Molecular and ionomic responses of Solanum lycopersicum L. (cv. Micro-Tom) plants treated with a novel calcium-based plant biostimulant

In this study, we investigated the leaf treatment effects of a novel trace elements calcium-based fluid mixture with a supposed biostimulant action on Solanum lycopersicum L. cv. Micro-Tom. Seedlings were grown on standard peat substrate and treated with two different products: a calcium-based fluid mixture and a common calcium fertilizer, CaCl₂. Both treatments were compared to an untreated control. We first investigated the effects of treatments on fruit yield and dry matter production in greenhouse-grown tomato. These effects were then assessed in leaves by gene expression profiling of 60 genes involved in different biological pathways and functional categories, and by ionomic analysis. Leaf treatment on tomato with the calcium-based fluid mixture allowed the highest fruit yield per plant (6.17 fruits plant⁻¹) and above-ground dry matter (13.99 g plant⁻¹) to be obtained. Also, 4 genes related to the nutrient transporter category, NCX, NRAMP3, SI BOR2, and CHLM, were upregulated in plants treated with the novel product. CRK, a gene related to the calcium-dependent protein kinases (CDPK), was upregulated in plants treated with the novel product whereas SODCC.1, a gene related to the superoxide dismutase family, was downregulated in the same plants. A substantial reduction of elemental contents was observed for CaCl₂-treated plants, while the novel Ca-based mixture increased the leaf mineral content of Zn (+61%) and Mn (+65%). These results highlighted the biostimulant activity of the novel product resulting in changes in fruit yield and dry matter production, gene expression, and ionome profiles of tomato leaves.