Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone. This zone has a unique role as the determiner of cell fate and root growth; this is accomplished by means of the complex system of a polar auxin transport circuits. The transition zone integrates diverse inputs from endogenous (hormonal) and exogenous (sensorial) stimuli and translates them into signalling and motoric outputs as adaptive differential growth responses. These underlie the root-apex tropisms and other aspects of adaptive root behaviour. Moreover, this zone is also extremely sensitive to aluminium toxicity and acts as nitrate sensing zone. Finally, also brassinosteroids, cytokinins, strigolactones, and gibberellic acids signalling cascades are unique in this zone.
Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone. This zone has a unique role as the determiner of cell fate and root growth; this is accomplished by means of the complex system of a polar auxin transport circuits. The transition zone integrates diverse inputs from endogenous (hormonal) and exogenous (sensorial) stimuli and translates them into signalling and motoric outputs as adaptive differential growth responses. These underlie the root-apex tropisms and other aspects of adaptive root behaviour. Moreover, this zone is also extremely sensitive to aluminium toxicity and acts as nitrate sensing zone. Finally, also brassinosteroids, cytokinins, strigolactones, and gibberellic acids signalling cascades are unique in this zone.