Gravitropism of roots: an evaluation of progress during the last three decades.

The response of plant roots to gravity has fascinated many botanists since the early days of plant physiology and much research has been devoted to the elucidation of the sequence of events between the physical reception of gravity and the visible growth response. In the last few decades the ideas on the graviresponse of roots have changed profoundly and much progress has been made in understanding parts of the process. One of the reasons for writing this review was my curiosity to know what has happened since the time I myself was involved in the study of root geotropism, as it was called, about 30 years ago. Some excellent reviews have appeared since then, e.g. Audus (1975), Jackson & Barlow (1981) and Moore & Evans (1986), which were more restricted in scope and, moreover, there have been several fascinating developments. The aim of this review is to discuss briefly all aspects of the graviresponse of roots and the progress made in understanding during the last three decades. Some data on other plant organs are included where appropriate.