Plant Physiol, May 2003, Vol. 132, pp. 196-205
Differential Effects of Elevated Ozone on Two Hybrid Aspen
Genotypes Predisposed to Chronic Ozone Fumigation. Role of Ethylene and
Salicylic Acid1
Jorma
Vahala,
Markku
Keinänen,2
Andres
Schützendübel,
Andrea
Polle, and
Jaakko
Kangasjärvi*
Institute of Biotechnology and Department of Biosciences,
University of Helsinki, Viikinkaari 9, FIN-00014 Helsinki, Finland
(J.V., M.K., J.K.); Department of Applied Biology, University of
Helsinki, (Latokartanonkaari 5-7), FIN-00014 Helsinki, Finland
(J.V.); Forstbotanisches Institut, Georg-August Universität,
Forstbotanik und Baumphysiologie, Büsgenweg 2, 37077 Göttingen, Germany (A.S., A.P.); and Laboratory of Plant
Physiology and Molecular Biology, Department of Biology, University of
Turku, FIN-20014 Turku, Finland (J.K.)
The role of ethylene (ET) signaling in the responses of two hybrid
aspen (Populus tremula L. × P.
tremuloides Michx.) clones to chronic ozone
(O3; 75 nL L
1) was investigated. The hormonal
responses differed between the clones; the O3-sensitive
clone 51 had higher ET evolution than the tolerant clone 200 during the
exposure, whereas the free salicylic acid concentration in clone 200 was higher than in clone 51. The cellular redox status, measured as
glutathione redox balance, did not differ between the clones suggesting
that the O3 lesions were not a result of deficient
antioxidative capacity. The buildup of salicylic acid during chronic
O3 exposure might have prevented the up-regulation of ET
biosynthesis in clone 200. Blocking of ET perception with
1-methylcyclopropene protected both clones from the decrease in net
photosynthesis during chronic exposure to O3. After a
pretreatment with low O3 for 9 d, an acute 1.5-fold O3 elevation caused necrosis in the
O3-sensitive clone 51, which increased substantially when
ET perception was blocked. The results suggest that in hybrid aspen, ET
signaling had a dual role depending on the severity of the stress. ET
accelerated leaf senescence under low O3, but under acute
O3 elevation, ET signaling seemed to be required for
protection from necrotic cell death.
1
This work was supported by the Maj and Tor
Nessling Foundation, by the Finnish Society of Forest Sciences, by the
Leo and Regina Wainstein's Foundation, and by the Academy of Finland, Centre of Excellence Program 2000-2005. M.K. was supported by Academy
of Finland Postdoctoral grant no. 48640.
2
Present address: Department of Biology, University of
Joensuu, POB 111, FIN-80101 Joensuu, Finland.
*
Corresponding author; e-mail jaakko.kangasjarvi{at}helsinki.fi;
fax 358-9-191-59552.
© 2003 American Society of Plant Biologists
