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Abstract

Paramylon, a β-1,3-glucan polysaccharide found in microalgae like Euglena gracilis, has attracted significant interest in nutrition, health, and agriculture due to its diverse applications. It is highly adaptable, utilizing nutrients from wastewater, CO₂ vaporization, or food waste, with waste-based cultivation yielding 1.77 g/L/day. Paramylon influences plant physiology, enhancing hormone content, photosynthetic efficiency, and dehydration tolerance. For example, during paramylon treatment, the photosynthetic efficiency of Solanum lycopersicum increased to 75%, compared to 50% in controls, while drought resistance rose to 80%, significantly higher than the 60% observed in untreated plants. It also improves water-use efficiency and regulates CO₂ diffusion, offering protection against abiotic stresses such as drought, salinity, nutrient deficiencies, and extreme temperatures. As a sustainable alternative to traditional fertilizers, paramylon functions effectively as a biostimulant, enhancing crop yield and quality while increasing plant tolerance to environmental stress. Despite its promising potential, the precise molecular mechanisms and long-term effects on different crops and soil ecosystems remain underexplored. Future research should focus on optimizing paramylon formulations to enhance bioavailability, exploring its synergistic effects with other biostimulants, and assessing its economic feasibility and scalability for commercial adoption. Additionally, studying its impact on soil microbiota and plant-microbe interactions could reveal broader ecological benefits. This review highlights paramylon's potential as a sustainable fertilizer alternative to improve agricultural productivity and crop quality. While current findings are promising, further interdisciplinary research is essential to unlock its full potential in modern agricultural systems.

Keywords

Paramylon plants growth microalgae

Introduction

Microalgae have attracted interest from both academia and business as a source of nutrients, bioactive substances, biofuels, and chemicals.¹ They are a significant potential source of metabolites, such as polysaccharides, proteins, pigments, and lipids.^2,3 In 2023, the global microalgae market was estimated to be worth USD 728.54 million. The market is anticipated to expand at a compound annual growth rate (CAGR) of 7.31% from USD 782.59 million in 2024 to USD 1376.42 million by 2032.⁴ E. gracilis, a unicellular, photosynthetic organism that is frequently grouped with eukaryotic algae, has chemicals that are of commercial importance, such as paramylon,⁵ wax esters,⁶ proteins, α-tocopherol, biotin, and polyunsaturated fatty acids.³ However, Paramylon is the microalga's special polysaccharide molecule. It consists of between 50-80% of the dry weight of the cell.⁷

Paramylon can be effectively produced using waste products as sources of carbon. This approach not only provides a sustainable method for paramylon production but also contributes to waste management by utilizing wastes from various industries.⁸ By converting waste materials into valuable biopolymers for paramylon production, this approach supports circular economy principles, reduces environmental impact, and promotes the advancement of eco-friendly agricultural practices.⁹ Due to their low cost and quantity of nutrients, particularly carbon and nitrogen for effective paramylon formation, food processing wastes have gained interest for microalgal cultivation.¹⁰ To date, paramylon has been produced from E. gracilis in potato liquor, maize steep solid, corn steep liquor, and brewer's residual grain using effective and reasonably priced methods.^11,12

Paramylon is recognized for its significant therapeutic effects, which include immunomodulation, wound healing, and potential protection against liver injury. Its diverse bioactive properties make it a promising candidate for various applications in the nutritional and pharmaceutical industries.¹³ Specifically, paramylon has demonstrated anti-HIV activities, inhibition of atopic dermatitis development, and anti-infection properties, showcasing its potential to combat a range of harmful diseases.¹² Additionally, paramylon exhibits hepatoprotective effects, anti-allergy properties, and antitumor activity, further highlighting its versatility as a therapeutic agent.¹⁴ Paramylon, has different potential benefits, such as improving metabolite production, enhancing growth, and assessing its role as a feed additive to boost plant health and resistance to diseases.¹⁵ Enhancing nutrient uptake and encouraging root development are two of paramylon's primary potential advantages for plant growth.¹⁵ Paramylon may also strengthen plant defenses against diseases, improving resilience and lowering the need for chemical pesticides.¹⁶ By combining these elements, Paramylon plays a very significant and diverse role in advancing sustainable farming methods and raising crop yields.¹⁷

Paramylon can be highly beneficial in sustainable farming as a plant biostimulant. It offers insights into a plant or crop's behavior and performance in response to biotic and abiotic challenges, including nutrient utilization, drought, high temperatures, and salinity.¹⁸ Utilizing paramylon as an elicitor may enhance a plant's resilience to drought by improving water retention and promoting root development, enabling more effective moisture access. Additionally, it could help mitigate stress responses under high temperatures and salinity, allowing plants to maintain metabolic functions and growth.^19,20 The main aim of this review is to evaluate how paramylon can be utilized as a biostimulant to enhance plant performance, focusing on its effects on nutrient utilization efficiency, stress resistance, and overall crop resilience. By investigating these aspects, the review seeks to provide insights into the potential of paramylon in promoting sustainable agricultural practices and improving crop yields.

