Keywords

15.1 Introduction

Crop production plays a critical role in an agricultural-based economy like India. The agriculture sector still decides the fate of 70% of its rural population (FAO 2015). Apart from cereal crops, India is a major exporter of crops with commercial standards. Presently, various innovative methods for crop enhancement are being sought to meet the rising demand of exponentially growing population. Fertilizers, PGRs, minerals and metal nanoparticles have proved their elicitor effect on various crops (Tripathi et al. 2016; Ahmad et al. 2019). However, their side effects and toxicity have always been a concern. Therefore, much recent research has been directed to explore some more sustainable and eco-friendly growth elicitors. Natural polysaccharides (NPs), besides being growth enhancers, are also antimicrobial, non-toxic, biocompatible and cheaper with no negligible side effects (Hu et al. 2005; Campo et al. 2009; Yan and Chen 2015). This makes NPs farmer-friendlier and a more sustainable option. Moreover, due to its greater biocompatibility, NPs legend with cell membrane and regulate membrane permeability. Various sources have asserted their eliciting effect on various crops with ample data to support (El-Mohdy 2017; Rabêlo et al. 2019; Saucedo et al. 2019). Figure 15.1 indicates different natural polysaccharides, i.e. chitosan, carrageenan and sodium alginate, and their growth-regulating attributes besides their biological properties.

Fig. 15.1
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Pictorial representation of the commercial applications of carrageenan, chitosan and sodium alginate along with their effect on plants

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15.2 Chitosan

Chitin [(1,4)-2-acetamido-2-deoxy-β-D-glucan] is the second most abundant molecule in nature (Yan and Chen 2015) and is found primarily in crustacean shells, insects and fungi (Yan and Chen 2015; Jia et al. 2016; Turk 2019). Chitosan is a deacetylated chitin polymer that contains β-(1 → 4)-linked D-glucosamine and N-acetyl-D-glucosamine subunits (Malerba and Cerana 2016). Chitosan and its derivatives can further enrich chitosan properties due to their different physicochemical properties (size, density, surface area, etc.) enabling them to cross-talk with the cell wall and membrane more efficiently (Kim and Rajapakse 2005; Muley et al. 2019a). Multiples studies have reported that chitosan imparts a general trend of positive influence on plant growth and overall productivity (Pichyangkura and Chadchawan 2015; Malerba and Cerana 2016; Rabêlo et al. 2019). Figure 15.2 traces the primary source of chitosan as well as induced responses in the biological systems.

Fig. 15.2
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Chitosan and its accompanied biological properties

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15.2.1 Biological Activities of Chitosan

Chitosan has been reported to encompass a wide array of biological activities including antimicrobial, antitumor, antidiabetic, immunity-enhancing and wound-healing properties (Hayashi and Ito 2002; Xing et al. 2008; Zeng et al. 2008). Antimicrobial activities of chitosan chiefly comprise its antifungal and antibacterial properties (Xing et al. 2008; Meng et al. 2010). These properties, however, depend on multiple factors such as species of the microbe, concentration, deacetylation rate and molecular weight of chitosan or the pH of the solution itself (Xu et al. 2007; Xing et al. 2008; Yen et al. 2009). Chitosan can also constrain the formation of fungal spore, germ tube as well as mycelia (Meng et al. 2010). Various studies have suggested that chitosan can be used in food preservation and packaging industry given its antimicrobial potential (Chien and Chou 2006). Moreover, chitosan is cheaper, biocompatible, biodegradable and non-toxic and thus can be used in diverse fields including preservation and packaging of edible items (Chien and Chou 2006; García et al. 2015). Chitosan has been found effective against various economically important fungal strains including Alternaria, Fusarium, Penicillium, Phytophthora as well as Botrytis ((Meng et al. 2010) and the references therein). Therefore, chitosan can also be used as food preserver. Chitosan can keep food products away from fungal spoilage and thus elongate their shelf life (Liu et al. 2007), a decisive step in global food security itself.

