Some information about our work on auxin transport....
The Cholodony-Went hypothesis for gravitropism suggests that differential elongation
between opposite flanks of graviresponding organs is linked to auxin transport,
concentration, and/or sensitivity of the responding tissue. When a root is positioned
horizontally, auxin redistributes to the lower side of the root. This redistribution
promotes growth on the upper side and inhibits growth on the lower side of roots,
resulting in downward curvature.
Auxin transport is clearly involved in root gravitropism since auxin transport inhibitors
such as naphthylphthalamic acid (NPA) and triiodobenzoic acid (TIBA) inhibit root
curvature and the differential induction of an auxin-responsive promoter. Despite the
strong correlation between auxin transport and gravitropism, the regulation of auxin
transport during, for example, graviresponse remains unclear.
The interaction between hormones and the cytoskeleton was the subject of a recent
paper
Hasenstein KH, Blancaflor EB, Lee JS (1999) The
microtubule cytoskeleton does not integrate auxin transport and gravitropism in maize
roots. Physiologia Plantarum 105: 729-738