Root Growth Under Water Deficits: Model Systems to the Field.

The growth of roots determines root system architecture and exploration of the soil profile, and is a critical component of plant adaptation to water-limiting conditions. However, the physiology of root growth responses to water deficits remains poorly understood, and moreover, much of what is known comes from studies using model systems in controlled environments, whereas little attention has been given to the regulation of root growth under drought conditions in the field. This presentation will focus on one important aspect of root adaptation to water deficits: how root growth is maintained in drying soil. This ability is characteristic of the primary root, in which it is important for seedling establishment, and also of the nodal roots of grasses such as maize. Nodal roots, which are produced from the stem nodes, form the framework of the mature root system and, under drought conditions, have to grow through dry surface soil to reach available water. Examples of mechanisms underlying primary and nodal root growth responses to water deficits will be highlighted, using both model system approaches and extending to drought conditions in the field. This knowledge base provides a foundation for the long-term goal of developing targeted approaches to improve crop productivity and food security under water-limiting conditions.