tailieunhanh - Plant physiology - Chapter 19 Auxin: The Growth Hormone

THE FORM AND FUNCTION of multicellular organism would not be possible without efficient communication among cells, tissues, and organs. In higher plants, regulation and coordination of metabolism, growth, and morphogenesis often depend on chemical signals from one part of the plant to another. This idea originated in the nineteenth century with the German botanist Julius von Sachs (1832–1897). Sachs proposed that chemical messengers are responsible for the formation and growth of different plant organs. He also suggested that external factors such as gravity could affect the distribution of these substances within a plant. Although Sachs did not know the identity. | Chapter 9 Auxin The Growth Hormone THE FORM AND FUNCTION of multicellular organism would not be possible without efficient communication among cells tissues and organs. In higher plants regulation and coordination of metabolism growth and morphogenesis often depend on chemical signals from one part of the plant to another. This idea originated in the nineteenth century with the German botanist Julius von Sachs 1832-1897 . Sachs proposed that chemical messengers are responsible for the formation and growth of different plant organs. He also suggested that external factors such as gravity could affect the distribution of these substances within a plant. Although Sachs did not know the identity of these chemical messengers his ideas led to their eventual discovery. Many of our current concepts about intercellular communication in plants have been derived from similar studies in animals. In animals the chemical messengers that mediate intercellular communication are called hormones. Hormones interact with specific cellular proteins called receptors. Most animal hormones are synthesized and secreted in one part of the body and are transferred to specific target sites in another part of the body via the bloodstream. Animal hormones fall into four general categories proteins small peptides amino acid derivatives and steroids. Plants also produce signaling molecules called hormones that have profound effects on development at vanishingly low concentrations. Until quite recently plant development was thought to be regulated by only five types of hormones auxins gibberellins cytokinins ethylene and abscisic acid. However there is now compelling evidence for the existence of plant steroid hormones the brassinosteroids that have a wide range of morphological effects on plant development. Brassino-steroids as plant hormones are discussed in Web Essay . A variety of other signaling molecules that play roles in resistance to pathogens and defense against herbivores have also