Expression of a phenylalanine ammonia-lyase gene in relation to aril breakdown in harvested longan fruit

Abstract

SummaryA full-length phenylalanine ammonia-lyase gene (PAL) cDNA, named DlPAL1, was isolated and characterised from harvested longan fruit. The expression pattern of DlPAL1 and PAL activities in relation to aril breakdown in longan fruit stored at different temperatures were investigated. The results showed that both PAL activity and the accumulation of DlPAL1 mRNA increased during storage at 25ºC and at 10ºC, which coincided with an increase in the aril breakdown index (ABI). The increase in PAL activity or in the accumulation of DlPAL1 mRNA coincided with the increase in ABI in fruit stored at 4ºC for 40 d, then transferred to 25ºC for 2 d. No accumulation of DlPAL1 mRNA throughout storage at 4ºC could be detected, although the increase in PAL activity was in accordance with the increase in ABI. Furthermore, changes in DlPAL1 mRNA accumulation were not fully in accordance with the changes observed in PAL activity, and a rapid increase in PAL activity in arils was observed as aril breakdown occurred rapidly whether fruit were stored at 25ºC, 4ºC, or 10ºC, or moved from 4ºC to 25ºC. These results suggested that PAL activity is closely involved in aril breakdown in longan fruit, and that PAL activity might be regulated at the post-transcriptional level during aril breakdown.