Der jahreszeitliche Rhythmus des Ascorbinsäuresystems in Nadeln von Picea abies

Abstract

Summary The ascorbic acid (AS) content of Picea abies follows a seasonal rhythm with a maximum of 1.9 mg/g fresh weight (f.w.) in April and a minimum of 0.6 mg/g f.w. in October. The dehydro-ascorbic acid (DAS) content is low (average 0.18 mg/g f.w.) and does not show significant seasonal variation. With increasing needle age AS decreases while DAS increases. DAS reductase shows an annual rhythm with minima of activity in April (0.22 units/g f.w.) and late August (0.55 units/g f.w.) and maxima of activity in July (0.75 units/g f.w.) and October (0.85 units/g f.w.). The curve of the annual rhythm of AS oxidase is in all details inverse to the curve for DAS reductase. The highest activity of AS oxidase is present in April (0.66 units/g f.w.), the lowest in October (0.27 units/g f.w.). It is assumed that increased levels of AS stimulate biosynthesis of AS-oxidase and inhibit biosynthesis of AS reductase, thus providing a control mechanism which prevents from extreme variations of the ascorbic acid level.