Paramylon Production from E. gracilis Using Waste Sources

E. gracilis is an invaluable microalga for synthesizing high-value compounds such as paramylon. However, raising paramylon productivity and lowering E. gracilis cultivation costs are our two most important concerns. Food manufacturing²¹ wastes have gained interest for microalgal production due to their low cost and quantity of nutrients, such as carbon and nitrogen. The ideal carbon source and its concentration were examined by Sunah et al¹⁰ for effective paramylon synthesis. In order to grow E. gracilis and produce paramylon, a discarded tomato byproduct produced by a tomato processing factory was used. The result indicated that with 15 g/L glucose, the highest paramylon concentration (1.2 g/L) and content (58.2%) were found. Jeon et al²² discovered that co-cultivating Pseudoalteromonas bacteria under heterotrophic conditions resulted in a 34% paramylon yield. Mixotrophic cultivation using sewage effluents as the growing medium has been reported to yield 50% paramylon contents in just 7 days. The paramylon production was 1.77 g/L/day after the hydrolysate-based medium was used in conjunction with waste-based cell immobilization cultivation.²³ This suggests that waste water treatment facilities can potentially be transformed into sustainable paramylon production facilities. A study done by Kim et al,¹² showed that Brewers’ waste grain and corn steep liquor were used to produce paramylon. When E. gracilis was grown using corn steep liquor, the paramylon content and yield were higher (46.3% w/w and 0.17 g/g, respectively) than when it was grown using brewer's waste grain (32.3% w/w and 0.11 g/g respectively). This demonstrated that utilizing corn steep liquor as an industrial byproduct can be a successful strategy for generating paramylon.

The main bottlenecks in the industrialization of Euglena were the high production costs and the purification of paramylon. The cultivation of E. gracilis for paramylon can be expensive, with carbon sources accounting for up to 50% of the total medium cost.¹² The high cost of organic carbon sources significantly impacts overall production costs. The global market for β-glucan, including paramylon, is anticipated to reach 727.50 million USD by 2025.²⁴ Utilizing food industry byproducts can help reduce these expenses. For instance, as discussed above and observed in Table 1, Tomato processing byproduct, sewage effluent with Waste Wine, brewer's leftover grain, and corn steep liquor have high paramylon content of E. gracilis with a value of 58.2%, 67.7%, 32.3%, and 46.3% respectively.

Table 1.

Production of Paramylon from Various Food Industry Wastes.

Waste Sources	Cultivation Condition	Paramylon Yield	key Finding	Reference
Tomato Processing waste	Heterotrophic method with 15 g/L glucose	1.20 g/L with concentration of 58.2% content	Using glucose as a carbon source produced the highest paramylon concentration.	²⁵
Waste wine combined with sewage effluent	Inclusion of mixotrophic, organic waste	67.70% content	Production of paramylon has significantly increased in comparison to synthetic medium.	²¹
Grain leftover by the brewer	Heterotrophic, with steep liquor from corn	32.30% content	reduced output of paramylon in contrast to corn steep liquor.	¹²
Corn steep liquor	Different organic wastes that are heterotrophic	46.30% content	A successful plan for producing paramylon at a reasonable cost.	²⁶
Molasses	Heterotrophic, complex media	Not specified	When mixed with other wastes, it promotes the growth of biomass and the synthesis of paramylon.	²³

The purification process of paramylon typically involves several steps. The purification of paramylon from E. gracilis involves specific extraction techniques that can be costly and complex. Efficient methods that require minimal processing can reduce these costs. Through optimizing extraction and purification methods can lead to more efficient processes. Research into alternative, less expensive techniques is essential for making paramylon more accessible for various applications.

