29 October 2004

"The Amateur Scientist" Classics:

The Effects of Gravity on Plant Growth

Shawn Carlson

I remember my mother's father as a wild-eyed, high-intensity, crazy man. His was born George Donald Graham. His friends called him Don, but I suspect that just about everyone else called him "that G.D. Graham," as my father did. That G.D. Graham got himself kicked out of college in the 1920's for recruiting prostitutes to pose nude for his art class, and his life only got wilder from there. He had been a wandering artist (some said bum) during the Depression. He made money as a prospector of rare minerals only because he'd never think twice about trespassing on private land. He was a brilliant but unsuccessful inventor, as well as an unapologetic atheist, an occasional pornographer, a frequent huckster and, at one time, the youngest taxidermist in the state of Kansas. And I am absolutely certain that he, like many great American geniuses, was also an undiagnosed manic-depressive.

My mother grew up around the darker depressed side of his nature when he was a pioneering survivalist living in fear of a foreign invasion. The stress of the Second World War made him a pathological doomster who was obsessed with a need to be ready for absolutely anything. He became an expert on weapons and homebrew poisons. My mother remembers too well how he terrorized his children with dramatic promises to kill them all in their beds if the "Japs" ever landed. He fortunately mellowed after the war. Still, when family life got too rough emotionally for him to deal with, he would up and abandon his wife and children and head out into the desert for weeks at a time with only a knapsack and a bedroll. Little wonder that one day on returning from one of his brooding walkabouts he discovered that his wife and children had abandoned him for good.

But while his depressive episodes drove away his family, his manic side earned him a reputation for being an energetic eccentric. He experienced long unbroken periods of hyper-creativity and quixotic self-confidence that inspired him to believe that he could move the entire world through the force of his will alone. Often he tried to, and sometimes he failed spectacularly. I suspect that his mania also occasionally slipped his grip on reality a few knots. He told incredible fish stories about his adventures with such conviction that some folks, including me, often wondered whether my grandpa had forgotten exactly where he had fallen through the looking glass. He landed full force into the counter-culture of the 60s, grew his hair long and openly experimented with marijuana.

But my grandfather's mania did have a benefit. It powered what I can only describe as his truly luminary genius. He created wonderful works of art during his manic periods. He composed music and wrote poetry that simply astonished me. And throughout his entire life he carried out extraordinary scientific projects in just about every field to which an amateur could contribute. In truth, while I have been privileged in my career to know Nobel Prize winners and members of the National Academy of Sciences, I have never met anyone with a greater raw scientific talent than Don Graham.

Once when he lived near a rural stretch of beach in Northern California, a whale washed ashore near his property. The then 64-year old systematically dissected the specimen, froze its organs in a meet locker, and spent two months cataloguing and cleaning the bones. He contacted whale experts all over the state and gave away choice fleshy parcels to any researcher who asked for one. Then he re-polished his taxidermy skills and painstakingly reassembled the entire skeleton on top of his house.

We visited his makeshift museum when I was eight and I vividly remember my parent's reaction as the odd exhibit came into view. My mother was, to put it mildly, shocked. Her mouth gapped in stupefied disbelief at the sight of the 40-foot monster on top of the house. It was as if she had been knocked four million years back through evolutionary time, as the only sound she managed to utter strongly resembled the call of an anguished gibbon or baboon. My father had no problem finding quite colorful ways to express his astonishment and exasperation. "Nut!" is perhaps the only repeatable epithet I heard during our short drive onto the Graham homestead.

But none of that affected me. Indeed, seeing that whale immediately convinced me that the wild man with the wind-sculpted face and the full grey mane was exactly the kind of nut that I wanted to be when I grew up. His creation was absolutely magical to me. My grandfather had built a whale on his house! I stared and stared at it wide-eyed as the grown-ups went through their obligatory "Good to see yas" and "How ya beens?" But as soon as the uncomfortable pleasantries had been dispensed with, my grandfather gently passed the hospitality duties on to his second wife, Martha, so he could give his one appreciative relative a personal introduction to his handiwork.

