Environmental and Experimental Botany 44 2000 95 – 103
Intraspecific differences in physiological response of 20 wheat cultivars to enhanced ultraviolet-B radiation under
field conditions
Li Yuan
a,b,
, Zu Yanqun
a
, Chen Jianjun
a
, Chen Haiyan
a
, Yang Jilong
a
, Hu Zhide
b
a
Department of En6ironmental Science, Yunnan Agricultural Uni6ersity, Kunming
650201
, People
’
s Republic of China
b
Department of Chemistry, Lanzhou Uni6ersity, Lanzhou
730000
, People
’
s Republic of China Received 11 November 1999; received in revised form 18 April 2000; accepted 23 April 2000
Abstract
Field studies were conducted to determine the potential for alterations in physiology and the intraspecific variation in sensitivity of 20 wheat Triticum aesti6um cultivars to enhanced ultraviolet-B UV-B, 280 – 315 nm radiation. The
supplemental UV-B radiation was 5 kJ m
− 2
, simulating a depletion of 20 stratospheric ozone. Out of 20 wheat cultivars from South China, North China and Mexico tested, 13 showed significant changes in total chlorophyll
content. In most of these sensitive species, chlorophyll a content was strongly reduced, and chlorophyll b content decreased in a lesser extent, leading to a decrease in chlorophyll ab ratio. However, some species had an increased
chlorophyll ab ratio under enhanced UV-B. The effect of UV-B on flavonoid content also showed intraspecific differences, a significant increase for one cultivar, decreases in 12 cultivars and no effect on the other seven cultivars.
Superoxide dismutase SOD activity of five cultivars was significantly increased, and that of six cultivars significantly decreased. Membrane permeability of 12 cultivars significantly increased, while only that of Dali 905 was significantly
decreased. Malonaldehyde MDA contents of eight cultivars were increased significantly, while that of three cultivars was significantly decreased. Although large intraspecific differences were found for the different parameters measured,
there was no clear correlation between them under UV-B radiation. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Chlorophyll; Flavonoid; Malonaldehyde; Membrane permeability; Superoxide dismutase; Triticum aesti6um; UV-B radiation
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1. Introduction
The rapid decline in stratospheric ozone con- centrations has been confirmed by satellite mea-
surements. The most pronounced thinning of the ozone layer has been measured over the Antarctic
Corresponding author. E-mail address
:
liyuanzupublic.km.yn.cn L. Yuan. S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 9 8 - 8 4 7 2 0 0 0 0 0 5 7 - 5
continent with up to 71 depletion during the Antarctic spring Kerr, 1993. Recent mathemati-
cal models predict a further increase in solar UV-B irradiation in future years Madronich et
al., 1995. UV-B effects on plants have been the subjects of considerable research Caldwell et al.,
1995. An examination of more than 200 plant species reveals that roughly 20 are sensitive,
50 are mildly sensitive or tolerant and 30 are completely insensitive to UV-B radiation Tera-
mura, 1983. Whilst the impact of enhanced UV-B radiation
on plant
physiology, morphology,
growth and biomass have been investigated exten- sively, little is known about intraspecific differ-
ences in physiological response to enhanced UV-B.
Recently, intraspecific
differences in
flavonoid in cucumber Murali and Teramura, 1986, soybean Teramura and Murali, 1986;
D’surney et al., 1993 and Arabidopsis thaliana Li et al., 1993; Fiscus et al., 1999, flavonoid and
chlorophyll in rice Teramura et al., 1991 have been reported. Plant species and even genotypes
within species can differ greatly in their responses to UV-B. In the recent experiment, the substantial
growth suppression of A. thaliana flavonoid mu- tants suggests that the disruption of secondary
metabolism at the chalcone isomerase site is af- fecting critical aspects of secondary metabolism.
This may result in an impairment of the normal growth and differentiation process Fiscus et al.,
1999. Due to our lack of understanding of the role of intraspecific response differences to UV-B
radiation, further studies on its importance should be undertaken.
On the other hand, most of the UV-B research in the past two decades has been conducted in
growth chambers and greenhouses where the un- natural spectral balance of radiation can lead to
unrealistic conclusions, which may have substan- tially changed plant sensitivity to UV-B. It is
important in experiments to maintain a realistic balance between various spectral regions since
both UV-A 315 – 400 nm and visible 400 – 700 nm radiation can have ameliorating effects on
responses of plants to UV-B Caldwell et al., 1995. In growth chamber and greenhouse experi-
ments, the visible and UV-A radiation is usually much less than in sunlight, thus, even if realistic
levels of UV-B are used in simulating ozone re- duction, the plant response may be exaggerated
relative to field conditions. Unfortunately, only 15 of the studies have been conducted under
field
conditions. While
the laboratory
and glasshouse studies provide information on mecha-
nisms and processes of UV-B action, only field studies can provide realistic assessments of what
will happen as the stratospheric ozone layer thins Caldwell et al., 1995; Yue et al., 1998.
Wheat is one of the major world food crops Teramura, 1983, the effects of enhanced UV-B
radiation on
photosynthetic characteristics,
growth, development, leaf quality, morphology, tiller number, crop structure, plant nutrients, de-
composition, competition
interaction between
wheat and wild oat, intraspecific response differ- ences, total biomass and yield have been studied
Li et al., 1998, 1999; Yue et al., 1998. Unfortu- nately, only few studies have been conducted un-
der field conditions. In this study, we grew 20 wheat cultivars in field under ambient and supple-
mental levels of UV-B radiation with the objective to 1 determine, if UV-B radiation affects wheat
physiology under field conditions; and 2 evalu- ate intraspecific differences in physiological re-
sponse of 20 wheat cultivars to UV-B radiation in the field. We hypothesized that enhanced UV-B
radiation will decrease chlorophyll content, and affect other physiological processes, i.e. insuffi-
cient protection by flavonoid will result in the production of oxygen radicals, and their insuffi-
cient removal by SOD will cause membrane dam- age which can be measured by membrane
permeability and MDA content. These changes will result in intraspecific differences in physiolog-
ical response under field conditions.
2. Materials and methods