Paramylon Production Techniques

Various methods and techniques are employed in the manufacturing of paramylon. In heterotrophic cultivation, E. gracilis is grown without light using organic carbon sources such as glucose or food industry waste (Table 2). The combination of light and dark conditions in the mixotrophic cultivation approach makes the use of organic and inorganic carbon sources possible. According to Matsui et al²¹ mixotrophic cultivation using organic wastes and sewage effluent is a viable and highly effective way for E. gracilis to create paramylon. Their results showed that the paramylon concentration was 67.7% and the paramylon productivity of E. gracilis in the sewage effluent containing waste wine reached 47.8 mg/L/d. The above experimental result showed that a successful conversion of substrates into this valuable polysaccharide (Paramylon) and Sewage effluent containing waste wine demonstrates the potential for high yields in a real-world application. The result also indicated that E. gracilis paramylon production was significantly increased by adding waste wine, corn steep liquor, molasses, and organic wastes to sewage effluent. A novel heterotrophic cultivation method for cultivating E. gracilis through a unique NaCl stress-induced process was also used to enhance paramylon content and production substantially. According to the results, the content and production of paramylon can be increased by 25.33% and 23.77%, respectively, by adding 16 g L−1 NaCl to the heterotrophic culture solution for 36 h during the stationary phase.²⁷ In another study, heterotrophic cultivation of E. gracilis in Stirred Tank Bioreactor (STR) was conducted by Ivusic et al²⁸ The results demonstrated that during the continuous bioprocess in STR with a complex medium containing 20 g/L of glucose and 25 g/L of CSS, E. gracilis accumulated a competitive paramylon content of 67.0% and the highest paramylon productivity of 0.189 g/Lh, in contrast to the batch, fed batch, and repeated batch bioprocesses. This suggests that continuous bioprocessing in an STR can significantly enhance the efficiency of paramylon production and STR can be an effective platform for paramylon production. In another research finding, using complex media, suitable cultivation of E. gracilis and paramylon production was conducted by Ivušic et al.¹¹ In order to develop biomass and synthesize paramylon, the data clearly demonstrate that E. gracilis can readily metabolize glucose (20 g/L) and fructose as carbon sources and corn steep solid (30 g/L) as complex nitrogen and growth factors. It determined that the best complex medium for the industrial culture of E. gracilis and the synthesis of paramylon is one that contains glucose than corn steep solid.

Table 2.

Summary of Paramylon Production Techniques and Yields.

Techniques Used for Production of Paramylon	Sources of Wastes Used for Paramylon Production	Cultivation Methods for Paramylon Production	Paramylon Yield	Finding of the Research	Reference
Heterotrophic cultivation	Tomato byproduct	Glucose supplementation	1.2 g/L (content of 58.2%)	High yield of paramylon with glucose; efficient utilization of leftovers from the food business.	²⁵
Mixotrophic cultivation	Sewage effluent + waste wine	Organic waste inclusion	67.7% content	Production of paramylon is improved by using both inorganic and organic carbon sources.	²⁹
Heterotrophic cultivation	Corn steep liquor	Organic waste inclusion	46.3% content	Greater yield in contrast to alternative organic sources.	³⁰
Heterotrophic cultivation	Brewer's leftover grain	Organic waste inclusion	32.3% content	Less effective than corn steep liquor.	³¹
Complex media	Various industrial byproducts	Synthetic and complex media	Not specified	Efficient in producing paramylon and growing biomass	¹¹

Franjo et al¹¹ conducted heterotrophic cultivation of E. gracilis to maximize the synthesis of paramylon using synthetic (Hutner medium) and complicated cultivation media. For the creation of complex media, they used a variety of industrial byproducts, including beef extract, molasses, yeast extract, and corn steep solid. The findings clearly indicate that Euglena gracilis serves as a valuable source for both paramylon production and biomass development.

Use of Paramylon as a Biostimulants

Materials that improve plant development, stress tolerance, and growth are known as biostimulants; they are not the same as fertilizers. When added to fertilizers, biostimulants help plants develop, absorb nutrients more readily, and become more resilient to abiotic stressors.¹⁸ Paramylon has shown promising biostimulant properties due to its ability to stimulate plant growth and improve nutrient uptake. The results demonstrated that the paramylon treatment allowed for the reduction of the optimal water regimen from approximately 8.64 L plant−1 day−1 to 0.36 L plant−1 day−1 without adversely affecting yield and ecophysiological indices.³² Paramylon has been found to promote plant growth by enhancing root development, increasing chlorophyll content, and stimulating photosynthesis. These effects can lead to improved plant vigor, increased biomass production, and enhanced crop yield.³³ Paramylon has been shown to improve nutrient uptake in plants, particularly nitrogen and phosphorus. By enhancing nutrient absorption, paramylon can help plants better utilize available nutrients in the soil, leading to improved nutrient efficiency and overall plant health.³² Paramylon has also demonstrated potential in enhancing plant stress tolerance, including resistance to abiotic stresses such as high temperature, salinity and drought. By boosting plant resilience, paramylon can help plants withstand environmental challenges and maintain productivity under adverse conditions.³⁴ The use of paramylon as a biostimulant aligns with sustainable agriculture practices by promoting eco-friendly solutions for enhancing crop production. By utilizing a natural polysaccharide derived from microalgae, farmers can reduce their reliance on synthetic chemicals and minimize environmental impact.³⁵

Biostimulants include proteins, amino acids, enzymes, vitamins, and other substances. The word “biostimulants” is frequently used to refer to natural stimulants, such as protein hydrolases, fulvic acids, salicylic acid, phenols, and humic^36,37 Organisms such as bacteria and fungus that alter the species composition of organisms in the soil or plants are an important class of plant biostimulants. Their existence can limit or quicken the rate at which systems degrade.^38,39 The definition of plant biostimulants under the recently implemented Regulation (EU) 2019/1009 is based on four agricultural functional claims. According to these claims, a plant biostimulant's only objective is to enhance one or more of the following characteristics of the plant and/or the plant rhizosphere by stimulating plant feeding processes, independent of the product's nutritional content: efficiency in using nutrients, resilience to (a)biotic stress, qualitative attributes, or accessibility of restricted nutrients in the rhizosphere or soil.⁴⁰

