Physio-biochemical and metabolomic responses of the woody plant Dalbergia odorifera to salinity and waterlogging

Abstract

Background: Trees have developed a broad spectrum of molecular mechanisms to counteract oxidative stress. Secondary metabolites via phenolic compounds emblematized the hidden bridge among plant kingdom, human health, and oxidative stress. Although studies have demonstrated that abiotic stresses can increase the production of medicinal compounds in plants, research comparing the efficiency of these stresses still needs to be explored. Thus, the present research paper provided an exhaustive comparative metabolomic study in Dalbergia odorifera under salinity (ST) and waterlogging (WL).

Results: High ST reduced D. odorifera's fresh biomass compared to WL. While WL only slightly affected leaf and vein size, ST had a significant negative impact. ST also caused more significant damage to water status and leaflet anatomy than WL. As a result, WL-treated seedlings exhibited better photosynthesis and an up-regulation of nonenzymatic pathways involved in scavenging reactive oxygen species. The metabolomic and physiological responses of D. odorifera under WL and salinity ST stress revealed an accumulation of secondary metabolites by the less aggressive stress (WL) to counterbalance the oxidative stress. Under WL, more metabolites were more regulated compared to ST. ST significantly altered the metabolite profile in D. odorifera leaflets, indicating its sensitivity to salinity. WL synthesized more metabolites involved in phenylpropanoid, flavone, flavonol, flavonoid, and isoflavonoid pathways than ST. Moreover, the down-regulation of L-phenylalanine correlated with increased p-coumarate, caffeate, and ferulate associated with better cell homeostasis and leaf anatomical indexes under WL.

Conclusions: From a pharmacological and medicinal perspective, WL improved larger phenolics with therapeutic values compared to ST. Therefore, the data showed evidence of the crucial role of medical tree species' adaptability on ROS detoxification under environmental stresses that led to a significant accumulation of secondary metabolites with therapeutic value.

Keywords: Abiotic stresses; Adaptability; Antioxidant; Medicinal tree; Metabolomic; Phenylpropanoids.

Fig. 1

Leaflet water content (A), leaflet relative turgidity (B), leaflet dry matter (C), leaflet moisture (D), leaflet relative conductivity (E) and dew-point water potential (F) in Dalbergia odorifera leaflets under waterlogging and salinity. The bars on the top show standard error and different lowercases indicate significant difference among different treatments according to Tukey’s multiple comparison tests, respectively (P < 0.05). CK: control; WL; waterlogging; ST; salinity

Fig. 2

Anatomical changes of the leaflets of Dalbergia odorifera exposed to waterlogging and salinity with the control (A1-A3), WL (B1-B3) and ST (C1-C3) treatment. Row 1 (A1, B1 and C1) represents the vein of a leaflet, row 2 (A2, B2 and C2) the cross-section of a leaflet and row 3 (A3, B3 and C3) the edge of a leaflet. All images were taken at a set of 20 × zoom level with CaseViewer and scale bars = 50 μm. The letters within the images are: de, down-epidermis; pd, palisade mesophyll cell; smc, spongy mesophyll cell; ue, upper-epidermis; vb, vascular bundle

Fig. 3

Plant flavonoids (A) and total of phenol (B) contents, ration between flavonoids and phenolics (C), polyphenol oxidase (PPO, D), phenylalanine ammonia-lyase (PAL, E) and plant lipoxygenase (LOX, F) activities in Dalbergia odorifera leaflets under waterlogging and salinity. The bars on the top show standard error and different lowercases indicate significant difference among different treatments according to Tukey’s multiple comparison tests, respectively (P < 0.05). CK: control; WL; waterlogging; ST; salinity

Fig. 4

Samples clustering heatmap (A-C), OPLS-DA S-plot (red indicates metabolites with VIP ≥ 1, and green indicates metabolites with VIP < 1) (D-F), principal component analysis (PCA) grouped 3D plot (G-I) of the metabolome in D. odorifera leaflets under salinity and waterlogging. CK: control; WL; waterlogging; ST; salinity

Fig. 5

Different metabolites detected in Dalbergia odorifera leaflets under control (CK), waterlogging (WL) and salinity (ST) (A). Venn diagrams of the number of up-regulated (B) and down-regulated (C) differential metabolites in WL versus ST, CK vs WL and CK vs ST

Fig. 6

Overview of the secondary metabolites with therapeutic value profiling results in Dalbergia odorifera leaflets under waterlogging and salinity versus control