Einfluß von Kupfer‐ und Stickstoffmangel auf die Aktivität der Phenoloxidase und den Gehalt an Phenolen in den Blättern der Sonnenblume (Helianthus annuus)

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Abstract
Effect of copper and nitrogen deficiency on phenol oxidase activity and content of phenols in leaves of sunflower (Helianthus annuus)In sunflower leaves of different insertion height the activity of phenol oxidase during the course of the whole vegetation period was determined. In leaves of normal plants this activity reached its maximum during the period of most intensiv growth and decreased continuously with increasing age. The highest activity was found in cotyledons. In normal leaves this maximum decreased with increasing insertion height.Copper deficiency led in cotyledons to a small, in leaves to a severe inhibition of the phenol oxidase activity. Here the decrease of copper content always led to an unproportional decrease of the enzyme activity. After the middle of July, no phenol oxidase activity in leaves of copper deficient plants could be determined.Nitrogen deficiency decreased the yield considerably, while it was lowering the phenol oxidase activity only slightly. Orthodihydroxyphenols, as substrates of phenol oxidase, showed a negative correlation to the enzym activity: The stronger the suppression of the phenol oxidase activity, the higher was the rise of the orthodiphenol content in full expanded leaves.With unsufficient copper supply the plants showed only week deficiency symptoms, although the phenol oxidase activity was completly inhibited. Therefore it is presumed that in sunflower leaves the role of phenol oxidase can partly be taken over by other enzymes.