Paramylon use as Plant Growth Performance

Paramylon, has been increasingly studied for its potential use as a plant growth promoter. Its bioactive properties have shown promising results in enhancing plant growth performance by stimulating various physiological processes in plants.¹⁵ Paramylon has been reported to promote plant root development by stimulating root elongation and branching. This enhanced root system allows plants to access more nutrients and water from the soil, leading to improved overall growth and productivity.⁴¹ Paramylon has the ability to enhance photosynthesis in plants by increasing chlorophyll content and improving the efficiency of light absorption. This results in higher carbon dioxide assimilation rates, contributing to increased biomass production and plant growth.⁴² It has been shown that paramylon influences the concentrations of plant hormones, particularly auxins and cytokinins, which are crucial for regulating a plant's growth and development. By modulating hormone signaling pathways, paramylon can promote cell division, elongation, and differentiation, enhancing growth performance.³⁴ Paramylon can improve nutrient uptake efficiency in plants by enhancing the activity of nutrient transporters and promoting nutrient assimilation processes. As a result, critical nutrients like nitrogen, phosphorus, and potassium are better utilized, which is beneficial for the best possible growth and development of plants.⁴³

Paramylon can be applied as a seed treatment to enhance germination rates, seedling vigor, and early root development. By priming seeds with paramylon, plants are equipped with the necessary resources to establish strong root systems and robust growth from the beginning.⁴⁴ Paramylon solutions can be used as foliar sprays to directly deliver bioactive compounds to plant leaves, promoting photosynthesis, nutrient uptake, and overall growth performance. Foliar application of paramylon can help plants overcome stress conditions and maximize their growth potential.³² Incorporating paramylon into the soil as a natural amendment can improve soil structure, microbial activity, and nutrient availability for plants. By enriching the soil with paramylon, farmers can create a conducive environment for plant growth and enhance overall crop performance.⁴⁵

Plants can be elicited by β-1,3-glucans like paramylon, which alter physiological responses and hormone levels. Plant hormones influence every stage of the life cycle of plants as well as how they react to biotic and abiotic environmental stressors.³⁴ Most research work showed that, the effects of a root treatment with E. gracilis paramylon affect photosynthetic activity, hormone levels in the xylem, and stress resulting from dehydration in tomato plants (Solanum lycopersicum L.).³⁴ The findings of Scartazza et al³⁴ also show that paramylon clearly affects photosynthetic efficiency, dehydration tolerance, and the hormone content of xylem sap in a dose-dependent manner. The abscisic acid, salicylic acid, and jasmonic acid levels were all adjusted. The rate of CO₂ assimilation, intercellular CO₂ concentration, transpiration rate, stomatal and mesophyll conductance, leaf water potential, water-use efficiency, and quantum yield of photosystem II were among the related physiological responses that were also investigated. Paramylon regulates the conductance of CO₂ diffusion from the air to the carboxylation sites. It increases the efficiency of water consumption, which can strengthen a plant's defenses against abiotic stresses like drought.³⁴

Tomatoes (Solanum lycopersicum L.), the most extensively farmed vegetable in the world, require much water and are severely impacted by water stress. Using Micro-Tom analysis on the microalga E. gracilis, the effects of β-(1,3)-glucan (paramylon) on fruit quality profile and drought tolerance were assessed. The findings demonstrate that paramylon significantly improves the fruit quality profile when grown under drought stress and increases plant tolerance to drought compared to untreated plants.⁴⁶

Plants use β-1,3-glucans, such as paramylon, as elicitors to alter their hormone levels and physiological reactions. Plant hormones influence every stage of the life cycle of plants as well as how they react to biotic and abiotic environmental stressors.³⁴ Paramylon regulates the conductance of CO₂ diffusion from the air to the carboxylation sites and increases the efficiency of water consumption, which can strengthen a plant's defenses against abiotic stresses like drought.³⁴ Euglena gracilis is a nutritional supplement rich in paramylon that functions similarly to dietary fiber and has various biological effects, including immune system regulation, antitumor, and anti-obesity properties. Xie et al⁴⁷ discovered that the hepatic histological abnormalities in mice caused by lipopolysaccharide/ D-galactosamine were relieved by sonicating and alkalizing paramylon. Future possibilities are greatly increased when Lactobacillus-derived products are enriched with E. gracilis or paramylon, as this can contribute to developing functional foods with improved nutritional profiles.⁴⁸

