β-glucanase and polygalacturonase activities are different in longkong (Lansium domesticumCorr.) fruit at two separation positions

Abstract

Longkong fruit drop was visually checked at two different positions: between the peduncle and the calyx (separation zone 1; SZ1), and between the calyx and the fruit (separation zone 2; SZ2). After color break, 10 weeks after full bloom (WAFB), the breaking strength (BS) at SZ1 only slightly decreased, while BS at SZ2 declined considerably and continued to decrease until the fully ripe stage at 15 WAFB. Fruit drop at SZ1 was induced by exposure of the fruit to ethylene, while at SZ2 separation required an external force exerted on the fruit. This study reports the change in polygalacturonase (PG) and β-glucanase activities at the two positions during fruit coloration and exposure to ethylene and 1-methylcyclopropene (1-MCP) after harvesting at 13 WAFB. The results indicate that at both positions, PG and β-glucanase activities were stable during fruit coloration, indicating that changes in PG and β-glucanase activities were not responsible for the separation zones weakening at this stage. After harvest, in the non-treated, control fruit, β-glucanase activity in SZ1 increased slightly but PG activity was stable. When longkong fruit were exposed to ethylene both PG and β-glucanase activities increased. In contrast, PG and β-glucanase activities decreased after exposure to 1-MCP. In SZ2, PG and β-glucanase activities increased with or without exposure to ethylene; after 1-MCP treatment, PG and β-glucanase activities were lower than the control. These data indicate that both enzymes participate in the cell separation process at both positions in response to ethylene, but other enzymes are also involved. It is postulated that the differential enzyme activities at the two positions, at different stages, provide a benefit to the survival of the plant depending on environmental conditions.