Treating seeds in menadione sodium bisulphite primes salt tolerancein Arabidopsis by inducing an earlier plant adaptation

For the majority of crops, salinity is one of the most important abiotic stresses, since about 20% of irrigated agricultural land is adversely affected by it. Menadione sodium bisulphite (MSB), a water-soluble vitamin K3 o menadione derivative, has been previously reported as a plant defence activator against several pathogens in a number of species. We have further explored the MSB effects on salt tolerance. In this study, Arabidopsis thaliana wild ecotype Col-0 plants were exposed to prolonged salt (50 mM) stress. Salt treatment resulted in severe growth inhibition. This detrimental effect was lower in terms of relative growth rate (RGR) in plants from seeds soaked in 20 mM of MSB. In these plants, the drop in RGR was nearly 30% lower than untreated plants after 7 days in salt. Furthermore, we found that the salt stress imposed was not enough to disturb photosystem II or induce the expression of several detoxification genes. These functional impairments are characteristic of ionic injuries due to high levels of reactive oxygen species (ROS). At the end of the second week of the experiment, salt-treated plants recover RGR levels close to those of the control. Under our experimental conditions plants seem to be challenged by an osmotic stress with a minimum ionic imbalance. Those from MSB-treated seeds were primed to induce an earlier proline accumulation. Although no significant expression of ROS detoxification genes was found, several transcription factors involved in ROS signalling were detected after salt addition. In this context, MSB treatment was able to prime these transcription factors, resulting in an early adaptation of plants in response to salt stress.