Paramylon nanofibers also positively affected tomato plants that were stressed by drought or a lack of water. The fruits of stressed untreated plants never reach the green ripening stage, but stressed paramylon-treated plants showed earlier flowering and fruit ripening than untreated, well-watered plants.⁴⁹ Paramylon activity can reduce the optimal plant water regimen by more than ten times. Water stress significantly impacted ecological parameters such as photosynthetic yield, stomatal conductance, and leaf water potential. These metrics all continuously decreased until saturation. All the criteria could return to the plants’ levels that get regular irrigation after root treatment with paramylon nanofibers. These findings show that paramylon nanofibers benefit stomatal activity, whose regulation increases water usage efficiency and wards off dehydration.¹⁵ This activity is linked to a brief alteration in the concentration of the three primary plant hormones: abscisic acid, jasmonic acid, and salicylic acid. The fruits of paramylon-treated plants exhibited significantly higher levels of physical-chemical and quality indices, such as antioxidant substances (phenols, β-carotene, Vitamin A/C/E, and lycopene) and carbohydrates (sucrose, glucose, and fructose), which improved their nutritional value and sensory quality. Furthermore, the increased dry matter content (ie, lower moisture) allowed for better post-harvest storage capacity, which increased the commercial product value and prolonged the commercial duration.^46,50 These findings demonstrate that paramylon significantly enhances the quality profile of the fruits and boosts plant resistance to drought compared to untreated plants produced under drought stress.

Paramylon Used as Physiological Process

E. gracilis, can be utilized to enhance various physiological processes in plants, ultimately leading to improved growth performance.³ Paramylon has been shown to stimulate cell division and elongation in plant tissues, promoting overall growth and development. By enhancing these processes, paramylon can contribute to forming new tissues and structures in plants.⁴³ Paramylon can modulate plant metabolic pathways, leading to increased energy production, nutrient assimilation, and biosynthesis of essential compounds. This can result in improved plant vigor and resilience to environmental stresses.⁵¹ Paramylon has been reported to enhance water uptake and retention in plants, helping them maintain optimal hydration levels for growth and physiological functions. This can be particularly beneficial during periods of drought or water stress.³² Paramylon can act as a stress modulator in plants by regulating the production of stress-responsive proteins and antioxidants. This can help plants cope with various abiotic and biotic stresses, such as heat, cold, salinity, and pathogen attacks.³⁴ Research showed that, using paramylon treatment, Solanum lycopersicum L's drought resistance is higher (80%) than the value obtained in control (60%).³²

Euglenoids have an extraordinary capacity to withstand harsh conditions: They can withstand large doses of heavy metals and are acidophilic. As a result, they can produce useful metabolites like paramylon and be employed in the bioremediation of contaminated waters.⁵² E. gracilis can be grown heterotrophically using nutrients extracted from wastewater.⁵³ For instance, solid sludge wastes can be hydrothermally converted to provide culture media rich in phosphoric acid and ammonia, supporting faster growth rates than the typical AF-6 culture medium. The authors emphasized that E. gracilis had a remarkable ability to withstand ammonia, with its concentration being ten times more than that of AF-6 medium.⁵⁴

The most widely grown produce in the world, tomatoes, are severely impacted by water stress and need a lot of water.⁵⁵ The effects of E. gracilis microalga's pure β-(1,3)-glucan (paramylon) on fruit quality profile and drought tolerance of Solanum lycopersicum L were assessed using Micro-Tom. The plants in the aeroponic system were grown under three different growing conditions such as an optimal water regimen, a water scarcity regimen, and a water scarcity regimen coupled with a paramylon root treatment.³² Throughout the plants’ lives, eco-physiological, physicochemical, and quality metrics were tracked and compared. The physicochemical and biochemical characteristics of paramylon-treated plants saw notable changes, but the eco-physiological parameters experienced only a temporary impact from drought stress.³² For instance, when stressed untreated plants were cultivated under an optimal water regime, the fruits of the paramylon-treated plants reached the first ripening stage two weeks earlier than the fruits of the untreated plants, which failed to develop past category II. The amount of soluble carbohydrates (sucrose, glucose, and fructose) and antioxidants (vitamins, carotenoids, and phenolic acid) in fruits from treated plants was also double that of fruits from untreated plants.⁴⁹ These results show that paramylon dramatically improves fruit quality profile and increases plant tolerance to drought when compared to untreated plants grown under drought stress.³²

The effects of β-(1,3)-glucan (paramylon), which was separated from the microalga E. gracilis, on water stress were also assessed by a team of Italian scientists Tiny Tom.³² Using an eco-physiological approach, this study identified a number of physiological and biochemical mechanisms that lead to enhanced water stress tolerance when paramylon nanofibers are applied. These mechanisms include: (i) increasing photosynthetic rate, and (ii) decreasing photosystem II's sensitivity to potential dehydration damages.

