INFLUENCE OF REDUCTION OF ENHANCED MOUNTAIN UV-RADIATION ON THE PHOTOSYNTHESIS AND GROWTH OF CULTURED C3-PLANTSValery Yu. Lyubimov ,
Alexander E. Kalevich, Institute of Soil Science and Photosynthesis RAS, Pushchino, Moscow
Region, 142292 Russia.
|
| Abstract | Results |
| Introduction | Discussion |
| Environment | Acknowledgment |
| Materials and Methods | Literature Cited |
Key words: C3-plants,
hormones, Pamir, photosynthesis, productivity, UV-radiation.
Abstract
Investigation was carried
out with small radish (Raphanus sativus L.), pot marigold (Calendula
officianalis L.), red pepper (Capsicum annuum L.), and bulb onion (Allium
cepa L.). Plants were grown at the high mountain place (Pamir, near Khorog, 2320 m
over sea level) under free sky (FS), under usual polyQ-film (UF), and under transforming
polyQ-film (TF). Last one captures from 60 to 30% of UV-radiation (from 300 to 400 nm
resp.) and effectively transforms it to visible light (600-700 nm). Under light condition
using the UF the photosynthetic rate (14CO2-assimilation per leaf
fresh weight) of all species was similar (± 3-5%) to this one under FS. The small radish
and pot marigold which were grown under TF exhibited the enhanced photosynthetic
assimilation of 14CO2 (+20%), red pepper exhibited the decreased
assimilation (-22%) and bulb onion did not changes the photosynthetic rate. There was
qualitative correlation between photosynthetic activity and growth of plants: the height
of small radish and pot marigold plants were increased by 20 and 95%, respectively. The
height of red pepper plants was reduced not significantly changed (-6%) and the height of
bulb onion plants was reduced by 24%. These changes of plant growth and productivity
parameters it seemed are associated with changes of hormonal status of plants. Reduction
of the natural enhanced UV-radiation leads to complex changes in photosynthesis, hormonal
status and growth of cultured plants.
Introduction.
The meaning of enhanced
UV-radiation for life cycle of terrestrial plants it seemed is more significant than for
other forms of life because plants are motionless and light competent organisms.
Especially, the influence of UV-radiation may be important in geographic zones with high
level of this ecological factor. Such zones are areas under ozone holes and specific
regions of high mountains such as Pamir mountain system.
The influence of UV-radiation upon whole
plant organism and its components was investigated rather a many times. In most research
works with using of whole plants investigations of influence of artificial enhanced
UV-radiation upon non-adapted plants prevail. In most cases after treatment with
additional UV-B radiation at short as well as long period a diminishing of various plant
activities was observed. So, after treatment of whole pea plants with UV-B radiation
during several days a decreasing of dry weight, fresh weight and photosynthetic rate was
occur [2]. Under similar experimental conditions the negative consequences for activity of
photosynthetic enzymes were observed with C3- as well as C4-plants
[8,9].
We have chosen other scheme of researches
of influence of UV-radiation upon higher plants. In the region with high natural level of
UV-radiation we investigated photosynthetic capacity, growth and hormonal status of
cultured higher plants at reduction of the natural level of UV-radiation.
Environment.
Experiments were carried
out at west side of Pamir mountain system near Khorog city at the height of 2320 m over
sea level. During April-July in this place UV-radiation has activity about 3.5 W/m2
at 290-320 nm and 60-70 W/m2 at 320-400 nm. Average temperature is 16.3oC
and average relative humidity of air is 46.7% (data are presented by the local
meteorological station).
Materials and methods.
For experiments we used
four plant species: small radish (Raphanus sativus L.), pot marigold (Calendula
officianalis L.), red pepper (Capsicum annuum L.) and bulb onion (Allium
cepa L.). Plants were grown as a mini-cenosis in natural soil under free sky, under UF
and under TF. In some cases plants were grown under UV-cutting polyQ-film. Three plant
groups were grown under these conditions during total period of vegetation. In the middle
of this period repeated radiometric measurements of photosynthesis were done using
field-adapted apparatus [5]. Growth parameters, content and biological activity of
hormones [3, pp 17-44] were measured during total vegetation.
