Accumulation of phenylpropanoid derivatives in chitosan-induced cell suspension culture of Cocos nucifera

Optimization of the fermentation media, mathematical modeling, and enhancement of paclitaxel production by Alternaria alternata after elicitation with pectin

Alternaria alternata fungus is a potent paclitaxel producer isolated from Corylus avellana. The major challenge is the lack of optimized media for endophytic fungi productivity. In the effort to maximize the production of taxoids by A. alternata, several fermentation conditions, including pH (pH 4.0-7.0), different types and concentrations of carbon (fructose, glucose, sucrose, mannitol, sorbitol, and malt extract), and nitrogen (urea, ammonium nitrate, potassium nitrate, ammonium phosphate, and ammonium sulfate) were applied step by step. Based on the results, A. alternata in a medium containing sucrose 5% (w/v) and ammonium phosphate 2.5 mM at pH 6.0 showed a rapid and sustainable growth rate, the highest paclitaxel yield (94.8 µg gFW-1 vs 2.8 µg gFW-1 in controls), and the maximum content of amino acids. Additionally, the effect of pectin was evaluated on fungus, and mycelia harvested. Pectin significantly enhanced the growth and taxoid yield on day 21 (respectively 171% and 116% of their corresponding on day 7). The results were checked out by mathematical modeling as well. Accordingly, these findings suggest a low-cost, eco-friendly, and easy-to-produce approach with excellent biotechnological potential for the industrial manufacture of taxoids.

Investigating the simultaneous effect of chitosan and arbuscular mycorrhizal fungi on growth, phenolic compounds, PAL enzyme activity and lipid peroxidation in Salvia nemorosa L

Considering the importance of Salvia nemorosa L. in the pharmaceutical and food industries, and also beneficial approaches of arbuscular mycorrhizal fungi (AMF) symbiosis and the use of bioelicitors such as chitosan to improve secondary metabolites, the aim of this study was to evaluate the performance of chitosan on the symbiosis of AMF and the effect of both on the biochemical and phytochemical performance of this plant and finally introduced the best treatment. Two factors were considered for the factorial experiment: AMF with four levels (non-inoculated plants, Funneliformis mosseae, Rhizophagus intraradices and the combination of both), and chitosan with six levels (0, 50, 100, 200, 400 mg L-1 and 1% acetic acid). Four months after treatments, the aerial part and root length, the levels of lipid peroxidation, H2O2, phenylalanine ammonia lyase (PAL) activity, total phenol and flavonoid contents and the main secondary metabolites (rosmarinic acid and quercetin) in the leaves and roots were determined. The flowering stage was observed in R. intraradices treatments and the highest percentage of colonization (78.87%) was observed in the treatment of F. mosseae × 400 mg L-1 chitosan. Furthermore, simultaneous application of chitosan and AMF were more effective than their separate application to induce phenolic compounds accumulation, PAL activity and reduce oxidative compounds. The cluster and principal component analysis based on the measured variables indicated that the treatments could be classified into three clusters. It seems that different treatments in different tissues have different effects. However, in an overview, it can be concluded that 400 mg L-1 chitosan and F. mosseae × R. intraradices showed better results in single and simultaneous applications. The results of this research can be considered in the optimization of this medicinal plant under normal conditions and experiments related to abiotic stresses in the future.

Biotechnological interventions for the production of forskolin, an active compound from the medicinal plant, Coleus forskohlii

Coleus forskohlii, an Indian-origin medicinal plant is the sole natural source of the labdane terpenoid forskolin (C22H34O7), with growing demand. Forskolin emerged as an industrially important bioactive compound, with many therapeutic applications in human health. It has established potential effects in the treatment of various diseases and conditions such as glaucoma, asthma, obesity, allergies, skin conditions and cardiovascular diseases. Moreover, clinical trials against different types of cancers are progressing. The mechanism of action of forskolin mainly involves activating adenylyl cyclase and elevating cAMP, thereby regulating different cellular processes. For the extraction of forskolin, tuberous roots of C. forskohlii are used as they contain the highest concentration of this metabolite. Approximately 2500 tonnes of the plant are cultivated annually to produce a yield of 2000-2200 kg ha-1 of dry tubers. The forskolin content of the root is distributed in the range of 0.01-1%, which cannot meet the increasing commercial demands from industries such as pharmaceuticals, cosmetics, dietary supplements, food and beverages. Hence, various aspects of micropropagation with different culture methods that employ precursors or elicitors to improve the forskolin content have been explored. Different extraction and analytical methods are also introduced to examine the yield and purity of forskolin. This review discusses the significance, clinical importance, mechanism of action and different approaches used for mass production including tissue culture for the lead compound forskolin to meet market needs.