During the paramylon treatment, stomatal and non-stomatal photosynthetic properties were evaluated to see whether the altered xylem hormone composition affects the tomato response at the leaf level. Each of the paramylon dosages significantly reduced the stomatal conductance. In tomatoes, paramylon may cause a coordinated control of mesophyll and stomatal conductance.³⁴ A research work showed that, during paramylon treatment, the Photosynthetic Efficiency of Solanum lycopersicum L possesses a higher value (75%) than the value obtained in the control (50%).³² β (1, 3) glucan-treated tobacco leaf epidermal peels have significantly impacted stomata movements in response to light, encouraging both closure and inhibiting opening.¹⁹ As with exogenous ABA therapy, drought, and other environmental changes, Paramylon may result in a coordinated modulation of tomatoes’ stomatal and mesophyll conductance.⁵⁶

Paramylon Used as Biochemical Process in Plant

Paramylon, a unique polysaccharide found in certain microalgae like E. gracilis, can be utilized as a biochemical process enhancer in plants. When applied to plants, paramylon can interact with various biochemical pathways and processes, leading to beneficial effects on plant growth, development, and stress tolerance.³ Paramylon can serve as a source of energy for plants by undergoing enzymatic degradation to release glucose molecules. This glucose can then be utilized by plant cells for energy production through processes like glycolysis and respiration, supporting metabolic activities essential for growth and development.²⁵ Paramylon can function as a carbon storage compound in plants, providing a reserve of energy-rich carbohydrates that can be mobilized when needed. By regulating the storage and utilization of carbon, paramylon helps plants maintain energy balance and sustain growth under changing environmental conditions.²⁵ Paramylon has antioxidant properties that can help plants combat oxidative stress caused by reactive oxygen species (ROS). By scavenging ROS and protecting cellular components from damage, paramylon maintains cellular homeostasis and promotes plant health.¹⁵ A Casas-Arrojo et al⁵⁷ perform antioxidant activities of paramylon. Their findings indicated that at a concentration of 500 µg mL⁻¹, the highest value of antioxidant activity was 5.40 ± 0.26%. The antioxidant activity assay using the DPPH method also showed that paramylon from E. gracilis had the highest antioxidant activity at a concentration of 200 µg mL⁻¹, with a result of 17.79 ± 0.57%. Paramylon can interact with plant immune signaling pathways, enhancing defense responses against pathogens and pests. By activating specific defense genes and signaling molecules, paramylon boosts the plant's ability to resist infections and mount effective immune responses.⁴⁹ Paramylon may influence gene expression in plants by modulating transcriptional regulators and signaling cascades. This can lead to the upregulation of genes involved in growth promotion, stress tolerance, and other physiological processes critical for plant performance.⁴⁹ Incorporating paramylon as a biochemical process enhancer in plant growth strategies can offer a sustainable and eco-friendly approach to improving crop productivity and resilience. Continued research into the molecular mechanisms underlying paramylon's effects on plant biochemistry will further elucidate its potential applications in agriculture and biotechnology.³²

The nutritional properties and numerous health benefits of paramylon have drawn attention. Paramylon is an indigestible polysaccharide, a dietary fiber with strong immunostimulating and cytokine-related effects.^58,59 According to recent research, pro-inflammatory factors (NO, TNF-α, IL-6, and COX-2) are upregulated in human lymphomonocytes when paramylon is sonicated and alkalized.⁶⁰ According to these reports, Euglena paramylon may function as a secure and valuable coadjutant element for the innate immune response. Additionally, when included in the diet, paramylon lowers cholesterol and in humans, it moderates the postprandial glucose and insulin response.^61,62 A paramylon derived from E. gracilis reduced the initial corneal inflammatory response from alkali burns and aided in healing epithelial wounds in vivo in mice.⁶³ Paramylon's antioxidant qualities prevented mice's liver damage by carbon tetrachloride¹⁴ and prevented the development of atopic dermatitis-like lesions.⁶⁴ In mice with transplantable sarcoma-180, paramylon has been shown to exhibit anticancer effects; this shows its effect in tumor treatment.⁶⁴ Koizumi et al⁶⁵ have demonstrated the preventive effects of paramylon and its isomer amorphous paramylon against the development of preneoplastic aberrant crypt foci (ACF) in the colon. Furthermore, a recent study employing a collagen-induced arthritis mouse model shown that paramylon decreased the temporary alterations in the visual assessment score of rheumatoid arthritis symptoms.⁶⁶ In the femoral trochlear groove, it was discovered that Euglena treatment reduced edema, inflammation, cell hyperplasia, granulation tissue formation, fibrosis, and articular cartilage loss.

