Measurements of the Geoelectric Effect in Coleoptiles

Geotropic Response of Coleoptiles under Anaerobic Conditions1

“…In non-decapitated coleoptiles the geoelectric effect develops rapidly, reaching a maximum value after approximately 30 minutes (2,Woodcock and Wilkins,unpublished). Geotropic curvature, on the other hand, develops much more slowly, especially in coleoptiles grown in red light (7,10), as were those used by Grahm and Hertz (4,5). The difference between the rates of development of the geoelectric effect and the geotropic response could well be accentuated in decapitated coleoptiles which had developed a physiological tip.…”

“…The lack of geoelectric effect under anaerobic conditions has also been found by Grahm and Hertz (4) Bearing in mind the consistency between the results in this paper and those of Ball and Dyke (1), Harrison (6) and Wilkins and Warren (9), the fact that we cannot detect a geotropic response in coleoptiles under anaerobic conditions makes it impossible for us to accept the views of Dedolph et al (2) on the lack of a direct relationship between the geoelectric and geotropic responses. There is a large amount of evidence which shows that both phenomena occur as the result of a lateral gradient in auxin concentratioln being set up in the organs (3,4,5,8,11). The finding of Grahm and Hertz (5) that the geoelectric effect develops in Zea coleoptiles after a single decapitation is not evidence for the occurrence of the geoelectric effect in the absence of auxin.…”

Aspects on gravity-induced movements in plants

“…In physiological sensory systems the absolute limits are theoretically set by the Brownian movement (see for example, discussion about the hearing mechanism (Harris, 1968)). This aspect on the threshold stimulation and the statolith theory has been discussed by Hertz (1964, as cited by Haupt, 1965 and Johnsson (1965). An outline of the argumentation can be given as follows.…”

“…The electric voltage shows a logarithmic stimulus-response dependence (Grahm & Hertz, 1964). An extrapolated presentation time of the order of 3 min can be found, in rather good accordance with the curvature measurements.…”

Early Events in Geotropism of Seedling Shoots

“…Is it insignificant that during the period identified by Grahm & Hertz (22, 23) as a lag, small transient "wrong-way" voltage gradients were sometimes observed (21)(22)(23)38)? Seedlings of oat or com would be particularly suitable for such studies, in that pretreatments controlling the manner of initiating curvature have been most numerous for the coleoptile.…”