Phenolics and terpenoids change in response to yeast extract and chitosan elicitation in Zataria multiflora cell suspension culture

Zataria multiflora is an important medicinal plant with antioxidant and anticancer properties attributed to its phytochemicals. To develop a method for bulk production of valuable phytochemicals, cell suspension culture of Z. multiflora were grown in liquid B5 medium and then treated in their log growth phase with chitosan (0, 10, 20, and 40 mg L^-1) and yeast extract (0, 400, 800, and 1200 mg L^-1) for 3 days. The levels of hydrogen peroxide (H₂O₂), nitric oxide (NO), malondialdehyde (MDA), and the main terpenoids and phenylpropanoids in the cell extracts were determined by HPLC and spectrophotometric techniques. The H₂O₂ and MDA levels significantly increased in the cells treated with both yeast extract and chitosan, while the NO level increased in those exposed to yeast extract. At their highest concentrations, both elicitors significantly increased PAL and TAL activities, as well as phenolic acids and flavonoids contents. Chitosan only induced the production of caffeic acid (22 µg g^-1 DW), benzoic acid (2 µg g^-1 DW), 4-hydroxy benzoic acid (6 µg g^-1 DW), epicatechin (63 µg g^-1 DW), and apigenin (5 µg g^-1 DW) in the cells, while yeast extract increased the contents of phenylpropanoids gallic acid (50 µg g^-1 DW), vanillin (35 µg g^-1 DW), salicylic acid (24 µg g^-1 DW), catechin (130 µg g^-1 DW) and terpenoids carvacrol (7 µg g^-1 DW) and thymol (24 µg g^-1 DW). In conclusion, changes in the production of phenolics and terpenoids are a defensive mechanism in Z. multiflora cells treated by yeast extract and chitosan.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03235-x.

Inhibiting tricin biosynthesis improves maize lignocellulose saccharification

Lignin is a technological bottleneck to convert polysaccharides into fermentable sugars, and different strategies of genetic-based metabolic engineering have been applied to improve biomass saccharification. Using maize seedlings grown hydroponically for 24 h, we conducted a quick non-transgenic approach with five enzyme inhibitors of the lignin and tricin pathways. Two compounds [3,4-(methylenedioxy)cinnamic acid: MDCA and 2,4-pyridinedicarboxylic acid: PDCA] revealed interesting findings on root growth, lignin composition, and saccharification. By inhibiting hydroxycinnamoyl-CoA ligase, a key enzyme of phenylpropanoid pathway, MDCA decreased the lignin content and improved saccharification, but it decreased root growth. By inhibiting flavone synthase, a key enzyme of tricin biosynthesis, PDCA decreased total lignin content and improved saccharification without affecting root growth. PDCA was three-fold more effective than MDCA, suggesting that controlling lignin biosynthesis with enzymatic inhibitors may be an attractive strategy to improve biomass saccharification.

Improvement of Phenylpropanoid Production with Elicitor Treatments in Pimpinella brachycarpa Nakai

Pimpinella brachycarpa Nakai, known as cham-na-mul in Korea, is a popular edible herb and vegetable. Phenolic compounds are recognized as a vital group of plant secondary metabolites that provide innumerable, valuable therapeutic properties. Elicitors are biofactors or chemicals from diverse sources that can trigger morphological and physiological responses in the target organism. This study examined the effect of methyl jasmonate (MeJA), salicylic acid (SA), and chitosan treatment on the accretion of phenolic compounds in P. brachycarpa Nakai. This plant was harvested under different concentration of elicitor treatment for time course. Eight phenolic compounds including were detected in response to elicitor using HPLC. While the untreated controls showed the lowest phenolic content, treatment with 0.3% chitosan, 0.1 mM SA, and 0.1 mM MeJA resulted in 1.43-, 1.39-, and 1.35-fold increase in the phenolic content, respectively. The highest content of most of the individual phenolic compounds followed a similar trend according to treatment type, with chitosan treatment showing the highest content, followed by SA and then MeJA treatments. Thus, we demonstrate that the treatment with optimal concentrations of these elicitors for an optimal period of time increases the production of phenolic compounds in P. brachycarpa Nakai.

