THE GRAVITROPIC RESPONSE OF ROOTS AND THE SHAPING OF THE ROOT-SYSTEM IN CEREAL PLANTS

The spatial distribution of seminal and nodal roots in cereals varies according to species and genotype. This is due to the plagiogravitropic growth of the axes. The plagiogravitropic response of a nodal root depends on its diameter and the position of the internode from which it emerges. The response also changes in the course of root growth and the stage of shoot development. The growth angle of the axes is, therefore, programmed and controlled by genetic, physiological and environmental factors. With respect to the latter, the seminal roots of wheat are sensitive to the water environment which may modify the growth angle as a result of the effect of hormonal regulators such as abscisic acid (ABA). Concerning the gravitropic response of nodal roots in rice, physiological controls may operate through assimilates coming from the shoot. It is concluded that the gravitropic response of axes, which determines the shape of the root system, is primarily controlled by genetic factors but is also influenced by environmental conditions.