Martha flashed him a knowingly smile as she ushered the rest of my family inside. When the coast was clear, my Grandpa Don scooped me up in one arm. Then he pointed to and named every major bone in the skeleton. He used large gestures with his free hand and swished his body to and fro, imitating the animal, to describe exactly how the bones functioned together to help this majestic mammal in life. Then, relying only on his most proven storytelling techniques, he traced the evolutionary history of the whale back to ancient times. He created a world with his words vivid enough for me to see it clearly in my minds eye. He put me in that distant place and time when a group of carnivorous mammals returned to the seaÑperhaps to escape their own land-bound predators. And he spoke with such infectious enthusiasm, not only about the whale, but also about the techniques he used to clean and prepare it, that he completely enthralled me. Science had interested me even way back then. But that wonderfully animated lecture hooked me forever.

From then on my Grandpa Don stood ten feettall. Our very rare family visits always catapulted my grandpa into mania, and so that was the only side of him I ever saw. When he was manic, Don Graham was more creative, more energetic, more alive than anyone I had ever known. I absolutely adored him. I still do.

Two years later I got to spend one week of my summer vacation with him and Martha, and it was during this time that I received my first real instruction in the methods of science. Amidst his delightful, impromptu lectures on mineralogy, chess, home-spun solar collectors, analytic geometry, and how to break the law without getting caught, he introduced me to his remarkable invention for confusing seedlings into behaving as if they were being grown in weightlessness. In fact, the device had just been published in Scientific American's legendary column "The Amateur Scientist." It was the first and only time he would ever be published in a major journal, and I remember vividly just how incredibly proud he felt to see his work described in such a prestigious national magazine.

I had never seen "The Amateur Scientist" before. But it was through that vehicle that I eventually came to realize that my grandfather was not alone. Growing up with that column month after month convinced me that there was a great community of amateur talent that badly needed to be served. Ultimately, it was the memories of that wonderfully wild man that inspired me to leave academe and dedicate my life to removing the roadblocks that keep so many amateurs on the sidelines.

You see, I have been blessed to inherit my grandpa's mania, but not his depression. It has made me a quixotic eccentric myself. And that has made all the difference in my life.

I hope you enjoy the article that got me started down this long path. May it inspire the manic muse in you.

The Effects of Gravity on Plant Growth

C. L. Stong, "The Amateur Scientist," Scientific American, June 1970.

Expanded by Shawn Carlson, October, 2004.

SOON AFTER a potted plant has been laid on its side the stem turns up and the roots turn down. Experiments indicate that such changes in the direction of growth are induced by gravity: plants tend to align themselves in the direction of the earth's gravitational field. Botanists refer to this tendency as geotropism and have discovered by experiment that it arises from the influence of gravity on certain substances in plants, namely the organic compounds known as auxins.

Auxins are a family of plant hormones that affect the rate of growth (or sometimes elogation) of plant cells. In fact, the word is derived from the Greek "auxein" meaning "to grow." Although it was experiments performed by none other than Charles Darwin in the 1880s that first proved the existence of a hormone that stimulated the elongation of the cells in plant stems, the first such chemical was not isolated in the laboratory until 1931. Two chemists named Kogl and Haagen-Smit realized that the bodies of plant-eating animals have little use for vegitable growth hormones; these chemicals aught to come out of the body in the urine. And so it was from human urine (the record is unclear as to whether it was Kogl's or Haggen-Smit's) that the duo isolated the first auxin; indol-3-acetic acid, also known as IAA. (This compound is chemically quite similar to the amino acid tryptophan, and it is well known that plants manufacture much of their IAA from this biologically abundant chemical.)

