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Unformatted text preview: A . thaliana, a tiny weed whose common name is “mouse ear cress,” grows low to the ground ( Fig. B.1 ) and produces clusters of small white ﬂowers in meadows and laboratories around the globe. Like more than 150,000 other species of ﬂowering plants, including roses, daisies, tomatoes, peas, beans, and maple trees, Arabidopsis is a dicotyledo-nous angiosperm— dicotyledonous because the mature embryo car-ries two specialized seed leaves (or cotyledons ), and angiosperm because its seeds are enclosed in an ovary within a ﬂower. Arabidopsis shares three basic characteristics with other plants: It is an autotroph, that is, a nutritionally self-sufﬁcient organism that produces its own food via photosynthesis; it is nonmotile, that is, rooted to one spot; and it pro-duces new organ systems continuously throughout its life cycle (which consists of alternations between a diploid [2 n ] sporophyte generation and a haploid [ n ] gametophyte generation). The impetus for studying a small ﬂowering weed with no com-mercial potential is straightforward: Plants are the chief source of food for life on our planet, and an understanding of how they grow and reproduce may make it possible to grow more nutritious, more copious crops in a wide range of environments. In addition, A . thaliana is one of the premier eukaryotic experimental model organisms. Much of what we have learned from this plant can be applied directly to animals and other eukaryotes. Classiﬁed in the same family as mus-tard and cabbage plants, A. thaliana has several features that make it an excellent ex-perimental model. Its general strategies of growth, development, ﬂowering, and seed production are the same as those of other higher plants, including many crop plants. However, it has a shorter generation time than most other plants, requiring only six weeks for seeds to germinate and develop into mature plants that produce more seeds. Moreover, like the peas that Mendel studied, it reproduces mainly by self-fertilization, yet cross-pollination—through the removal of stamen from one plant’s ﬂowers and the application of pollen from another plant’s ﬂowers onto the stigma of the stamen-deprived ﬂowers—is possible. Whether self- or cross-pollinated, wild-type Arabidopsis plants produce a very large number of seeds—from 10,000–40,000 per plant—and these seeds have a high rate of germination. Such rapid, abundant reproduction makes it possible for geneticists to screen large populations of seedlings for speciﬁc phenotypes. Finally, A. thaliana grows well in the laboratory, requiring relatively little light (illumination from cool, white ﬂuorescent bulbs is sufﬁcient) and temperatures in the range of Because the plant is small, researchers can grow hundreds of thousands of them a year in a modest-sized laboratory with no special growth facilities....
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