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RESEARCH: ETHYLENE STUDIES |
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Ethylene is 5,000
times more toxic to plants than carbon monoxide is to humans.
A carbon monoxide level of 100 ppm causes headaches in humans, but
an ethylene level of only 0.02 ppm begins to reduce pollination and
fruit set in plants. We have conducted an extensive series of studies on the sensitivity of
plants to atmospheric ethylene levels. These studies resulted in three
published manuscripts (J. of Plant Physiology; Crop Science; and
ICES). |
CLICK ON THE TITLES TO VIEW ABSTRACTS:
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SUMMARY Ethylene levels on the International
Space Station have been maintained at 50 ppb, but our previous studies
clearly show that plant growth and yield are significantly reduced by
levels as low as 20 ppb. Since plants themselves produce ethylene, it
is extremely difficult to maintain atmospheric levels below 20 ppb.
We have conducted comprehensive tests of state-of-the-art ethylene
scrubbing technologies. Potassium permanganate (KMnO4,
Purafil) binds ethylene and is far superior to UV-catalyzed
degradation, but the air flow rates and quantity that are needed to
keep ethylene below 10 ppb (0.01 ppm) are extremely expensive. By
comparison, LiOH is used for CO2 removal, but it is only
necessary to maintain CO2 at 5,000 ppm. This is 500,000
times the required ethylene level.
Fortunately, studies with Arabidopsis over the past 10 years
have demonstrated that it is possible to genetically modify plants to
have both reduced production of ethylene and reduced sensitivity to
elevated levels. A few of these genetic changes have been transferred
to tomato germplasm and we have begun to examine these lines. These
plants, however, have undesirable side effects, such as increased
sensitivity to pathogens, and need additional genetic modification
before they are appropriate for space research. The Crop Physiology
hopes to rigorously determine ethylene synthesis and sensitivity in
existing crop plants, as well as genetically modify tomatoes to have
reduced synthesis and sensitivity to ethylene without undesirable side
effects.
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Ethylene Synthesis and Sensitivity
in Crop Plants
Steve Klassen
and B. Bugbee - 2004
HortScience 39(7):1546-1552 |
ABSTRACT Closed and semi-closed
plant growth chambers have long been used in studies of plant and crop
physiology. These studies include the measurement of photosynthesis
and transpiration via photosynthetic gas exchange. Unfortunately,
other gaseous products of plant metabolism can accumulate in these
chambers and cause artifacts in the measurements. The most important
of these gaseous byproducts is the plant hormone ethylene (C2H4).
In spite of hundreds of manuscripts on ethylene, we still have a
limited understanding of the synthesis rates throughout the plant life
cycle. We also have a poor understanding of the sensitivity of intact,
rapidly growing plants to ethylene. We know ethylene synthesis and
sensitivity are influenced by both biotic and abiotic stresses, but
such whole plant responses have not been accurately quantified. Here
we present an overview of basic studies on ethylene synthesis and
sensitivity.
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Temperature
Effects on Ethylene Sensitivity in Dwarf Tomatoes
Tim Hudelson, S. Klassen, and B.
Bugbee - 2003
Habitation Meeting
Jan,
2004; Orlando, FL
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ABSTRACT The sensitivity of wheat
to C2H4 appears to be influenced by
temperature. A previous study showed that yields of USU-Apogee and
USU-Perigee wheat were significantly reduced by 100 nmol mol-1
C2H4 (0.1 ppm; 100 ppb), and that
sensitivity decreased with increasing temperature (unpublished data).
This study examined C2H4-temperature
interactions in Red Robin and Micro-Tina tomatoes at 0, 10, and 30
nmol mol-1 and 22 and 28 oC. Treatments were
randomly assigned to twelve flow-through, 0.17 m2, acrylic
chambers, which were divided into equal halves for both cultivars.
The system was located in a greenhouse and received 29 mol m-2
d-1 PPF from supplemental HPS lighting and five to 12 mol m-2
d-1 PPF from sunlight. CO2 was elevated to 1200
µmol mol-1, and
temperature was maintained at +/- 1oC of the set point. C2H4
treatment began on day 18 after emergence, three days before
flowering, temperature treatment began on day 20, and both were
maintained for the duration of the study. C2H4-sensitivity
appeared to decrease more dramatically with increasing temperature for
Red Robin than for Micro-Tina. At 22 oC, Red Robin yield
in the 30 nmol mol-1 treatment was about 42% less than
control with no apparent decrease at 28oC. Micro-Tina
yield in the 30 nmol mol-1 treatment decreased by about 22%
at 22oC with no apparent decrease at 28oC. Red
Robin yield was 20 to 60% less than Micro-Tina in all treatments.
