New insights into the cell wall preservation by 1-methylcyclopropene treatment in harvest-ripe strawberry fruit

Abstract

The purpose of the present work was to provide novel knowledge about the mechanisms underlying the preservation of strawberry fruit by 1-methylcyclopropene (1-MCP) treatment during storage. Harvest-ripe strawberries were treated with 1-MCP for ten hours at 22 °C and then stored for ten days at 4 °C and two days at 20 °C. 1-MCP treatment significantly delayed the loss of fruit firmness and the accumulation of anthocyanins during storage, whereas sustained pH, titratable acidity, total sugars, and phenolic compounds values. 1-MCP treatment reduced the in vitro growth of fungal pathogens Botrytis cinerea and Rhizopus stolonifer when using isolated fruit cell walls as only carbon source. Also, 1-MCP treatment was effective in delaying the appearance of fungal lesions and reducing their severity in comparison with non-treated fruit. 1-MCP treated fruit showed higher amounts of ionically bounded pectins and hemicellulose fractions than controls. Treated fruit showed an increase of pectin methylesterase activity, and the inhibition of polygalacturonase, β-galactosidase, α-arabinofuranosidase, and β-xylosidase activities. 1-MCP application modified the expression of relevant genes related to strawberry fruit firmness, increasing the FaPME1 and FaXTH1 mRNA abundance and down-regulating FaPG1, FaPLC, and FaXTH2 expression. Treatment delayed the in vitro cell wall swelling and the collapse of the hemicellulose-cellulose mesh during storage. The effect of 1-MCP on the cell wall composition and its accessibility to necrotrophic pathogens through an up-regulation of endogenous pectin methylesterases and xyloglucan transglycosylases and a down-regulation of lyases and hydrolases is the first report in commercial-ripe strawberries. Moreover, the effect of 1-MCP treatment combined with a dip in a CaCl2 solution on the firmness of strawberry fruit was evaluated. As a result, 1-MCP/CaCl2 treatment rendered significantly firmer fruit when compared with control, and also with 1-MCP, or CaCl2 individual applications.