Cinétique de la rhizogenèse adaptative à la sécheresse. Relation avec I'évolution des paramètres hydriques et morphologiques chez le Sinapis alba, à deux niveaux d'énergie lumineuse

Kinetics of adaptive drought rhizogenesis, as related to growth and water deficits in Sinapis alba, at two irradiance levels .
The rhizogenic activity in Sinapis alba L., subjected to progressively increasing water deficit during growth, shows a sigmoidal pattern of kinetics with three phases: initiation or latent phase, rapid exponential increase, and stationary phase. This pattern remains unchanged if the level of irradiance during growth is reduced. The same number of short tuberized roots is obtained as under high irradiance, although initiation of rhizogenesis appears to be delayed by a few days. However, this delay is not observed if the rhizogenesis is analyzed as a function of the water potential of aerial organs or as a function of the soil water deficit. Since the rate of dehydration depends upon the evaporative demand, which is modulated by high or low irradiance, drought rhizogenesis seems to be directly related to water deficits in the soil-plant system. The onset of drought rhizogenesis, starting at the end of the growth period of the aerial organs, appears concomitant with the transpiration decline which is induced by water stress at both irradiance levels.