Science Fair Project Encyclopedia
Arabidopsis thaliana, or Thale Cress, a small flowering plant related to cabbage and mustard, is one of the model organisms for studying plant sciences, including genetics and plant development. It plays the role for agronomy that mouse and fruit fly (Drosophila) play in human biology.
The genome of Arabidopsis, consisting of five chromosomes, has been sequenced. The finished sequence was published in 2000 and represented the first sequenced plant genome. At 125 million base pairs, it is a small genome for a plant species. Since the sequencing of the genome, much work has been done of assigning function to the 26,000 genes so far found in the genome, many of which have no known function.
Scientists from Purdue University studying Arabidopsis discovered what one termed a "parallel path of inheritance", an alternative to previously known mechanisms of DNA repair. A mutation in a gene named HOTHEAD which when mutated cause abnormalities in stems and flowers. After spending over a year eliminating simpler explanations, studies indicated that the plants "recorded" versions of their genetic code going back at least four generations. Arabidopsis was able to use earlier records as templates to correct the hothead mutation. Early evidence suggests that the record may be RNA-based. 
Studies of phototropism
Arabidopsis has been used extensively in the study of the genetic basis of phototropism, chloroplast alignment, and other light-influenced processes. Study of this organism has led to discoveries such as positive phototropic responses of root cells to red, far red and infrared light.
While gravitropic response of Arabidopsis root organs is the predominant tropic effect in these organs, specimens treated with mutagens and then selected for the absence of gravitropic action have shown both negative phototropic response to blue or white light, and positive phototropic response to red light. The photosensitive pigments phytochrome A and phytochrome B mediate this red light based phototropic response.
- The Arabidopsis Information Resource (TAIR)
- Nature Gateway on Arabidopsis
- The Arabidopsis Book - comprehensive electronic book
- Arabidopsis thaliana: another "model organism" from Kimball's Biology Pages
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