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Increased activities of phenyalanine ammonia lyase, peroxidase, and cinnamyl alcohol dehydrogenase in relation to pericarp hardening after physical impact in mangosteen (Garcinia mangostana L.)

Summary We previously reported that physical (mechanical) impact results in increased lignin concentrations in the pericarp of mangosteen (Garcinia mangostana L.) fruit. Here, we observed the effects of physical impact on fruit firmness and enzyme activities. Increases in fruit firmness and in lignin levels were detectable within 15 min of impact. Cellulose levels in the pericarp and water contents changed significantly, suggesting that the main increase in pericarp firmness was due cell wall cross-linking, possibly due to lignification. However, the increase in pericarp lignin level was not directly related to a concomitant decrease in the levels of free phenolics, potential substrates for lignin synthesis. The activities of pericarp phenyalanine ammonia lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD), all enzymes involved in lignin biosynthesis, showed a significant increase 15 min after impact, then decreased. It was concluded that the increase in the firmness of mangosteen pericarp after impact was related to increased activities of the enzymes required for lignin biosynthesis and not to the biosynthesis of phenolic compounds.