Journal of Experimental Botany, Vol 50, 363-372, Copyright © 1999 by Oxford University Press
M Strohm, M Eiblmeier, C Langebartels, L Jouanin, A Polle, H Sandermann and H Rennenberg
Untransformed hybrid poplar (Populus tremula x
P. alba) and transgenic lines overexpressing
glutathione synthetase (GshS) in the cytosol (200-300-fold) or glutathione
reductase (GR) either in the cytosol 5-fold) or in the chloroplast
(150-200-fold) were exposed to 0 (control), 100, 200 or 300 nl
l-1 ozone for 3 d for 7 h
d-1. Following acute ozone stress treatments,
wild-type and transgenic poplar suffered from visible foliar injury
consisting of dark brown necrotic lesions on the laminae. Necrotic lesions
were sharply separated from photosynthetically active cells by a band of
red-violet discoloured cell lines showing yellow autofluorescence by blue
light, and blue autofluorescence by UV-light excitation. When plants were
exposed to 100 nl l-1 ozone, leaf injury was in
general negligible, but when 200 and 300 nl l-1
ozone was applied, in both untransformed poplar and transgenic lines
overexpressing GshS or GR up to 60% and 80%, respectively, visible injury
developed on mature leaves. The mean percentage of injured leaf area
amounted to 20-30% (200 nl l-1) and 40-60% (300 nl
l-1). Irrespective of transformation, young leaves
of poplar trees were only slightly affected by ozone treatments. In
support of these observations, net CO2 assimilation rates of mature leaves
were decreased by up to 65% (300 nl l-1 ozone) in
wild-type and transformed poplar, whereas net photosynthesis of young
leaves remained unaffected even under severe stress conditions. Leaf
conductance was significantly decreased by all ozone treatments, but was in
the same range in young and mature leaves, and in wild-type and transformed
poplar, pre- and post-exposure to ozone. It can therefore be assumed that
the ozone doses effectively taken up into the leaf tissue were not
dependent on leaf development and that the strength of the ozone stress
exerted was similar in all types of poplar trees investigated in this
study.From these data it is concluded that: (i) elevated foliar activities
of glutathione synthetase or glutathione reductase alone are not sufficient
to improve tolerance of hybrid poplar to acute ozone stress, and (ii) the
sensitivity of poplar leaves to acute ozone stress is controlled by unknown
factors closely related to leaf development rather than by foliar
activities of glutathione synthetase and glutathione reductase, or leaf
conductance.Key words: Transgenic plants,
antioxidative systems, glutathione, ozone stress, visible injury, gas
exchange.
ARTICLES
Responses of transgenic poplar (Populus tremula x P. alba) overexpressing glutathione synthetase or glutathione reductase to acute ozone stress: visible injury and leaf gas exchange
Albert-Ludwigs-Universitat Freiburg, Institut fur Forstbotanik und Baumphysiologie, Professur fur Baumphysiologie, Am Flughafen 17, D-79085 Freiburg, Germany; Institut fur Biochemische Pflanzenpathologie, GSF-Forschungszentrum fur Umwelt und Gesundheit, Ingolstadter Landstrasse 1, D-85764 Oberschleissheim, Germany; Laboratoire de Biologie Cellulaire, INRA, Route de St Cyr, F-68026 Versailles Cedex, France; Corresponding author
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