The Effect of Gravitational Forces on Arabidopsis Thaliana Development

Transcription

1 NASA Student Launch Initiative 2006 The Effect of Gravitational Forces on Arabidopsis Thaliana Development Final Report Madison West High School 30 Ash Street Madison, WI Ed Holmes, Principal

2 VEHICLE REPORT Construction The two-stage vehicle was constructed using fiberglassed phenolic body tubes, both for the booster and the sustainer. The booster was an 84 long fiberglass phenolic tube with a diameter of 6. The six fins on the booster were constructed of 1/8 G10 fiberglass. For the sustainer, the G10 fins were stronger 3/16 G10 fiberglass. The body tube of the sustainer, also made from fiberglass phenolic tubing, was 4 in diameter and 89 long (including the LOC plastic nosecone). Bulkheads in the booster were made out ½ plywood, and in the sustainer out of 1/4 plywood. Vehicle Drawings Figure 1: A 2D RockSim rendition of the vehicle with the CP and CG marked Figure 2: A 3D computer model of the rocket. The red sections indicate where the accelerometer/altimeters was located. The payload was in the green sections. The recovery systems for both stages were above the payload in each stage to allow each stage to decent in the upside up manner. The yellow sections mark the location of the propulsion system in both stages. Parachute Size and Ejection Charges Based on the weight of the various stages and the descent rates, the following parachute sizes together with ejection charges of specified weight were used: Parachute Size (in) Descent Rate (fps) Weight (lbs) Weight of Ejection Charges (grams) First Stage Main w/piston Second Stage Drogue w/o piston Second Stage Main+Drouge 70 (main) + 15 (drogue) w/piston

3 All parachutes deployed properly and brought both stages to a safe descent, indicating that the sizes of the parachutes were correct. Flight Electronics Booster (powered by K630 Contrail hybrid motor) A Perfectflite MAWD altimeter was used to deploy the booster s main parachute at apogee (approximately 500 ft.). The booster apogee was 647ft AGL and the altimeter deployed the parachute as expected. Sustainer (powered by J800 Thunder Aerotech solid composite motor) A Perfectflite MTAG timer ignited the second stage, firing 2.8 seconds after the g-switch detected liftoff. A G-Wiz accelerometer and an MAWD Perfectflite timer both fired the same charge at apogee to deploy the drogue. The G-Wiz accelerometer and the same altimeter fired another charge at 500 ft for the deployment of the main parachute. Both events occurred as expected. Flight Data Altitude vs. Time We have tested the rocket before the official SLI launch. The test flight was carried out in the exact configuration as the official flight at NASA s SLI launch and the flight apogee was 5,292ft. Based on this result, we have decided not to add any ballast as long as the wind conditions are similar (which was the case). However, as shown on the graph below, during the official launch, the sustainer reached apogee of 6047ft (at 22s after liftoff), which is significantly higher than expected. We attribute this difference to the following factors: Different air temperature (and thus air density): air temperature during our test flight was 52F while temperature at the SLI launch was close to 80F

4 Earlier ignition of the second stage: we have observed that the second stage ignited while the whole rocket was moving still fairly fast, on the other hand during our test flight the whole vehicle slowed down significantly before the second stage ignited. Angled second stage trajectory: during our test flight in April, the second stage did not separate perfectly and the sustainer flew under a noticeable angle. Acceleration vs. Time Naturally, we are mostly interested in the acceleration profile. This profile was measured by an on-board G-Wiz accelerometer. The accelerometer was place in the electronic bay in the sustainer and thus could record the acceleration profile during whole flight. The measured acceleration profile is shown on the graph below. The graph clearly shows two distinct thrust phases. The first phase (K630 Contrail motor) generated maximum acceleration of 6g which is sufficient for swift and stable boost (the rule of thumb requires 4-5g). The booster motor burnt for about 2.5 seconds and delivered the vehicle to about 600ft. The second stage motor (J800 Thunder) ignited at about 3.0s after the liftoff which is in fair agreement with the ignition timer setup (it was set up to fire at 2.8 seconds after the liftoff detection). The sustainer burn generated maximum acceleration of 13g and ended at 5 seconds after liftoff. The rocket then went through a short period of rapid deceleration (-3g) after the motor cut-off and then gradually transition to 1g sustained deceleration until the apogee charges fired at 22 seconds after the liftoff. The last peak on the graph most likely represents the drogue parachute deployment.

