Specialized Metabolite Profiling-Based Variations of Watercress Leaves (Nasturtium officinale R.Br.) from Hydroponic and Aquaponic Systems

Abstract

Watercress (Nasturtium officinale), a freshwater aquatic plant in the Brassicaceae family, is characterized by its high content of specialized metabolites, including flavonoids, glucosinolates, and isothiocyanates. Traditionally, commercial cultivation is conducted in submerged beds using river or spring water, often on soil or gravel substrates. However, these methods have significant environmental impacts, such as promoting eutrophication due to excessive fertilizer use and contaminating water sources with pesticides. This study aimed to explore two emerging cultivation strategies, i.e., hydroponics and aquaponics, to grow watercress and evaluate its specialized metabolite content using an untargeted metabolomic approach. The goal was to characterize metabolic profiles, identify component variations, and assess changes in metabolite accumulation at two harvest times. Two culture systems (hydroponic and aquaponic) and two harvest stages ('baby leaf' and traditional harvest) were examined. The results revealed 23 key metabolites, predominantly glucosinolates and flavonoids, that significantly influenced the metabolic profile discrimination, with the aquaponic system yielding the highest diversity and relative abundance of metabolites (variable importance in the projection (VIP) > 1). Important condition-related compounds were identified via cross-validation (area under the curve (AUC) > 0.7), including isorhamnetin sophoroside-glucoside and gluconasturtiin at the traditional harvest in the hydroponic system and glucoarabin at the 'baby leaf' stage in the aquaponic system. These findings highlight the potential of aquaponic and hydroponic systems as sustainable alternatives for watercress cultivation, offering environmental benefits and enhanced metabolite quality.

Keywords: Brassicaceae; aquaponics; glucosinolates; hydroponics; phytochemical profiling.

Figure 1

Totalized chromatogram under comparative reconstruction of the watercress samples obtained from a principal component analysis (PCA) on the entire data set (72 samples × 3937 features), using Pareto-scaled data without centering (ParN), with the Pareto variance applied as the base weight type. Blue numbers over signals represent influential metabolites detected by the employed ParN-PCA.

Figure 2

(a) Orthogonal partial least squares regression analysis (OPLS-DA)-derived score-plot for individual watercress leaf samples, supervised by cultivation system, i.e., hydroponic cultivation system (HCS), aquaponic cultivation system (ACS), and traditional outdoor cultivation (TOC). The data set was autoscaled using unit variance (UV); Principal Component 1 (PC1) vs. PC2 (t[1] × t[2], R²_Xcum = 0.83, Q²_Xcum = 0.72). (b) Loadings line obtained after combination of X loading weight p and Y loading weight q to one vector (pq[1]) obtained from PLS-DA along t[1]. (c) Loadings line (pq[2]) along t[2]. * represents multiplication of vector t with a constant depending on the X data distribution.

Figure 3

Box plots represent the distribution of the relative abundance of specialized metabolites: (a) glucosinolates; (b) flavonoids; and (c) indole phytoalexin.

Figure 4

The most differential metabolites per cultivation system between harvest times t₁ vs. t₂ on the LC–MS-derived metabolite profile data from watercress leaves collected from (a) hydroponic cultivation system (HCS) and (b) aquaponic cultivation system (ACS). Each two-chart panel per cultivation system and differential metabolite comprises the receiver operating characteristic (ROC) curve (left) and the box plot showing the normalized levels per harvest time (right). Area under curve AUC > 0.70 as choice criteria; gluconasturtiin (AUC = 0.833), isorhamnetin sophoroside–glucoside (AUC = 0.708), glucoarabin (AUC = 0.762), and brassicasterol (10) (AUC = 0.741).

Figure 5

(a) Traditional outdoor culture (TOC); (b) hydroponic cultivation system (HAS); (c) aquaponic cultivation system (modified from a previous design [34]; (d) first harvest time (t₁) or ‘baby leaf’; and (e) second harvest time (t₂) or traditional harvest.