Hart's Daylilies
Daylilies and Epigenetics
Epigenetics is the study of the influence of various compounds on the action of genes. DNA is the double helix compound in a chromosome which contains the genes. Genes are portions of the DNA strand, many of which are responsible for the production of enzymes. Enzymes regulate the rate of biological reactions. Chromosomes in plants and animals and are composed of DNA covered with proteins called histones. Which particular genes are functional depends on enzyme actions on the genes and histones. Presently the compound being looked at is methyl (CH3) groups on DNA or histones but there may be other compounds studied in the future. Genes which have methyl groups attached are said to be methylated. Commonly, the more methyl groups that are attached to the DNA, the less active a gene is.
An example of epigenetic action in humans might be illustrative. During the Second World War the Dutch went through a period of starvation. Many women who were pregnant during this period gave birth to babies that apparently had an increased amount of methylated genes. We assume that this stress and the associated addition of methyl groups is what caused many of the children to become obese in later life. The methylation has been passed to the future generations. It has since been found that stress of any kind may increase the methyl group attachments. In humans the stress may be mental, or physical. Both too little food and too much food have been found to influence methylation.
Chemicals such as folic acid, zinc, vitamin B12 and choline have been noted to decrease the effect of stress in some human cases. Are there other chemicals which will increase epigenetic affects?
Very little epigenetic study has been done on plants. The mustard genus Arabidopsis has been examined to some degree. The size of the plant and its flowering time are affected by the presence of methyl groups. Stress caused by disease or insects may epigenetically cause a decrease in plant size and, in this case, stimulate genes which increase the resistance of the plants to various pathogens. The gene causes the plant, and its offspring, to act like it is under attack. Genetically identical plants will grow normally.
Another example in Arabidopsis is the change in flowering time without a genetic change. These plants normally flower in the spring time but some have changed to flower later. There has been no genetic change in the DNA of this well studied plant. This might be related to a series of late stressful springs that caused an increase in methylation and decreasing the action of the DNA thus decreasing the production of flower producing enzymes.
Another example may be the growth of many plants in warm climates compared to the same species in cooler climates. Most species have slower growing, shorter plants under the stressful more northern or higher altitude conditions. When these northern plants or their offspring are moved to a warmer climate, they retain their smaller condition.
We might want to consider what epigenetics might have to do with daylilies, even though no research has been done on these plants at this point. We know that stress may cause the methylation of DNA or its histone covering. This stress will often decrease the activity of the affected genes but at times may actually stimulate these genes. Most of us try to grow our daylilies with as little stress as possible. What might happen if our plants were extremely stressed? Could we decrease the activity of the genes involved with the breakdown of tissues after one day of flowering? Could we increase the disease and pest resistance of daylilies even though they might grow somewhat slower? Many of the daylily hybridizers destroy their seedlings after three years or so, sooner in the south. Are we actually killing off plants that might have more disease resistance? This might be a logical conclusion if the plants were stressed enough to have increased methylation of the DNA or histones. Stress may be as simple as a drought or cold weather during the growing (especially flowering) season.
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