Rapeseed plant: biostimulation effects of plant growth-promoting Actinobacteria on metabolites and antioxidant defense system under elevated CO₂ conditions

Background: The present study set out to evaluate the potential of plant growth-promoting Actinobacteria (PGPB) in improving some physiological and molecular parameters of rapeseed (Brassica napus L.) plants under ambient and elevated CO₂ conditions by assessing some nitrogen- and sulfur-containing metabolites, antioxidant defense system and antimicrobial activity. With this aim, a pot experiment was conducted where the rapeseed plants were treated with Actinobacterium sp. strain NCO2 (OQ451136) and were grown under two levels of air CO₂ concentrations: ambient CO₂ (aCO₂ , 410 μmol CO₂ mol^-1 ); and elevated CO₂ (eCO₂ , 710 μmol CO₂ mol^-1 ).

Results: There was an increase in the photosynthetic pigments (+35-80%) and photosynthesis rate (+20-34%) in PGPB-treated plants under eCO₂ compared to control plants, resulting in further growth and biomass production (+53-294%). These results were associated with an enhancement in the content of total antioxidant capacity (+15-128%), polyphenols (+21-126%) and α-tocopherols (+20-138%) under both eCO₂ and PGPB application (in combination or individual application), while only the combined treatment (eCO₂ + PGPB) led to a significantly higher accumulation of antioxidant enzymes (+88-197%), β-tocopherols (+177%) and flavonoids (+155%). Moreover, nitrogen- and sulfur-containing metabolites (glucosinolates and amino acids) were improved by PGPB treatment and/or CO₂ levels, in which PGPB increased the amino acid-derived glucosinolate induction by eCO₂ with low levels of effective sulforaphane.

Conclusions: Therefore, the interaction effects of beneficial Actinobacteria and eCO₂ are expected to boost the level of antioxidant molecules and to have a helpful role in improving plant biomass and adaptability to complicated climate changes in the future. © 2023 Society of Chemical Industry.