Menadione Sodium Bisulphite (MSB): beyond seed-soaking. Root pretreatment with MSB primes salt stress tolerance in tomato plants

Salinity and drought are considered significant abiotic plant stressors with major impact on plant development that causes serious agricultural yield losses. Amongst the strategies to face this problem, the use of compounds capable of inducing abiotic stress tolerance is still little explored. Menadione sodium bisulphite (MSB), a water-soluble vitamin K3 derivative, was previously shown to prime salt stress tolerance when Arabidopsis seeds were pre-soaked with this compound. However, this method has some technical problems regarding seed storage and longevity. In order to overcome these handicaps, we assessed the effect of supplying MSB to roots to prime the response to salinity stress, analysing the effect of two NaCl concentrations (100 and 150¿mM). We selected tomato plants, the most economically important horticultural crop, as our biological model. In this new system, MSB primes salt tolerance in tomato plants by improving net photosynthesis, regulating stomatal aperture and maintaining water balance. Furthermore, MSB induces a faster proline accumulation and ion homeostasis by up-regulating several ion transporter genes, and increases antioxidant activity. As a result, a clear positive effect on plant growth was observed, indicated by the relative growth rate (RGR), These findings again highlight the potential usefulness of MSB as a priming agent for enhancing crop tolerance in the field under adverse environmental conditions.