Xiong Jie, Lu Han, Lu Kaixing, Duan Yuxing, An Lingyao, Zhu Cheng
State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, People's Republic of China.
Planta. 2009 Sep;230(4):599-610. doi: 10.1007/s00425-009-0970-y. Epub 2009 Jun 26.
Cadmium (Cd) is toxic to crown roots (CR), which are essential for maintaining normal growth and development in rice seedlings. Nitric oxide (NO) is an important signaling molecule that plays a pivotal role in plant root organogenesis. Here, the effects of Cd on endogenous NO content and root growth conditions were studied in rice seedlings. Results showed that similar to the NO scavenger, cPTIO, Cd significantly decreased endogenous NO content and CR number in rice seedlings, and these decreases were recoverable with the application of sodium nitroprusside (SNP, a NO donor). Microscopic analysis of root collars revealed that treatment with Cd and cPTIO inhibited CR primordia initiation. In contrast, although SNP partially recovered Cd-caused inhibition of CR elongation, treatment with cPTIO had no effect on CR elongation. L: -NMMA, a widely used nitric oxide synthase (NOS) inhibitor, decreased endogenous NO content and CR number significantly, while tungstate, a nitrate reductase (NR) inhibitor, had no effect on endogenous NO content and CR number. Moreover, enzyme activity assays indicated that treatment with SNP inhibited NOS activity significantly, but had no effect on NR activity. All these results support the conclusions that a critical endogenous NO concentration is indispensable for rice CR primordia initiation rather than elongation, NOS is the main source for endogenous NO generation, and Cd decreases CR number by inhibiting NOS activity and thus decreasing endogenous NO content in rice seedlings.
镉（Cd）对水稻幼苗的冠根（CR）具有毒性，而冠根对于维持水稻幼苗的正常生长发育至关重要。一氧化氮（NO）是一种重要的信号分子，在植物根系器官发生过程中起着关键作用。在此，研究了镉对水稻幼苗内源性NO含量和根系生长状况的影响。结果表明，与NO清除剂cPTIO类似，镉显著降低了水稻幼苗内源性NO含量和冠根数量，而施用硝普钠（SNP，一种NO供体）可使这些降低得以恢复。对根颈的显微镜分析显示，镉和cPTIO处理抑制了冠根原基的起始。相反，尽管SNP部分恢复了镉对冠根伸长的抑制作用，但cPTIO处理对冠根伸长没有影响。L-NMMA是一种广泛使用的一氧化氮合酶（NOS）抑制剂，显著降低了内源性NO含量和冠根数量，而硝酸盐还原酶（NR）抑制剂钨酸盐对内源性NO含量和冠根数量没有影响。此外，酶活性测定表明，SNP处理显著抑制了NOS活性，但对NR活性没有影响。所有这些结果支持以下结论：临界内源性NO浓度对于水稻冠根原基的起始而非伸长是不可或缺的，NOS是内源性NO产生 的主要来源，镉通过抑制NOS活性从而降低水稻幼苗内源性NO含量来减少冠根数量。
