Abstract
In dark-grown seedlings of tomato, we have found that phytochrome is responsible for apical-hook coiling (exaggerated hook curvature): 1) Hook coiling is induced by a red-light (R) pulse, being slightly reversed by a far-red-light (FR) pulse. 2) A single pulse of FR also induces hook coiling. 3) The coiling angle increases in continuous R as well as FR. 4) The phyA-deficient mutant shows hook coiling by R-pulse, being completely reversed by FR, but does not show hook coiling in response to FR in either pulse or continuous irradiations. 5) The phyB1-deficient mutant is less sensitive to R than wild type below 0.1 μmol m-2 s-1 of continuous irradiation. These results indicate that phyA mediates hook coiling via very low fluence response and FR-high-irradiation-response, and phyB1 partially regulates it via R-high-irradiation-response. Here, we also report the involvement of ethylene in the phytochrome-controlled hook coiling.
