Expression of PAL and HSPs in fresh-cut banana fruit

Wounding of plants is a widespread stress in nature. Physical damage frequently occurs during harvesting, handling and marketing of fresh produce. Phenylalanine ammonia-lyase (PAL) is a key enzyme involved in plant wound related phenylpropanoid metabolism while heat shock proteins (HSPs) are involved in abiotic, including wounding, and biotic stress responses in plants. However, little is known about postharvest expression at gene and protein levels of PAL and HSPs in wounding (fresh-cut) fruits. In the present study, expression patterns of PAL and HSPs in fresh-cut and intact banana fruit pulp were characterized by Northern and Western blot analyses. Cuting enhanced Ma-PAL2 mRNA accumulation, new PAL protein synthesis, and PAL activity; thereby resulting in accumulation of total phenolics. HSP70 protein and Ma-HSP70-2 transcript were constitutively expressed and were not affected by cutting. However, Ma-HSP70-1 transcript levels increased in fresh-cut pulp tissue at 2–18 h after cutting. Ma-sHSP-1-CI, Ma-sHSP-3-CII, Ma-HSP90, and Ma-HSP101 transcripts also accumulated in fresh-cut tissues at 2–18 h after cuting, but Ma-sHSP-2-CI did not accumulate. Accumulation of sHSP (HSP17.6), HSP90 and HSP101 proteins exhibited the same pattern of expression as their mRNA. There was no evidence of a possible suppressive effect of HSPs synthesis on PAL protein accumulation. Thus, PAL, sHSP, HSP90 and HSP101 were regulated by cutting both at translational and transcriptional levels while HSP70 (Ma-HSP70-1) was regulated by cutting only at transcription level.