Chitosan has been found effective against numerous bacteria as well (Du et al. 2009; Badawy et al. 2014). Chitosan solution has antipathogenic activity against the spread of many crop-threatening bacterial strains including Xanthomonas (Li et al. 2008). Keeping in view its action against fungi, it could be hypothesized that chitosan might inhibit bacterial biofilm formation and its further development by interacting with lipid bilayer and destabilizing bacterial membrane. As chitosan solution is generally prepared in acids given its low solubility in neutral or basic media, it can be argued that these properties might perhaps be more associated with acidic solvents. Thus, the extent of chitosan efficacy against such microbes is debatable. Recently, few chitosan derivatives with higher solubility in water were prepared and checked for various activities (Badawy and Rabea 2012; Tan et al. 2013; Badawy et al. 2014). It seemed more plausible that antimicrobial properties are to be more attributed to chitosan rather than the acidic solvent itself.

15.2.2 Role of Chitosan in Plant Growth Regulation

Chitosan has been reported as a growth promoter and signalling molecule in plants (Wang et al. 2015; Malerba and Cerana 2016; Muley et al. 2019b). Chitosan may also indulge in a complicated cascade of signal transduction that results in positive modulation of photosynthesis and multiple other related phenomena (Zhang et al. 2018). Chitosan being an important plant signalling molecule may target the nucleus and chloroplast (Pichyangkura and Chadchawan 2015; Rabêlo et al. 2019). Multiple genes associated with light reaction including those encoding for chlorophyll a/b binding protein and oxygen-evolving protein complex could be enhanced with chitosan application (Chamnanmanoontham et al. 2014). This might stabilize photosystem II and increased its efficiency and result in enhanced photosynthetic productivity. Similar regulatory effect was demonstrated in maize (Rabêlo et al. 2019), mint (Ahmad et al. 2019), potato (Muley et al. 2019b) and wheat (Zou et al. 2015).

Chlorophyllase is a crucial enzyme that catalyses the degradation of chlorophyll. Chitosan can suppress the expression level of the genes encoding for chlorophyllase resulting in increased photopigment content (Zhang et al. 2018). Chitosan is also capable of upregulating the translation of transcripts associated with photosynthesis as well as of those pertaining to the metabolism of carbon, nitrogen and amino acid (Zhang et al. 2018). Increased C- and N-assimilation plays a crucial role in source-sink potential and in the biosynthesis of growth- and yield-related molecules such as proteins and phenols (Chamnanmanoontham et al. 2014).

Plant mitochondria and chloroplasts produce different kinds of reactive oxygen species (ROS) and reactive nitrogen species (RNS) including peroxides and superoxides during various physiological processes under normal environment (Turk 2019). These compounds, collectively known as oxidants, have the tendency to damage lipid membrane via lipid peroxidation or alter membrane permeability via electrolyte leakage (Gupta et al. 2018; Zehra et al. 2020). Antioxidants are a group of compounds produced by plants as a counter-mechanism to regulate such phenomena. This cross-talk between oxidant and antioxidant signalling cascades contributes to ROS pathway and is directly linked with plant innate immunity (Rı et al. 2002; Gupta et al. 2018; Kohli et al. 2019).

Multiple studies (El-tantawy 2009; Chatelain et al. 2014; Wang et al. 2015; Ahmad et al. 2019; Muley et al. 2019b) have established that chitosan in different forms could enhance overall growth and yield in various crops. Chitosan also influences expression level of multiple glycolysis-related enzymes that might provide more energy to the plant (Chamnanmanoontham et al. 2014). However, chitosan might also exhibit some other different responses in different plants due to the fact that these responses chiefly depend on plant species and the concentration of chitosan used (Pongprayoon et al. 2013). As a general spectrum of chitosan effect on various plant phenomena, it has been reported to improve the biosynthesis of photosynthetic pigments, i.e. chlorophyll and carotenoids (Ahmad et al. 2017). Similar eliciting effects are also exhibited by source-sink potential through providing more efficient mineral uptake and their assimilation (Ahmad et al. 2017). Chitosan also plays a decisive role in plants during adverse environmental conditions. It upregulates antioxidant metabolism and ROS pathway and assists in enhanced production for various enzymatic as well as non-enzymatic antioxidants to resist the cellular damage (Chandra et al. 2015). These regulations, ultimately, help the plant to exhibit enhanced growth and overall production and also to survive in a stressful environment (Muley et al. 2019b; Rabêlo et al. 2019). Table 15.1 emphasizes on particular phenomena that were associated with application of chitosan and its derivatives in different plants of economic importance.