Both cultivars had 40 to 60% higher yield at 22 than at 28 oC.
These trends were similar when expressed as fruit number and dry
mass. Ground cover fraction was measured with a digital camera and
was reduced by only about 5% at 30 nmol mol-1 in both
cultivars. The C2H4 sensitivity of yield
appears to decrease with increasing temperature in both Red Robin and
Micro-Tina, but the interaction does not appear to be as dramatic in
the higher yielding Micro-Tina cultivar.
(Supported by the NASA Advanced Life Support Program)
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Temperature Effects on Ethylene Sensitivity
Tim Hudelson, S. Klassen, and B.
Bugbee - 2003
American Society
of Agronomy
Nov 2-6,
2003; Denver, CO
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ABSTRACT Ethylene is an endogenously synthesized plant hormone
that dissipates quickly in rural field conditions, seldom
exceeding 1 to 5 nmol mol-1 (1-5 ppb), but which can accumulate to
10-100 times that in controlled environments. The best known
effects of ethylene are its impacts on leaf senescence and fruit
ripening, however, ethylene influences growth and development
throughout the life cycle. To identify how temperature
influences ethylene-sensitivity from the early developmental
stage of flowering through harvest, we examined
ethylene-temperature
interactions in Micro-Tina tomatoes at 0, 20, and 40
ppb C2H4 and 22 and 28 oC in a greenhouse. At 22 oC, the 20 and 40
ppb red
fruit yields were 50 and 11% of the control. At 28 oC,
yields were 33 and 5% of the control. Red fruit yield at 22 oC was
2.1, 3.7, and 6.6 (0, 20, and 40 ppb) times greater than at 28
oC.
Vegetative growth was only slightly inhibited by
ethylene.
Ethylene-sensitivity of tomato at anthesis increased
with increasing temperature.
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Sensitivity of wheat and rice to low levels of atmospheric ethylene
Steve Klassen and B. Bugbee - 2002
Crop Science, 42:746-753 |
ABSTRACT Ethylene (C2H4) gas
is produced throughout the life cycle of plants and can
accumulate in closed growth chambers to levels 100 times
higher than in outside environments. Elevated atmospheric C2H4
can cause a variety of abnormal responses, but the sensitivity
to elevated C2H4 is not well
characterized. We evaluated the C2H4
sensitivity of wheat (Triticum aestivum L.) and rice (Oryza
sativa L.) in five studies. The first three studies compared
the effects of continuous C2H4 levels
ranging from 0 to 1000 nmol mol-1 (ppb) in a
growth chamber throughout the life cycle of the plants. A
short-term 1000 nmol mol-1 treatment was included
in which exposure was stopped at anthesis. Yield was reduced
by 36% in wheat and 63% in rice at 50 nmol mol-1 and
both species were virtually sterile when continuously
exposed to 1000 nmol mol-1. However, the yield
reductions were much less with exposure that stopped at
anthesis, suggesting the detrimental effect of C2H4
on yield was greatest around the time of seed set. Two
additional studies evaluated the differential sensitivity of
two wheat cultivars (Super Dwarf and USU-Apogee) to 50 nmol
mol-1 C2H4 at three CO2
levels [350, 1200, 5000 µmol mol-1 (ppm)] in a greenhouse.
Yield of USU-Apogee was not significantly reduced by C2H4
but the yield of Super Dwarf was reduced by 60%. Elevated
CO2 did not influence the sensitivity to C2H4.
A difference in the C2H4 sensitivity of
USU-Apogee between greenhouse and growth chamber trials
suggests that C2H4 sensitivity is
dependent on the environment. Collectively, the data suggest
that relatively low levels of C2H4 could
induce anomalous plant responses by accumulation in
greenhouses and growth chambers with inadequate
ventilation. The data also suggest that C2H4
sensitivity can be reduced by both genetic and environmental
manipulations.
