SP-401 Skylab, Classroom in Space

[66] Part II - Student Experiments

Chapter 5: Embryo Development in Space.

The second crew saw this view of the spent Saturn rocket from its Apollo spacecraft.

The second crew saw this view of the spent Saturn rocket from its Apollo spacecraft.

 

[67] Not only is the cell fundamental to all living organisms, it is also the seat of all life. Whether it be the seed of a plant or the egg of an animal, all life begins with the cell. The fertile seed or egg undergoes cellular division and growth as the embryonic stages of life develop.

Some plant development begins in the seed. Although plants have evolved reproductive mechanisms quite different from those of animals, the basic steps are much the same. The new plant life begins when a sperm nucleus from a pollen grain unites with an egg nucleus, and the resulting cell begins developing into a seed. The seed, in turn, develops into an embryo and begins to grow after it is exposed to water. Other lower forms of plant life, such as algae, develop directly through cell division without the seed or embryo stages.

Animal life begins in a manner similar to that of the higher order plants. The union of the sperm and the egg initiates the cell division that ultimately results in the embryonic development of a new animal.

Two of the Skylab student experiments involved aspects of embryonic development. One proposed a rather complete investigation of the embryonic development of a chicken; the other was concerned with the development of seedling rice plants.

 

Plant Growth and Plant Phototropism

Two similar proposals were submitted by Donald W. Schlack of Downey High School, Downey, Calif., and Joel G. Wordekemper of Central Catholic High School, West Point, Nebr. Wordekemper was interested in discovering how the roots and stems of germinating seedlings would orient themselves without the influence of gravity in Skylab. Schlack's idea was to germinate seedlings within an enclosed cell of agar, exposed to light from only one side to determine if phototropism would influence the direction of growth of both stems and roots in the absence of gravity. He also suggested that exposing different seedlings to various light intensities would determine the illumination level required to produce the phototropic effect. The objectives of these two experiments were similar enough that they could be accommodated in a common experiment.

Phototropism is the characteristic exhibited by plants as they grow in the direction of their primary light source. It is commonly observed that leaves of plants by a window or along a wall orient themselves toward the Sun. Geotropism is a plant's reaction to the force of gravity. Plant roots react positively to geotropism and grow down, while the stem exhibits a negative response and grows in the opposite direction.

The growth container for their experiment consisted of eight compartments arranged in two parallel rows of four. Each had two windowed surfaces to allow periodic photography of the developing seedlings from both a front and side view. The side windows were always covered except during the photographic sessions, so that as...

 


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picture of Donald W. Schlack

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Donald W. Schlack is shown above with science adviser Loren Miller.

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Donald W. Schlack suggested an experiment for Skylab wherein the effects of light on a seed developing in zero gravity would be studied. He is shown above with science adviser Loren Miller.


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Joel G. Wordekemper, shown seated above with science adviser Loren Miller, had an idea similar to Schlack's. He proposed an experiment to see how the lack of gravity would affect the growth of roots and stems of plants.

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Joel G. Wordekemper, shown seated above with science adviser Loren Miller, had an idea similar to Schlack's. He proposed an experiment to see how the lack of gravity would affect the growth of roots and stems of plants.

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The container for the seedlings was positioned near one of the high-intensity lights used in the orbital workshop of Skylab.

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The container for the seedlings was positioned near one of the high-intensity lights used in the orbital workshop of Skylab.


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To activate the experiments proposed by Schlack and Wordekemper, Scientist Pilot Gibson used the technique shown in this series of pictures made aboard Skylab.

To activate the experiments proposed by Schlack and Wordekemper, Scientist Pilot Gibson used the technique shown in this series of pictures made aboard Skylab. After removing the back cover from the container (1), the seeds were planted three each to the eight compartments (2), (3), (4), (5), and the windows were exposed for photography (6).

 

[71] .... the seedlings grew, they received light from only the front window. If the seedlings exhibited phototropism, the stems would grow toward the window, their only light source. Five of the front windows were covered with special filters and two were blocked to prevent any light from reaching the seedlings, while the remaining window had no filter, allowing passage of all ambient light. Three rice seeds were inserted into each compartment through covered holes in the back wall. This technique allowed 24 rice seeds to be planted, to germinate, and to grow in the weightless environment of Skylab. The plants were not under the influence of gravity. Those in the two dark compartments were not influenced by phototropism and served as a control group to determine how light affected the development of the other seedlings. The filters were to determine the illumination level required to influence the plants to grow toward light in zero gravity.

The rice seeds were implanted in the nonnutrient agar medium by Edward Gibson, scientist pilot of the third crew. He thus became what might be called the first space farmer. Photographs of the seedling development were taken at regular intervals for 30 days. Dr. Gibson also recorded his visual observations of the plant development. (Unfortunately, due to a camera malfunction, the photographs taken on four of the days were not exposed. Analysis of growth for a period of 14 days was, thus, based entirely on Gibson's verbal descriptions, which are subject to interpretation.) On the 25th day the front container cover, with the neutral-density filters, was removed and the plants pulled to the surface of the agar to allow them free access to the Skylab environment.

Schlack and Wordekemper analyzed their data after the mission and found that plant growth was first observed on the 4th day after seed planting, somewhat slower than expected for Earth-grown rice. Growth then progressed at a normal rate, but the direction was extremely irregular and inconsistent, with stems for some reason making 1 80-degree turns away from the light and many plant tips demonstrating curled patterns. The stems seemed to exhibit no phototropic effect.

