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Diverting the downhill flow of auxin to steer growth during tropisms
Author(s) -
Spalding Edgar P.
Publication year - 2013
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.3732/ajb.1200420
Subject(s) - auxin , biology , biophysics , gravitropism , phototropism , membrane , efflux , microbiology and biotechnology , biochemistry , arabidopsis , mutant , physics , gene , optics , blue light
Polar auxin transport can be likened to water following the path of least resistance as it flows downhill. In the case of auxin, the hill is the difference in electrochemical potential of the auxin anion (IAA − ). H + ‐ATPases and H + ‐IAA symporters at the plasma membrane create the electrical and IAA − concentration gradients that constitute this thermodynamic hill. PIN and ABCB transporters also at the plasma membrane bias the direction and limit the rate of downhill flow out of the cell. This article will present the thermodynamic basis for this view and critically examine how well the molecular biological descriptions of the polar auxin transport process fit the framework. An auxin concentration gradient across an organ has long been recognized as the cause of bending growth during tropisms. Its generation can be viewed as a result of redirected polar auxin transport. This article will examine how molecular regulation of the paths of least resistance to auxin efflux diverts the downhill flow of auxin to steer growth during tropisms.