Reduced photoinhibition under low irradiance enhanced Kacip Fatimah (Labisia pumila Benth) secondary metabolites, phenyl alanine lyase and antioxidant activity.

Mohd Hafiz Ibrahim,Hawa Z E Jaafar

doi:10.3390/ijms13055290

Mohd Hafiz Ibrahim, Hawa Z E Jaafar

Open Access

https://doi.org/10.3390/ijms13055290

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Abstract

A randomized complete block design experiment was designed to characterize the relationship between production of total flavonoids and phenolics, anthocyanin, photosynthesis, maximum efficiency of photosystem II (Fv/Fm), electron transfer rate (Fm/Fo), phenyl alanine lyase activity (PAL) and antioxidant (DPPH) in Labisia pumila var. alata, under four levels of irradiance (225, 500, 625 and 900 μmol/m2/s) for 16 weeks. As irradiance levels increased from 225 to 900 μmol/m2/s, the production of plant secondary metabolites (total flavonoids, phenolics and antocyanin) was found to decrease steadily. Production of total flavonoids and phenolics reached their peaks under 225 followed by 500, 625 and 900 μmol/m2/s irradiances. Significant positive correlation of production of total phenolics, flavonoids and antocyanin content with Fv/Fm, Fm/Fo and photosynthesis indicated up-regulation of carbon-based secondary metabolites (CBSM) under reduced photoinhibition on the under low light levels condition. At the lowest irradiance levels, Labisia pumila extracts also exhibited a significantly higher antioxidant activity (DPPH) than under high irradiance. The improved antioxidative activity under low light levels might be due to high availability of total flavonoids, phenolics and anthocyanin content in the plant extract. It was also found that an increase in the production of CBSM was due to high PAL activity under low light, probably signifying more availability of phenylalanine (Phe) under this condition.

Highlights

Phenolics are carbon-based secondary metabolites, primarily produced through the pentose phosphate pathway (PPP), phenylpropanoid and shikimate acid pathways
Our results indicate that the manipulation of irradiance levels may be an effective method to increase the expression of secondary metabolite compounds in Labisia pumila
Phenolics, and anthocyanin levels were demonstrated in Labisia pumila when the irradiance level was at its lowest (225 μmol/m2/s)

Summary

Introduction

Phenolics are carbon-based secondary metabolites, primarily produced through the pentose phosphate pathway (PPP), phenylpropanoid and shikimate acid pathways. The oxidative PPP provides precursor erythrose-4-phosphate for the shikimate pathway. This pathway converts these sugar phosphates to aromatic amino acids such as phenylalanine, which becomes the precursor for the phenylpropanoid pathway that synthesizes polyphenols. Phenolics are involved in the strengthening of plant cell walls during growth by polymerization into lignans and lignins [1,2]. Plant phenolics have potential health benefits, mainly due to their antioxidant properties, such as reactive oxygen species scavenging and inhibition, electrophilic scavenging, and metal chelation [3]. Plant phenolics have been reported to exhibit pharmacological properties such as antitumor, antiviral, antimicrobial, anti-inflammatory, hypotensive and antioxidant activity [8,9]

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