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Genetic and
environmental interactions with ethylene sensitivity in crops
Steve Klassen, T. Hudelson, and B. Bugbee - 2002
Poster: ASGSB
Nov 6-9, 2002; Cape
Canaveral, FL
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ABSTRACT
Elevated levels of C2H4 gas cause a variety of abnormal responses
in plants including shortened height, leaf rolling, premature
senescence and sterility. Levels as high as 1000 ppb (1ppm) have been
measured in space studies and were implicated as the cause of
sterility in wheat grown on MIR (Campbell et al., 2001). Catalytic
air scrubbing systems will reduce C2H4 levels in space environments
but will not likely be sufficient to maintain levels low enough for
normal plant growth and reproduction. In these studies we compared
the ethylene sensitivity of wheat, rice, lettuce, and tomato. Yields
of these crops were reduced at an C2H4 level of 50 ppb. However,
there were significant differences in the C2H4 sensitivity of closely
related wheat cultivars. Ethylene induced sterility was also found to
decrease with increasing temperature in wheat. Overall, our studies
suggest that genetic screening and control of environmental factors
affecting C2H4 sensitivity and production will help reduce
C2H4
induced problems in space. (Supported by NASA Advanced Life Support
Program)
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Comparative floral development of Mir-grown and
ethylene-treated
earth-grown Super Dwarf wheat
William Campbell, F. Salisbury, B. Bugbee, S. Klassen,
et al. - 2001
J. of Plant Physiology 158: 1051-1060
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ABSTRACT To study plant growth in microgravity, we grew Super-Dwarf wheat (Triticum aestivum L.) in the Svet growth chamber
onboard the orbiting Russian space station, Mir, and in identical
ground control units at the Institute of BioMedical Problems in
Moscow, Russia. Seedling emergence was 56 % and 73 % in the two
root-module compartments on Mir and 75 % and 90 % on earth. Growth was
vigorous (produced ca. 1 kg dry mass), and individual plants produced
5 to 8 tillers on Mir compared with 3 to 5 on earth-grown controls.
Upon harvest in space and return to earth, however, all inflorescences
of the flight-grown plants were sterile.
To ascertain if Super Dwarf wheat responded to the 1.1
to 1.7 umol · mol-1
atmospheric levels of ethylene measured on the Mir prior to and during
flowering, plants on earth were exposed to 0, 1, 3, 10, and 20
umol · mol-1 of ethylene gas
and 1200 umol · mol-1 CO2
from 7 d after emergence to maturity. As in our Mir wheat, plant
height, awn length, and the flag leaf were significantly shorter in
the ethylene-exposed plants than in controls; inflorescences also
exhibited 100 % sterility. Scanning-electron-microscopic (SEM)
examination of florets from Mir-grown and ethylene-treated,
earth-grown plants showed that development ceased prior to anthesis,
and the anthers did not dehisce. Laser scanning confocal microscopic (LSCM)
examination of pollen grains from Mir and ethylene-treated plants on
earth exhibited zero, one, and occasionally two, but rarely three
nuclei; pollen produced in the absence of ethylene was always
trinucleate, the normal condition. The scarcity of trinucleate pollen,
abrupt cessation of floret development prior to anthesis, and excess
tillering in wheat plants on Mir and in ethylene-containing
atmospheres on earth build a strong case for the ethylene on Mir as
the agent for the induced male sterility and other symptoms, rather
than microgravity.
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Ethylene Sensitivity
of Crops in Controlled Environments
Steve Klassen and
B. Bugbee
American Society
of Agronomy
Oct,
2000; Minneapolis, MN |
ABSTRACT
Ethylene is a potent
plant hormone. Actively growing crop plants produce up to 1 nmol of
ethylene kg-1 s-1 and this accumulates in the air of closed plant
growth chambers. Ethylene levels in the field rarely rise above 1 ppb
(0.001 ppm), but levels well above 1 ppm have been measured on MIR and
the ethylene level rose to 0.8 ppm in a study at NASA-JSC. Ethylene
levels in closed plant growth chambers at NASA-KSC routinely increase
to 0.05 to 0.1 ppm. Reduced seed set and even complete sterility have
been associated with elevated ethylene levels, but no controlled
studies have been done to clearly implicate ethylene in the poor seed
set.
We examined ethylene levels from 1 to 20 ppm on Super-Dwarf wheat in
replicate growth chambers and compared the effects to control chambers
without ethylene. Plants grew well at even 20 ppm ethylene but plant
height decreased as ethylene increased. There was no effect on the
rate of development as indicated by the time of heading. Seed set and
yield were excellent in the control chambers, but plants in all the
ethylene chambers were completely sterile.
