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Lateral roots extend horizontally from the radicle, or primary root, and serve to anchor the plant securely into the soil. This branching of roots also play a role in water uptake, and facilitates the extraction of nutrients required for the growth and development of the plant.

Auxin Signaling
Auxin is a critical plant hormone in the formation of lateral roots, which was found evident in a study of auxin transport in Arabidopsis.

The first morphological stage is indicated by the division of pairs of pericycle founder cells. In Arabidopsis, these occur in groups of eight or 10, suggesting that before this initial morphological stage, transverse divisions must be conducted first in order to precede lateral root initiation.

An auxin transport inhibitor, N-1-naphthylphthalamic acid (NPA) causes indoleacetic acid (IAA) accumulation in the root apical meristem, while simultaneously decreasing IAA in radical tissue required for lateral root growth.

Numerous mutants associated with auxin indicated an effect on lateral root development:


 * alf4, which blocks initiation of lateral root emergence.
 * alf3, which inhibits the development of plant organs shortly after later root emergence.

The results from these mutants indicate that IAA is required for lateral roots in various stages of development.

In addition, researchers found a close relationship between the position of the first division of lateral root formation and the root tip. A cycB1:1::uidA transgene marker was used as a reporter for lateral root initiation and its early mitotic events. This marker was histochemically stained for beta-glucuronidase (GUS) in Arabidopsis seedlings, which highlighted activity in the lateral root primordium and the transition zone between the hypocotyl and the root. Seedlings were harvested everyday for a week and stained for GUS activity, then measured the primary root length as well as the distance to the root tip, thee ratio between these two numbers being consistent. From this study, the following was concluded:


 * There is a defined distance from the initiation of the lateral root and leaf primordia to their apical meristems.
 * The tissues with zones of lateral root initiation are co-localized with the same root tissues that are involved in basipetal auxin transport.
 * Basipetal auxin transport is necessary for the localization of IAA to the zone of lateral root initiation.