Phototropism of rice (Oryza sativa L.) coleoptiles: fluence-response relationships, kinetics and photogravitropic equilibrium

Abstract

Phototropism of rice (Oryza sativa L.) coleoptiles induced by unilateral blue light was characterized using red-light-grown seedlings. Phototropic fluence-response relationships, investigated mainly with submerged coleoptiles, revealed three response types previously identified in oat and maize coleoptiles: two pulse-induced positive phototropisms and a phototropism that depended on stimulation time. The effective ranges of fluences and fluence rates were comparable to those reported for maize. Compared with oats and maize, however, curvature responses in rice were much smaller and coleoptiles straightened faster after establishing the maximal curvature. When stimulated continuously, submerged coleoptiles developed curvature slowly over a period of 6 h, whereas air-grown coleoptiles, which showed smaller phototropic responsiveness, established a photogravitropic equilibrium from about 4 h of stimulation. The plot of the equilibrium angle against log fluence rates yielded a bell-shaped optimum curve that spanned over a relatively wide fluence-rate range; a maximal curvature of 25 degrees occurred at a fluence rate of 1 micromole m-2 s-1. This optimum curve apparently reflects the light sensitivity of the steady-state phototropic response.

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

“…However, cpt1 roots were found to show some small curvature. We also confirmed that cpt1 coleoptiles do not show any detectable phototropism even under submerged condition, which is known to enhance the phototropic responsiveness of coleoptiles (Neumann and Iino, 1997). For example, the wild-type coleoptiles submerged 6 h before the onset of blue light showed a mean curvature of 23.68 (SE ¼ 1.58, n ¼ 14) after 6-h blue light stimulation at 1 mmol m ÿ2 s ÿ1 , whereas the cpt1 coleoptiles treated in the same way showed a mean curvature of ÿ1.68 (SE ¼ 0.58, n ¼ 14).…”

“…In red light-grown rice coleoptiles, a steady phototropic curvature is established by 6 h of continuous stimulation with unilateral blue light (Neumann and Iino, 1997). The fluence rate-response curve obtained under this steady state condition indicated that cpt1 coleoptiles do not show any detectable curvature (Figure 1).…”

“…The coleoptile of rice appeared to be less phototropic as compared with those of oats and maize, but it could be resolved that the fluence-response characteristics of rice are similar to those of oats and maize (Neumann and Iino, 1997). Molecular genetic studies of phototropism with rice will provide results that, along with those from Arabidopsis, contribute to our overall understanding of higherplant phototropism.…”

Impaired Induction of the Jasmonate Pathway in the Rice Mutant hebiba

“…The response is swift and exclusively based on an inhibition of cell elongation concomitant with a block of basipetal auxin transport from the perceptive site in the coleoptile tip to the major site of cell elongation in the basal region (Furuya et al, 1969). The light signal is perceived almost exclusively through the phytochrome system (Pjon and Furuya, 1967;Takano et al, 2001), whereas bluelight receptors are of negligible importance in rice coleoptiles (Neumann and Iino, 1997). The only hormonal inducer of cell growth seems to be auxin; GAs and brassinosteroids are not effective in coleoptiles (Toyomasu et al, 1994;Sekimata et al, 2001).…”

Application of the equilibrium concept to the development of agaric fruit-bodies, with special reference to their straight downward growth in light from below

“…Finally, I will apply this model to various axial organs other than agaric fruit-bodies. For studying responses of axial organs to external stimuli, e.g., light and gravity, measurement of their growth direction or bending angle has often been employed, e.g., for basidiomycete fruit-bodies (Monzer et al, 1994;Kher et al, 1992), for Phycomyces sporangiophores (Galland and Russo, 1985;Ootaki et al, 1991) and for plant shoots (Neumann and lino, 1997;Kiss et al, 1997;Tarui and lino, 1997). In these past studies, the term 'equilibrium' was often used to mean vectoral balance among plural tropisms.…”