Developmental changes in lipoxygenase activity in cotyledons of cucumber seedlings

Abstract

Dry cucumber seeds have no lipoxygenase activity, but the activity in the cotyledons from light-grown seedlings increased rapidly from 3 days after germination, peaking at days 4–6 and declined significantly thereafter. The activity in the cotyledons from dark-grown seedlings increased in the same manner as observed in the light, but the enhanced activity persisted for a longer time. Transfer experiments showed that whether the cotyledons had been illuminated or not till day 6 lipoxygenase activity in the cotyledons degraded rapidly in the light concomitant with greening while it remained at the higher levels in the dark. Immunoblot analyses using antilipoxygenase serum indicate that the increase and decrease of lipoxygenase activity are mostly due to changes in the amount of lipoxygenase protein. The activity in the cotyledons from which the embryonic axis and the testa had been removed increased more rapidly than that in the cotyledons that had developed on the seedlings. Especially in the dark, lipoxygenase activity in the excised cotyledons increased by as much as 3.6-fold compared with the highest value observed with the intact cotyledons. Furthermore, detachment of the cotyledons from hypocotyl and roots at day 4 enhanced lipoxygenase activity. The enhancement was again marked in the dark.