PLANT GROWTH IN EXPERIMENTAL SPACE FLIGHT MAGNETIC FIELD
CONDITIONS
SILVIA NEAMŢU, V.V. MORARIU
National R & D Institute of Isotopic & Molecular
Technologies, P.O.Box 700, Cluj-Napoca 5, 400293, Romania
Abstract:
Seeds germination rate and the early stage of seedling growth of eight species
of plants were investigated in the absence of the main static component of
geomagnetic field (ZMF) and in geomagnetic field as control (GMF), in quiet and
increased geomagnetic field activity (GMA). We found a similar rate of seeds
germination both in ZMF and GMF, in quiet GMA periods. In the presence of major
storm, the germination rate of Medicago sativa L. and Secale cereale L. seeds
was stimulated in ZMF conditions. After four days of incubation, the growth of
the tested plants was prevalently inhibited in ZMF in the early stage of stem
elongation. However some plant species were stimulated. The results show that
ZMF conditions could increase the rate of seeds germination in the presence of
natural magnetic disturbance and affect the early stage of seedling growth in
the dynamic growth phase. The response of plants to ZMF depends on plant
species.
Keywords:
zero magnetic fields, geomagnetic field, geomagnetic activity, seeds
germination, seedling growth.
INTRODUCTION
The behavior
of living organisms in space flight condition is a subject of current interest.
At large distances from Earth, and on some celestial bodies there is no
magnetic field comparable to Earth geomagnetic field (GMF). In upper
magnetosphere and interplanetary environment magnetic field intensities attain
near zero values (nT). Also during spacecraft revolution in near earth orbit,
living organisms can be exposed to an average value of magnetic field intensity
close to zero [3]. Such near zero magnetic field conditions can be obtained in
laboratory by compensating the geomagnetic field (ZMF) or by shielding method
(WMF). Literature offer scarce information concerning plants growth in ZMF. We
started a systematic study of plants growth in ZMF i.e the germination of
seeds, the early stage of seedling growth and growth of crop plants
respectively. In this paper we present the growth characteristics of some
species of plants to ZMF during periods of quiet and increased geomagnetic activity.
MATERIALS AND METODS
Seeds
germination and the early stage of seedling growth were investigated on eight
species of plants in ZMF and in GMF as control. The basic static component of
GMF was compensated in a pair of Helmholtz coils oriented along and against
geomagnetic field. In this volume the geomagnetic field was reduced by a factor
of ~ 100. We conventionally call this partially compensated field as a ZMF. A
directional magnetometer with 1nT precision was used to determine the magnetic
field map on the exposure surface chosen for work. At different position the
field varied within the range of 0500 nT. The values included the diurnal
variation of geomagnetic field. The natural magnetic fluctuation still remains
operative in this volume. To determine the influence of the magnetic
fluctuations induced during magnetic storm, all the experimental data were
analyzed in relation to the GMA variation in the time interval of seeds
incubation. The magnitude of GMA represented by Ap index was downloaded from
National Geophysical Data Center, USA for each period of the experiment [1]. As
a measure of the GMA variation we used the standard deviation of the daily Ap
index (Sd Apindex).
Seeds of
alfalfa (Medicago Sativa, var. Luzerne Euver), Triticum aestivum L. and Secale
cereale L. were provided by Salonic University, Greece and seeds of Tagetes
patula L., Calendula oficinalis L., Fagopyrum esculentum L., Lepidium sativum
L., Lens culinaris L. by Agricultural Sciences and Veterinary Medicine University,
Cluj-Napoca. Prior to germination, seeds were sterilized using a washing
protocol with HgCl2, EDTA and KCl sterile solutions or were soaked in
double-distilled water. Experimental and control groups consisted on two or
four Petri dishes of 4050 seeds disposed on a layer of filter paper and cotton
pad, soaked with the same quantity of water. These dishes were packed in paper
and than exposed in zero magnetic fields and geomagnetic field respectively, in
the same temperature and humidity conditions.
