1-MCP delayed softening and affected expression of XET and EXP genes in harvested cherimoya fruit

Cherimoya, a typical climacteric fruit, is very susceptible to postharvest losses, due to rapid softening. It has been reported that xyloglucan endotransglycosylases (XET) and expansins (EXP) contribute to fruit softening while 1-methylcyclopropene (1-MCP) is used to delay softening in many fruit. However, the effects of 1-MCP on cherimoya fruit softening and in relation to the expression of XET and EXP genes remain unclear. In this study, three different full length XET cDNAs, termed AcXET1, AcXET2 and AcXET3, were isolated and characterized. Delay in cherimoya fruit softening by 1-MCP in relation to the expression of XET and EXP genes was investigated. Cherimoya fruit stored at 20 degrees C softened rapidly within 5 d and displayed a typical climacteric pattern of ethylene production. Application of 1-MCP greatly delayed and inhibited ethylene production and softening of fruit during storage at 20 degrees C. Northern blot analysis showed that three AcXETs or AcEXPs exhibited different expression patterns during fruit softening while mRNAs of AcXET2,AcEXP1 and AcEXP3 significantly accumulated on day 3 and mRNAs of AcXET1 or AcEXP2 accumulated on day 5 or day6. 1-MCP treatment not only delayed the accumulation of AcXET1,AcEXP1 and AcEXP3 for 1, 3 and 2 d, respectively, but also reduced the mRNA levels of AcXET1, AcXET2, AcXET3, AcEXP1, AcEXP2 and AcEXP3. These data suggest that differential expression of AcXETs and AcEXPs is associated with fruit softening of cherimoya and application of 1-MCP retarded or suppressed the expression of AcXETs or AcEXPs, which may be attributed at least or partially to 1-MCP delayed fruit softening. (C) 2008 Elsevier B.V. All rights reserved.