Preparation of a synthetic seed for the common reed harboring an endophytic bacterium promoting seedling growth under cadmium stress.

Bacterial seed endophytes can facilitate germination and early plant development. Therefore, the introduction of seed-borne endophytes may improve selected plant characteristics across generations. In this study, regenerated plantlets of common reed (Phragmites australis) were inoculated with activated sludge to obtain a specific functional endophytic bacterium. Denaturing gradient gel electrophoresis demonstrated that abundant endophytic bacteria could be enriched in the roots. A siderophore-producing endophytic bacterium was isolated from the roots and identified as Herbaspirillum frisingense RE3-3 based on 16S rRNA sequences. This endophyte secrets indole-3-acetic acid to promote plant growth and cadmium-binding siderophores. The strain was successfully colonized into synthetic seeds using bacterium-propagule co-cultivation and transmitted to regenerated seedlings. These seedlings exhibited improved growth under cadmium stress. This study identifies Herbaspirillum colonization and transmission as a potentially valuable strategy to improve the phytotoxin resistance of reeds for constructed wetlands.