Cell wall metabolism during durian fruit dehiscence

Changes in cell wall composition and enzyme activities were studied during durian fruit dehiscence. Water-soluble pectin concentrations remained constant for 2 days in both the husk and the dehiscence zone (DZ), and then increased in the DZ toward the end of storage. Chelator-soluble pectin was higher in the DZ at harvest and throughout storage. This pectin fraction increased steadily in both tissues. Na2CO3-soluble pectin content was about the same in the husk and the DZ, but slightly decreased during the dehiscence process. Hemicellulose (1 and 4 M KOH-soluble fractions) slowly decreased in the husk and the DZ during storage. The molecular size distribution of the three pectin fractions shifted from a larger molecular size to a smaller size, during durian dehiscence. The DZ was found to contain smaller pectin molecules than the husk. There was no change in molecular size in the 1 M KOH fraction and only a minor change toward the smaller molecular size in the 4 M KOH fraction during the later period of durian dehiscence. Pectin methyl esterase activity, both in the husk and in the DZ, was the same at the beginning of storage. However, differences were observed by the time storage had ended. Polygalacturonase activity slowly increased in both tissues during 8 days of storage, with the activity always being higher in the DZ than in the husk, especially at late dehiscence. β-1,4-Endoglucanase activity increased more in the DZ than in the husk during the dehiscence process. β-Galactosidase activity increased during the first half of fruit ripening, and then declined. The results suggested that the durian dehiscence process mainly involved degradation of chelator-soluble pectin by polygalacturonase.