References

126 M.L. Lanteri et al.
Fig.9.1. Schematic model showing nitric oxide (NO) participation in different processes
during root growth and morphogenesis. NO generated endogenously or applied exogenously
has been implicated in signaling pathways associated with root physiology and
development: (1) adventitious root formation from parenchyma cells at the root–shoot
junction (Pagnussat et al. 2002); (2) lateral root development from differentiated pericycle
cells (Correa-Aragunde et al. 2004); (3) root hair induction (Lombardo and Lamattina, unpublished
results); (4) root cell elongation, stimulation at low NO concentrations (Gouvea
et al. 1997) and inhibition at high ones (Correa-Aragunde et al. 2004); (5) cell division,
NO positively regulates cell cycle-promoting genes during lateral root primordia formation
(Correa-Aragunde et al., submitted); (6) gravitropic response (Hu et al. 2005)
from the activity of the microorganisms living in the rhizosphere, among
them the plant growth-promoting bacteria, must also be considered (Creus
et al. 2005).
In this context, it becomes evident that NO could be synthesized in
roots and that its synthesis depends on root environment and internal
conditions. Evidence suggests that auxin could be an important factor in
determining NO production in roots. Here we summarize the tight linkage
between auxins and NO signaling during root development, particularly
during lateral and adventitious root formation (ARF).