Responses of spruce seedlings (Picea abies) to exhaust gas
under laboratory conditionsÐII ultrastructural changes
and stomatal behaviour
E.-L. Viskari*, T. Holopainen, L. Ka
È
renlampi
Department of Ecology and Environmental Science, University of Kuopio, PO Box 1627, FIN-70211 Kuopio, Finland
Received 6 September 1998; accepted 15 May 1999
Abstract
This study examines the eects of exhaust gas exposure on the epistomatal wax structure and mesophyll ultrastructure in needles
of Norway spruce (Picea abies (L.) Karst.) seedlings. Stomatal diusive resistance was also measured. Two independent exhaust gas
fumigations were performed: 100 and 200 ppb measured as NO
x
, for 10 days and 50, 100 and 200 ppb NO
x
for 19 days. The
obstructive eect of exhaust gas exposure on epistomatal wax tubules was apparent. The stomata became covered by ¯at and solid
wax resulting from the structural degradation of the wax crystalloids. Increasing the exhaust gas concentration in the chamber
atmosphere exacerbated the degradation of the wax structure. Exhaust gas exposure induced aggregation and electron translucence
of plastoglobuli, swelling of thylakoids, increase of cytoplasmic lipids and slight increase of vesiculation of cytoplasm in mesophyll
cells of current and previous year needles. These changes were exempli®ed in current year needles. Damage to the epicuticular waxes
and mesophyll ultrastructure of spruce needles most likely re¯ects the NO
x
and volatile hydrocarbon fraction. The alterations in
epicuticular waxes and mesophyll ultrastructure can be related to accelerated senescence of the youngest, photosynthetically active,
needle generation. The exhaust gas also resulted in decreased diusive stomatal resistance at night which indicates that the exhaust
gas exposure disturbed the gas exchange of spruce seedlings. The results show that even relatively short-term exposure to realistic
concentrations of exhaust gas in the atmosphere can induce rather severe injuries to the needle surface structure as well as ultra-
structure at the cellular level. # 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Norway spruce; Exhaust gas; Epistomatal wax; Mesophyll ultrastucture; Diusive resistance
1. Introduction
Spruce needles are covered with rod-like crystals con-
centrated in and around the epistomatal chamber. The
needle surface, between the stomata, is covered with
tubular crystals (Bermadinger-Stabentheiner, 1994;
Huttunen, 1994; Turunen, 1996). The epicuticular wax
layer on plant leaves is a barrier between the plant and
its environment and is one of the ®rst targets of atmo-
spheric pollutants (Sauter et al., 1987; Bermadinger-
Stabentheiner, 1994; Gu
È
nthardt-Goerg et al., 1994). The
wax crystals fuse and ¯atten with age, but in polluted air
the erosion rate of the wax structures increases (Sauter
and Voû, 1986; Gu
È
nthardt-Goerg et al., 1994; Huttu-
nen, 1994). At worst the epistomatal chamber of the
needle may be plugged totally by the fused wax, inhi-
biting transpiration which could have far-reaching phy-
siological consequences, such as prevention of gas
exchange and photosynthesis (Sauter and Voû, 1986;
Kammerbauer et al., 1987; Sauter et al., 1987). The
accelerating eect of various air pollutants (SO
2
,O
3
,
acid precipitation, dust, UV-B) on epicuticular wax
erosion has been shown in many studies (e.g. Turunen
and Huttunen, 1990; Gu
È
nthardt-Goerg et al., 1994;
Huttunen, 1994; Turunen, 1996). Exposure of spruce
seedlings to motor vehicle emissions in the laboratory as
well as along a highway, has revealed clear evidence of
accelerated structural degradation of the epistomatal
waxes (Sauter et al., 1987; Sauter and Pambor, 1989)
and also decreases in transpiration and net photosynth-
esis rate (Kammerbauer et al., 1987).
0269-7491/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S0269-7491(99)00127-X
Environmental Pollution 107 (2000) 99±107
www.elsevier.com/locate/envpol
* Corresponding author. Tel.: +358-17-163-194; fax: +358-17-
163-230.
E-mail address: Eeva-Liisa.Viskari@uku.® (E.-L. Viskari).