Controlled atmosphere and heat shock affect PAL1 and HSP90 mRNA accumulation in fresh-cut endive (Cichorium intybus L.)

Abstract

Stored fresh-cut endive gradually turns red, since tissue wounding induces de novo synthesis of phenylalanine ammonia-lyase (PAL), which activates the phenylpropanoid pathway. Once the pool of phenolic substrates is increased, polyphenols are oxidized and cause discoloration. Modified atmosphere packaging (MAP) and controlled atmosphere storage (CA) have been used to control browning. This paper describes the combined effects of heat shock (46 °C/120 s) and CA on the quality of cut endive stored at 10 °C. Heat shock protein (HSP90) and PAL expression patterns were analysed in endive sliced tissues. Real-time quantitative PCR (qPCR) was performed for PAL1 and PAL2 as well as for degenerated HSP90 primers. PAL1 and PAL2 were strongly expressed in unheated cut tissues, in which maximum accumulation of PAL1 mRNA occurred 12 h after cutting. Heat shock significantly reduced the level of PAL1 transcripts in sliced endive, which was related to the prevention of discoloration. Controlled atmosphere storage had an effect on PAL1 but not on PAL2 transcription. Peak levels of HSP90 transcript accumulation were found after 6 h, with an increasing and apparently cumulative effect of wounding and CA. Image analysis of the slices after 48 h clearly showed that heat-treated samples were similar to the control, with no significant difference between air and CA storage. These results show that there could be inhibition of PAL1 isoform expression in endive slices after heating.