Table 15.1 Eliciting effects of chitosan and its derivatives on various plant species
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15.3 Carrageenan

Carrageenan is generic name for the water-soluble and sulphated linear polysaccharides mainly found in the cell walls of various red algae (Mercier et al. 2001). It is composed of D-galactose and 3,6-anydrogalactose units joined through α-1,3 and β-1,4-glycosidic linkage (Di Rosa 1972; Necas and Bartosikova 2013). Carrageenan can however vary based on the number and position of the sulphate groups and the content of 3,6-anhydrogalactose units (Hashmi et al. 2012; Necas and Bartosikova 2013). Kappa (one sulphate group), iota (two sulphate groups) and lambda (three sulphate groups) are three such commercially utilized carrageenan variants (De Ruiter and Rudolph 1997). Higher sulphate ester levels confer lower solubility temperature and thus weaker gel strength (Necas and Bartosikova 2013). These sulphate groups make carrageenan chemically active, giving it various biological properties. Figure 15.3 unfolds carrageenan from its primary source along with its interaction with multiple plant phenomena.

Fig. 15.3
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Carrageenan and its accompanied biological properties

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15.3.1 Biological Activities of Carrageenan

Carrageenans (CGs) consist of numerous biological properties including induction of experimental inflammation and inflammatory pain. Aside from these functions, they found to have several potential pharmaceutical formulations including antitumour, antihyperlipidemic, immunomodulatory and anticoagulant activities (Morris 2003; Zhou et al. 2004; Campo et al. 2009). Recent researches have demonstrated that carrageenan is an extraordinarily potent infection inhibitor of a wide range of genital human papillomaviruses (HPVs), and it is also indicated that HPV transmission may be cured by carrageenan-based sexual lubricant gels (Buck et al. 2006). However, questions about the safety of CG uses as food additive and pharmaceutical adjuvant have been raised. Besides, its long-term safety is a major concern as CG is used as an inducer of inflammatory responses in laboratory animals for the investigation of anti-inflammatory drugs (Li et al. 2014).

Several research studies also mentioned the anti-HIV properties of CG, but their usual mode of action in anticoagulant is considered to be an adverse reaction when used as a therapeutic drug for AIDS (Necas and Bartosikova 2013). Although all kinds of CGs possess antioxidant activity, λ carrageenan exhibited the highest antioxidant and free radical scavenging activity. A positive correlation has been observed between sulphate content and antioxidant activity (Rocha De Souza et al. 2007). A few CGs are found to affect strong macrophage activation, while some restrict macrophage functions. An experiment conducted on Fischer 344 rats, feeding on foods containing 15% kappa/lambda CGs from Gahnia radula, showed a cholesterol-reducing effect (Zia et al. 2017).

15.3.2 Role of Carrageenan in Plant Growth Regulation

To achieve crop protection, by activating or eliciting their natural defence system to introduce desired resistance, is the most effective way and an environmentally safer approach to the problem. The strong elicitors narrated in literature are diverse in nature including oligosaccharides, polysaccharides, peptides, proteins and lipids, and it has been confirmed that polysaccharides purified from seaweeds as well as derived oligosaccharides play a significant role in plant defence responses (Bi et al. 2011). Carrageenans are considered to play a significant role in plant signalling and defence under several adverse environmental conditions (Mercier et al. 2001). Several experiments have been conducted to scrutinize the elicitor activity of carrageenans. Hypnea musciformis , a rich source to obtain kappa carrageenan, has been evaluated as an elicitor or inducer of plant defence responses in terms of phytoalexin synthesis and induced browning and resulted as a potent plant protector as well as growth-promoting agent in plants (Arman and Qader 2012). Carrageenans and their oligomeric form, the oligocarrageenans (OCs), modulate the activity of different plant defence pathways, including jasmonate, salicylate and ethylene signalling pathways which in turn induce plant defence responses against viruses, viroids, bacteria, fungi and insects (Shukla et al. 2016).

