粪产碱菌与水稻根的联合过程

ATTACHMENT OF ASSOCIATIVE DIAZOTROPH Alcaligenes faecalis TO RICE ROOTS

应用^(15)N同位素标记菌体和Tn5转座子诱变的突变株研究固氮粪产碱菌对宿主水稻的联合进程,结果表明,粘附作用是结合过程的第一步,接种3h后粘附在根表的菌体数量达最大值,约占接种量的3.7％。粘附的菌体易脱离根表,表明粘附作用是细菌与宿主植物间的弱的相互作用。在根表定位是结合过程的第二步。接种15h后,定位菌体数量达最大值,约占接种量的21％。经振荡处理不能使定位菌体脱离根表。定殖是结合过程的第三步,接种20h后定殖菌体紧密结合于根表,剧烈振荡亦不易使其脱离根表。定殖后菌体开始出现果胶酶活性。采用趋化(Che)和胞外多糖(Exo)突变株研究表明,趋化性和胞外多糖的合成是影响细菌在根表结合的重要因素。粪产碱菌在水稻根表没有专一的粘附部位,但粪产碱菌的定位和定殖主要发生在主根根表,尤其是主、侧根交接处。

The process of attachment of diazotroph Alcaligenes faecalis to host plant rice was studied by using 15N-labelled bacteria and Tn5-induced mutants.A three-step attachment mechanism of A.faecalis to rice root surface is proposed by us on the basis of experimental data.Adsorption is the first step of attachment.The number of adsorbed bacteria reaches maximal level after 3 h of inoculation,it consists 3.7% of the total number of bacteria inoculated.Adsorbed bacteria could be removed from rice root surface quantitatively by shaking in water.Therefore,the adsorption forces are weak.Anchoring is the second step.It begins only after 9h of inoculation and reaches a maximal level (21%) after 16 h.Anchored bacteria could not be removed by shaking.Colonization is the third step.After 20h of inoculation,part of anchored bacteria colonizes on rice root surface tightly,and it can not be removed by vortex.At this time,the pectolytic activity of bacteria appears.Chemotaxis and exopolysac-charide(EPS) play important roles in the attachment of A.faecalis to rice root surface.EPS mutants (Exo-,Exo++) showed less anchoring-capability in comparison with wild type of bacterium,but they rimained the adsorption capability.While chemotaxis (Che-)mutants are defective in adsorption,but not in anchoring.Che-,Exo-mutant lost both adsorption and anchoring capabilities.A.faecalis absorbed on all part of rice root such as main roots,lateral roots,root caps etc,but the anchoring and colonization of bacteria were occured mainly on root hairs,particularly on the joint area of main root and lateral root.