Phytochrome is required for the occurrence of time-dependent phototropism in maize coleoptiles
Time-dependent phototropism (TDP), sometimes called second positive curvature, occurs when the duration of phototropic stimulation with blue light (B) exceeds a few minutes. TDP was characterized in maize (Zea mays L.) coleoptiles raised under continuous red light (R). Subsequently, coleoptiles adapted to darkness were used to investigate the effect of R on TDP. It was found that TDP, which is induced in R-grown coleoptiles, does not occur in dark-adapted coleoptiles and that dark-adapted coleoptiles begin to show TDP after treatment with R. The TDP responsiveness became maximal 1-2 h after treatment with a R pulse and decreased during the next few hours. At least 10 min was required after a short pulse of R before the coleoptile began to respond to B for the induction of TDP. The effect of R in establishing the TDP responsiveness was totally suppressed by a pulse of far-red light given immediately after an inductive pulse of R. It is concluded that the mechanism of TDP requires for its establishment a R signal perceived by phytochrome. The TDP of R-grown and R-pretreated coleoptiles showed relationships to stimulation times and fluence rates that are similar to those reported for oat coleoptiles, except that TDP of maize showed a sharp increase in its magnitude within a narrow range of stimulation times as short as 5-10 min.
Liu
Y J
YJ
Botanical Gardens, Osaka City University, Japan.
Iino
M
M
D018548:Cotyledon / Q000254:growth & development / Q000528:radiation effects*; D003624:Darkness; D007259:Infrared Rays; D008027:Light; D018524:Phototropism / Q000528:radiation effects*; D010834:Phytochrome / Q000528:radiation effects*; D012399:Rotation; D013997:Time Factors; D003313:Zea mays / Q000254:growth & development / Q000528:radiation effects*
D010834:Phytochrome