treatment, in addition to blue light irradiation, and stressful environment conditions, increase MIZ1 expression in plants. Arabidopsis plants are dependent on MZ1 for displaying hydrotropic behavior in response to water gradients. The originating environment of a plant dictates the degree of hydrotropic behavior that they display; in dry regions plants exhibit more hydrotropic activity, and in wet regions they display less. The importance of auxin transport for pea plant hydrotropism and gravitropism was proven in experiments that used a multitude of auxin inhibitors. It has been hypothesized that ABA modulated by hydrotropism has an effect on auxin. ABA helps dictate which side of the root grows at a faster rate, and thus which direction the root will grow. In gravitropism, the gradient between cytosolic and apoplastic calcium levels plays a large role in initiating a physiological response in other tropisms, and it is hypothesized that a similar process occurs in hydrotropism. Calcium, auxin and ABA are all proposed signals for the initiation of hydrotropic root growth behavior. Misconceptions The greater growth of roots in moist soil zones than in dry soil zones is not usually a result of hydrotropism. Hydrotropism requires a root to bend from a drier to a wetter soil zone. Roots require water to grow so roots that happen to be in moist soil will grow and branch much more than those in dry soil. Roots cannot sense water inside intact pipes via hydrotropism and break the pipes to obtain the water. Roots cannot sense water several feet away via hydrotropism and grow toward it. At best hydrotropism probably operates over distances of a couple millimeters″ References Further reading Tropism Auxin action