Enhanced plumbagin production in Plumbago indica root culture by simultaneous and sequential dual elicitations using chitosan with ʟ-alanine and methyl-β-cyclodextrin

The simultaneous and sequential dual elicitation effect on plumbagin production in Plumbago indica L. root cultures, revealed that combination of chitosan (150 mg L−1) with ʟ-alanine (5 mM) or methyl-β-cyclodextrin (MCD; 2 mM) significantly increased plumbagin production, but in the different treatment manners. The simultaneous treatment using chitosan + ʟ-alanine on a 14-day-old culture enhanced plumbagin production to 14.62 mg g−1 DW, while the sequential additions of MCD to a 12-day-old culture followed by chitosan after 48 h enhanced production of plumbagin to 14.33 mg g−1 DW. The plumbagin productivity from both treatments were up to 1.3- and 8-fold higher than the chitosan treated (10.93 mg g−1 DW) and untreated root cultures (1.76 mg g−1 DW). Moreover, the present studies provided new information on the effect of simultaneous and sequential elicitation on plumbagin-producing P. indica root cultures using chitosan in combinations with MCD or ʟ-alanine.

Tree Fern Cyathea lepifera May Survive by Its Phytotoxic Property

Cyatheaceae (tree ferns) appeared during the Jurassic period and some of the species still remain. Those species may have some morphological and/or physiological characteristics for survival. A tree fern was observed to suppress the growth of other ligneous plants in a tropical forest. It was assumed that the fern may release toxic substances into the forest floor, but those toxic substances have not yet been identified. Therefore, we investigated the phytotoxicity and phytotoxic substances of Cyathea lepifera (J. Sm. ex Hook.) Copel. An aqueous methanol extract of C. lepifera fronds inhibited the growth of roots and shoots of dicotyledonous garden cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), and alfalfa (Medicago sativa L.), and monocotyledonous ryegrass (Lolium multiflorum Lam.), timothy (Phleum pratense L.), and barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.). The results suggest that C. lepifera fronds may have phytotoxicity and contain some phytotoxic substances. The extract was purified through several chromatographic steps during which inhibitory activity was monitored, and p-coumaric acid and (-)-3-hydroxy-β-ionone were isolated. Those compounds showed phytotoxic activity and may contribute to the phytotoxic effects caused by the C. lepifera fronds. The fronds fall and accumulate on the forest floor through defoliation, and the compounds may be released into the forest soils through the decomposition process of the fronds. The phytotoxic activities of the compounds may be partly responsible for the fern's survival.

Carbohydrate polymers exhibit great potential as effective elicitors in organic agriculture: A review

Some carbohydrate polymers, usually oligosaccharides or polysaccharides, have great potential as an elicitor of plant defense. However, due to the complexity and diversity of poly- and oligosaccharide structure, the molecular mechanisms and structure-activity relationships of carbohydrate elicitors are still not well understood, which hinders the application of carbohydrate elicitors in agriculture. This review introduces the mechanisms of carbohydrate elicitor perception and signaling in plants. The structure and activity relationships of main poly- and oligosaccharides studied for the control of plant diseases are discussed and summarized. Additionally, the effects of carbohydrate elicitors on the secondary metabolite production are also summarized.

Chitosan enhances rosmarinic acid production in shoot cultures of Melissa officinalis L. through the induction of methyl jasmonate

BACKGROUND

Chitosan is a polycationic polysaccharide derived from chitin that has been recognized as an effective elicitor in the production of secondary metabolites of many medicinal plants. In this study, the effect of abiotic elicitor (chitosan) at various concentrations on rosmarinic acid (RA) and total phenolic accumulation in shoot cultures of lemon balm was investigated.

RESULTS

Treatment of shoots by chitosan led to a noticeable induction of phenylalanine ammonia-lyase (PAL), catalase (CAT), guaiacol peroxidase (GPX) and lipoxygenase (LOX) activities. Besides, the expression of PAL1, TAT and RAS genes and accumulation of RA and phenolic compound increased in chitosan-treated lemon balm shoots. Chitosan treatment also increased H2O2 accumulation and the expression of RBOH, an essential gene implicated in ROS production. Also, the up-regulation of the OPR gene by exogenous chitosan was associated with the induction of endogenous JA determined by GC-MASS.

