Lycopene concentration in tomato fruit is increased by enhanced potassium nutrition

Abstract

Raw and processed tomatoes are the major dietary source of lycopene in the U.S.; serum lycopene concentrations are inversely related with risk of chronic disease. In greenhouse tomato plants, we investigated the effects of different levels of potassium application on: 1) fruit concentrations of lycopene and the colorless precursors, phytoene and phytofluene; and 2) expression of carotenoid biosynthetic genes. Plants were grown in silica sand with nutrient solution containing selected potassium concentrations from 0 to 10 meq/L. Fruit potassium concentration was linearly related to potassium application level (r = 0.81). Phytoene, phytofluene, and lycopene concentrations were highly correlated with potassium concentration in the fruit (r = 0.69, 0.68, 0.70, respectively). Lycopene concentration increased from 39.3 ± 9.09 μg/g (0 meq/L potassium) to 55.6 ± 6.71 μg/g (10 meq/L potassium) (P < 0.007). Phytoene and phytofluene concentrations increased from 3.79 ± 0.79 μg/g and 2.79 ± 0.59 μg/g, respectively, to 7.84 ± 1.86 μg/g and 5.25 ± 1.26 μg/g, respectively (P < 0.002). Expression of carotenoid biosynthetic genes was analyzed by RT-PCR and RNA dot hybridization. Preliminary results indicated an increase in potassium application from 0 meq/L to 10 meq/L resulted in up-regulation during ripening of genes for phytoene synthase, phytoene desaturase, and carotenoid isomerase. Future research will elucidate the relation between potassium nutrition of the tomato plant and carotenoid biosynthesis. Supported by USDA/CDFIN 2004-06096.