engleski

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 aim of our study was to compare the needles of Norway spruce trees growing on differently poluted sites in the city of Osijek (Croatia) regarding photosynthetic pigment content, chloroplast ultrastructure and the efficiency of photosystem II. Material and Methods: Materials for the studywere previous-season needles collected from the middle crown of ten, about 25 year-old cultivated Norway spruce (Picea abies L. Karst.) trees grown in the City of Osijek, 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 extarcted with absolute acetone and quantified spectrophotometrically. For electron microscopy, the plant material was fixed in glutaraldehyde, dehydrated and embadded in Spurr`s resin. Ultrathin sections were contrasted with lead citrate and uranil acetate. The measurements of chlorophyll fluorescence were performed with pulse-ampliture-modulated photosynthesis yield analyser (Mini-PAM, Waltz), using pulse-saturating method. The plant material was dark-adapted for 30 minutes. Minimal (Fo) and maximal (Fm) fluorescence yields were measured in the dark-adapted samples. The same parameters (F and F`m, respectively) were measured at two different irradiance levels: low light (125 µmol photons m-2 s-1) and high light (1400 µmol photons m-2 s-1). Results and Conclusions: The concentration of photosynthetic pigments was lower in more affected needles than in the refernce ones. However ; only changes in chlorophyll b revealed statistical difference, 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 more pronounced thylakoid swelling than the chloroplast from the reference needles. Maximal photochemical efficiency of photosystem II (Fv/Fm) measured in the dark-adapted samples was almost the same for both samples, while lower values of the effective qantum yield of photosystem II (ΔF/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.

Picea abies ; photosynthesis ; air polution

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