The trend of
seeds germination follows a sigmoid curve with a slope that characterizes the
rate of germination. This curve was determined by the percent of seeds
germinated at every three hours. ZMF effect was estimated from the normalized
difference of the rate of germination given by x0 parameter of the Boltzman
fitted curve of the experimental data.
The early
stage of plants growth was characterized after four-five days of seeds
incubation by the length and branching of seeds root in the case of wheat and
rye. ZMF effect was estimated from the normalized difference of the root, stem
and total plant length. The influence of ZMF on root branching was
characterized by the average values and distribution of root number/seeds. To
evaluate the significance of the experimental data we used Students t-test.
RESULTS AND DISCUSSION
SEEDS GERMINATION
In Table 1
were summarized the values of seeds germination rate in ZMF and GMF, the effect
of ZMF and Ap index of geomagnetic activity during the period of seeds
incubation. Ap index shows quiet magnetic field periods in the interval of the
experiment.
Table 1
Seeds germination in GMF (M) and ZMF (P), ZMF influence
and GMA variation in the days of the experiments
Plant species
x0
(%/hour)
ZMF
effect (%)
GMA
(Ap index)
Medicago sativa
M 30.49 M 0.87; P 29.67 0.98
2.6
210
Tagetes patula
M 26.5 M 1.50;
P 26.92 1.09
1.5
28
Calendula oficinalis
M 26.06 M 0.13; P 26.03 0.64
0.11
28
Fagopyrum esculentum
M 33.76 M 0.23; P 33.28 0.10
1.42
28
Triticum aestivum
M 9.09 M 0.16;
P 8.79 6 0.12
3.3
211
Secale cereale
M 8.93 M 0.31;
P 9.11 0.11
2
211
Lepidium sativum
M 8.05 M 0.05;
P 8.49 0.02
5.1
27
The rate of
seeds germination was not significantly different in ZMF compared with GMF for
all plants investigated. According to these results, the lack of static
component of geomagnetic field does not represent a stress for the plants in
the phase of seeds germination.
Similar
results were obtained in our previous investigations on alfalfa seeds carried
in 19982001 period. The effect of ZMF on seeds germination rate and the
variations of GMA during these experiments are illustrated in Fig. 1. Most of
the experiments were performed in quiet GMA periods. In these conditions the
rate of alfalfa seeds germination was similar both in ZMF and in GMF as in the
cases discussed above. The effect determined in ZMF was less than 5%.
Significant
GMA variations were recorded in the other experiments presented also in Fig. 1.
The analysis of the relation ZMF effect GMA variation shows the following:
The presence
of a moderate storm (Ap = 53) at the beginning of the experiment (Exp 2.) is
associated with a statistically significant stimulation of seeds germination
rate (10%).
If a more
intense magnetic storm (Ap = 80) appear at the end of seeds incubation period,
no biological effect is recorded (Exp. 6);
The
appearance of a minor storm (Ap = 41) during the experiment corresponds to
increases of seeds germination rate with 6% (Exp 9).
These results
show that the rate of alfalfa seeds germination is significantly stimulated in
the presence of magnetic storm if it occurred at the beginning of this process.
Fig. 1. The variation of GMA during the period of alfalfa
seeds incubation and the effect of ZMF on seeds germination. Ap index and the
day of magnetic storms occurrence are specified on the plot.
Recently we
found similar behavior in the case of Secale L. germination. In the presence of
a major magnetic storm (Ap = 61.55) the rate of seeds germination was
stimulated with 10.2 e 0.23% in ZMF. After 13 hours of incubation, the percent
of seeds germinated in ZMF was 133% higher than in GMF. These findings support
the idea that the rate of seeds germination can be stimulated in disturbed
period of geomagnetic activity in ZMF conditions.
