Impact of Elevated Carbon Dioxide on Primary, Secondary Metabolites and Antioxidant Responses of Eleais guineensis Jacq. (Oil Palm) Seedlings

Mohd Hafiz Ibrahim,Hawa Z.E Jaafar

doi:10.3390/molecules17055195

Abstract

A split plot 3 by 3 experiment was designed to investigate the relationships among production of primary metabolites (soluble sugar and starch), secondary metabolites (total flavonoids, TF; total phenolics, TP), phenylalanine lyase (PAL) activity (EC 4.3.1.5), protein and antioxidant activity (FRAP) of three progenies of oil palm seedlings, namely Deli AVROS, Deli Yangambi and Deli URT, under three levels of CO2 enrichment (400, 800 and 1,200 µmol·mol−1) for 15 weeks of exposure. During the study, the treatment effects were solely contributed by CO2 enrichment levels; no progenies and interaction effects were observed. As CO2 levels increased from 400 to 1,200 µmol·mol−1, the production of carbohydrate increased steadily, especially for starch more than soluble sugar. The production of total flavonoids and phenolics contents, were the highest under 1,200 and lowest at 400 µmol·mol−1. It was found that PAL activity was peaked under 1,200 µmol·mol−1 followed by 800 µmol·mol−1 and 400 µmol·mol−1. However, soluble protein was highest under 400 µmol·mol−1 and lowest under 1,200 µmol·mol−1. The sucrose/starch ratio, i.e., the indication of sucrose phosphate synthase actvity (EC 2.4.1.14) was found to be lowest as CO2 concentration increased from 400 > 800 > 1,200 µmol·mol−1. The antioxidant activity, as determined by the ferric reducing/antioxidant potential (FRAP) activity, increased with increasing CO2 levels, and was significantly lower than vitamin C and α-tocopherol but higher than butylated hydroxytoluene (BHT). Correlation analysis revealed that nitrogen has a significant negative correlation with carbohydrate, secondary metabolites and FRAP activity indicating up-regulation of production of carbohydrate, secondary metabolites and antioxidant activity of oil palm seedling under elevated CO2 was due to reduction in nitrogen content in oil palm seedling expose to high CO2 levels.

Highlights

Elaeis guineensis (Jacq.), known as oil palm, is the highest yielding vegetable oil crop in the World and is believed to originate from Africa [1]
phenylalanine lyase (PAL) had established a considerable (p ≤ 0.05) positive relationship with total phenolics (R2 = 0.744) and flavonoids (R2 = 0.842), which might indicate an up-regulation of plant secondary metabolite production with increased PAL activity. This is basically true by the fact that phenylalanine is a precursor of total phenolics and flavonoids biosynthesis [26]. These results suggested that the up-regulation of the plant secondary metabolites production in oil palm seedlings under high CO2 could be due to an increase in the PAL activity
The current work has demonstrated that high levels of CO2 are able to alter the synthesis of flavonoids and phenolics in oil palm seedlings

Summary

Introduction

Elaeis guineensis (Jacq.), known as oil palm, is the highest yielding vegetable oil crop in the World and is believed to originate from Africa [1]. The health benefitd of oil palm are believed to be due to its flavonoids and phenolics content [6]. Flavonoids and phenolics are the most important groups of secondary metabolites and bioactive compounds in plants [7]. These compounds have been identified as natural antioxidants that may reduce oxidative damage to the human body [8]. Their function in human health is supported by the ability to induce human protective enzyme systems, and by a number of epidemiological studies suggesting protective effects against cardiovascular disease, cancers and other related diseases [9]

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