Exogenous Application of 5-Aminolevulinic Acid Promotes Coloration and Improves the Quality of Tomato Fruit by Regulating Carotenoid Metabolism

Junwen Wang; Jing Zhang; Jing Li; Mohammed Mujitaba Dawuda; Basharat Ali; Yue Wu; Jihua Yu; Zhongqi Tang; Jian Lyu; Xuemei Xiao; Linli Hu; Jianming Xie

doi:10.3389/fpls.2021.683868

Exogenous Application of 5-Aminolevulinic Acid Promotes Coloration and Improves the Quality of Tomato Fruit by Regulating Carotenoid Metabolism

Front Plant Sci. 2021 Jun 9:12:683868. doi: 10.3389/fpls.2021.683868. eCollection 2021.

Authors

Junwen Wang¹, Jing Zhang¹, Jing Li¹, Mohammed Mujitaba Dawuda², Basharat Ali³, Yue Wu¹, Jihua Yu^{1

4}, Zhongqi Tang¹, Jian Lyu¹, Xuemei Xiao¹, Linli Hu¹, Jianming Xie¹

Affiliations

¹ College of Horticulture, Gansu Agricultural University, Lanzhou, China.
² Department of Horticulture, FoA, University for Development Studies, Tamale, Ghana.
³ Department of Agronomy, University of Agriculture, Faisalabad, Pakistan.
⁴ Gansu Provincial Key Laboratory of Aridland Crop Science, Lanzhou, China.

Abstract

5-Aminolevulinic acid (ALA) plays an important role in plant growth and development. It can also be used to enhance crop resistance to environmental stresses and improve the color and internal quality of fruits. However, there are limited reports regarding the effects of ALA on tomato fruit color and its regulatory mechanisms. Therefore, in this study, the effects of exogenous ALA on the quality and coloration of tomato fruits were examined. Tomato (Solanum lycopersicum "Yuanwei No. 1") fruit surfaces were treated with different concentrations of ALA (0, 100, and 200 mg⋅L^-1) on the 24th day after fruit setting (mature green fruit stage), and the content of soluble sugar, titratable acid, soluble protein, vitamin C, and total free amino acids, as well as amino acid components, intermediates of lycopene synthetic and metabolic pathways, and ALA metabolic pathway derivatives were determined during fruit ripening. The relative expression levels of genes involved in lycopene synthesis and metabolism and those involved in ALA metabolism were also analyzed. The results indicated that exogenous ALA (200 mg⋅L^-1) increased the contents of soluble sugars, soluble proteins, total free amino acids, and vitamin C as well as 11 kinds of amino acid components in tomato fruits and reduced the content of titratable acids, thus improving the quality of tomato fruits harvested 4 days earlier than those of the control plants. In addition, exogenous ALA markedly improved carotenoid biosynthesis by upregulating the gene expression levels of geranylgeranyl diphosphate synthase, phytoene synthase 1, phytoene desaturase, and lycopene β-cyclase. Furthermore, exogenous ALA inhibited chlorophyll synthesis by downregulating the genes expression levels of Mg-chelatase and protochlorophyllide oxidoreductase. These findings suggest that supplementation with 200 mg⋅L^-1 ALA not only enhances the nutritional quality and color of the fruit but also promotes early fruit maturation in tomato.

Keywords: 5-aminolevulinic acid; coloration; internal quality; lycopene synthesis; tomato fruit.