Fuente: WIPO "tomato" A method of increasing at least one of the chlorophyll-a concentration and the chlorophyll-b concentration in the leaves of a plant of the genus Hordeum which has been hydroponically grown from seed over a 2 to 4 week duration, including germinating the seed at from 20 to 40° C.; transferring the germinated seed into an aqueous hydroponic dispersion having a temperature of from 20 to 40° C. and containing NPs of magnesium aluminate (MgAl2O4) having a cubic spinel structure; for the duration of 2 to 4 weeks after transferring, maintaining the aqueous hydroponic dispersion at from 20 to 40° C. under dark period-to-light period cycling; and, for the duration of 2 to 4 weeks after transferring, periodically adding NPs of MgAl2O4 having a cubic spinel structure to the aqueous hydroponic dispersion to maintain the concentration of the NPs in the aqueous hydroponic dispersion at from 20 to 200 mg/L.