Peroxidase activity associated with suberization processes of the muskmelon (Cucumis melo) rind

The rind of fruits of muskmelon (Cucumis melo L. var. reticulatus) contains a network of suberized tissue referred to as the 'netting', and peroxidase (EC 1.11.1.7) activity is necessary to the polymerization of the aromatic domain of suberin. Peroxidase activity increased dramatically during the early stages of melon fruit netting, and in fruits exhibiting incomplete netting, peroxidase activity was significantly higher in netted than in non-netted regions of the same fruit. Moreover, analysis of peroxidase activity in three varieties of smooth-rind melons (Cucumis melo var. inodorous) indicated lower levels of the activity in rind samples, taken throughout fruit development, than in rinds of netted varieties. Netting-associated anionic peroxidase (NAPOD) was isolated from the melon rind at an early stage of netting development, partially purified, microsequenced and its cDNA was cloned. It was found to be a single-copy gene within the genome of netted and smooth melon varieties, and highly homologous to other Cucurbitaceous anionic peroxidases. A high transcript level was only detected in the rind of the netted variety. Monitoring the gene expression of netting-associated anionic peroxidase, together with other enzymes involved in the netting will shed light on the molecular control of the suberization processes in the melon rind and in plants in general.