Photosystem II efficiency, chloroplast pigments and fine structure in previous-season needles of Norway spruce (Picea abies L. Karst.) affected by urban pollution

Background and Purpose: Industry and road traffic are considered to be main sources of air pollutants in urban areas. Changes in chloroplast structure, biochemistry and function appeared as very fast and reliable indicators of stress conditions. The arm of our study was to compare the needles of Norway spruce trees growing on differently polluted sites in the city of Osijek (Croatia) regarding photosynthetic pigment content, chloroplast ultra-structure and the efficiency of photosystem II. Material and Methods: Materials for the study were previous-season needles collected from the middle crown of ten, about 25 year-old cultivated Norway spruce (Picae abies L. Karst.) trees grown in the City of Os jell, Croatia. According to the data on pollution levels obtained from the Croatian National Institute of Public Health, two sampling plots were defined: less (reference) and more polluted. Photosynthetic pigments were extracted with absolute acetone and quantified spectrophotometrically.. For electron microscopy, the plant material was fixed in glutaraldehyde, dehydrated and embedded in Spurr's resin. Ultrathin sections were contrasted with lead citrate and uranyl acetate. The measurements of chlorophyll fluorescence were performed with the pulse-amplitude-modulated photosynthesis yield analyser (Mini-PAM, Waltz), using pulse-saturating method. The plant material was dark-adapted for 30 minutes. Minimal (Fo) and maximal (Fin) fluorescence yields were Measured in the dark-adapted samples. The same parameters (F and Pin, respectively) were measured at two different irradiance levels: low light (125 mu mol(PHOTONS) m(-2)z s(-1)) and high light (1400 mu mol(PHOTONS) m(-2) s(-1)). Results and Conclusions: The concentration of photosynthetic pigments was lower in more affected needles than in the reference ones. However; only changes in chlorophyll b revealed statistical signficance, increasing the chlorophyll a to chlorophyll b ratio. Chloroplast ultrastructure and shape were changed in more affected needles: these chloroplasts were roundish with much bigger starch grains and snore pronounced thylakoid swelling than the chloroplast from the reference needles. Maximal photochemical efficiency of photosystem II (Fv/Fm) measured in the dark-adapted samples teas almost the same for both samples, while lower values of the effective quantum yield of photosystem II (Delta F/F'm) were determined in more affected needles. It can be concluded that after a prolonged period of exposure to a higher pollution level (two years), spruce needles revealed biochemical, ultrastructural and functional changes when compared with the needles exposed to a lower pollution level.