Effects of Exogenous Abscisic Acid on Bioactive Components and Antioxidant Capacity of Postharvest Tomato during Ripening

Abstract

Abscisic acid (ABA) is a phytohormone which is involved in the regulation of tomato ripening. In this research, the effects of exogenous ABA on the bioactive components and antioxidant capacity of the tomato during postharvest ripening were evaluated. Mature green cherry tomatoes were infiltrated with either ABA (1.0 mM) or deionized water (control) and stored in the dark for 15 days at 20 °C with 90% relative humidity. Fruit colour, firmness, total phenolic and flavonoid contents, phenolic compounds, lycopene, ascorbic acid, enzymatic activities, and antioxidant capacity, as well as the expression of major genes related to phenolic compounds, were periodically monitored. The results revealed that exogenous ABA accelerated the accumulations of total phenolic and flavonoid contents; mostly increased the contents of detected phenolic compounds; enhanced FRAP and DPPH activity; and promoted the activities of PAL, POD, PPO, CAT, and APX during tomato ripening. Meanwhile, the expressions of the major genes (PAL1, C4H, 4CL2, CHS2, F3H, and FLS) involved in the phenylpropanoid pathway were up-regulated (1.13- to 26.95-fold) in the tomato during the first seven days after treatment. These findings indicated that ABA promoted the accumulation of bioactive components and the antioxidant capacity via the regulation of gene expression during tomato ripening.

Keywords: abscisic acid; antioxidant capacity; bioactive components; enzymatic activity; gene expression; tomato.

Figure 1

Effect of abscisic acid (ABA) on colour (a) and firmness (b) in the tomato during storage at 20 °C. Vertical bars represent the standard deviation (SD, n = 3). Asterisks (*) represent significant differences (p < 0.05) between the ABA and control treatments.

Figure 2

Effect of ABA on the total phenolic (a) and flavonoid (b) content in the tomato during storage at 20 °C. Vertical bars represent the standard deviation (SD, n = 3). Asterisks (*) represent significant differences (p < 0.05) between the ABA and control treatments.

Figure 3

The visual results of the composition of phenolic compounds in the tomato at the mature green, breaker, turning, and red stages, respectively.

Figure 4

Effect of ABA on lycopene (a) and ascorbic acid (b) contents in the tomato during storage at 20 °C. Vertical bars represent the standard deviation (SD, n = 3). Asterisks (*) represent significant differences (p < 0.05) between the ABA and control treatments.

Figure 5

Effect of ABA on PAL (a), POD (b), and PPO (c) activities in the tomato during storage at 20 °C. Vertical bars represent the standard deviation (SD, n = 3). Asterisks (*) represent significant differences (p < 0.05) between the ABA and control treatments.

Figure 6

Effect of ABA on CAT (a) and APX (b) activities in the tomato during storage at 20 °C. Vertical bars represent the standard deviation (SD, n = 3). Asterisks (*) represent significant differences (p < 0.05) between the ABA and control treatments.

Figure 7

Effect of ABA on total antioxidant capacity FRAP (a) and DPPH radical scavenging activity (b) in the tomato during storage at 20 °C. Vertical bars represent the standard deviation (SD, n = 3). Asterisks (*) represent significant differences (p < 0.05) between the ABA and control treatments.

Figure 8

Effect of ABA on the gene expression of the phenylpropanoid pathway in the tomato during storage at 20 °C. Vertical bars represent the standard deviation (SD, n = 3). Asterisks (*) represent significant differences (p < 0.05) between the ABA and control treatments.

Figure 9

Effect of ABA on correlations between gene expression, phenolic compounds, and antioxidant capacities. The heatmap was produced based on obtained Pearson’s correlation coefficients with the relative levels of all indexes in ABA-treated fruits (the levels in control fruits were all normalized to one) on days 1, 7, 11, and 15. The red (+1) and blue (−1) colours represent the positive and negative correlations, respectively, between different indexes. (For interpretation of the references to colour in the Figure 9 legend, the reader is referred to the web version of this article.)

Figure 10

Schematic diagram of the phenylpropanoid pathway and the expression of partial genes involved in this pathway. The control treatment was used as a reference sample for gene expression analysis, calculated based on the 2^−ΔΔCt method. The results are shown in the heatmap. The red and blue colours represent the maximum and minimum expression levels, respectively. Enzyme names are abbreviated as follows: PAL, phenylalanine ammonia-lyase; C4H, cinnamate 4-hydroxylase; 4CL, 4-coumarate-CoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase; FLS, flavonol synthase; UFGT, UDP flavonoid glucosyltransferase; RT, flavonoid 3-O-glucoside-rhamnosyltransferase.