Láposi, Réka

Mile, Orsolya

Mészáros, Ilona

Veres, Szilvia

Acta Biologica Szegediensis

English

University of Debrecen Electronic Archive

Volume 46(3-4):243-245, 2002
Acta Biologica Szegediensis
http://www.sci.u-szeged.hu/ABS
Department of Botany, Debrecen University, Debrecen, Hungary
R Láposi*, Sz Veres, O Mile, I Mészáros
ABSTRACT                          The effects of exclusion of UV-B radiation on leaf physiology of beech seedlings
regenerating in a deforested area were studied in field. Under UV-B exclusion the chlorophyll
content of leaves was higher, the chlorophyll a/b ratio and the carotenoid content was lower
than in leaves under the ambient level of UV-B radiation. In leaves developed under the
exclusion of UV-B a smaller degree of conversion of violaxantin to zeaxantin and atheraxantin
was found at noon. The results showed that the ambient level of UV-B radiation decreased
the maximum photochemical efficiency (Fv/Fm) of the dark-adapted leaves, especially at noon.
Beech leaves contained significantly higher quantities of UV-B absorbing compounds on the
basis of leaf area at the ambient UV-B than under the UV-B exclusion. Flavonoid accumulation
took place in close correlation with the increase of specific leaf weight as compared to the
leaves developed under UV-B exclusion. Acta Biol Szeged 46(3-4):243-245 (2002)
KEY WORDS
beech
Fagus sylvatica
photochemical efficiency
UV-B radiation
xanthophyll cycle
*Corresponding author. E-mail: laposir@delfin.klte.hu
243
Photosynthesis-ecophysiological properties of beech (Fagus
sylvatica L.) under the exclusion of ambient UV-B radiation
Proceedings of the 7th Hungarian Congress on Plant Physiology, 2002
S6-P02
In natural vegetation long-life trees are potentially impressed
by the global environmental changes. Due to the depletion
of stratospheric ozone the enhanced level of UV-B radiation
is an important stress factor for plants as it causes a number
of direct and indirect effects on the photosynthetic apparatus,
which may influence the whole plant development. Under
natural conditions UV-B radiation is always accompanied by
the visible part of the solar spectrum, which in itself can
induce photoinhibition and photodamage. In this work we
investigated the responses of beech seedlings regenerating in
a deforested area to different UV-B/PAR ratio using UV-B
exclusion in field. Our attention was focused on the alteration
of photosynthetic pigment composition, including
xanthophyll cycle components, furthermore, on the maximal
(Fv/Fm) photochemical efficiency of PSII. We also examined
the effects of reduction of UV-B on specific leaf weight
(SLW) and accumulation of UV-B absorbing compounds in
leaves. Ecophysiological responses to artificial exclusion of
UV-B were also compared to the features of seedlings grown
in the forest edge of southern exposure and the forest
understory.
Materials and Methods
The experimental site is located in the Bükk Mountains (NE
Hungary) at 550 m above the sea level where a nature beech
forest was clear-cut in 1981. The forest has been allowed to
regenerate naturally at the site. In the deforested area 5 beech
seedlings of similar morphological characteristics were
selected for the study. One branch of southern exposure per
seedlings was covered by polyester filter to exclude the UV-
B radiation before budding time in the middle of April 2000.
We performed comparative measurements on the covered and
uncovered branches of seedlings after the large period of leaf
expansion in May in the same year and a year later. Potential
photochemical activity of leaves was measured after 20 min
dark adaptation by using PAM 2000 fluorometer (Walz Co.,
Germany). Chlorophyll content was measured in 80%
acetone extract with spectrophotometric method (Wellburn
1994), and the carotenoid composition was analysed by
reversed phase HPLC method with application of zeaxantin
as standard. Accumulation of UV-B absorbing compounds
was estimated  on the basis of absorbances of
MeOH:HCl:H2O (90:1:1 volume) extracts at 300 nm (Day
and Demchick 1996). Absorbances were expressed on leaf
area basis. PAR was measured by the light sensor of AP-4
Porometer (Delta-T Devices, UK) and the UV-B by the IL
1400 A radiometer (International Light INC. USA).
Results and Discussion
There were differences in the physiological parameters
between the filtered (-UV-B) and unfiltered (ambient) fully
expanded leaves which already appeared in the first growing
season. Under UV-B exclusion the chlorophyll content of
leaves was higher, the chlorophyll a/b ratio and the
carotenoid content was lower than in leaves under the
ambient level of UV-B (Table 1). The main changes in the
carotenoid content are resulted from the increase of the