The same
positive influence of increased GMA on plants growth was determined indirectly
by Kamenir at al. [2]. He found that the inhibitory effect induced by
corona-discharge field on the growth parameter of wheat (germination, mean
length and mass of sprouts) was significantly diminished in the periods with
high number of solar spots. The authors assigned the augmentation of seeds
germination power to the presence of geomagnetic disturbances.
THE EARLY STAGE OF SEEDLING GROWTH
The early
stage of seedling growth in ZMF was quantified after five days of seeds
incubation by root, stem and entire seedling length. In most cases, the growth
of the plants tends to be inhibited in ZMF as we can see in Fig. 2.
Fig. 2. The effect of ZMF on the early stage of plants
growth
Calendula L
was not significantly influenced in ZMF. The growth of wheat and rye root was
inhibited both as total length and as the process of branching. In the cases of
tap-roots plants we found a statistically significant inhibition in the phase
of stem elongation (p < 0.05). The root length and total length of these
plants were not significantly inhibited. We assumed that after five days of
incubation the stem elongation was the dynamic growth phase of the tap-root
plants that are sensitive to ZMF conditions. The growth of Lepidium sativum L.
and Medicago sativa L was stimulated in ZMF. This variability of the plant
response suggests that the influence of ZMF on the early stage of plants growth
depend on plant species and can be either positive or negative.
Some
experiments were performed in increased GMA periods. Minor storms were recorded
in the third or on the fifth day of alfalfa seeds incubation (Ap = 44, Ap = 35)
(Fig. 3.) and on the fourth and fifth days of the wheat and rye seeds
incubation (Ap = 47, Ap = 40) (Fig. 4.). In most experiments alfalfa growth was
stimulated in ZMF conditions. The effect determined in these cases was not
influenced in disturbed GMA periods (Fig. 3). Significant stimulation of
alfalfa seedling growth was noted both in quiet and in disturbed periods.
The growth of
the rye and wheat roots was significantly inhibited in ZMF in quiet GMA periods
(Fig. 4, Exp 1 and Exp. 2). In the presence of magnetic storms (Exp. 3) the
inhibition of the root length was diminished in the case of rye and was not
affected for wheat.
Fig. 3. The effect of ZMF on alfalfa seedling growth and
the variation of GMA during the period of seeds incubation.
Fig. 4. The effect of ZMF on wheat and rye seedling
growth in 3 experiments performed in quiet and in increased GMA periods.
At the same
time, the sensitivity of the stem growth seems to be enhanced in increased GMA
periods (Exp. 3). In these conditions the stem elongation was inhibited. We
should mention that magnetic storms occurred in the second part of the
experiment. It can be expected more pronounced effects if the growth of
seedlings would be initiated under increased GMA variations.
CONCLUSIONS
In ZMF
conditions (as defined in this work) the rate of seeds germination is increased
during magnetic storms for some plant species. ZMF affect the early stage of
plant growth in the dynamic phases of growth. The response of plants to ZMF
varies with the type and species of plants.
Acknowledgements. This work was supported by a grant of the Romanian
Aerospatial Agency
REFERENCES
1. http://sec.noaa.gov/Data/index.html#indices.
2. Kamenir, E.A., A.K. Kirillov, Effect of cosmophysical
factors on germination of wheat seeds subjected to corona-discharge field,
Biophysics, 1995, 40, 765770.
3. NEIGISHI, Y, A. HASIMOTO, M. TSUSHIMA, C. DOBROTA, M.
YAMASHITA, T. NAKAMURA, Growth of pea epicotyls in low magnetic field.
Implication for space research, Adv. Space Res., 1999, 23, 20292032.
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46
Silvia
Neamţu, V.V.Morariu
45
Plant growth
in zero magnetic field conditions
_______________________
Received July
2005;
in final form September 2005.
ROMANIAN J. BIOPHYS., Vol. 15, Nos. 14, P. 4146,
BUCHAREST, 2005