Yamada Kosumi, Hasegawa Tsuyoshi, Minami Eiichi, Shibuya Naoto, Kosemura Seiji, Yamamura Shosuke, Hasegawa Koji
Institute of Applied Biochemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
J Plant Physiol. 2003 Mar;160(3):255-9. doi: 10.1078/0176-1617-00950.
The role of myrosinase (beta-thioglucoside glucohydrolase, EC 3.2.3.1) in the phototropic response in radish hypocotyls was investigated. Unilateral illumination with blue light abruptly up-regulated the activity of myrosinase, which releases bioactive 4-methylthio-3-butenyl isothiocyanate (MTBI) from inactive 4-methylthio-3-butenyl glucosinolate (MTBG), in the illuminated halves of radish hypocotyls 10 min after onset of phototropic stimulation, peaking after 30 min and decreasing thereafter. The myrosinase activity in the shaded halves also increased, but was significantly lower than that in the illuminated halves. Furthermore, whether blue light illumination induces myrosinase gene expression was studied. Northern blotting analysis indicated that myrosinase mRNA levels were increased markedly in unilaterally illuminated hypocotyls, reaching maximum signal intensity within 10 min after onset of blue illumination, declining nearly to the control level thereafter. These results suggested that phototropic stimulation promotes myrosinase gene expression and myrosinase activity in the illuminated side, resulting in the conversion of inactive MTBG to active MTBI and simultaneously producing more active raphanusanins, causing a phototropic response.
研究了黑芥子酶（β-硫代葡萄糖苷葡萄糖水解酶，EC 3.2.3.1）在萝卜下胚轴向光性反应中的作用。用蓝光单侧照射后，萝卜下胚轴受光一侧的黑芥子酶活性在向光性刺激开始10分钟后突然上调，该酶可将无活性的4-甲硫基-3-丁烯基硫代葡萄糖苷（MTBG）转化为具有生物活性的4-甲硫基-3-丁烯基异硫氰酸酯（MTBI），30分钟后达到峰值，随后下降。遮光一侧的黑芥子酶活性也有所增加，但明显低于受光一侧。此外，还研究了蓝光照射是否诱导黑芥子酶基因表达。Northern印迹分析表明，单侧光照的下胚轴中黑芥子酶mRNA水平显著增加，在蓝光照射开始后10分钟内达到最大信号强度，随后几乎降至对照水平。这些结果表明，向光性刺激促进了受光一侧黑芥子酶基因的表达和黑芥子酶的活性，导致无活性的MTBG转化为活性MTBI，并同时产生更多具有活性的萝卜硫素，从而引起向光性反应。
