The combination of a microbial and a non‐microbial biostimulant increases yield in lettuce (Lactuca sativa) under salt stress conditions by up‐regulating cytokinin biosynthesis

• DOI: 10.1111/jipb.13755
• Publication Date: 2024-08-07T13:28:14Z
• Authors: Patricia Benito; Marina Celdrán; Javier Bellón; Vicente Arbona; Miguel González‐G...; Rosa Porcel; Lynne Yenush; José M. Mulet
• Keywords: Chlorophyll; 0301 basic medicine; 10.- Reducir las desigualdades entre países y dentro de ellos; Cytokinins; Salt stress; Lettuce; Salt Stress; Antioxidants; 02.- Poner fin al hambre, conseguir la seguridad alimentaria y una mejor nutrición, y promover la agricultura sostenible; Up-Regulation; 12.- Garantizar las pautas de consumo y de producción sostenibles; Abscisic acid; Isopentenyladenosine; 03 medical and health sciences; Biostimulants; 01.- Erradicar la pobreza en todas sus formas en todo el mundo; Plant Growth Regulators; Gene Expression Regulation, Plant; BIOQUIMICA Y BIOLOGIA MOLECULAR; Bacillus megaterium; 03.- Garantizar una vida saludable y promover el bienestar para todos y todas en todas las edades; 13.- Tomar medidas urgentes para combatir el cambio climático y sus efectos; Lactuca

ABSTRACTSalinization poses a significant challenge in agriculture, exacerbated by anthropogenic global warming. Biostimulants, derived from living microorganisms or natural extracts, have emerged as valuable tools for conventional and organic agriculture. However, our understanding of the molecular mechanisms underlying the effects of biostimulants is very limited, especially in crops under real cultivation conditions. In this study, we adopted an integrative approach to investigate the effectiveness of the combined application of plant growth‐promoting bacterium (Bacillus megaterium strain BM08) and a non‐microbial biostimulant under control conditions (normal watering) and salt stress. After confirming the yield increase under both conditions, we investigated the molecular mechanisms underlying the observed effect by measuring a number of physiological parameters (i.e., lipid peroxidation, antioxidants, chlorophylls, total phenolics and phytohormone content), as well as RNA sequencing and primary metabolite analyses. Our findings reveal that the combined effect of the microbial and non‐microbial biostimulants led to a decrease in the antioxidant response and an up‐regulation of genes involved in cytokinin biosynthesis under salt stress conditions. This, in turn, resulted in a higher concentration of the bioactive cytokinin, isopentenyladenosine, in roots and leaves and an increase in γ‐aminobutyric acid, a non‐proteic amino acid related to abiotic stress responses. In addition, we observed a decrease in malic acid, along with an abscisic acid (ABA)‐independent up‐regulation of SR‐kinases, a family of protein kinases associated with abiotic stress responses. Furthermore, we observed that the single application of the non‐microbial biostimulant triggers an ABA‐dependent response under salt stress; however, when combined with the microbial biostimulant, it potentiated the mechanisms triggered by the BM08 bacterial strain. This comprehensive investigation shows that the combination of two biostimulants is able to elicit a cytokinin‐dependent response that may explain the observed yield increase under salt stress conditions.