CONCLUSION

The present study showed that the induced production of rosmarinic acid by chitosan involves the trigger of defense-related enzymes, up-regulated expression of TAT and RAS genes, and stimulation of JA biosynthesis.

Influence of Chitosan, Salicylic Acid and Jasmonic Acid on Phenylpropanoid Accumulation in Germinated Buckwheat (Fagopyrum esculentum Moench)

The present study investigated the effects of jasmonic acid (JA), chitosan, and salicylic acid (SA) on the accumulation of phenolic compounds in germinated buckwheat. A total of six phenolics were detected in the buckwheat treated with different concentrations of SA (50, 100, and 150 mg/L), JA (50, 100, and 150 μM), and chitosan (0.01, 0.1, and 0.5%) using high-performance liquid chromatography (HPLC). The treatment with 0.1% chitosan resulted in an accumulation of the highest levels of phenolic compounds as compared with the control and the 0.01 and 0.5% chitosan treatments. The treatment with 150 μM JA enhanced the levels of phenolics in buckwheat sprouts as compared with those observed in the control and the 50 and 100 μM JA-treated sprouts. However, the SA treatment did not affect the production of phenolic compounds. After optimizing the treatment concentrations of elicitors (chitosan and JA), a time-course analysis of the phenolic compounds detected in the germinated buckwheat treated with 0.1% chitosan and 150 μM JA was performed. Buckwheat treated with 0.1% chitosan for 72 h showed higher levels of phenolic compounds than all control samples. Similarly, the germinated buckwheat treated with JA for 48 and 72 h produced higher amounts of phenolic compounds than all control samples. This study elucidates the influence of SA, JA, and chitosan on the production of phenolic compounds and suggests that the treatment with optimal concentrations of chitosan and JA for an optimal time period improved the production of phenolic compounds in germinated buckwheat.

Chitosan oligosaccharides affect xanthone and VOC biosynthesis in Hypericum perforatum root cultures and enhance the antifungal activity of root extracts

Water-soluble chitosan oligosaccharides (COS) affect xanthone and volatile organic compound content, as well as antifungal activity against human pathogenic fungi of extracts obtained from Hypericum perforatum root cultures. Several studies have demonstrated the elicitor power of chitosan on xanthone biosynthesis in root cultures of H. perforatum. One of the major limitations to the use of chitosan, both for basic and applied research, is the need to use acidified water for solubilization. To overcome this problem, the elicitor effect of water-soluble COS on the biosynthesis of both xanthones and volatile organic compounds (VOCs) was evaluated in the present study. The analysis of xanthones and VOCs was performed by HPLC and GC-MS headspace analysis. The obtained results showed that COS are very effective in enhancing xanthone biosynthesis. With 400 mg L^-1 COS, a xanthone content of about 30 mg g^-1 DW was obtained. The antifungal activity of extracts obtained with 400 mg L^-1 COS was the highest, with MIC₅₀ of 32 µg mL^-1 against Candida albicans and 32-64 µg mL^-1 against dermatophytes, depending on the microorganism. Histochemical investigations suggested the accumulation of isoprenoids in the secretory ducts of H. perforatum roots. The presence of monoterpenes and sesquiterpenes was confirmed by the headspace analysis. Other volatile hydrocarbons have been identified. The biosynthesis of most VOCs showed significant changes in response to COS, suggesting their involvement in plant-fungus interactions.

