Mechanisms of regulation of arbuscular mycorrhizal colonisation with root exudates

缺磷洋葱根系分泌物促进丛枝菌根真菌的生长。其促进机制尚不清楚。通过大量收集缺磷洋葱根分泌物，研究了用色谱法纯化的部分对菌丝生长的影响。洋葱（Allium cepa）在3种P浓度（0.0 （P0）、0.1 （P0.1）和8.0 (P8)）的溶液培养中生长，收集根分泌物。根渗出液用Amberlite XAD-4树脂分离成亲疏水两部分，并用硅胶- tlc（己烷：乙酸乙酯8:1）、ODS-TLC（90%甲醇）和Sephadex LH-20柱层析纯化。AM真菌Gigaspora margarita孢子在这些馏分和去离子水（对照）中培养10天。测定菌丝长度和菌丝分枝。P0和P0.1处理的菌丝长度和分枝均大于对照和P8处理。通过ODS-TLC得到B1部分（Rf0.21），菌丝长度和分枝增加。B1中75%以上的菌丝分支为二级分支。说明缺磷根系分泌物中含有促进菌丝伸长和分枝的物质，这些物质增加了共生体与寄主接触的机会。

Root exudates of phosphorus (P) deficient onion promote the growth of arbuscular mycorrhizal (AM) fungi. Mechanisms of promotion is still unknown. Effect of purified fractions with chromatography on hyphal growth was investigated by mass collection of P deficient onion root exudates. Onion (Allium cepa cv. Senshuchukoki) was grown in solution culture of three P concentrations (0.0 (P0), 0.1 (P0.1) and 8.0 (P8)) and root exudates were collected. Root exudates were fractionated to hydrophilic and hydrophobic fractions with Amberlite XAD-4 resin and further purified by silicagel-TLC (Hexane:Ethylacetate 8:1) , ODS-TLC (90% Methanol) and Sephadex LH-20 column chromatography. Spores of AM fungi Gigaspora margarita were incubated in these fractions and deionized water (control) for 10 days. Hyphal length and hyphal branch were measured. Hyphal length and branch were larger in P0 and P0.1 treatments than that in control and P8 treatments. B1 fraction (Rf0.21) was obtained by ODS-TLC and increased hyphal length and branch. More than 75% of hyphal branch in B1 consisted of secondary order branch. It is suggested that P deficient root exudates contain the substances which promote hyphal elongation and branch and these substances increase opportunity of contact between symbiont and host.