In a second study, ethylene effects of 0.25, 0.50, 0.75, 1.0 ppm on
USU-Apogee wheat were compared to a control chamber. A single
treatment receiving 1.0 ppm ethylene prior to anthesis and no ethylene
following boot stage was also tested. As in the previous study, there
was a linear decrease in plant height with increasing ethylene.
Longitudinal leaf rolling (into cylinders) was visually apparent at
all ethylene levels as compared to flat leaves on control plants. Leaf
rolling is a sensitive indicator of ethylene pollution in closed
chambers. Seed set was reduced at all ethylene levels except the
pre-anthesis treatment.
We are now configuring a GC for automated ethylene monitoring of 16
chambers and plan to use this capability to quantify short- and
long-term ethylene effects at different stages of the life cycle.
Ethylene efflux appears to be correlated with growth rate and may peak
during anthesis. These studies are an essential prerequisite to the
design and sizing of ethylene scrubbing equipment for bioregenerative
life support.
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Differential
Sensitivity of Crops to Ethylene
and Interactions with Elevated CO2
Steve Klassen and B. Bugbee
Life Support and
Biosphere Science - 2000
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ABSTRACT
Ethylene is a potent
plant hormone that can accumulate in closed growth chambers at levels
well above which crop plants are normally adapted. Based on the
results of both ground and space studies, ethylene has been clearly
identified as an important air contaminant that must be scrubbed in
order to prevent yield reductions in wheat. Although present scrubbing
technologies can remove ethylene below 50 ppb, this is still 10 to 50
times higher than levels in the field. The potential for system
failures must also be recognized and the ability of plants to tolerate
ethylene fluctuations evaluated. Our studies indicate that ethylene
levels as low as 50 ppb result in a 25 % yield reduction in wheat (cv.
USU-Apogee). We have also determined that wheat is most susceptible to
ethylene induced sterility around the time of anthesis. Our current
efforts focus on the differential sensitivity of wheat cultivars and
other crop plants, and potential interactions with elevated CO2.
The results of two experiments in progress will be presented. One
designed to evaluate the differential sensitivity of two wheat
cultivars (Super Dwarf and. USU-Apogee) to 50 ppb ethylene at three
levels of CO2 (350, 1200, 5000 ppm). The second mimics
previous studies on wheat but investigates the sensitivity of Super
Dwarf rice to ethylene levels ranging from 50 to 1000 ppb. Preliminary
data indicates ethylene levels as low as 50 ppb significantly reduce
yield and delays heading in Super Dwarf rice. Interestingly, levels as
high as 20 ppm had no effect on days to heading in wheat. Future
research will focus on the effects of short-term ethylene fluctuations
and the ethylene sensitivity of other crops.
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Effects of low ethylene
levels on USU-Apogee and Super Dwarf wheat
Steve Klassen, B. Bugbee, and W. Campbell - 1999
Proceedings International Conference on Environmental Systems (ICES)
July 12-15, 1999; SAE Paper # 1999-01-2025
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ABSTRACT Ethylene is a potent plant
hormone. Actively growing crop plants produce up to 1 nmol of ethylene
kg-1 s-1 and this accumulates in the air of
closed plant growth chambers. Ethylene levels in the field rarely rise
above 1 ppb, but levels well above 1000 ppb have been measured on MIR
and the ethylene level rose to 800 ppb in a study at NASA-JSC.
Ethylene levels in closed plant growth chambers at NASA-KSC routinely
increase to 50 to 100 ppb. Reduced seed set and even complete
sterility has been associated with elevated ethylene levels, but no
controlled studies have been done to clearly implicate ethylene in the
poor seed set. We examined ethylene levels from 1 to 20 ppm on
super-dwarf wheat in replicate growth chambers and compared the
effects to control chambers without ethylene. Plants grew well at even
20 ppm ethylene but plant height decreased as ethylene increased.
There was no effect on the rate of development as indicated by the
time of heading. Seed set and yield were excellent in the control
chambers, but plants in all the ethylene chambers were completely
sterile. We are now quantifying ethylene effects of 250, 500, 750, &
1000 ppb on two wheat cultivars (USU-Apogee & Super-dwarf) compared to
a control chamber. As in the previous study, there is a linear
decrease in plant height with increasing ethylene. Longitudinal leaf
rolling (into cylinders) is visually apparent at all ethylene levels
as compared to flat leaves on control plants. Leaf rolling may be a
sensitive indicator of ethylene pollution in closed chambers. Seed set
appears to be reduced at the higher ethylene levels. We are
configuring a GC for automated ethylene monitoring of 16 chambers and
plan to use this capability to quantify short- and long-term ethylene
effects at different stages of the life cycle. Ethylene efflux appears
to be correlated with growth rate and may peak during anthesis. These
studies are an essential prerequisite to the design and sizing of
ethylene scrubbing equipment for bioregenerative life support.
