Auxin metabolism and transport during gravitropism

Auxins are endogenous, growth‐regulating compounds in plants: for decades investigators have hypothesized that plants change their growth rates and patterns in response to environmental signals by changing their transport of, metabolism of, or sensitivity to their endogenous auxins. The Cholodny‐Went hypothesis, for example, postulates that plants respond to tropic signals by changing the distribution of free indoleacetic acid within their tissues. This hypothesis was based on data from experiments investigating phototropism and gravitropism in oat (Avena sativa L.) and maize (Zea mays L.) coleoptiles. The results of recent experiments support the Cholodny‐Went hypothesis for maize coleoptile gravitropism. Recent experiments conducted on the gravitropisms of other developmental stages of grasses, and other species of plants, however, indicate that the Cholodny‐Went hypothesis may not adequately describe how all plants respond to gravity.