Various endogenous and environmental factors such as light, hormones, temperature and nutrient availability affect plant growth and development. Moreover, it has been observed that marine algae oligosaccharides stimulate plant growth. Various treatments of oligocarrageenans K, L and I exhibited increased growth of commercial tobacco plants by enhancing photosynthesis, basal metabolism, nitrogen assimilation and cell division, as well as that of other plants of commercial interest, and enhanced protection against tobacco mosaic virus (TMV) infection in tobacco plants (Castro et al. 2012). In addition, accumulation of several phenylpropanoid compounds (PPCs) with microbial activity increased by oligocarrageenans improves protection against viral, fungal and bacterial infections in tobacco plants. Moreover, OCs induce the level of essential oil and increase cellulose content and some PPCs with antimicrobial activities, indicating that defence against pathogen may also be cured (González et al. 2013). A red macroalga, Kappaphycus alvarezii , has a great economic importance due to its production of kappa carrageenan. It produces and accumulates photoprotective compounds such as carotenoids and mycosporin-like amino acids (MAAs), which absorb UVR energy directly or indirectly (Schmidt et al. 2010).

Liquid extracts of seaweeds have been reported to enhance the growth of plants, increase yield and quality, improve resistance to disease and pest, increase mineral uptake from soil and antioxidant properties and amend resistance to abiotic stresses (salinity, drought, heavy metal stress and extreme temperatures). Carrageenans are the best characterized seaweed elicitors that have the potential to activate disease resistance in plants and animals (Mousavi et al. 2018). OC kappa enhances C-, N- and S-assimilation and improves growth-promoting hormone content and growth in pine trees; therefore, it may account for useful biotechnological tool to increase growth in pine forests (Saucedo et al. 2015). Several research experiments have been conducted and analysed the effects of carrageenan on growth and secondary metabolite status in plants. Several physiological and biological activities such as plant growth, physiological attributes, herbage yield and content and yield of alkaloids (vincristine, vinblastine) of periwinkle and the content and yield of essential oil in mint improved after foliar application of the degraded marine polysaccharides (Naeem et al. 2012a, 2015a).

It is well studied that growth and development in plants, algae, mammals and nematodes is controlled by the kinase target of rapamycin (TOR). It is a key regulatory kinase of the TOR pathway and is a phosphoinositol-related kinase (PIK) having protein serine/threonine protein kinase activity. In E. globulus trees, the stimulation of growth induced by OC kappa, by the activation of TOR pathway and increased expression of genes encoding protein involved in photosynthesis and enzymes of basal metabolism, has been reported (Saucedo et al. 2019). Table 15.2 weights on the eliciting effects of carrageenan and its derivatives on growth and physiology of various crops.

Table 15.2 Eliciting effects of carrageenan and its derivatives on various plant species
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15.4 Sodium Alginate

Alginates are natural polysaccharides chiefly derived from marine brown algae (Phaeophyceae) (Mollah et al. 2009; Khan et al. 2011). Commercial varieties of alginate are extracted from seaweed, including giant kelp Macrocystis pyrifera, Ascophyllum nodosum, Ecklonia maxima, Sargassum sinicola and various types of Laminaria (Hernández-Carmona et al. 2013). Sodium alginate (NaC6H7O6) is the sodium salt of alginic acid and is composed of poly-β-(1, 4) D-mannuronic acid and poly-α-(1, 4) L-guluronic acid (Xu et al. 2006; El-Mohdy 2017). It ranges from white to yellowish brown and have filamentous, granular and powdered forms and is widely used in pharmaceutical, biotechnological and food sectors (Mollah et al. 2009; Khan et al. 2011). Annexed Fig. 15.4 represents sodium alginate and its chief source. Consecutive effects of sodium alginate and its derivatives on various plants and microbes are also illustrated in the same figure.

Fig. 15.4
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Sodium alginate and its accompanied biological properties

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15.4.1 Biological Activities of Sodium Alginate

Sodium alginate plays a major role in the structural component of the cell wall and intercellular matrix in organisms from Phaeophyceae and Laminaria (Hernández-Carmona et al. 2013). This marine polysaccharide consists of residues of mannuronic acid (M-block) and guluronic acid (G-block) (El-Mohdy 2017). Monomers are arranged in three types of block structure. These blocks may be homopolymeric block (M-block, G-block) or heteropolymeric block (MG-block). MG-block is known for its most flexible chain formation while M-block for its strong immuno-stimulating property (Pegg 2012). The fraction of mannuronic acid (M-block) and guluronic acid (G-block) of sodium alginate showed antibacterial activity against Escherichia coli, Staphylococcus aureus and Bacillus subtilis (Hu et al. 2005).

