriptions of PG1gene （evm entry.TU.Supercontig₂50.6）, CX3gene （evm entry.TU.Supercontig₄44.5）, CX4gene （evm entry.TU.Supercontig₈0.122）, PME1gene （evm entry. TU. Supercontig₁540.1）, endoglucanase3gene （evm entry. TU. Supercontig₂.231）, β-galactosidase gene （evm entry. TU. Supercontig₉3.34）, endo-xylanase1gene （evm entry. TU.Supercontig₁06.45）, endo-xylanase2gene （evm entry. TU. Supercontig₁06.45）.On the ninth day, the gene transcription level of above genes were166.88,2.01,153.84,36.82,19.35,416.46,8.52,416.46respectively which were below9553.66,12.38,573.87,914.76,30.78,507.08,139.78,13.31.respectively, there was a significant difference between CK fruit and treated fruit （P≤0.01）In a word, there were some close relationships between the high firmness, abnormal softening and the low levels in endoglucanase and P-galactosidase enzymes of papaya fruit,especially endoglucanase was the most significant among the enzymes related with softening.