Strategies of seedlings to overcome their sessile nature: auxin in mobility control.
Plants are sessile organisms that are permanently restricted to their site of germination. To compensate for their lack of mobility, plants evolved unique mechanisms enabling them to rapidly react to ever changing environmental conditions and flexibly adapt their postembryonic developmental program. A prominent demonstration of this developmental plasticity is their ability to bend organs in order to reach the position most optimal for growth and utilization of light, nutrients, and other resources. Shortly after germination, dicotyledonous seedlings form a bended structure, the so-called apical hook, to protect the delicate shoot meristem and cotyledons from damage when penetrating through the soil. Upon perception of a light stimulus, the apical hook rapidly opens and the photomorphogenic developmental program is activated. After germination, plant organs are able to align their growth with the light source and adopt the most favorable orientation through bending, in a process named phototropism. On the other hand, when roots and shoots are diverted from their upright orientation, they immediately detect a change in the gravity vector and bend to maintain a vertical growth direction. Noteworthy, despite the diversity of external stimuli perceived by different plant organs, all plant tropic movements share a common mechanistic basis: differential cell growth. In our review, we will discuss the molecular principles underlying various tropic responses with the focus on mechanisms mediating the perception of external signals, transduction cascades and downstream responses that regulate differential cell growth and consequently, organ bending. In particular, we highlight common and specific features of regulatory pathways in control of the bending of organs and a role for the plant hormone auxin as a key regulatory component.
Department of Plant Systems Biology, Flanders Institute for Biotechnology, Ghent Belgium ; Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent Belgium.
Petra
P
Žádníková
Department of Physiology, Laboratory of Functional Plant Biology, Ghent University, Ghent Belgium.
Dajo
D
Smet
Institute of Science and Technology Austria, Klosterneuburg Austria.
Qiang
Q
Zhu
Department of Physiology, Laboratory of Functional Plant Biology, Ghent University, Ghent Belgium.
Dominique
D
Van Der Straeten
Institute of Science and Technology Austria, Klosterneuburg Austria.
Eva
E
Benková
apical hook; auxin; differential growth; gravitropism; hormonal crosstalk; phototropism