Exogenous naringenin improved digestible protein accumulation and altered morphology via VrPIN and auxin redistribution in Vigna radiata

Abstract

Naringenin exposure altered auxin redistribution via VrPIN1 leading to morphological alterations and significantly reduced the protein precipitable tannins that further enhanced the protein accumulation and bioavailability. Flavonoid exposure is known to affect the antioxidant profile of legumes. However, a detailed study evaluating the effect of flavonoid naringenin on morphology and biochemical profile of legume is lacking. The present study is a novel report of improved in planta protein bioavailability and antioxidant potential of legume mungbean on naringenin exposure. The quantitative evaluation revealed significant protein accumulation (64-122 μg/g FW) on naringenin exposure. Further, an increase in protein solubility and digestibility compared to control was evident. Naringenin mediated altered α-amylase activity improved the mungbean seed germination rate. Naringenin induced auxin redistribution and altered PIN formed transcript expression reduced lateral root density and increased stem length that was subsequently reverted on exogenous indole acetic acid application. Naringenin enhanced polyphenolic accumulation and improved the antioxidant potential of mungbean. Additionally, the responsiveness of the early gene of the flavonoid biosynthetic pathway, Chalcone isomerase to naringenin concentration was revealed indicating a probable feedback regulation. Further, the presence of alternate liquiritigenin biosynthesis was also evident. The present study, thus reveals the probable potential of phytochemical naringenin towards agricultural sustainability in the changing environmental conditions.

Keywords: Alternate biosynthesis; Antioxidant; Auxin; Chalcone isomerase; Germination; Liquiritigenin; Mungbean; Naringenin; Protein; VrPIN1; α-Amylase.

Fig. 1

Effect of naringenin exposure on mungbean germination rate. a The germination rate of mungbean without and with naringenin exposure was recorded at 24, 48, 72 and 96 h. Naringenin exposure enhanced the germination rate of mungbean. b The line graph shows enhanced α-amylase activity of mungbean seeds on naringenin exposure in a concentration-dependent manner compared to control. Data is represented as mean ± standard deviation of three independent measurements (*P < 0.05, **P < 0.01, ***P < 0.001)

Fig. 2

IAA induced variation in the mungbean shoot length and lateral root count in the presence and absence of naringenin. a Comparison of three days old mungbean stem length and number of lateral roots grown in the absence and presence of naringenin. The naringenin exposed mungbean showed a significant increment in stem length and reduced density of lateral roots compared to control. b Gel documentation system image shows a variation in the lateral root number of V. radiata with and without naringenin. Naringenin exposure reduced the lateral root density compared to control. c Image representing the reversal of shoot elongation and rescue of lateral root density after ten days of IAA spray. d The image is a close view representing the rescue of lateral root count in mungbean post 10 days of IAA spray

Fig. 3

Comparative gene expression analysis of control and naringenin exposed mungbean. a The bar diagram represents the integrated density values (IDV) of VrPIN1 amplicon as measured with ImageJ software in shoot and root of control and 1 mM naringenin exposed mungbean before (a) and after (b) IAA spray. Each bar in the bar diagram presents the IDV of the amplicons representing genes, (c) VrSOD, (d) VrCAT and (e) VrAPX in control and naringenin exposed mungbean. f The bar graph shows the IDV of VrCHI transcript expression in control and naringenin exposed mungbean. The gene encoding 26 s rRNA was used as an internal control. Data is represented as mean ± standard deviation of three independent measurements (**P < 0.01, ***P < 0.001)

Fig. 4

Effect of naringenin exposure on the accumulation and bioavailability of protein in mungbean. a Bar graph shows an increase in the protein content of naringenin exposed mungbean plants compared to the control. Each bar represents the mean of three independent measurements (***P < 0.001). b The bar diagram shows the protein in vitro digestibility of mungbean in control and naringenin supplemented soil. c The graph depicts the protein solubility in response to naringenin concentrations with respect to control. d The bar diagram shows the percent of protein precipitable phenolics estimated from mungbean grown in the absence and presence of naringenin. Naringenin supplementation increased the protein content with a significant increment in protein in vitro digestibility and solubility. The considerable reduction in the fraction of protein precipitable phenolics was also evident