Plants sense gravity using statoliths in their roots. By cutting a cross section of the root and staining them, the researchers found that statoliths are present in adventitious root nodes no matter the age of the node. In order to study the variable of gravity when it came to the adventitious root growth, they used different experiments. First, they used a clinostat experiment, where the plants were planted and mounted and rotated for three days. After the rotation, the rotated stems had a root angle of 106°, as opposed non rotated stems which had an angle of 120.4°. The stems that were being rotated were unable to feel a constant directional effect of gravity, while the non rotated stems did, which means that gravity had a 14.4° change on the root angle.
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Interestingly, a plant that was exposed to white light and ethylene for two days and then grew in darkness for two days. In the case of this plant, its roots initially grew downwards for the first two days, and then they grew upwards for the next two days, giving the roots a kinked shape by the end of the four days. Similar to that, a plant grown in darkness for two days and then white light for two days grew upwards for the first two days and downwards for the final two days. This created a kinked shape in the roots, however it was in the opposite direction. Upon researching the effects of gravity on the growth of the roots, they found that gravity affected the root growth in a less impactful way.
In addition to red light, they tested the effects of blue light on the plants. Blue light is received by phototropins in plants. Phototropins are in control of stomatal opening and chloroplast movement. When the rice stems were exposed to the blue light, it had a dosage dependent pattern. At a low fluence rate of blue light, the rice stems had similar root growth and angle to rice stems that were grown in the dark. In comparison, at a high fluence rate of blue light, the rice stems had similar root growth and angle to stems that were grown in white light. The direction of rice roots growth in response to white light was found to be reversible. They studied four different rice plants in different setups; one plant was exposed to white light and ethylene for four days, and it grew roots that went downwards. The next plant was grown in darkness, and its roots grew upwards.
However, the roots that penetrated in the light grew at a 45° angle, while the roots that penetrated in the dark grew at a 119°. This difference exhibited the fact that light is the major contributor of which direction the adventitious roots will grow. The plants that were not submerged underwater in this experiment did not grow any adventitious roots. This can be attributed to the the ethylene levels not being able to reach a high enough level in the three days the experiment was conducted, while the ethylene could get trapped and reach a high enough level in the submerged plants. An important note to make is that the adventitious roots grow in the same patterns in different media: water, soil, and styrofoam beads. This is indicative that the growth patterns are independent of the medium.
Initially, they studied the rice plants root growth in response to white light and total darkness. Over five days, one batch of excised rice stems was grown in a light environment and another was grown in a dark environment. At the end of the growth period, the stems that had grown in the dark had sprouted roots, while the stems grown in the light did not. The root angle of the dark grown stems stayed consistent throughout the time period at an average of 119°, and the roots grew at a consistent rate. This experiment showed that darkness is a stimulus for the plant to increase root penetration in order to find more nutrients, which is how the plants know when to grow adventitious roots underwater. When full plants were grown in light and dark while submerged, the plants grown in the light grew adventitious roots.
Adventitious root growth is stimulated by a gaseous hormone called ethylene. While that may sound simple to orchestrate, scientists wondered how the plants decided what directions to grow the roots. In the paper, Control of Adventitious Root Architecture in Rice by Darkness, Light, and Gravity, Chen Lin and Margret Sauter describe their findings on the mechanisms behind the architecture of root growth in rice plants. They investigated this adventitious root growth in response to different light stimuli and different gravitational stimuli, and found some interesting results.
Rice, also known as Oryza sativa, is a major staple in kitchens all around the world. This semi-aquatic plant has many subspecies, yet for this experiment only the japonica and indica subspecies were studied. These suspecies are mostly grown in Southern Asia. Rice is semi-aquatic because the plants are adapted to survive and grow even when partially flooded. This ability is most commonly seen in the beautiful vistas of rice paddy fields where the rice field is flooded in order to suppress weed growth and increase rice growth. One of the reasons for the rice’s aptitude for being partially submerged is its ability to grow adventitious roots. An adventitious root is a root that grows from any organ other than a root. In the case of rice, these roots grow from the stems, which enable the plants to extend their reach into a more oxygen rich area when they are flooded.
Thomson takes it a step further by saying if the woman has bars installed but the robber still gets in through her open windows, it would be absurd to call it her fault that the robber got in. However, when women get pregnant because of malfunctioning birth control, they are often seen as voluntarily getting pregnant. Thomson also brings up the people-seed scenario, where there are people-seeds floating around outside, so you install very fine mesh screens to prevent them from getting in once you open your window. However, when one gets past the screen and takes root in your house, Thomson asks if it is your responsibility to keep the plant. The only way to really prevent those seeds from getting in, is to never open your windows in the first place. In summary, Thomson is saying that there are scenarios where the fetus has right to its mother body, and some scenarios where it doesn’t. It is impossible to make a blanket statement specifying when a pregnancy is voluntary or involuntary and when an abortion is just or unjust.
On pages 58-59, Thomson writes about how some opponents of abortion support the independence of the fetus, and how the fetus has a right to the mother’s body when it was conceived through voluntary intercourse. People often say the only case of involuntary pregnancy comes from rape. However, Thomson writes that it is a slippery slope to choose when a woman voluntarily or involuntarily becomes pregnant, as details can make a huge difference. First, Thomson describes a scenario where a woman opens her window because her room is stuffy, which allows a burglar to get in. Thomson then says how absurd it would be to say that the burglar has a right to stay in the room now that they have gotten in, even though the women technically allowed him to get in by opening her window. Although that may be absurd, a parallel could be drawn between this situation and woman becoming pregnant.
For the group studying how the frequency of lawn mowing and landscaping affects the species richness, they will need to find areas in which lawns are mowed at different frequencies. In order to find this information, they will call the physical plant to find when areas on campus are mowed.
Similar to the group studying lawn mowing and landscaping, the group studying species richness in relation to how recently the grass was planted will contact the physical plant in order to find out the ages of grass plots around campus. The group will find multiple areas of varying age in order to compare it to the species richness.
Finally, the group studying species richness in relation to elevation and water runoff should find areas of high elevation in the Orchard Hill residential area, and then find areas of low elevation below the Orchard Hill residential area and study the species richness in the plots.
Once all of the groups are done, they can all compare their results to figure out which variable has the most significant impact on the plants.