Gibson's commentary on the 22d day of growth summarized the plant development, ". . . Okay, generalizations. Those [seeds] which have long stems that make it to the point where they can see some light, turn green. I would not say there's any preferential growing, though, toward the front of the case [light source]. I see green stems turn around and start heading right on back toward the other direction. One case is here in compartment I, it just makes a 135-degree turn, [and] goes straight back, looks like it was folded. Now, the one over in compartment 6. The stem which comes down, goes toward the back, makes a big U-turn from the bottom right-hand side and then goes up toward the front again, and that's one that has turned slightly green. . . But that's the only one that demonstrates it [ phototropism ] to me . . . I've got to face it right now. I can't find any consistent pattern . . . Some make a turn and go back; some make a turn and go forward . . . No consistent trend, unfortunately. Roots go to the front, toward the light; stems go to the back, away from the light; some do; some don't."

From photographs as well as Gibson's observations, Schlack set about the task of reconstructing the growth patterns of the roots and stems of each seedling. Of the 24 seeds planted, only 10 developed. This is a number which is close to the germination ratio of 12 out of 24 observed in the control group planted on Earth.

The longest stems to develop in testing on Earth were approximately 2 inches long. It is interesting that one leaf from compartment 4 of the Skylab container grew to 4.2 inches. While it was impossible to measure precisely the leaf and root dimensions or growth rates from photographs, the results indicated that the Skylab rice plants grew as fast or faster than the Earth plants after the seeds had germinated.

The percentage of seeds that developed was too small to provide significant information regarding the threshold light level required for seed development in zero gravity. Two plants grew in totally dark compartments, while the three largest plants grew in compartments I, 4, and 6, with filter transmission factors of 100 percent, 3 percent, and 2 percent. Thus, the illumination level did not appear to be a contributing factor to the growth rates of the small sample of seeds aboard the space station.

The proposed explanation for the lack of any phototropic effect demonstrated by the rice seedlings is that the auxin distribution system of the plants relies upon gravity. Auxins are plant-growth hormones that cause cells to elongate or grow. They are produced in the tips of both the stems....

 


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After 27 days in orbit, the seedlings looked like this when the front cover of the experiment was removed.

After 27 days in orbit, the seedlings looked like this when the front cover of the experiment was removed.- continued

After 27 days in orbit, the seedlings looked like this when the front cover of the experiment was removed. The main shoot of the plant in compartment No. 4, approximately 4.2 inches long, extends all the way to compartment No. 8. One of its leaves also branches into compartment No. 3.

 

....and the roots, and are distributed basipetally (away from the tip) into the '`area of elongation." Without gravity the auxins may have been distributed unevenly, with pockets collecting somewhat randomly, causing irregular stem and root growth.

It is also possible that the light-sensing mechanism in the stem tip that triggers the auxin distribution reacted differently in zero gravity. But the operation of this sensing mechanism is not understood well enough to hypothesize its reaction to zero gravity, and it is not obvious that there should be any effect at all.

Research is conducted on Earth with clinostats, devices that rotate slowly so that the plants on [73] them are inverted the same amount of time as they are upright, with results that many believe to be comparable to the effects of short-duration zerogravity exposure. Skylab experiment results suggest that the effects of longer duration spaceflight is not simulated by testing with clinostats.

The student experiment program presented the first opportunity for botanical experiments of longer than 3 days' duration to be performed in space. The results of this experiment indicate that much can be learned about plant physiology through chemical analysis of plants in space, an environment that cannot be duplicated in a laboratory on Earth.

 


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picture of Kent M. Brandt

Kent M. Brandt, shown with science adviser Jack Skadman, proposed one of the most complex experiments for Skylab. It consisted of hatching at least one chicken and returning it alive to Earth.

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Kent M. Brandt, shown with science adviser Jack Skadman, proposed one of the most complex experiments for Skylab. It consisted of hatching at least one chicken and returning it alive to Earth.

 

Chick Embryology

A classic high school biology investigation was proposed: the development of a chicken embryo. Kent Brandt of Grand Blanc Senior High School, Grand Blanc, Mich., suggested such an investigation for Skylab. He designed a rigorous experiment involving the incubation of eggs, opening eggs periodically for 20 days to observe and photograph the developing embryos until one chick was allowed to hatch, providing for the sustenance of the chick during its stay in Skylab, and ultimate return of the chick to Earth for further analyses.

Of the 25 student experiments, Brandt's was probably the most intriguing to the review committee. Significant efforts were made to define the container required to insure that the eggs survived the launch, incubation over a 21-day period, and safe return of at least one chick.

A protocol was developed whereby further development of the embryo could be chemically terminated and each of the six eggs preserved at different stages of development for return to Earth. An experimental model of an incubator that could maintain the critical temperature and humidity ranges required for development of fertile eggs was built.

With regret, the decision was made that the experiment required too much crew time, and the weight and volume requirements were greater than could be allocated to a single student experiment. Also, the detail design, fabrication, testing, and flight qualification of the necessary incubator could not be carried out in the 9 months available prior to launch.

Brandt was therefore affiliated with John Lindberg of the Northrop Corporate Laboratories, on his experiment concerning the circadian rhythm of [75] pocket mice. Unfortunately, this experiment experienced a power failure early in its performance, and no data were returned.

Despite the disappointments accruing to Brandt, Skylab did provide laboratory facilities for significant experiments in the study of cellular development and plant growth with experiments such as those of Schlack and Wordekemper.


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