Involvement of an autotoxic compound in asparagus decline

Asparagus (Asparagus officinalis L.) is a widely cultivated perennial veritable and can be harvested more than ten years. However, the crop quality and yield decline after a few year's cultivation, which is called "asparagus decline". Even though those asparagus plants were replaced with new young asparagus plants, the productivity and quality of the crop remain relatively low, which is known as a "asparagus replant problem". One of the possible reasons for "asparagus decline" and "asparagus replant problem" is thought to be autotoxicity of asparagus. However, the compounds involved in the autotoxicity is not clear. The objective of this study was therefore to determine the potential role of autotoxicity in the "asparagus decline" and "asparagus replant problem". An aqueous methanol extract of 10-year-asparagus-cultivated soils inhibited the growth of asparagus seedlings and other two test plants with concentration dependent manner. The result confirmed that the asparagus soils have autotoxic activity. The extract was then purified by several chromatographies with monitoring the inhibitory activity and a potent growth inhibitory substance causing the autotoxic effect was isolated. The chemical structures of the compound was determined by spectral data to be trans-cinnamic acid. trans-Cinnamic acid inhibited the growth of asparagus seedlings at concentrations greater than 10 μM. The concentrations required for 50% growth inhibition of asparagus (IC₅₀) were 24.1-41.6 μM. trans-Cinnamic acid accumulated 174 μM in the 10-year-asparagus-cultivated soils, which may be enough levels to cause the growth inhibition on asparagus considering its IC₅₀ value. Therefore, trans-cinnamic acid may contribute to the autotoxic effect of asparagus soils, and may be in part responsible for "asparagus decline" and "asparagus replant problem".

Biochemical characterization of a key step involved in 2H4MB production in Decalepis hamiltonii

Decalepis hamiltonii is widely known for its flavour molecule 2-Hydroxy-4-Methoxy Benzaldehyde (2H4MB), a structural isomer of vanillin. As the biosynthetic pathway of 2H4MB is not known, we hypothesised 2H4MB origins could be from phenylpropanoid pathway (PPP). Accordingly, a study was conducted using PPP inhibitors (viz. piperonylic acid, MDCA and propanil) against in vitro root cultures of D. hamiltonii to find the branch of PPP which catalyses the 2H4MB formation. HPLC analysis was carried out to quantify 2H4MB levels in control and respective inhibitor treated root cultures in vitro. The results obtained revealed that piperonylic acid did not inhibit 2H4MB biosynthesis in the given period, whereas MDCA and propanil had the marked inhibitory effect. The inhibitory effect was evident with 13.2, 33.6 and 37.9% decrease in 2H4MB levels at 50, 100 and 150mM concentration of MDCA respectively in comparison with control roots. Similarly, the inhibitory effect of propanil on 2H4MB biosynthesis was obvious with 23.7, 49.5 and 57.9% decrease in 2H4MB levels at 50, 100 and 150μM concentration of inhibitor respectively when compared with control roots. Propanil showed a greater slow down effect on 2H4MB biosynthesis compared to MDCA. Incorporation of 0.1, 0.5 and 1.0mM ferulic acid as a precursor to in vitro root cultures of D. hamiltonii showed an increase in 2H4MB levels at the rate of 3.1, 107 and 94.1% respectively as quantified by HPLC analysis. However, ferulic acid in conjunction with propanil did not show any increase in 2H4MB levels. This clearly explains that ferulic acid is channelled through the 4-CL (4-coumarate CoA ligase) enzyme, where it would be converted to feruloyl-CoA and could be further converted to 2H4MB in D. hamiltonii.

Enhanced accumulation of phytosterols and phenolic compounds in cyclodextrin-elicited cell suspension culture of Daucus carota

In this work, suspension-cultured cells of Daucus carota were used to evaluate the effect of β-cyclodextrins on the production of isoprenoid and phenolic compounds. The results showed that the phytosterols and phenolic compounds were accumulated in the extracellular medium (15100μgL(-1) and 477.46μgL(-1), respectively) in the presence of cyclodextrins. Unlike the phytosterol and phenolic compound content, β-carotene (1138.03μgL(-1)), lutein (25949.54μgL(-1)) and α-tocopherol (8063.82μgL(-1)) chlorophyll a (1625.13μgL(-1)) and b (9.958 (9958.33μgL(-1)) were mainly accumulated inside the cells. Therefore, cyclodextrins were able to induce the cytosolic mevalonate pathway, increasing the biosynthesis of phytosterols and phenolic compounds, and accumulate them outside the cells. However, in the absence of these cyclic oligosaccharidic elicitors, carrot cells mainly accumulated carotenoids through the methylerythritol 4-phosphate pathway. Therefore, the use of cyclodextrins would allow the extracellular accumulation of both phytosterols and phenolic compounds by diverting the carbon flux towards the cytosolic mevalonate/phenylpropanoid pathway.

