89.ダイコン下胚軸の光屈性におけるイソチオシアネートの役割(口頭発表)

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Blue light induces many adaptive responses in plants, including the inhibition of shoot growth and phototropism. In radish hypocotyls, raphanusanins and their precursor, 4-MTBI, were isolated and identified as candidate inhibitors involved in this phenomenon. Previously, we found in the early stage of the phototropic response that unilateral illumination with blue light promotes myrosinase activity on the illuminated side of radish hypocotyls, releasing bio-active 4-MTBI from bio-inactive glucosinolate (4-MTBG), and simultaneously producing bio-active raphanusanins. We found that phototropic stimulation induces H_2_O_2 accumulation via the up-regulation of 4-MTBI and probably of raphanusanins. We also found that these compounds contribute to their growth inhibitory activity by promoting H_2O_2 synthesis and subsequent lignification, which could increase the stiffness at the primary cell-wall level. These results suggest a close association between an oxidative burst and phototropic curvature. Furthermore, the unilateral application of these compounds suppressed the growth of the hypocotyl on the treated side, inducing a differential growth gradient, and causing the hypocotyl to bend towards the side of application. Thus, it is concluded that phototropism is triggered by a local gradient, induced at the site of illumination, of blue light-induced growth inhibitors interfering with the action of the evenly distributed auxin.
2010-10-01