Interestingly, IAA and other auxins don't always stimulate growth. In fact, in some plant tissues they actually retard growth, and it is this effect that allows a plant to respond to gravity. Auxins stimulate the growth of the green parts of the plant, but under certain conditions they suppress the growth of roots. When a potted plant is inclined from the vertical, auxin concentrates in the lower sides of both the stem and roots. The increased concentration causes the lower side of the stem to grow faster than the upper side and so the stem bends upward. However, auxin in the lower side of the roots retards growth while the upper side continues to grow at the normal rate. This causes the root to turn downward.

These effects can be observed through a simple experiment. With India ink draw a set of evenly spaced marks along the lower side of both the root and the stem of a seedling. Lay the seedling horizontally in a moist container for 24 hours and then examine the marks. The spacing between the marks will have increased on the lower side of the stem where it bent upward but will not have increased on the lower side of the roots.

Of course, this experiment does not prove that gravity is responsible for reshaping the plant. The tops of plants grow toward sources of light, and the leaves of many plants follow the sun. The unequal distribution of auxin is also responsible for this effect, which is known as phototropism. Sunlight eradicates the chemical, leaving an over abundance on the shady side of a stem. You can identify the side of the stem that grows faster by drawing evenly spaced rings of India ink around the stem of a potted plant, placing the pot upright near a window and measuring the spacing of the rings as the stem bends toward the light. This experiment casts doubt on the assumption that the stem of an inclined plant turns upward in response to gravity. Perhaps the stem is merely seeking light, which usually comes from above.

All doubt concerning the role of geotropism in plant growth can be resolved by another experiment that was first performed about 180 years ago. In this experiment upright pots that contain seeds or seedlings are uniformly illuminated on all sides, but the gravitational field is tilted from the vertical by mounting the pots upright on the rim of a wheel that turns in the horizontal plane. (Each pot is enclosed in a transparent container for protection against currents of air.) When the wheel turns, the pots are acted on by two components of inertial force: a horizontal component arising from the circular motion of the wheel and a vertical component resulting from the acceleration of gravity. The resultant force acts at an intermediate angle that is determined by the speed of the wheel.

The roots of plants that are grown on the continuously rotating wheel extend outward and downward at precisely the angle of the resultant force. The stems grow inward and upward in exact alignment with the roots. The lines of resultant force along which the plants grow trace a cone in space as the wheel rotates. The altitude of the cone varies inversely with the speed of the wheel, an experimental result that can be explained only on the assumption that inertial force strongly influences the direction in which plants grow.

The development of space vehicles got one amateur to think about how geotropism might be important in the space age. 1969 Don Graham, a commercial artist in Petrolia, California, began to wonder how a plant might react if it were grown in a weightless state. Graham decided to undertake the experiment but could think of no way of eliminating gravity without putting plants into orbit. Instead he devised an apparatus that interferes with the natural response of auxin to the gravitational field. Plants that are grown in the apparatus apparently lose their sense of direction.

Graham built a pot that rotates slowly but continuously in all coordinates of three-dimensional space and undertook to grow corn in it. Graham's experiment predated Skylab and the modern space station, and so today we know that plants grown in Graham's apparatus are not identical to those grown in space. The constant rotation stresses a seedling's tissues constantly, and this effect results in a relatively high but evenly distributed concentration of auxin that saturate the plant's the tissues. However, plants grown in space experience essentially no stress whatsoever, which results in relatively low concentrations of auxin. Since the concentration of auxin is everywhere the same in both cases, the plant cannot select a particular direction in which to go. Nevertheless, one cannot expect plants grown in Graham's apparatus to behave identically in all respects to plants grown in space.

Still, the behavior is remarkably similar. And since Graham's apparatus brings the earth-bound botanist as close to space one is ever likely to get, the method provides a great vehicle to do exploratory work on geotropism near zero G. Graham describes his experiment as follows:

"My apparatus consists essentially of a cylindrical pot that rotates simultaneously on its axis and in the horizontal plane [see illustration]. The hollow cylinder, made of the wire mesh known as hardware cloth, is a foot long (30.5 cm) and about four inches (10 cm) in diameter. The ends of the cylinder are closed by two wood disks. The cylinder is supported by a shaft that passes through snugly fitting holes in the center of the disks and is rotated on its axis by a pulley on one end. The shaft is supported at its ends by a pair of vertical brackets that are fastened to a horizontal wood base.

