|MadSci Network: Botany|
Dan, Whether or not ethylene affects germination is an interesting question. because there could be some logic to the same trigger that softens fruit, also sending a message for the seeds inside to sprout. I am not aware of any reports that ethylene gas speeds germination and a recent call to the Cooperative Extension Service (RI) indicated it did not affect seeds. That is no reason to abandon your experiment, you may be onto something. Also your question illustrates the care that must be taken in setting up an experiment so that you actually answer the question you are asking and get results that are useful. What is widely known is that ethylene gas, which acts as a plant hormone, promotes ripening of fruit and triggers dropping of leaves, fruit and flowers (along with abscisic acid). It is also involved with thigmotropism (that is the uneven growth when part of a plant contacts a solid material, useful for twining vines and tendrils) and ethylene along with auxin can result in stocky growth in some cases. I would need a little more information to give you specific advice, but I can start by making some assumptions about the missing information. Let's start by discussing the experimental set-up. You do not mention what kind of seeds you are using. Let me assume you are using apple seeds, perhaps still in the apple. Since ou want to know if ethylene gas affects seed germination you must set up your experiment so that presence or absence ethylene gas is the ONLY factor. Are you doing that if the seeds are in the apples, in contact with a source of moisture (known to improve germination) and possibly exposed to other hormones or chemicals from the fruit? To help isolate the effect of ethylene given off by the apples, apple tissue should not be in contact with the seeds. If you are starting seeds in a covered flat, the ethylene gas will reach the seeds even if the apples are not near them. This could also aide in the control of fungus or at least limit it to a small area of your container. Now let's talk about seeds. Apples grow in temperate areas that have cold winters. Many seeds require that cold period (called stratification) to germinate (You can find out if this applies to appleseed by checking in a seed starting book or calling the Cooperative Extension Service in your state). Are the seeds contained in apples that have been stored in a refrigerator? If so, did both sets of seeds get the same handling? Are they from the exact same type of apple, or better yet the same apple? All these factors must be carefully eliminated so that ethylene is the only difference. Next let's talk a little about your results. You mention that about 1/3 of your seeds germinated in the presence of apples, but only 4 germinated without. I cannot tell from the information you give if these numbers are very different. (If you planted 12 seeds, they are the same). But I can tell you that the difference may have meaning. While your initial idea was to see if ethylene sped up germination, you may have found that it improves germination if the percentage of seeds that sprout is higher in the presence of ethylene compared to seeds without ethylene. If this is true you have made an unexpected discovery, one of the most fun parts of science! You can make a stronger case for the effect of ethylene if you can show a relationship between the amount of ethylene gas (estimated from the amount of apple material) to the result. For example if there is 25% germination with no apple, 40% with 5 ounces of apple and 60% with 10 ounces of apple, you have an even stronger case. Last but not least, should you try other seeds? If fungus is a problem, you might want to look at faster sprouting seeds that will sprout before the fungus gets too nasty. You also might want to test whether any effect you see applies to other types of seeds. Good Luck!
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