Exhausted plant cell culture media as potential biostimulants to enhance plant growth and nitrogen use efficiency in tomatoes under optimal and reduced nitrogen supply

Background: Inefficient nitrogen (N) use leads to economic losses and environmental harm. Improving N use efficiency (NUE) is crucial. The use of plant biostimulants (PBs), integrated with good agronomic practices, offers a sustainable solution. Aims: The study explores the potential use of exhausted cell culture media from plant cell cultures (Nicotiana sp. and Gardenia sp.) as PBs, assessing their role in enhancing plant physiological status and NUE. It also compares their effectiveness against commercial PBs. Methods: Two experiments (Experiments 1 and 2) were conducted using cherry tomato plants. In the first one, the two media were applied at different concentrations as a foliar spray to define the optimal dose. This outcome was used to set up Experiment 2, in which both media were compared to commercial PBs under optimal and reduced N supply. Measurements included plant growth, chlorophyll (Chl) content, and NUE indices. Moreover, Experiment 2 examined gene expression related to N assimilation, transport, and response to oxidative stress. Results: Both experiments demonstrated a significant increase in leaf area (approximate to 11%) and aboveground biomass (approximate to 13%) using exhausted media. Furthermore, Experiment 2 demonstrated enhancements in Chl content (approximate to 10%) and plant N accumulation (approximate to 20%). These findings indicate that exhausted media has a comparable efficacy to commercial PBs. Conclusions: The study underscores the practical viability of exhausted cell culture media as effective PBs for tomato growth in both N conditions. This approach aligns with sustainability objectives by repurposing by-products to enhance plant resilience against abiotic stress and potentially improve the efficiency of N fertilizers.