Several investigations have also documented paramylon's antibacterial properties. There have been reports of paramylon's antibacterial properties against Staphylococcus aureus and Escherichia coli.⁶⁷ The sulfated paramylon derivative obtained from E. gracilis inhibited the cytopathic effect of HIV-1 and HIV-2 on cultivated MT-4 cells, as well as HIV replication and HIV antigen expression in human peripheral blood mononuclear cells^65,68 and influenza virus infection in mice.⁶⁹ Oral administration of paramylon has been shown to have immunological stimulatory and growth-promoting effects in fish, leading to an increase in adaptive responses and resistance to bacterial infections in experiments.^70,71 Therefore, paramylon offers considerable biotechnological potential for use in medicine and veterinary care, even though its current industrial demand is low. On the other hand, it has been established that a paramylon overdose is detrimental to hepatocytes and lipid metabolism,⁷² indicating that a thorough dose-response investigation on the nutritional benefits and adverse effects of paramylon produced from Euglena is necessary.

Interaction and Coordination of Paramylon with Plant Hormones

It is true that paramylon can interact with plant hormones and help plants’ hormonal signaling pathways work together. Another term for plant hormones is phytohormones, which are signaling molecules that regulate several aspects of a plant's growth, development, and response to external stimuli.^34,74 Some ways in which paramylon can interact with plant hormones are listed in the following sub section and Table 3.

Table 3.

The way in Which Paramylon Interacts and Coordinates with Other Plant Hormones, Such as Gibberellin, Ethylene, Abscisic Acid (ABA), Cytokinin, and Auxin.

Plant Hormone	Role in Plant Growth/Development	Interaction with Paramylon	Reference
Auxin	Controls fruit growth, root formation, and cell elongation.	Auxin distribution influenced by Paramylon, improving root development and reaction to environmental cues.	¹⁸
Cytokinin	Slows the senescence of leaves and encourages cell division and shoot development.	By increasing cytokinin activity, paramylon may promote cell division and general plant health.	⁷⁵
Abscisic Acid (ABA)	Involved in controlling stomatal closure, stress reactions, and seed dormancy.	Paramylon may help regulate ABA levels, which would help with water management and stress tolerance.	⁴³
Gibberellin	promotes flowering, seed germination, and stem elongation.	Under the right circumstances, paramylon may interact with gibberellin pathways to encourage growth and development.	⁷⁶
Ethylene	Controls the ripening of fruit, the wilting of flowers, and the abscission of leaves.	Paramylon may have an impact on ripening processes and stress responses via influencing ethylene signaling.	⁷⁵

Auxin Regulation

Auxins are a class of plant hormones that are crucial for regulating cell elongation, apical dominance, and root growth. Paramylon may affect auxin signaling pathways by affecting the expression of genes involved in auxin synthesis, transport, and response. This interaction leads to modifications in the growth patterns and developmental processes of plants.⁷⁷

Cytokinin Response

Plant hormones called cytokinins encourage cell division, shoot growth, and postpone senescence. By modifying the activity of cytokinin receptors or other downstream elements of the cytokinin signaling pathway, paramylon impacts cytokinin signaling. This relationship may impact processes like stress reactions, leaf withering, and shoot branching.⁷⁸

Abscisic Acid (ABA) Regulation

ABA is a plant hormone involved in stress responses, seed dormancy, and stomatal regulation. Paramylon influence ABA-mediated signaling pathways by modulating the expression of ABA-responsive genes or affecting ABA receptor interactions. This interaction enhance plant tolerance to abiotic stresses like drought and salinity.⁷⁹

Gibberellin Metabolism

Gibberellins are hormones found in plants that control blooming, seed germination, and stem elongation. By modifying the activity of enzymes involved in gibberellin production or catabolism, paramylon affect gibberellin metabolism. Plant development transitions and growth processes are impacted by this interaction.⁸⁰

Ethylene Signaling

An ethylene plant hormone controls fruit ripening, senescence, and reactions to biotic and abiotic stressors. Paramylon interacts with ethylene signaling pathways by modulating the expression of ethylene-responsive genes or affecting ethylene receptor functions. This interaction affects processes such as fruit development, leaf senescence, and stress tolerance.⁸¹ By interacting with plant hormones and influencing hormonal signaling pathways, paramylon can modulate different aspects of plant physiology and development. Gaining knowledge of the interactions between paramylon and plant hormones can help develop new approaches to improve plant performance in general, stress tolerance, and crop productivity.³⁴