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Ultrastructural Characteristics of
Ethylene-Induced Sterile Wheat
Florets
William Campbell, B. Bugbee, D. Strickland, W. McManus, F. Salisbury, and G. Bingham
American Society of Agronomy
Oct.
1999; Salt Lake City, UT
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ABSTRACT Mankind's
long-term presence in space will require the production of plants from
seed-to-seed to supply food and oxygen and remove CO2 and nitrogenous
waste. Wheat, Triticum aestivum L., cv Super Dwarf, seeds were
planted in a nutrient-charged zeolite called Balkanine onboard the
Russian Space Station, Mir. Seedlings were harvested at various
stages of ontogeny and stored in plastic bags containing 4%
formaldehyde: 1% glutaraldehyde. Upon harvest and return, 1 mm
diameter leaf segments were excised and dehydrated with increasing
concentrations of ETOH and acetone and embedded in Spurr's resin.
Microscopic examination of Mir-grown wheat showed that reproductive
development ceased at the onset of anthesis, resulting in 100%
sterility. Dried pollen grains stained with propidium iodide and
viewed with a laser scanning confocal microscope showed 0, 1 and 2
nuclei but rarely 3. Thin sections (50 - 70 nm) of leaf tissue for
Mir showed that integrity and distribution of organelles in leaves of
wheat had swollen and disrupted membranes. Ground-based studies
indicated that ethylene, which was measured at 1.1 to 1.7 mg kg-1 at
various location on Mir, could have caused the sterility.
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Effects of Low Ethylene Levels on Wheat
Steve Klassen, W. Campbell, and B. Bugbee
American Society
of Agronomy
Oct.
1999; Salt Lake City, UT |
ABSTRACT
Ethylene levels in
the field rarely rise above 1 ppb, but levels in closed plant growth
chambers at NASA-KSC routinely increase to 100 ppb. Reduced seed set
and complete sterility have been associated with elevated ethylene
levels, but no controlled studies have been done to clearly implicate
ethylene. We examined ethylene levels from 0.25 to 20 ppm on wheat in
replicate growth chambers and compared the effects to control chambers
without ethylene. A single treatment received 1 ppm ethylene prior to
anthesis and no ethylene following boot stage. There was no effect on
the rate of development and plants grew well at 20 ppm ethylene, but
plant height decreased as ethylene increased. Seed set was reduced at
all ethylene levels except the pre-anthesis treatment. Longitudinal
leaf rolling (into cylinders) appears to be a sensitive indicator of
ethylene pollution in closed chambers. These studies are an essential
prerequisite to the design and sizing of ethylene scrubbing equipment
for bioregenerative life support.
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Ethylene Sensitivity of Crop Plants:
Implications for Advanced Life Support and Space Flight
Steve Klassen, B. Bugbee, and
W. Campbell
American Society for Gravitational and
Space Biology
Nov. 1999; Seattle, WA
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ABSTRACT
Crop plants are
adapted to ethylene levels less than 5 ppb, but levels well above 1
ppm have been measured on MIR. Complete sterility in wheat has been
associated with ethylene levels in tightly sealed growth chambers on
MIR and at NASA-JSC. However, few controlled studies have been done
to clearly implicate ethylene. We examined ethylene levels from 0.25
to 20 ppm on wheat in replicate growth chambers and compared the
effects to control chambers without ethylene. A single treatment
received 1 ppm ethylene prior to anthesis and no ethylene following
boot stage. There was no effect on the rate of development and plants
grew well at 20 ppm ethylene, but plant height decreased as ethylene
increased. Seed set was reduced at all ethylene levels except the
pre-anthesis treatment. Longitudinal leaf rolling (into cylinders)
appears to be a sensitive indicator of ethylene pollution in closed
chambers. The results of a current study examining ethylene levels
down to 0.05 ppm on wheat and rice will also be presented. These
studies are an essential prerequisite to the design and sizing of
ethylene scrubbing equipment for bioregenerative life support.
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