Liszkay Anja, van der Zalm Esther, Schopfer Peter
Institut für Biologie II der Universität, D-79104 Freiburg, Germany.
Plant Physiol. 2004 Oct;136(2):3114-23; discussion 3001. doi: 10.1104/pp.104.044784. Epub 2004 Oct 1.
Cell extension in the growing zone of plant roots typically takes place with a maximum local growth rate of 50% length increase per hour. The biochemical mechanism of this dramatic growth process is still poorly understood. Here we test the hypothesis that the wall-loosening reaction controlling root elongation is effected by the production of reactive oxygen intermediates, initiated by a NAD(P)H oxidase-catalyzed formation of superoxide radicals (O(2)(.-)) at the plasma membrane and culminating in the generation of polysaccharide-cleaving hydroxyl radicals ((.)OH) by cell wall peroxidase. The following results were obtained using primary roots of maize (Zea mays) seedlings as experimental material. (1) Production of O(2)(.-), H(2)O(2), and (.)OH can be demonstrated in the growing zone using specific histochemical assays and electron paramagnetic resonance spectroscopy. (2) Auxin-induced inhibition of growth is accompanied by a reduction of O(2)(.-) production. (3) Experimental generation of (.)OH in the cell walls with the Fenton reaction causes wall loosening (cell wall creep), specifically in the growing zone. Alternatively, wall loosening can be induced by (.)OH produced by endogenous cell wall peroxidase in the presence of NADH and H(2)O(2). (4) Inhibition of endogenous (.)OH formation by O(2)(.-) or (.)OH scavengers, or inhibitors of NAD(P)H oxidase or peroxidase activity, suppress elongation growth. These results show that juvenile root cells transiently express the ability to generate (.)OH, and to respond to (.)OH by wall loosening, in passing through the growing zone. Moreover, inhibitor studies indicate that (.)OH formation is essential for normal root growth.
植物根生长区的细胞伸长通常以每小时最大局部生长速率为长度增加50%的速度进行。这一显著生长过程的生化机制仍知之甚少。在此，我们检验了这样一个假说：控制根伸长的细胞壁松弛反应是由活性氧中间体的产生所介导的，该过程由质膜上NAD(P)H氧化酶催化超氧阴离子自由基（O₂⁻）的形成引发，并最终由细胞壁过氧化物酶生成多糖裂解性羟基自由基（·OH）。使用玉米（Zea mays）幼苗的初生根作为实验材料，得到了以下结果。（1）利用特定的组织化学分析和电子顺磁共振光谱法，可以在生长区检测到O₂⁻、H₂O₂和·OH的产生。（2）生长素诱导的生长抑制伴随着O₂⁻产生的减少。（3）通过芬顿反应在细胞壁中实验性地生成·OH会导致细胞壁松弛（细胞壁蠕变），特别是在生长区。另外，在NADH和H₂O₂存在的情况下，内源性细胞壁过氧化物酶产生的·OH也可诱导细胞壁松弛。（4）用O₂⁻或·OH清除剂、NAD(P)H氧化酶或过氧化物酶活性抑制剂抑制内源性·OH的形成会抑制伸长生长。这些结果表明，幼根细胞在穿过生长区时会短暂地表现出产生·OH以及通过细胞壁松弛对·OH作出反应的能力。此外，抑制剂研究表明，·OH的形成对于正常根生长至关重要。