Optical properties of usual and
UV-transforming films are given in Fig. 1 a and Fig. 1 b. UV-transforming film [contains 0.01% of Eu(NO3)2
-2-phenantrolin] absorbs from 60% of UV-B to 30% of UV-A radiation and efficiently
transforms it to the visible light (600-700 nm). In the UV-B region usual film absorbs
about 30% of radiation and has no any re-emitting properties. The UV-cutting film captures
approximately 40% of UV-A and 90% of UV-B radiation, and not re-emits visible light, too.
Results.
Experimental plants had
different response on the reduction of UV-radiation. Leaves of small radish and pot
marigold which grown at lower level of UV exhibited more high photosynthetic rate (about
+20%) as compare to FS as well as UF condition (Fig. 2a). At
the same time the increasing of leaf area of small radish was occur. On the other hand, we
observed the diminishing of photosynthesis in leaves of red pepper which grown under TF (Fig. 2b). Photosynthetic rate of bulb onion practically not
changed. As it was mentioned above, the rate of 14CO2 assimilation
was measured in the middle of vegetation at the end of June - beginning of July. In the
early period of plant ontogenesis (up to middle of June) there were no significant
differences between growth of all species which grown under different light conditions. In
the middle of vegetation (end of June - beginning of July) we have measured statistically
reliable changes of growth of plants under TF. So, stem height of small radish and pot
marigold was more than in control on 20 and 55%, respectively (Fig.
3a). At the end of vegetation this value for pot marigold achieved 95%. At the same
time the growth of red pepper and bulb onion was inhibited on about 20%. When plants were
grown under UV-cutting film results were qualitatively the same (Fig.3b).
The increasing of growth of small radish and pot marigold was about 25-30% and growth of
red pepper and bulb onion was not significantly changed.
It is well known, that growth processes
use photosynthetic assimilates and are controlled by content and activity of hormones and
inhibitors [3, pp 93-101 and 104-121]. In most cases the treatment of plants with UV leads
to the shift of hormone-inhibitor balance toward inhibitors' predominance [6]. As our data
indicate (Fig. 4), in leaves of small radish growing under both
experimental films the increasing of gibberellin activity is occur. There is only
quantitative distinction between activity of different chromatographic zones of GA.
Similar results were received with pot marigold plants. Auxin activity was higher in these
two plants under TF, too (data not shown). In opposite, in leaves of red pepper and bulb
onion under condition of lower UV-radiation the decreasing of gibberellin activity and
increasing of inhibitor activity were found out.
The enhancement of photosynthetic
activity, increasing of growth and gibberellin activity correlate with productivity of
plants. So (Fig. 5), small radish which grown under TF had more
leaves (+30%), grater whole plant mass (+45%) and greater edible root mass (+60%). It is
easy to see, that most additional mass is concentrated in roots.
Discussion.
It was shown in many papers
[4, 7] that UV-irradiation of plants leads to repression of different physiological and
biochemical activities. Only a few papers demonstrate the absence of UV effect upon plants
[1]. Our experimental data had demonstrated inhibitory as well as stimulatory effect of
UV- radiation upon photosynthesis and plant growth. The influence of UV-radiation upon
higher plants it seemed is not inhibitory in any case. It depends, probably, on the plant
species. In this way, the trend and degree of UV-effect may depend on geographic
occurrence of the plant. Species which occurs from subtropical regions (red pepper)
responses on reduction of UV-radiation by decreasing of photosynthetic rate and growth. In
opposite, in small radish diminished UV-level results activation of physiological
processes as well as the additional biomass accumulation. Changes of photosynthetic
activity, growth rate and hormone-inhibitor balance under changed UV-conditions correlate
one another. The simultaneous increasing of leaf mass and area and activation of
photosynthesis yield adequate enhancement of the whole plant mass.
Acknowledgments.
We are grateful for accommodation and
maintenance of conditions for work to Aknazarov A.A., the vice-director of Pamir
Biological Institute, Tajik AS.
Literature cited.