Abstract
To determine whether ethylene production was related to locular tissue breakdown in watermelon, plugs from ripe `Jubilee', `Black Diamond', `Tiger Baby', `Mirage', and `King of Hearts' were taken from the skin (epidermis and hypoderm), rind (hypoderm and mesocarp), and placenta (locular and heart) tissues. ACC oxidase activity was <0.05 nmol·g–1·h–1 in locule and heart locations for all cultivars. Skin tissue had the highest activity, ranging from 0. 1 8 for `Jubilee' to 0.5 to 0.62 nmol·g–1·h–1 for the other four cultivars. ACC (1-aminocyclopropane-1-carboxylic acid) and ACC oxidase activity were measured in unripe, ripe, and overripe `Jubilee' melons. ACC oxidase activity from skin tissue was lowest in unripe (0.05 nmol·g–1·h–1) and highest in overripe (0.13 nmol·g–1·h–1) melons, and was 0.05 nmol·g–1·h–1 or less in all other tissues. Free ACC was highest in the skin tissue (1.3 nmol·g–1·h–1), but there was no difference in ACC content with stage of ripeness for any tissue. Results indicate that ethylene may be transported from the outer skin and rind tissues to locular areas and that wounding of the skin tissue could lead to deleterious ethylene production.
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