Tsun-Thai Chai

Water stress-induced oxidative damage and antioxidant responses in micropropagated banana plantlets

Oxidative injury and antioxidant responses were investigated in two banana genotypes (Musa AAA ‘Berangan’ and Musa AA ‘Mas’) subjected to 40 % PEG-induced water stress. PEG treatment resulted in oxidative injury, as expressed in increased lipid peroxidation and reduced membrane stability index, in both cultivars; however, greater oxidative injury was detected in ‘Mas’. Under PEG treatment, catalase activity and glutathione reductase activity were enhanced in both cultivars, but were higher in ‘Mas’. Ascorbate peroxidase activity was enhanced in ‘Berangan’ under water stress, but was unaffected in ‘Mas’. Meanwhile, superoxide dismutase activity was inhibited in both cultivars under water stress, but higher activity was detected in ‘Berangan’. Higher ascorbate peroxidase and superoxide dismutase activities were associated with greater protection against water stress-induced oxidative injury.

Photosynthetic Performance and Fertility Are Repressed in GmAOX2b Antisense Soybean

The alternative oxidase (AOX) is a cyanide-resistant oxidase that provides an alternative outlet for electrons from the respiratory electron transport chain embedded in the inner membrane of plant mitochondria. Examination of soybean (Glycine max) plants carrying a GmAOX2b antisense gene showed AOX to have a central role in reproductive development and fecundity. In three independently transformed antisense lines, seed set was reduced by 16% to 43%, whereas ovule abortion increased by 1.2- to 1.7-fold when compared with nontransgenic transformation control plants. Reduced fecundity was associated with reductions in whole leaf cyanide-resistant, salicylhydroxamic acid-sensitive respiration and net photosynthesis, but there was no change in total respiration in the dark. The frequency of potential fertilization events was reduced by at least one-third in the antisense plants as a likely consequence of prefertilization defects. Pistils of the antisense plants contained a higher proportion of immature-sized, nonfertile embryo sacs compared with nontransgenic control plants. Increased rates of pollen abortion in vivo and reduced rates of pollen germination in vitro suggested that the antisense gene compromised pollen development and function. Reciprocal crosses between antisense and nontransgenic plants revealed that pollen produced by antisense plants was less active in fertilization. Taken together, the results presented here indicate that AOX expression has an important role in determining normal gametophyte development and function.

A GmAOX2b antisense gene compromises vegetative growth and seed production in soybean

The alternative oxidase mediates the cyanide-resistant respiratory pathway in plant mitochondria. In non-thermogenic plants, the role of alternative oxidase in plant growth and development is not well understood. Soybean (Glycine max) lines carrying a GmAOX2b antisense gene had compromised vegetative growth and reproductive performance under typical glasshouse growth conditions. The reduction in vegetative growth was demonstrated by reduction in shoot height, the number of leaves per plant and the green leaf area. Antisense plants also had decreased pod formation and seed to pod ratios, which together led to a reduction in the number and total mass of seed produced. The negative effects of the antisense gene on pod set, seed set, ovule availability and total seed mass were primarily confined to the branches, rather than the main stem. The preferential effect of alternative oxidase suppression in the branches is discussed in relation to the reproductive potential of soybean under stress. Taken together, these results demonstrate that alternative oxidase provides the benefit of sustaining plant vegetative growth and reproductive capacity in soybean.

Antioxidant properties of aqueous extracts of Selaginella willdenowii

Selaginella willdenowii is a plant used as traditional medicine and vegetable in some Asian countries. Unlike other medicinally important Selaginella species, little is known about the pharmacological properties of S. willdenowii. This study was therefore conducted to evaluate the antioxidant properties of aqueous extracts of leaves and stems of S. willdenowii, both fresh and dried prepared with or without heat treatment. Total phenolic and flavonoid contents of the leaf extracts were consistently higher compared with stem extracts. Total phenolic and flavonoid contents of hot water extracts of fresh leaves were up to 4.4-fold and 10.7-fold higher, respectively, when compared with all other extracts. Radical scavenging and ferric reducing activities of the leaf extracts were also consistently higher compared with stem extracts. Trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant power (FRAP) of hot water extracts of fresh leaves were up to 5.5-fold and 5.3-fold higher, respectively, when compared with all other extracts. Correlation analysis revealed that total phenolic content is likely a key determinant of the radical scavenging and ferric reducing abilities in the leaf extracts. Overall, our findings affirm the value of S. willdenowii as a medicinal herb as well as a source of dietary antioxidant.

Antioxidation and cytotoxic activities of selected medicinal herbs used in Malaysia

Free radicals, with their single electrons and reactive nature, could easily interact with different cellular compartments and cause oxidative damage. Prolonged oxidative stress could lead to DNA mutations, neurodegenerative diseases and heart disorders. These disorders could deteriorate our overall wellbeing and prove to be fatal. Medicinal herbs, rich in their secondary metabolites, could provide the antioxidants and scavengers needed to eliminate the free radicals. In this study, we tested six medicinal herbs used in Malaysia for their scavenging activities, in three different radical scavenging assays. We also tested their total phenolic and flavonoid levels. Among the herbs tested, Scutellaria barbata, Prunella vulgaris and Lophatherum gracile consistently demonstrated the highest activities in all three radical scavenging assays and trolox equivalent antioxidant capacity. Higher levels of total phenolic and flavonoid contents were also detected in these three herbs. Additionally, brine shrimp lethality assays also indicated low cytotoxicity in these herbs. In short, our results provided evidence for the safe use of these herbs as treatment for ailment in which free radical damage is implicated.

