Ammonium excretion, auxin production and effects of maize inoculation with ethylenediamine-resistant mutants of Pseudomonas sp.

ABSTRACT Plant growth-promoting bacteria (PGPB) comprise part of plant microbiome of biotechnological interest due to their potential to decrease the use of agrochemicals in agriculture. Among the commonly found PGPB species, the Pseudomonas genus is known for high competitiveness and efficiency in expressing growth-promotion traits. To increase the contribution of diazotrophic Pseudomonas sp. to the plant nitrogen nutrition, the strain AZM-01 was chemically mutagenized with methyl methanesulfonate (MMS), following the selection for resistance to ethylenediamine (EDA). From the 13 EDA-resistant mutant strains selected, four showed increased the ammonium excretion, with the highest value reaching up to 284% increase as compared to the wild strain, and six strains were found to produce significantly more auxins than the wild strain. Two independent inoculation trials with the wild and EDA-resistant Pseudomonas were performed on maize, with the objective to study the influence of bacteria on seed germination and its potential to promote maize growth under N-limiting condition. In general, Pseudomonas inoculation modified the root architecture of germinating seeds, and increased biomass of maize plants grown under N-limiting conditions. Shoot dry weight of maize was increased by inoculation with several EDA-resistant mutants as compared to the strain AZM-01, with emphasis on the EDA-5 strain which supports biomass accumulation at equivalent amount of plants grown under full N supply. Significant correlations between in vitro and in vivo parameters were found although low coefficient values predominate. The strategy of random mutagenesis was found suitable to develop PGPB strains with higher potential to supply maize plants with nitrogen.

摘要：植物促生细菌（Plant Growth-Promoting Bacteria，PGPB）是植物微生物组的组成部分，因其具备降低农业生产中农用化学品使用量的潜力而具有重要的生物技术研究价值。在常见的PGPB物种中，假单胞菌属（Pseudomonas）以极强的竞争力和高效表达促生性状的能力而广受认可。为提升固氮假单胞菌属菌株对植物氮营养的贡献，研究人员以抗乙二胺（Ethylenediamine，EDA）为筛选标记，采用甲磺酸甲酯（Methyl Methanesulfonate，MMS）对菌株AZM-01进行了化学诱变。从筛选获得的13株EDA抗性突变菌株中，有4株的铵盐分泌能力显著提升，最高较野生菌株提升达284%；另有6株产生的生长素含量显著高于野生菌株。研究人员以野生型及EDA抗性假单胞菌为材料，开展了两组独立的玉米接种试验，旨在探究该类细菌对种子萌发的影响，以及其在氮限制条件下促进玉米生长的潜力。总体而言，假单胞菌接种可改变萌发种子的根系构型，并提升氮限制条件下玉米植株的生物量。相较于原始菌株AZM-01，多株EDA抗性突变菌株的接种可提升玉米地上部干重，其中EDA-5菌株表现尤为突出，其介导的生物量积累量与全氮供给条件下生长的玉米植株相当。尽管多数相关系数值较低，但研究仍发现体外与体内参数间存在显著相关性。结果表明，随机诱变策略可用于培育具备更高玉米供氮潜力的植物促生细菌菌株。