Gravitropism of maize and rice coleoptiles: dependence on the stimulation angle

Abstract

Gravitropism of maize and rice coleoptiles was investigated with respect to its dependence on the angle of displacement or the initial stimulation angle (ISA). Close examination of curvature kinetics and the response to a drop in stimulation angle (SA) indicated that the gravtropic response during an early but substantial part of the curvature development is directly related to the ISA, there being no effect of the reduction of SA resulting from the curvature response itself. On the basis of this finding, the relationship between the steady SA and the curvature rate was determined. In maize, the curvature rate increased linearly with the sines of SAs up to an SA of 90 degrees. Rice coleoptiles, however, showed a saturation curve in the same range of SAs. The saturation profile was nearly identical between coleoptiles grown in air and those submerged in water, although the latter elongated much faster. Rice coleoptiles appeared to be far more sensitive to gravity than maize coleoptiles. It is concluded that the sensitivity to gravity, assessed through dependence on ISA, is a property inherent to a given gravitropic organ. Long-term measurements of curvature indicated that the coleoptiles bend back past the vertical. This overshooting was marked in submerged rice coleoptiles.

The Rice COLEOPTILE PHOTOTROPISM1 Gene Encoding an Ortholog of Arabidopsis NPH3 Is Required for Phototropism of Coleoptiles and Lateral Translocation of Auxin

“…Gravitropic response of coleoptiles to 308 displacement was further compared between the two genotypes under a submerged condition ( Figure 2C). As reported in Iino et al (1996), wild-type coleoptiles showed a gravitropic curvature to the extent that the tip substantially overshoots the vertical position. Mutant coleoptiles showed a very similar time course.…”

“…Rice seedlings were prepared essentially as described in Iino et al (1996). In brief, surface-sterilized caryopses were sown on 0.7% agar in 4.5-mL acrylic cuvettes (Elkay; Kendall Healthcare, Mansfield, MA).…”

Circumnutation of rice coleoptiles: its relationships with gravitropism and absence in lazy mutants

“…We have not investigated how submergence potentiates circumnutation. This effect of submergence may be related to the stimulation of elongation growth of rice coleoptiles (Iino et al 1996). Small nutational movements occurred gradually in red-light-treated and submerged coleoptiles without gravitropic stimulation, indicating that these coleoptiles can resume circumnutation spontaneously.…”

“…When the movement in clinorotated seedlings was analysed, shoot images were recorded with a CCD camera and a time-lapse video (Iino, Tarui & Uematsu 1996); the infrared-absorbing filter of the CCD camera was removed to allow recording of infrared views. The camera's viewing axis was set perpendicular to the rotation axis of the clinostat.…”

Beyond the sine law of plant gravitropism

“…Accordingly, the gravitropic response should be proportional to the sine of the angle between the organ axis and the vertical; thus, a stem placed horizontally would show the strongest response, which would then gradually decline as the stem approaches the vertical. Since its formulation, Sachs' sine law has been validated repeatedly, sometimes with minor modifications (5,6). It was also noted that the sedimentation of statoliths within gravisensing cells would lead to some form of sinusoidal dependence on angle (7,8).…”