5 Speed vs. Time While the speed is not as important to our experiment as acceleration, the examination of the speed vs. time graph still provides additional information. We can clearly see that neither stage broke though the sound barrier, so the transonic phenomenons do not come to play. Again, we can observe two distinct burn stages on the graph and we also notice that the sustainer traveled about as four times faster as the booster. In summary, the vehicle fulfilled its assigned role of generating two different acceleration jolts and it also delivered the payload to 1 mile of altitude (and even higher). All recovery systems functioned as designed and both payloads landed softly.

6 PAYLOAD REPORT Pre-Flight On April 27 th, nine days prior to the launch, we prepared, using aseptic technique, sixteen Petri dishes of Arabidopsis Thaliana using seed lines obtained from our mentor Sara Patterson. Eight of these were from an agravitropic seed line designated ARG-1, and eight were from a standard wild type strain. The seeds were then placed into a refrigerator for one night a procedure known as cold treatment that increases germination rate by simulating the cooler winter weather. On April 28 th, all plates were removed from cold treatment and placed under growth lamps, where they remained until May 3 rd. On the Wednesday before the launch (May 3 rd ), the plants were transferred to their plantsporters Styrofoam coolers with florescent lights mounted inside them to keep the plants growing as they made their way down to Alabama. On the afternoon of the May 6 th launch, we inspected our astronauts and segregated them into our three data groups after eliminating the four least-healthy-looking dishes (poor germination, size), leaving six dishes each of wild type and agravitropic (ARG-1) plants. Two ARG-1 dishes and one wild type were loaded into the space-constrained sustainer section, and three wild type and two agravitropic dishes were loaded into the larger booster payload section. Two dishes of each type were marked as Control plants and placed in a safe, dark location during the launch. Launch & Recovery The launch, of course, was a resounding success, with the booster reaching an altitude of approximately 600 feet and the sustainer, 6047 feet. Both sections floated back to Earth gently under their main chutes. Immediately after returning the sections to the staging area, we removed the dishes and returned each Petri dish to the plantsporters. One dish an ARG-1 unit in the sustainer was cracked and blackened by a nearby ejection charge. We marked and excluded this dish from our data collection because we cannot know whether the effects seen on that dish were due to acceleratory forces or the damage caused by the ejection charge. We awaited a return to Madison for data collection. It should be noted in a discussion of the acceleratory forces applied to our plants that shortly after the ground support vehicle (mentor Pavel Pinkas 1995 Mercury Villager) departed from the Huntsville Holiday Inn, it was broadsided at an intersection by another vehicle. Pavel, fortunately, was unharmed, but the same cannot be said for the car, and it is unknown whether the plants were affected by these acceleratory forces. This poses a possible source of experimental error. Initial Observation & Transplantation Upon return to Madison, the plants were once again placed under growth lamps, where there remained for several days. Then, on May 12 th, we transplanted some of the Arabidopsis to soil. We chose one dish from each data point (one control wild type, one control booster, etc) to be tenderly removed from their agar media in which they had been grown and placed into potting soil. Once in their new home, the transplanted Arabidopsis were placed once again under the growth lights where they were closely observed and tended to. On May 12 th, immediately prior to transplantation, we took formal observations of the plants progress. As a part of these observations, we took photographs of all the dishes so that future observations could be made. Here is a sampling of the pictures taken during our

7 observations (4/27 is the date planted; green lettering is the control group, yellow the booster, and red the sustainer; col is wild type, arg1 is agravitropic): Figure 1. Wild type, control group (no flight) Figure 2. Agravitropic type, control group (no flight)

8 Figure 3. Wild type, booster group (exposed to 6g acceleration) Figure 4. Agravitropic type, booster group (exposed to 6g acceleration)

