The properties of an Arabidopsis mutant called det2 made it clear that brassinosteroids are naturally occurring plant hormones. When grown in darkness, seedlings homozygous for the det2 allele differ dramatically from wild-type seedlings: In many respects, they look like wild-type seedlings grown in the light. Treatment of dark-grown det2 mutant seedlings with brassinosteroids causes them to grow normally—that is, like wild-type plants grown in the dark. These results, supported by chemical analysis, showed that det2 plants are unable to synthesize their own brassinosteroids, and that lack of the hormone results in abnormal growth.

Some of the effects of light on plant development result from effects on the signal transduction pathway for brassi-nosteroids. Others may result from alterations in brassinos-teroid levels in the plant. Let's now look more closely at how plants sense environmental cues such as light.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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