"The base is rotated in the horizontal plane by a vertical shaft that is coupled to a slow-speed motor by a belt. The motor turns at eight revolutions per minute. A 1:8 pulley ratio reduces the speed of the vertical shaft to one revolution per minute. The pulley that drives the cylinder is coupled by a belt to a fixed pulley attached to the frame on which the motor is mounted. None of the dimensions are critical, but the diameter of the fixed pulley should not be a multiple of the diameter of the driven pulley, because this ratio would generate a cyclical pattern of cylinder positions. A 7:11 ratio works well.

"The cylinder is filled with a mixture of four parts of sphagnum moss to six parts of rich loam. I moistened the soil and packed the cylinder as though it were an ordinary pot. Sweet corn was selected for the experiment, because the seedlings of corn develop in the form of a series of concentric whorls that appear to be stronger and sturdier than most plants are during the first few days of germination.

"Seven uniformly spaced openings, each 1/2 inch square, were cut in the a wire mesh to form a helical path of one full turn that extends to within an inch of the ends of the cylinder. With tweezers I pushed a seed through each opening and into the soil to a depth of two inches, which is to say to the middle of the cylinder. The cylinder was wrapped with a single sheet of clear polyethylene to conserve moisture.

"The apparatus was placed on the ground in the backyard, where it would receive full sunlight. The motor was turned on and operated continuously for 14 days, except during brief intervals when it was stopped for a check on the temperature and moisture of the potted soil. During this entire period seven additional seeds of the same stock were growing in an adjacent garden area that contained identical soil. These plants served as controls.

"On the 14th day all seedlings (both the experimental ones and the controls) were removed from the soil, washed gently, measured and replanted in the garden. All seven control seedlings had grown to an average height of 2-1/2 inches. They appeared to be normal in every respect. The most vigorous measured seven inches from the tip of the root to the tip of the longest leaf.

"The experimental seedlings had grown as vigorously as the controls. The largest measured nine inches from root tip to leaf tip. There the similarity ended. Whereas the controls grew straight up and down, most of the seedlings were sadly misshapen. Only one plant had found daylight; it grew about 2-1/2 inches beyond the wire. The root, which was about 3-1/2 inches long, bent randomly through the soil. One seedling grew in reverse: the root penetrated the wire and the stem remained in the soil. The root and stem of another seedling grew parallel in the same direction! One seed failed to germinate. Another produced a short root and an even shorter parallel stem. No experimental seedling had grown in the normal up-down direction. As the plants were removed I made a record of the direction in which each had grown with respect to its position in he cylinder. The record indicated that the direction of growth had been random.

"All seedlings matured in the garden, where they were cultivated and weeded regularly. The controls grew to heights ranging from five to nine feet and yielded an average of four ears of corn per stalk. In contrast, the confused seedlings matured at a height of less than three feet. Only one experimental plant produced an ear, and it was a distorted, underdeveloped runt [see illustration].

"Other experiments involving geotropism come to mind. For example, how long can a germinating plant survive without damage in the absence of a normal gravitational field? My plants were rotated for 14 days. How much damage might have been evident if I had transplanted the seedlings after the fourth or the eighth day? How would a plant react to an increase or a decrease in the intensity of the gravitational field?

"I can think of no practical apparatus for lowering the strength of gravity on the earth to, say, that of the planet Mars. On the other hand, it is easy to investigate the influence on germinating seeds of an inertial force greater than the earth's gravity by growing plants on the rim of a wheel that is spinning. It might be interesting to find out how sweet corn would grow on Jupiter, where gravity at the surface is 2.6 times stronger than it is on the earth.