amount of the xantophyll cycle components. High light
intensity increased the activity of xanthophyll cycle, the
important protective mechanism against photoinhibition and
photodamage of PSII (Long et al. 1994). Under the exclusion
of UV-B a smaller degree of conversion of violaxantin to
zeaxantin and atheraxantin was found at noon (DEEPS-
index), but it was higher than in the leaves of seedlings grown
in the forest edge and in the forest understory (Fig. 1). The
b-carotene content changed in correlation with the increases
of vaz-pool at noon in seedlings of every habitat (Fig. 1).
Chlorophyll fluorescence analysis showed that the ambient
level of UV-B decreased the maximum photochemical
efficiency (Fv/Fm) of the dark-adapted leaves, especially at
244
noon (Table 1). Flavonoids can effectively screen the UV-B
radiation thereby protect the primary metabolism, and
furthermore they have antioxidant properties. Thus flavonoid
accumulation can improve plant tolerance to abiotic stresses
such as UV-B radiation by reducing damage to the photo-
synthetic apparatus (Estiarte et al. 1999). Beech leaves
contained significantly higher quantities of UV-B absorbing
compounds on the basis of leaf area at the ambient UV-B than
under the UV-B exclusion (Table 1). Flavonoid accumulation
took place in close correlation with the increase of SLW as
compared to the leaves developed under UV-B exclusion
(Table 1). Similarly to other species in the case of beech
flavonoid accumulation also proved to be a useful indicator
of leaf UV-B screening ability and potential plant sensitivity
to increased UV-B radiation (Wand 1995). Responses of
photosynthetic apparatus of seedlings under UV-B exclusion
were similar to the seedlings of forest edge, where the period
of high irradiance is shorter than in the clear-cut area. Results
of the second year were very similar to those we could
observe in the first year. The present study indicates that
shortly after the budding time, the ambient level of solar UV-
B radiation can have subtle effects on the maximal photo-
chemical efficiency of beech seedlings, and cause signi-ficant
changes in the photosynthetic pigment composition, the
accumulation of the UV-B absorbing compounds and the
morphological properties of leaves. The photosynthetic
responses of seedlings in the three contrasting habitats were
similar to results we observed in previous studies in the
experimental site (Mészáros et al. 1995, 1998, 2002).
Acknowledgments
The present study was supported by INCO-Copernicus
Project IC15-CT98-0126.
Table 1. Concentrations of leaf photosynthetic pigments, chlorophyll a/b ratio, maximal photochemical efficiency (Fv/Fm) in dark
adapted leaves, accumulation of flavonoids estimated by absorbances of leaf metanolic extracts at 300 nm) and specific leaf
weight (SLW) of seedlings under different irradiances. For pigments each value represents the average of 6 replicates ±SE, for Fv/
Fm, flavonoids and specific leaf weight each value indicates the average of 9 replicates ±SE.
Clear-cut area Clear-cut area Forest edge Forest understory
ambient UV-B UV-B exclusion
Chlorophyll  (mg g-1 d.w.)
2000.05.05. 6.18±1.06 6.81±0.95 5.60±1.12 6.55±0.68
2001.05.15. 4.99±0.84 6.57±1.59 5.60±0.65 7.41±0.66
Chlorophyll a/b
2000.05.05. 3.04±0.06 2.97±0.23 3.03±0.02 2.81±0.05
2001.05.15. 2.82±0.16 3.18±0.01 2.93±0.11 3.15±0.23
Carotenoids (mmol mol-1 chl.)
2000.05.05. 444.07±24.61 398.81±50.72 394.10±40.28 359.10±40.75
2001.05.15. 438.34±95.25 408.92±73.04 423.32±18.42 312.58±46.81
VAZ-pool (mmol mol-1 chl.)
2000.05.05. 134.83±19.32 97.98±18.33 97.90±15.04 51.87±5.38
2001.05.15. 112.70±30.37 104.65±31.49 114.29±11.20 47.95±10.61
Fv/Fm
2000.05.05. 0.705±0.007 0.743±0.006 0.735±0.006 0.752±0.003
2001.05.15. 0.744±0.004 0.751±0.008 0.735±0.004 0.741±0.004
A300nm cm
-2
2000.05.05. 1.757±0.306 0.995±0.106 0.897±0.026 0.563±0.039
2001.05.15. 2.740±0.742 1.860±0.129 2.536±0.906 1.832±0.261
SLW (g dm-2)
2000.05.05. 0.51±0.10 0.48±0.08 0.43±0.04 0.33±0.03
2001.05.15. 0.62±0.09 0.54±0.11 0.46±0.12 0.31±0.05
Figure 1. Changes in the de-epoxidation state of xanthophyll cycle
(zeaxantin+0.5*antheraxantin/viola+anthera+zeaxantin) and the β-
carotene content in leaves of beech seedlings in the morning (8 a.m.)
and at noon (13 p.m.) in the three habitats. Each value represents
the average of 6 replicates ±SE.
245
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Photosynthesis-ecophysiological properties of beech (Fagus sylvatica L.) under the exclusion of ambient UV-B radiation

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Photosynthesis-ecophysiological properties of beech (Fagus sylvatica L.) under the exclusion of ambient UV-B radiation

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