Marine polysaccharides are highly reactive and peculiar compounds with thermo-reversible gel formation ability and have widespread use in pharmaceutical industry and bioengineering products (Hien et al. 2000; Aftab et al. 2014). Alginates are also exploited in drug delivery and as hydrogels for immobilizing cells and enzymes due to their mild conditions of cross-linking through bivalent cations (Ca2+) (Russo et al. 2007; Liu and Li 2016). These characteristics can also be further altered by chemical modification, blending and integrating biodegradable additives which allows to tailor the final properties of the polysaccharides and opens the doors to wider applications, particularly in pharmaceutical area (Gomez d’Ayala et al. 2007).

Commercially, sodium alginates are also exploited in gel formation given their efficient and rapid water-absorbing property, sometimes absorbing multiple times of its own weight in water (Jamaludin et al. 2017). Moreover, carbohydrates like sodium alginate, chitosan, carrageenan, cellulose and pectin help in recycling bio-resources and reducing environmental pollution. These carbohydrates in various forms can induce different kinds of biological activities including antimicrobial activity and phytoalexin induction (Kume et al. 2002).

15.4.2 Role of Sodium Alginate in Plant Growth Regulation

Sodium alginate in various forms and concentrations can impart a general trend of improved overall vegetative growth in different crops. SA has the potential to enhance plant height, biomass (both fresh and dry weight), number of tillers and leaves as well as leaf area (Hien et al. 2000; Iwasaki and Matsubara 2000; Kume et al. 2002; Hu et al. 2004; Hegazy et al. 2009; Mollah et al. 2009; Qureshi 2010; Sarfaraz et al. 2011; Naeem et al. 2015b). In addition to overall growth, sodium alginate renders stimulating effects on seed germination as well (Jamsheer 2010; Khan et al. 2011). The effect of alginate-derived oligosaccharide concentration on α- and β-amylase activities in different germination stages of maize seeds enhanced the seed germination by increasing the activities of several enzymes beneficial for germination (Hu et al. 2004). These SA-induced effects could also be attributed to the sodium alginate’s interaction with plant cell signalling and its perceived regulation of gene expression (Khan et al. 2011).

These SA-induced responses can be understood by the fact that application of SA can induce multiple physiological and biochemical changes in plants. On a molecular level, SA is capable of regulating the biosynthesis of various enzymes (Ma et al. 2010; Khan et al. 2011) and the references therein) including those pertaining to nitrogen and carbon metabolism. Nitrate reductase (NR) is a key enzyme in nitrogen metabolism that assists in the first step of nitrogen assimilation in plant system through conversion of nitrate into nitrite. Thus, an efficient NR enzyme provides enough raw materials for the synthesis of various structural and functional biomolecules including amino acids and lipids. Various studies reported the direct influence of SA on the NR activity where it was found that SA can significantly (p ≤ 0.05) upregulate the activity of NR enzyme in various crops of economic importance, e.g. fennel (Sarfaraz et al. 2011), lemongrass (Idrees et al. 2012) and mint (Naeem et al. 2012b). As a result, SA assist in maintaining a higher nitrogen content that ultimately influences the content of photosynthetic pigments (i.e. chlorophyll and carotenoid) through amino acid, protein and lipid biosynthesis (Idrees et al. 2012). Another key enzyme in carbon metabolism is carbonic anhydrase (CA). SA has also been reported to upregulate the CA activity in different crops (Luan et al. 2003; Khan et al. 2011; Naeem et al. 2015b).

Another aspect of SA-induced physiological response can be observed on plant gas exchange modules. Net photosynthetic rate (PN) and stomatal conductance (gs) can play a decisive role in determining overall plant growth and productivity. SA positively influence both PN (Luan et al. 2003) and gs (Naeem et al. 2015b) possibly because of the SA-induced photosynthetic pigment content (Mollah et al. 2009; Sarfaraz et al. 2011) and enhanced membrane permeability (Khan and Srivastava 1998). Due to its regulating effects on membrane permeability as well as on protoplast formation, alginate and its derivatives have also been labelled as endogenous elicitors (Akimoto et al. 1999). Similar regulating effects of SA on secondary metabolism were noted otherwise where the content of secondary metabolites exhibited positive correlation with sodium alginate application (Idrees et al. 2011; Khan et al. 2011; Naeem et al. 2015b).

