Water Stress Project

Project by group gehsbeardsleyfall2019

Explore Our project will study the relationship between soil water content, abscisic acid, and the effects on Arabidopsis thaliana seed types’ germination rates and health. Abscisic acid is a hormone found in plants in periods of harsh conditions, including desiccation. It induces dormancy in nascent seeds, so they will delay germination until it’s environment is better for growing. It signals for the plant to close its stomata in order to preserve water, shutting down photosynthesis. These functions help the plant survive in overly dry conditions. In the Arabidopsis thaliana wild type, the gene ABI5 encodes a basic leucine transcription factor, which regulates seed maturation, germination, and stress and hormone signaling. This responds to the presence of ABA and implement the aforementioned methods to preserve the plant. In our mutant seed, abi5-1, there is a mutation at nucleotide 34,017, which results in an early translation termination, so the mutant lacks 81 amino acids, including the leucine zipper function. This means that the plant is not responsive to the presence of the ABA hormones, so it won’t postpone germination rates or close its stomata and stop photosynthesis to retain water. Some things that we needed help figuring out were: How much water we should give the plants in each part of our experiment. We don’t know the average conditions for our control group, or how much less water we should give each of our experimental groups. We also weren’t sure if we should decrease the water incrementally in the water deprived ones, or just automatically have a sharp decrease in the water we give. Another thing was how to measure the plant health, we decided on plant height and leaf length, but are there any more conclusive things to look at as well or instead?
Research Question We want to study the relationship between abscisic acid and it’s affects on germination rates and plant health. We came up with this idea because our stress was soil water content, and the abi5-1 was abscisic acid resistant, which upon further research we found out that ABA in the plant plays a big role in responding to water deprived environment. Our research question goes with the topic because it will track the responses to ABA from desiccation and how that effects the plant.
Predictions In hydrated conditions (our control group), the wild type and mutant will both germinate and grow equally well. In the dry conditions (our experimental group) with a shortage of water, the wild type seeds will have a lower germination rate than the abi5-1 mutants. However, the wild seeds that do germinate will have better health compared to the germinated mutant seeds in the dehydrated conditions. We think this because the wild types will respond to the ABA hormone, so it will inhibit germination and photosynthesis, which will help the plant survive. The mutant seeds will not respond to ABA so they won't close their stomata, letting the plant dry out.
Experimental Design In our experiment, the independent variable will be the amount of water administered to the plants. The dependent variables are the germination rates, plant height, and leaf length. The second two will determine the overall health of the plant. Our controlled variables will be sunlight, temperature, and soil type. We’re going to have 6 setups in total, 2 of them will test germination rates for both seeds in dry conditions. The other 4 will look at ABA effects on plant health and growth for both the wild type and mutant seed, in both normal and dry conditions. We will have one setup each for the wild type and the mutant seeds, where they will be watered regularly with a normal amount of water (still to be determined). We will also have one setup each for the wild type and the mutant seeds, where they will be kept in regular conditions, with normal water amounts, until they germinate. After germination, these seeds will be dehydrated, and watered with much less water (still to be determined). We will track the plants’ health by measuring the height of the plant and leaf length. We will also have two Petri dishes, one for each seed type, and will start them off immediately in dry conditions, and study the seed types’ germination rates. We will test how well the different seed types respond to a lack of water, and how that effects their germination rates. We will measure germination by tracking the days when both cotyledons of the plants are visible.
Conclusion Water shortages affect the germination, leaf width, stem length, and flowering time in Arabidopsis plants. A water deficiency in the soil causes the production of ABA, which stresses the plant. In wild types, ABA induces premature flowering, creating spindly stems and brittle leaves. This happens because the plant diverts its energy into flowering early and producing seeds, instead of allocating the energy to the leaves—where it should go at this stage under normal conditions. In the ABI5-1 mutants, some plants managed to grow with more normalcy, because they did not respond to the ABA or sense water shortage. However, some of the mutant plants still grew poorly in the water deprived environment because there was not enough water for healthy growth, resulting in premature flowering, similar to the wild types. Furthermore, open stomata in these plants may have resulted in the drying out of leaves.