engleski

Organization of photosynthetic membranes in etiochloroplasts of spruce seedlings treated with norflurazon

The ability of cotyledons of spruce seedlings to biosynthesize chlorophyll in the dark was used to study the effect of the bleaching herbicide norflurazon on the formation of photosynthetic membranes in their etiochloroplasts. In cotyledons of 14-day-old seedlings grown in the dark on norflurazon, the biosynthesis of carotenoids was heavily inhibited. Very strong reduction of carotenoid content, in particular that of beta-carotene and violaxanthin, was obtained with concentrations of norflurazon of 200 ľM and 20 ľM. With lower concentrations of norflurazon this effect was proportionally reduced. At the same time, the content of chlorophylls was also reduced, although to a much lesser degree than that of carotenoids. Analyses of membrane proteins indicated that in norflurazon-treated plastids the content of polypeptides of the LHC II complexes, the major light-harvesting complexes of photosystem II, was impaired. Ultrastructural analyses supported these biochemical results: in norflurazon-treated etiochloroplasts the quantity of thylakoids, in particular of grana-thylakoids, was reduced. The membranes were structurally changed, resulting in uncompleted thylakoid stacking. Only seedlings with less altered plastids were able to develop some photosynthetic activity. High concentrations of norflurazon (200 ľM or 20 ľM) caused bleaching of the tissues and damage of their plastids, when dark-grown seedlings were kept in the light for some days. The experiments confirmed the necessity of carotenoids in the formation of a thylakoid apparatus capable of photosynthetic activity.

picea; etiochloroplasts; photosynthetic membranes; norflurazon

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