فصلنامه فرآیند و کارکرد گیاهی
سال یازدهم شماره 5 (پیاپی 51، Aug and Sep 2022)

Phycobilins, as open-chain tetrapyrrole pigment molecules, serve as accessory photosynthetic light-harvesting pigments in red algae and cyanobacteria. Phycobilin pigments are covalently linked with proteins which form phycobiliproteins organized into large macromolecular complexes called phycobilisomes on the top of the thylakoid membranes. In deep water, only green light is available, thus phycobilisomes are able to absorb this part of light very efficiently and allowing cyanobacteria to survive. Cyanobacteria are capable of adjusting the quantitative pigment composition of phycobilisomes in response to changes in environmental conditions. Phycocyanin is a kind of phycobiliproteins which is characterized by an intense blue color and has been widely used as most important natural dye and antioxidant. The free radical scavenging properties of cyanobacterial phycocyanin are well documented. Phycocyanin eliminates reactive oxygen and nitrogen species and therefore prevents oxidative stress that leads to major damage in the structure of biomolecules of the cell. The variety of applications, from its involvement in the prevention of free radical-related diseases including cancer and Alzheimer's, to its antimicrobial effects, from its use in research laboratories and industry to its significant financial turnover, highlights the importance of reviewing studies on phycocyanin. Hence, this review describes recent findings about the sources, structure, function, production, extraction techniques and different applications of phycocyanin.

Glutathione s transferase (GST) is one of the largest protein and multigene families present in all plant species and other living organisms. With respect to these proteins, which are highly ‌inducible to stress and internal and external stimuli, several functions in plants have been identified, including implication in secondary metabolism, growth and development, detoxification of herbicides, as well as coping with environmental stresses such as drought, heat, and salinity through antioxidant activity. These enzymes lead to cell detoxification by binding glutathione to a variety of substrates such as endobiotics and xenobiotics. Most GSTs are cytoplasmic soluble enzymes, but mitochondrial and microsomal isoforms are also have been known in plants and animals. This article presents some of the most important recent findings on the evolution of GST, its frequency and structural features, with an emphasis on their role in plants. Also, the latest applications of this family of proteins in environmental biotechnology will be mentioned.

Melatonin (N-acetyl-5-methoxytryptamine) is an indole metabolite derived from tryptophan which is synthesized in plant cells in the chloroplasts and mitochondria. Melatonin is present in all plant species, with large variations in its level depending on the plant organ or tissue, and is a molecule endowed with a multitude of functions that makes it worthy to be referred to as a plant growth regulator. One of the main functions of melatonin in plants is its substantial influence on plant hormones such as auxin, gibberellins, cytokinins, and abscisic acid. Melatonin functions in plants are similar to the antioxidant activities of auxin. Melatonin has many beneficial actions, generally improving physiological responses such as seed germination and growth, photosynthesis (pigment content, photorespiration, stomatal conductance, and water economy), seed and fruit yield, osmoregulation, and the regulation of the different metabolic pathways. Its ability to strengthen plants subjected to abiotic stress such as drought, cold, heat, salinity, chemical pollutants, herbicides, and UV radiation makes melatonin an interesting candidate for use as a natural bio-stimulating substance. In addition, melatonin is involved in numerous cellular functions as an antioxidant. It acts as an excellent scavenger of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in plants. The studies showed that melatonin act as a direct antioxidant, neutralizing several ROS/RNS and other radical species harmful to the cell, and also acts as an activator of the antioxidant response, up-regulating various transcription factors that triggers the activity of antioxidant enzymes such as superoxide dismutases, catalases, peroxidases, and those involved in the ascorbate-glutathione cycle. Melatonin also acts as a circadian regulator, cyto-protector, and growth promoter, rhizogenesis, cellular expansion, and stress protection, in plants. All these data lead us to the idea that exogenous melatonin treatment might help crops resist under biotic and abiotic stressful environmental conditions.

The production of reactive oxygen species occurs during the natural metabolism of oxidative-breathing cells. Among reactive oxygen species, hydrogen peroxide is more dangerous to cell life due to its long half-life, meanwhile it is an important regulatory molecule in redox signaling in living things. Peroxidases are one of the key antioxidant enzymes that are widely distributed in nature and promote the oxidation of various electron donor substrates simultaneously with the decomposition of hydrogen peroxide which lead to production of water during reducing hydrogen peroxide and other hydroperoxides. Meanwhile, peroxidases, in addition to their known peroxide inhibitory properties, have physiological oxidizing functions.Based on the chemistry of the active site in the interaction with the peroxide, peroxidases are classified to non-heme and heme bearing peroxidases. The former contains heme in its catalytic center, and the latter has a reactive selenol or thiol in its active site. Iron-based plant peroxidases are divided into three classes I, II and III. Thiol plant peroxidases include glutathione peroxidase and proxy reduxins. The present article explains the structural and metabolic, and properties of peroxidases and provides certain practical procedures for determination of their enzymatic activities.

In recent years, the number of reports of nanoparticle production using green methods has increased exponentially. Green methods of nanoparticle production are based on oxidation and reduction reactions in which metal ions are reduced to nanoparticles with the help of compounds in living organisms or their extracts, including antioxidants. The presence of biomolecules, including antioxidants in plant extracts in a reducing and stabilizing role, can help produce metal nanoparticles. In living cells, free radicals are produced during the cellular oxidation process. Free radicals are highly reactive due to the presence of a single electron, and are therefore highly toxic to the cell. Antioxidants (natural and synthetic) are compounds that prevent free radicals from damaging the cell, and their presence is essential for living organisms. Green nanoparticles produced with plant extracts, in addition to greater stability and better size than nanoparticles produced using other living organisms, also have improved biological properties. The antioxidant property of the extract is an important parameter to control the green synthesis of metal nanoparticles. The antioxidant properties of plant extracts can lead to a better selection of plant extracts for the synthesis of nanoparticles with desired properties. Plant antioxidants have reducing properties and can be purified and used for the production of green metal nanoparticles.

Marine algae are known to contain a wide variety of antioxidant compounds. Natural antioxidants, found in many algae, are important bioactive compounds that play an important role against various diseases and aging processes through protection of cells from oxidative damage. At present, there is a global interest in finding new and safe antioxidants from natural sources. Algae can have a variety of primary and secondary metabolites including biosynthesis, metabolism, accumulation and secretion, including carotenoids, phenolic compounds, phycobilins, sulfated compounds, as well as vitamins. All of these compounds are of great value in the medical, pharmaceutical, nutritional, and cosmetic industries. The purpose of this study is to introduce algae as a valuable rich antioxidant natural resource that can be used in various industries.

Oxidative stress which is caused by overproduction of free radicals or oxygenated radical species, plays a major role in causing many diseases. The findings suggest the use of antioxidants as compounds to control the release of these radicals or directly prevention of their formation. Therefore, antioxidants can be used as drugs to reduce or prevent oxidative stress. Herbal medicines are the basis of modern pharmacy and many antioxidant compounds are derived from plant extracts. Due to the extinction danger of medicinal plants, the industrial production of many plant antioxidants is not possible. As a result, introducing endophytic fungi as a new source of natural antioxidant compounds could be a new way to access and produce natural antioxidants in food and pharmaceutical industries. In this review, the potential of endophytic fungi to produce phenolic compounds with antioxidant activities was investigated. Most endophytic fungi with antioxidant properties belong to the genera Fusarium and Aspergillus. We hope this review provides useful information for readers to understand the potential of endophytic fungi in the production of new antioxidants, and to encourage scientists to undertake projects that may lead to the development of novel natural antioxidant drugs.