Paramylon Used in Abiotic

Paramylon can help plants cope with osmotic stress caused by drought or high salinity conditions. The effects of water removal on tomato plants treated with paramylon were observed by Scartazza et al³⁴ They proposed that the paramylon enhanced tomato plants’ capacity to minimize water loss. Paramylon can stabilize plant cells’ turgor pressure and stop water loss by functioning as an osmoprotectant. When there is a shortage of water or a high concentration of salt, this can help plants survive. Paramylon has been shown to possess antioxidant properties, which can help plants combat oxidative stress induced by abiotic stresses such as high light intensity or heavy metal exposure. Plant cells can be shielded from oxidative damage by paramylon, which scavenges reactive oxygen species (ROS) and increases plant tolerance to stress.⁸² Paramylon may modulate the expression of stress-responsive genes in plants, activating defense mechanisms against abiotic stresses. Plant resistance to external stresses can be increased by paramylon by controlling the genes’ expression in stress signaling pathways. Paramylon supplementation has been reported to improve photosynthetic efficiency in plants under stressful conditions.³⁴ By promoting chlorophyll synthesis, maintaining optimal photosystem functioning, and enhancing carbon assimilation, paramylon can help plants maintain growth and productivity even under adverse environmental conditions.⁸² Paramylon may influence stomatal conductance and water use efficiency in plants exposed to drought stress. By regulating stomatal aperture and transpiration rates, paramylon can help plants conserve water and maintain proper gas exchange, thus improving their ability to withstand water scarcity.⁸³ Paramylon can enhance nutrient uptake and homeostasis in plants growing under nutrient-deficient or toxic soil conditions. By promoting nutrient absorption and translocation, paramylon can support plant growth and development even in challenging environments.⁸⁴

Paramylon regulates the conductance of CO₂ diffusion from the air to the carboxylation sites and increases the efficiency of water consumption, which can strengthen a plant's defenses against abiotic stresses like drought.⁷² Paramylon modulates the conductance to CO₂ diffusion from air to the carboxylation sites and improves water use efficiency (WUE) to strengthen plant defense responses to abiotic stress, such as drought.³⁴ The microalgae E. gracilis’ Paramylon (β-(1,3)-glucan was applied to Solanum lycopersicum L. In the study of Barsanti et al³² The findings demonstrated that fruit's elevated concentrations of antioxidant compounds (carotenoids, phenolic acid, and vitamins) and soluble carbohydrates (glucose, fructose, and sucrose) correlated with drought.

Conclusion

Paramylon, derived from microalgae such as Euglena gracilis, has demonstrated significant potential in enhancing agricultural productivity and promoting plant growth. As a biostimulant, paramylon improves physiological functions in plants, making them more resilient to abiotic stressors such as salinity, drought, and nutrient deficiencies. Research indicates that paramylon enhances water-use efficiency, regulates hormone levels, and increases photosynthetic efficiency, resulting in healthier plants and higher crop yields. In addition, paramylon serves as an environmentally friendly alternative to traditional fertilizers, as it can be sustainably produced from waste materials, aligning with the principles of sustainable agriculture. Despite these promising attributes, a comprehensive understanding of paramylon's interaction with plant metabolic pathways remains limited. Further research is needed to elucidate its precise molecular mechanisms and how it influences gene expression related to stress responses. Long-term field studies across diverse climatic conditions are essential to assess its effectiveness, stability, and environmental impact under real-world agricultural practices. Future research directions should focus on optimizing paramylon formulations to enhance its bioavailability and efficacy. Investigating its combined use with other biostimulants or conventional fertilizers could reveal potential synergistic effects. Additionally, exploring the cost-effectiveness and scalability of paramylon production will be critical for its widespread agricultural adoption. Research into the impact of paramylon on soil microbiota and nutrient cycling is also necessary to understand its broader ecological implications.

In conclusion, paramylon holds substantial promise as a sustainable and effective biostimulant capable of improving crop productivity and resilience to abiotic stresses. However, addressing the existing knowledge gaps through multidisciplinary and field-based research is vital for realizing its full potential and facilitating its integration into sustainable agricultural systems.

Footnotes

Acknowledgments

The authors thank Debre Tabor University (DTU) for giving them a chance to do this review.

ORCID iD

Limenew Abate Worku

Ethical Considerations

This article does not contain any studies with human or animal subjects.

Author Contributions/CRediT

The idea and design of the study were contributed to by all authors. Limenew Abate Worku handled the data collecting, analysis, and material preparation. Limenew Abate Worku wrote the manuscript's initial draft. Woinshet Kassie Alemu is the author of the tables. Rakesh Kumar Bachheti offered feedback on earlier drafts of the work. The final manuscript was read and approved by all writers. Every contributor contributed to the article's revision as well.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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A Review of Application of Paramylon (β-1,3-Glucan) in Plant Growth and Production

Abstract

Keywords

Introduction

Paramylon Production from E. gracilis Using Waste Sources

Paramylon Production Techniques

Use of Paramylon as a Biostimulants

Paramylon use as Plant Growth Performance

Paramylon Used as Physiological Process

Paramylon Used as Biochemical Process in Plant

Interaction and Coordination of Paramylon with Plant Hormones

Auxin Regulation

Cytokinin Response

Abscisic Acid (ABA) Regulation

Gibberellin Metabolism

Ethylene Signaling

Paramylon Used in Abiotic

Conclusion

Footnotes

Acknowledgments

ORCID iD

Ethical Considerations

Author Contributions/CRediT

Funding

Conflicting Interests

References