Auxins

Auxins (AWK-suhnz) are hormones involved in plant-cell elongation, shoot and bud growth, and rooting. A well-known natural auxin is indoleacetic (IN-DOHL-uh-SEET-ik) acid, or IAA. Developing seeds produce IAA, which stimulates the development of fleshy structures such as fruit. An experiment with strawberries, shown in Figure 31-1, provides one form of experimental evidence about the role of IAA in plants. The removal of the seed-containing parts from a strawberry prevents the fleshy structure from enlarging. However, if IAA is then applied, the strawberry enlarges normally.

figure 31-1

(a) Strawberry plants normally produce a fleshy, heart-shaped "berry."The "berry" is not truly a fruit—it is a swollen flower receptacle. The yellowish "seeds" covering the "berry" are truly complete fruits, each containing a seed.

(b) if the "seeds" are removed from a young "berry," it does not enlarge.

(c) But if the "berry" is then treated with IAA, it grows normally.

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