The plant growth promoting rhizobacterium Azospirillum brasilense Sp245 enhances biomass production in cereals and horticultural species and is an interesting model to study the physiology of the phytostimulation program. Although auxin production by Azospirillum appears to be critical for root architectural readjustments, the role of cytokinins in the growth promoting effects of Azospirillum remains unclear. Here, Arabidopsis thaliana seedlings were co-cultivated in vitro with A. brasilense Sp245 to assess whether direct contact of roots with bacterial colonies or exposure to the bacterial volatiles using divided Petri plates would affect biomass production and root organogenesis. Both interaction types increased root and shoot fresh weight but had contrasting effects on primary root length, lateral root formation and root hair development. Cell proliferation in root meristems analyzed with the CYCB1;1::GUS reporter decreased over time with direct contact, but was augmented by plant exposure to volatiles. Noteworthy, the expression of the cytokinin-inducible reporters TCS::GFP and ARR5::GUS increased in root tips in response to bacterial contact, without being affected by the volatiles. In A. thaliana having single (cre1-12, ahk2-2, ahk3-3), double (cre1-12/ahk2-2, cre1-12/ahk3-3, ahk2-2/ahk3-3) or triple (cre1-12/ahk2-2/ahk3-3) mutations in canonical cytokinin receptors, only the triple mutant had a marked effect on plant growth in response to A. brasilense. These results show that different mechanisms are elicited by A. brasilense, which influence the cytokinin-signaling pathway.

促进植物生长的根际细菌Azospirillum brasilense Sp245 可提高谷物和园艺物种的生物量生产，是研究植物刺激计划生理学的有趣模型。尽管固氮螺菌产生的生长素似乎对根系结构的调整至关重要，但细胞分裂素在固氮螺菌的生长促进作用中的作用仍不清楚。在这里，拟南芥幼苗与A. brasilense在体外共培养Sp245 用于评估根与细菌菌落的直接接触或使用分开的 Petri 板暴露于细菌挥发物是否会影响生物量产生和根器官发生。两种相互作用类型都增加了根和枝条的鲜重，但对初生根长度、侧根形成和根毛发育有不同的影响。用CYCB1;1::GUS报告基因分析的根分生组织中的细胞增殖随着时间的推移随着直接接触而减少，但植物暴露于挥发物会增强。值得注意的是，细胞分裂素诱导型报告基因 TCS::GFP和ARR5::GUS的表达在根尖响应细菌接触而增加，而不受挥发物的影响。在拟南芥中具有单一 (cre1-12 , ahk2-2 , ahk3-3) , 双 ( cre1-12/ahk2-2 , cre1-12/ahk3-3 , ahk2-2/ahk3-3 ) 或三 ( cre1-12/ahk2-2/ ahk3-3 ) 经典细胞分裂素受体的突变，只有三重突变体对响应A. brasilense的植物生长有显着影响。这些结果表明A. brasilense引发了不同的机制，这些机制影响了细胞分裂素信号通路。