Some other miscellaneous SA-induced effects on plant system includes enhanced water-use efficiency (Idrees et al. 2011); phosphoenolpyruvate (PEP) carboxylase activity and protein content (Idrees et al. 2012); content of nitrogen, phosphorus and potassium (leaf NPK); and phytoalexin induction (Mollah et al. 2009; Khan et al. 2011; Sarfaraz et al. 2011; Idrees et al. 2012). Sodium alginate has also been attributed to provide resistance against various disease and adverse environmental conditions, thus contributing in plant defence system by ameliorating antioxidant metabolism and reactive oxygen species pathway (Hien et al. 2000; Liu et al. 2009; Ali et al. 2014). The combination of Alteromonas macleodii (common marine bacterium), as exogenous elicitor, and alginate oligomers, acting as both endogenous elicitor and scavenger of active oxygen species, reportedly minimized the cell growth inhibition and enhanced 5′-phosphodiesterase production in periwinkle (Aoyagi et al. 2006).

Various researches have demonstrated that SA is significantly potent in imparting an eliciting effect on the overall productivity and plant yield. SA can enhance the weights of seed and capsule in opium (Khan et al. 2011), oil production in lemongrass (Idrees et al. 2012) and herbage yield in periwinkle (Naeem et al. 2015b) along with the productivity of barley, carrot, cabbage, maize, peanut rice, tea and tomato (Hien et al. 2000; Hu et al. 2004; Hegazy et al. 2009; Liu et al. 2009). Table 15.3 represents plant growth, productivity and immunity promotion in different crops by sodium alginate and its derivatives.

Table 15.3 Eliciting effects of sodium alginate and its derivatives on various plant species
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Similar to chitosan and carrageenan, sodium alginate is also an efficient plant growth regulator which not only hampers yield loss during adverse environment but also promotes overall plant growth and productivity. Although the exact mechanism for these effects is not yet fully known, in the light of current advancements, we can assume that these NPs interact extensively with various vital physiological processes which play a decisive role in determining the fate of overall plant growth and productivity (Chamnanmanoontham et al. 2014). A general idea for this mechanism can be understood by annexed Fig. 15.5., where a hypothetical model for oligomeric action of chitosan, carrageenan and sodium alginate in plants is portrayed.

Fig. 15.5
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Hypothetical model for the mechanism of carrageenan, chitosan and sodium alginate in oligomeric form. (13-HPOT, 13-hydroperoxy-linolenic acid; OPDA, 12-oxophytodienoic acid; DAG, diacylglycerol; IP3, inositol triphosphate; JA, methyl jasmonate; PKP, protein kinase phosphatase; PLC, phospholipase C; TF, transcription factors)

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15.5 Conclusion and Future Prospective

Marine polysaccharides (chitosan, carrageenan and sodium alginate) in various forms seem to enhance overall plant growth and productivity. It is now known that these marine polysaccharides can act as a signalling molecule which interact with plant physiology in a complex cascade mechanism and produce these favourable effects (Mercier et al. 2001; Khan et al. 2011; Shukla et al. 2016). While all the three reviewed polysaccharides, i.e. chitosan, carrageenan and sodium alginate, have a general positive influence on plant overall growth and productivity, they possess few attributes that make a distinction among them. While chitosan can be used in preservation and safety of food and dairy products, sodium alginate can be exploited as a gelling or hydrating agent (Piculell 1995; Chien and Chou 2006; Liu et al. 2007). Similarly, carrageenan can be extensively used in pharmaceutical and drug development industries.

Although this review assessed the role of chitosan, carrageenan and sodium alginate on plant biology, there are few questions still left to be answered. Further investigations could reveal important insights about the exact mechanism responsible for such NP-induced responses in various crops. Additionally, critical evaluation of such responses through transcriptomics, epigenetics, radiation biology and bioinformatics might give us a better understanding of the cross-talk of NPs with other signalling pathways in various crops.