Abstract
It is well known that apical hook openings occur upon exposure to light in dicotyledonous seedlings. We confirmed these phenomena in Arabidopsis, cabbage etc. However, under the same experimental conditions, we found that tomato, cucumber, carrot, etc. exhibited enhanced hook curvature upon exposure to red light (R) and far-red light (FR) through phytochrome-mediated low-fluence-response (LFR) and very-low-fluence-response (VLFR), respectively. In tomato seedlings, the phyA-deficient mutant lacked FR-induced hook curvature of VLFR. Although phyA- or phyB1-deficient mutant was sensitive to R pulse irradiation of LFR, they partially lost sensitivity to continuous irradiation of R. PhyA and phyB may regulate hook curvature via R-high-irradiance-response.
The hook curvature is a growth response of the apical part of the hypocotyl. Time-dependent analyses of hook structure during curvature will be reported in LFR, VLFR, or HIR, and the process of growth will be discussed in relation to phytohormones.
