Chloroplast ultrastructure and chlorophyll levels in vegetative buds and needles of Norway spruce (Picea abies L. Karst.)

Background and Purpose: Vegetative buds of spruce are initiated on young shoots in spring and further differentiate during summer. In autumn they enter a resting period until next spring when they proliferate into new shoots. The objective of this study was to characterize chloroplast ultrastructure and chlorophyll formation in the vegetative buds and needles of Norway spruce during the period of dormancy. Materials and Methods: Vegetative buds and current year needles were sampled from the lower crown of ct 25-year-old Norway spruce tree (Picea abies (L.) Karst.) during autumn and winter. The tissue for ultrastructural studies was fixed in 1% glutaraldehyde in Na-cacodylate buffer postfixed in 1% OsO4, dehydrated and embedded in Araldite. Ultrathin sections were stained with uranyl acetate and lead citrate and examined by electron microscopy. Photosynthetic pigments from isolated buds and needles were extracted with acetone and quantified spectrophotometrically. Results and Conclusion: The chloroplast ultrastructure in vegetative buds was characterized by a weakly developed thylakoid system and relatively large starch grains. There were no changes during autumn and winter. In spite of the exclusion of light due to the surrounding lignified brown scales, the shoots within the vegetative buds were brightly green; the presence of chlorophyll was confirmed spectrophotometrically. It is possible that the plastids of developing Norway spruce vegetative buds contain a light-independent NADPH-protochlorophyllide oxidoreductase, which permits chlorophyll syn thesis in the dark. In the current year needles, the chloroplasts maintained, until autumn, a well developed thylakoid system, big starch grains and a limited number of small plastogiobuli. In winter these chloroplasts became chubby, the plastoglobuli were darker, more numerous and grouped together, some swelling was present in the stroma thylakoids, and there were no starch grains. The chlorophyll concentration (chl(a+b)) in mature needles was nearly constant, during the whole period.