AOBPreview originally published online on October 23, 2003
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Annals of Botany 92: 779-793, 2003
© 2003 Annals of Botany Company
Cell Structural Changes in the Needles of Norway Spruce Exposed to Long-term Ozone and Drought
1 Department of Ecology and Environmental Science, University of Kuopio, PO Box 1627, FIN-70211 Kuopio, Finland, 2 Finnish Forest Research Institute, Suonenjoki Research Station, FIN-77600 Suonenjoki, Finland, 3 Finnish Forest Research Institute, Joensuu Research Center, PO Box 68, FIN-80101 Joensuu, Findand, 4 Swedish Environmental Research Institute, PO Box 47086, SE-402 58 Göteborg, Sweden and 5 Botanical Institute, University of Göteborg, PO Box 461, SE-405 30 Göteborg, Sweden
* For correspondence. E-mail minna.kivimaenpaa{at}uku.fi
Received: 14 March 2003; Returned for revision: 1 May 2003; Accepted: 1 September 2003 Published electronically: 23 October 2003
Effects of ozone and/or drought on Norway spruce needles were studied using light microscopy and electron microscopy. Saplings were exposed to ozone in open-top chambers during 1992–1995 and also to drought in the late summers of 1993–1995. Samples from current and previous year needles were collected five times during 1995. Ozone increased the numbers of peroxisomes and mitochondria, which suggests that defence mechanisms against oxidative stress were active. The results from peroxisomes suggest that the oxidative stress was more pronounced in the upper side of the needles, and those from mitochondria that defence was more active in the younger needle generation. Possibly due to the good nitrogen status and the active defence, no ozone-specific chloroplast alterations were seen. At the end of the season, older needles from ozone treatments had smaller central vacuoles compared with other needles. Cytoplasmic vacuoles around the nucleus were increased by ozone in the beginning of the experiment, and did not increase towards the end of the season as in the controls. These results from vacuoles may indicate that ozone affected the osmotic properties of the cells. Decreased number and underdevelopment of sclerenchyma cells and proliferation of tonoplast were related to nutrient imbalance, which was enhanced by drought. Larger vascular cylinders and more effective starch accumulation before and after the drought periods compensated for the reduced water status. Numbers of peroxisomes and mitochondria were increased in the drought-exposed needles before the onset of drought treatments of the study year, i.e. these changes were memory effects. Interactions between ozone and drought were few.
Key words: Picea abies, Norway spruce, needles, ozone, drought, light microscopy, transmission electron microscopy, peroxisome, mitochondrion, chloroplast, starch, vacuole.
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