Salzwedel J L, Dazzo F B
Department of Microbiology, Michigan State University, East Lansing 48824.
Mol Plant Microbe Interact. 1993 Jan-Feb;6(1):127-34. doi: 10.1094/mpmi-6-127.
The activities of salt-elutable peroxidases from roots of white clover and pea were examined during the early interaction of these legume hosts with strains of Rhizobium leguminosarum in homologous and heterologous combination. Peroxidase-specific activity from clover root hairs began to increase 6 hr after inoculation with R. l. bv. viciae RL300 and was localized over the entire area of their deformations. In contrast, the onset of elicitation of peroxidase activity from root hairs was delayed after inoculation with R. l. bv. trifolii ANU843 and was localized only at the site of infection thread initiation. Three wild-type strains (R. l. bv. trifolii ANU843, R. l. bv. viciae RL300 and 1003) and one hybrid transconjugant strain of R. leguminosarum containing pSym from R. l. bv. viciae 248 (RBL5715) elicited increased specific activity of peroxidases eluted from pea and clover roots in heterologous combination. A comparison of peroxidase activity eluted from pea roots inoculated with ANU843 or its pSym-cured derivative indicated that pSym is required for elicitation of peroxidase on this heterologous host. The level of peroxidase activity elicited by nodE mutants (which have extended host range) is decreased on their new host. An extracellular fraction of RL300 contained flavonoid-dependent, heat-stable, and ethanol-soluble elicitor(s) of peroxidase activity. Treatment of clover seedlings with this cell-free fraction decreased the number of root hairs infected by ANU843. We propose that elicitation of root hair peroxidase may contribute to the infection process in this Rhizobium-legume symbiosis by altering root hair wall structure at sites of incipient penetration.
在白三叶草和豌豆根部的盐溶性过氧化物酶与豆科根瘤菌菌株在同源和异源组合中的早期相互作用过程中，对其活性进行了检测。用豌豆根瘤菌蚕豆生物型RL300接种三叶草根毛6小时后，过氧化物酶的比活性开始增加，并定位在根毛变形的整个区域。相比之下，用三叶草根瘤菌三叶生物型ANU843接种后，根毛过氧化物酶活性的激发延迟，且仅定位在感染丝起始部位。三株野生型菌株（三叶草根瘤菌三叶生物型ANU843、豌豆根瘤菌蚕豆生物型RL300和1003）以及一株含有豌豆根瘤菌蚕豆生物型248的共生质粒（pSym）的豆科根瘤菌杂交转导子菌株（RBL5715），在异源组合中可使从豌豆和三叶草根部洗脱的过氧化物酶比活性增加。对接种ANU843或其共生质粒缺失衍生物的豌豆根洗脱的过氧化物酶活性进行比较表明，在这种异源宿主上激发过氧化物酶需要共生质粒。结瘤因子E（nodE）突变体（具有扩展的宿主范围）在其新宿主上激发的过氧化物酶活性水平降低。RL300的细胞外部分含有过氧化物酶活性的类黄酮依赖性、热稳定且可溶于乙醇的激发子。用这种无细胞部分处理三叶草幼苗可减少被ANU843感染的根毛数量。我们认为，根毛过氧化物酶的激发可能通过改变初始穿透部位的根毛壁结构，促进这种根瘤菌 - 豆科植物共生关系中的感染过程。