9 Figure 5. Wild type, sustainer group (exposed to 13g acceleration) Figure 6. Agravitropic type, sustainer group (exposed to 13g acceleration)

10 On May 16 th the Arabidopsis, having grown for several days in soil, were once again photographed (Figures 6-9). The first letter refers to which part of the rocket the plants are from (C-control, B- booster, S-sustainer). The second refers to the plant type (A-agravitropic, C-wild type). Figure 7. After transplantation: control group, no flight; left: agravitropic type, right: wild type Figure 8. After transplantation: Booster group, no flight; left: agravitropic type, right: wild type

11 Figure 9. After transplantation: Sustainer group, no flight; left: agravitropic type, right: wild type The dish of note (marked 4/27 col FS, on Figure 5 and also SC on Figure 9 (after transplantation)) was the dish of wild type plants in the sustainer. These were noticeably smaller than the other plants at the time of transplantation, and have failed to continue to develop once placed into soil. Clearly some factor has affected the development of these plants in a strong, negative manner, but we cannot say with certainty that it was due to the acceleration of the rocket upon examining the dishes, this one was found to have been slightly blackened after the flight, likely by a nearby ejection charge. While there were no evident cracks or holes in the dish, we cannot rule out the possibility that it was heat, pressure or some other factor from an ejection charge that has impeded the growth of the plants, rather than the acceleratory forces of the launch. The remaining dishes, however, showed far less dramatic results. Our observations taken of the plants in their dishes and as they grew in soil showed little or no changes between the control plants and the corresponding flown plants. The transplanted Arabidopsis, save the control sustainer group, had nearly identical heights, root lengths and general health. One apparently significant difference was observed early in data-gathering: that the ARG-1 control group plants (agravitropic strain that was not flown) had limited growth within the dish at the time of transplantation (see Figures 2 and 7). This was initially thought perhaps to hint at a beneficial effect of acceleratory forces on agravitropic plants. Further Growth Observations After several weeks of observing the plant s further growth, we were able to make further generalizations about their health. Among the wild type plants, noticeable differences between the different flight stages began to emerge. Sustainer plants continued to be severely stunted, while the other two groups continued to grow, the booster growing significantly less than the ground plants. There was a definite inverse correlation between the stress experienced and plant height among the wild type plants. The agravitropic plants showed no such correlation: the plants in the sustainer were actually slightly higher than the others. All the agravitropic plants were ultimately

12 comparable in height to the ground wild type plants and approximately the same size. Thus we conclude that the rocket s acceleration had little or no effect on the agravitropic plants development. DR5-GUS Analysis The last analysis of the plants that we preformed was a microscopic examination of auxin expression in the roots and leaves of the Arabidopsis. To do this, we first selected representative plants from each data group and soaked their roots and leaves in X-gluc to activate the DR5-GUS gene. This gene, inserted into all of the plants is a specialized marker which dyes cells blue if they are expressing auxin a growth hormone which shows us where and if the plants are growing. Then we immersed the plant parts in ethanol to neutralize the chlorophyll, making it easier to see the blue cells. We examined the each sample individually under a high-power dissecting scope, and took photographs of the plants for later analysis. Here is a sampling of the auxin-stained plants: Wild Type Agravitropic Sustainer (1) Sustainer (2)

13 Booster Control We have only included images of the Arabidopsis leaves as the pictures of the roots were inconclusive: all root samples showed blue cells at root tips and junctions. The leaves images are in the above table, at magnifications from 10x to 50x. The wild type plants from the sustainer and booster show markedly fewer blue cells than those from the control group: this supports our earlier macroscopic observations of wild type plants. The presence of stained cells in all agravitropic groups, however, is relatively uniform, suggesting (again, in accordance with our earlier observations) that flight stress had little to no effect on these plants. Conclusions Based on our results, we conclude that short acceleratory stresses in range from 6g to 13g inhibit future growth in wild type Arabidopsis Thaliana. Arabidopsis plants possessing the agravitropic trait, however, are uninhibited by acceleratory forces. We realize, however, that our relatively small sample size reduces the accuracy of our conclusions. To make a definitive conclusion, therefore, further trials with more plants would be necessary.