Enzyme-Assisted Discovery of Antioxidant Peptides from Edible Marine Invertebrates: A Review

Marine invertebrates, such as oysters, mussels, clams, scallop, jellyfishes, squids, prawns, sea cucumbers and sea squirts, are consumed as foods. These edible marine invertebrates are sources of potent bioactive peptides. The last two decades have seen a surge of interest in the discovery of antioxidant peptides from edible marine invertebrates. Enzymatic hydrolysis is an efficient strategy commonly used for releasing antioxidant peptides from food proteins. A growing number of antioxidant peptide sequences have been identified from the enzymatic hydrolysates of edible marine invertebrates. Antioxidant peptides have potential applications in food, pharmaceuticals and cosmetics. In this review, we first give a brief overview of the current state of progress of antioxidant peptide research, with special attention to marine antioxidant peptides. We then focus on 22 investigations which identified 32 antioxidant peptides from enzymatic hydrolysates of edible marine invertebrates. Strategies adopted by various research groups in the purification and identification of the antioxidant peptides will be summarized. Structural characteristic of the peptide sequences in relation to their antioxidant activities will be reviewed. Potential applications of the peptide sequences and future research prospects will also be discussed.

Water fraction of edible medicinal fern Stenochlaena palustris is a potent α-glucosidase inhibitor with concurrent antioxidant activity.

This study aimed to isolate a potent antiglucosidase and antioxidant fraction from Stenochlaena palustris. Extraction was performed with hexane, chloroform, ethyl acetate, methanol, and water. Antiglucosidase, 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging and ferric reducing antioxidant power (FRAP) assays found methanol extract (ME) to be the most active. Water fraction (WF) of ME was a stronger α-glucosidase inhibitor (EC50 2.9 μg/mL) than quercetin, with weak antiamylase activity. WF was a competitive α-glucosidase inhibitor. DPPH scavenging activity of WF (EC50 7.7 μg/mL) was weaker than quercetin. WF (EC50 364 μg/mL) was a stronger hydrogen peroxide scavenger than gallic acid (EC50 838 μg/mL) and was equally strong as quercetin in scavenging superoxide. WF possessed moderate copper chelating activity. WF was enriched in total phenolics (TP) and hydroxycinnamic acids (THC). TP correlated with antioxidant activity (R(2) > 0.76). Only THC correlated with antiglucosidase activity (R(2) = 0.86). Overall, WF demonstrated concurrent, potent antiglucosidase and antioxidant activities.

Investigation of antibacterial mechanism and identification of bacterial protein targets mediated by antibacterial medicinal plant extracts

In this paper, we investigated the antibacterial mechanism and potential therapeutic targets of three antibacterial medicinal plants. Upon treatment with the plant extracts, bacterial proteins were extracted and resolved using denaturing gel electrophoresis. Differentially-expressed bacterial proteins were excised from the gels and subjected to sequence analysis by MALDI TOF-TOF mass spectrometry. From our study, seven differentially expressed bacterial proteins (triacylglycerol lipase, N-acetylmuramoyl-L-alanine amidase, flagellin, outer membrane protein A, stringent starvation protein A, 30S ribosomal protein s1 and 60 kDa chaperonin) were identified. Additionally, scanning electron microscope study indicated morphological damages induced on bacterial cell surfaces. To the best of our knowledge, this represents the first time these bacterial proteins are being reported, following treatments with the antibacterial plant extracts. Further studies in this direction could lead to the detailed understanding of their inhibition mechanism and discovery of target-specific antibacterial agents.

Alternative oxidase, a determinant of plant gametophyte fitness and fecundity

The alternative oxidase (AOX) is the terminal oxidase that comprises the cyanide-resistant respiratory pathway in plant mitochondria. While the role of AOX in plant thermogenesis is well established, its role in the reproductive development of non-thermogenic species is not well understood. AOX genes can be separated into two groups based on sequence homology, AOX1 and AOX2. Reverse genetic experiments carried out primarily in Arabidopsis and tobacco have largely focussed on examining the role of AOX1-type genes in stress responses. We recently reported a systematic characterisation of the reproductive phenotypes of three AOX2 antisense lines of soybean. This addendum summarises the key evidence in our recent paper that points to a role for AOX in the development and function of both male and female gametophytes. Furthermore, we discuss the relative importance of AOX in the reproductive biology of plant species examined to date and highlight practical implications of our findings to crop improvement research.

Edible freshwater macrophytes: a source of anticancer and antioxidative natural products—a mini-review

Edible freshwater macrophytes (EFM) are edible, macroscopic freshwater plants, many of which are also used as traditional/folk medicine. This mini-review highlights phytochemical and pharmacological evidence pertaining to anticancer and antioxidative natural products derived from EFM, with special attention to Centella asiatica (Indian pennywort), Nelumbo nucifera (sacred lotus), Nasturtium officinale (watercress), Ipomoea aquatica (water spinach) and Ludwigia adscendens (water primrose). Current knowledge gaps and further research opportunities are also discussed. EFM is a promising source of anticancer and antioxidative natural products which warrants more extensive exploration. More research is needed before such natural products can be exploited for application in food and medicine.