Effects of a new biostimulant on gene expression and metabolic responses of tomato plants

The effects of a new biostimulant, EXPANDO®, containing different bioactive compounds such as mineral elements (potassium, phosphorus and molybdenum), amino acids, vitamins and phytohormone-like substances, developed mainly for fruit growth, were investigated both in greenhouse and open field experiments. The preliminary agronomic trials carried out in different crop species, showed plant growth promotion and an increase in final yield. Since, no information was available on plants treated with this new biostimulant at transcriptomic level, we started this research project aimed to investigate the changes on gene expression in tomato plants (Solanum lycopersicum 'Micro-Tom') grown in growth chamber and treated with EXPANDO® (3.5 mL L-1). To determine metabolic targets of this new biostimulant, a microarray analysis was carried out on EXPANDO®-treated and untreated 20-day-old tomato plants. For expression profiling, Agilent Tomato Gene Expression Microarray (4×44K) and four biological replicates were used. A preliminary analysis of the microarray data showed that the treatment with EXPANDO® was able to modulate the expression level of about 4,000 genes (>1,700 up-regulated and >2,000 downregulated) which were found to be involved in several biological processes like transcription, stress responses, signal transduction, carbohydrate metabolism, transport, protein metabolism and secondary metabolism. Moreover, to investigate the metabolic responses of tomato to EXPANDO® treatment and the possible correlation with trascriptomic analyses, several biochemical parameters such as content of soluble proteins, photosynthetic pigments, total phenolic compounds and activity of three ROS scavenging enzymes (superoxide dismutase, peroxidase and catalase) were evaluated. In general, EXPANDO® did not affect the levels of the metabolites in analysis in growth chamber conditions, however, the treatment enhanced the modulation of the ROS scavenging enzyme genes and a good correlation was found between the level of transcripts and the enzyme activity.