Fuente: WIPO "tomato" The present invention relates to the field of biotechnology. More precisely, a gelatinous nutrient substrate containing at least meta-topolin and melatonin and the method of its production are described. An artificial seed is also described, which comprises a container filled with a nutrient substrate comprising at least melatonin and meta-topolin into which a plant propagule is placed. The invention also describes a method of in vitro plant hardening, in which meristematic and/or embryonic tissues grown in vitro are placed in a nutrient substrate comprising at least meta-topolin and melatonin with subsequent exposure to the stress conditions commonly found in the field, allowing the plant propagule to develop into an adult plant. Preferably, the meristematic and/or embryonic plant tissues used are those from plant species that can be propagated vegetatively.