9416015 Evans There is a specialized zone of cells with a prominent role in the tropistic responses of maize roots. This zone the "postmitotic isodiametric growth" (PIG) zone is located between the meristem and the elongation zone (EZ). Gravistimulation induces rapid membrane potential changes in this zone and, unlike the EZ, auxin stimulates elongation in these cells. Prior work has shown that gravity-induced asymmetric enhancement of elongation in the PIG zone is not mediated by auxin. This project proposes to determine whether a comparable PIG zone exists in Arabidopsis and to test whether it plays a role in root gravitropism and thigmotropism in Arabidopsis. The work will 1) use a new growth analysis system for localized growth rate analyses, 2) combine a curvature analysis system with feedback control of localized tissue orientation in order to investigate the limits of the zone of gravity sensing, and 3) investigate the role of electrical signaling in the coordination of root gravitropic and thigmotropic responses. This work may provide new detailed information on the nature of plant sensing of environmental signals and the manner in which this sensing leads to a coordinated growth response. ***