"One should not place too much confidence in the outcome of a single experiment. Nonetheless, having observed the reaction of my confused corn, I suspect that no plant in an advanced stage of evolution can grow normally in a weightless environment. Nor can such a plant reproduce itself for more than a few generations, notwithstanding the fact that one of mine developed seeds. Perhaps lower marine organisms such as algae, corals or fungi could multiply in the absence of a gravitational field. So far as higher plants are concerned, however, gravity appears to be as essential to growth as sunlight. In my opinion, an orbiting spacecraft would make a poor garden."

If you'd like more about experimenting with how plants grow, check out the following articles from "The Amateur Scientist" in Scientific American magazine. All of these can be found on "The Amateur Scientist 2.0 CD-ROM."

Tropisms

Growing Plants at Less Than One G, S. Carlson, February 1996

Growing Plants at Less Than One G, Extensive Supplement (CD-ROM only)

The Clinostat, Jeff Smith (CD-ROM only)

Geotropism, One Last Time, S. Carlson, Mar. 2001

Experiments in Phototaxis: the Response of Organisms to Changes in Illumination, C. L. Stong, 1964

A Young Amateur Experiments with a Plant That Collapses Its Leaves When Touched, Mar. 1961

Plant Growth

Stimulating Plant Growth with Ultrasoninc Vibrations, C. L. Stong, August 1966

On Experiments with Gibberellic Acid Which Stimulate the Growth of Plants, C.L. Stong, Dec. 1958

Some Experiments on the Effects of Ionizing Radiation on Plants, C. L. Stong, Dec. 1963

Extraction of Growth Promoting Substances from Cantaloupe, C. L. Stong, Aug. 1964

Growth Substances in Plants, C. L. Stong, Aug. 1967

Experiments with a Plant Growth Inhibitor, C. L. Stong, Apr. 1962

Experimental Techniques

On the Culture of Plants Without Soil, A. G. Ingalls, Oct. 1952

Two Kinds of Apparatus for Growing Plants in a Controlled Environment, C. L. Stong, Mar. 1967

How to Cultivate Slime Molds and Perform Experiments on Them, C. L. Stong, Jan. 1966

How to Study the Life of a Pond and to Cultivate Aquatic Insects

Museum Secrets of Preserving Plants, S. Carlson, June 1999

The Pleasures of Pond Scum, S. Carlson, Mar. 1998

Mostly About the Collection and Study of Fossilized Seeds, C. L. Stong, May, 1956

Some Current Research on Geotropism (Not on AmSci CD)

DM Obenland, and CS Brown (1994) "The Influence of Altered Gravity on Carbohydrate Metabolism in Excised Wheat Leaves." Journal of Plant Physiology, 144:696-699.

Hoson T, Kamisaka S, Masuda Y, and Yamashita M (1992) "Changes in Plant Growth Processes Under Microgravity Conditions Simulated by a Three-Dimensional Clinostat." The Botanical Magazine, 105:53-70.

Hoson T, Kamisaka S, Miyamoto K, Ueda J, Yamashita M, and Masuda Y (1993) "Vegetative Growth of Higher Plants on a Three-dimensional Clinostat." Microgravity Science and Technology, 6:278-281.

Hoson T, Kamisaka S, Yamamoto R, Yamashita M, and Masuda Y (1995) "Automorphosis of maize shoots under simulated microgravity on a three-dimensional clinostat." Physiologia Plantarum, 93:346-351.

Kaufman PB, Thompson A, Partide D, Bernal J, and Haidle A (1995) Role of Micro-G and Hyper-G in "Synthesis of Secondary Metabolites of Medicinal Importance in Plants." ASGSB Bulletin, 9:25.

Lorenzi G, and Perbal G (1990) "Root Growth and Statocyte Polarity in Lentil Seedling Roots Grown in Microgravity or on a Slowly Rotating Clinostat". Physiolgia Plantarum, 78:532-537.