Phenylpropanoid Defences in Nicotiana tabacum Cells: Overlapping Metabolomes Indicate Common Aspects to Priming Responses Induced by Lipopolysaccharides, Chitosan and Flagellin-22

Plants have evolved both constitutive and inducible defence strategies to cope with different biotic stimuli and stresses. Exposure of a plant to a challenging stress can lead to a primed state that allows it to launch a more rapid and stronger defence. Here we applied a metabolomic approach to study and compare the responses induced in Nicotiana tabacum cells by microbe-associated molecular pattern (MAMP) molecules, namely lipopolysaccharides (LPS), chitosan (CHT) and flagellin-22 (FLG22). Early response metabolites, extracted with methanol, were analysed by UHPLC-MS/MS. Using multivariate statistical tools the metabolic profiles induced by these elicitors were analysed. In the metabolic fingerprint of these agents a total of 19 cinnamic acid derivatives conjugated to quinic acids (chlorogenic acids), shikimic acid, tyramine, polyamines or glucose were found as discriminant biomarkers. In addition, treatment with the phytohormones salicylic acid (SA), methyljasmonic acid (MJ) and abscisic acid (ABA) resulted in differentially-induced phenylpropanoid pathway metabolites. The results indicate that the phenylpropanoid pathway is activated by these elicitors while hydroxycinnamic acid derivatives are commonly associated with the metabolic response to the MAMPs, and that the activated responses are modulated by both SA and MJ, with ABA not playing a role.

N-acyl-ω-aminoaldehydes are efficient substrates of plant aminoaldehyde dehydrogenases

Plant aminoaldehyde dehydrogenases (AMADHs, EC 1.2.1.19) belong to the family 10 of aldehyde dehydrogenases and participate in the metabolism of compounds related to amino acids such as polyamines or osmoprotectants. Their broad specificity covers ω-aminoaldehydes, aliphatic and aromatic aldehydes as well as nitrogen-containing heterocyclic aldehydes. The substrate preference of plant AMADHs is determined by the presence of aspartic acid and aromatic residues in the substrate channel. In this work, 15 new N-acyl derivates of 3-aminopropanal (APAL) and 4-aminobutanal (ABAL) were synthesized and confirmed as substrates of two pea AMADH isoenzymes (PsAMADH 1 and 2). The compounds were designed considering the previously demonstrated conversion of N-acetyl derivatives as well as substrate channel dimensions (5-8 Å × 14 Å). The acyl chain length and its branching were found less significant for substrate properties than the length of the initial natural substrate. In general, APAL derivatives were found more efficient than the corresponding ABAL derivatives because of the prevailing higher conversion rates and lower K m values. Differences in enzymatic performance between the two isoenzymes corresponded in part to their preferences to APAL to ABAL. The higher PsAMADH2 affinity to substrates correlated with more frequent occurrence of an excess substrate inhibition. Molecular docking indicated the possible auxiliary role of Tyr163, Ser295 and Gln451 in binding of the new substrates. The only derivative carrying a free carboxyl group (N-adipoyl APAL) was surprisingly better substrate than ABAL in PsAMADH2 reaction indicating that also negatively charged aldehydes might be good substrates for ALDH10 family.

Medicinal plant cell suspension cultures: pharmaceutical applications and high-yielding strategies for the desired secondary metabolites

The development of plant tissue (including organ and cell) cultures for the production of secondary metabolites has been underway for more than three decades. Plant cell cultures with the production of high-value secondary metabolites are promising potential alternative sources for the production of pharmaceutical agents of industrial importance. Medicinal plant cell suspension cultures (MPCSC), which are characterized with the feature of fermentation with plant cell totipotency, could be a promising alternative "chemical factory". However, low productivity becomes an inevitable obstacle limiting further commercialization of MPCSC and the application to large-scale production is still limited to a few processes. This review generalizes and analyzes the recent progress of this bioproduction platform for the provision of medicinal chemicals and outlines a range of trials taken or underway to increase product yields from MPCSC. The scale-up of MPCSC, which could lead to an unlimited supply of pharmaceuticals, including strategies to overcome and solution of the associated challenges, is discussed.

Enhanced lignin monomer production caused by cinnamic Acid and its hydroxylated derivatives inhibits soybean root growth

Cinnamic acid and its hydroxylated derivatives (p-coumaric, caffeic, ferulic and sinapic acids) are known allelochemicals that affect the seed germination and root growth of many plant species. Recent studies have indicated that the reduction of root growth by these allelochemicals is associated with premature cell wall lignification. We hypothesized that an influx of these compounds into the phenylpropanoid pathway increases the lignin monomer content and reduces the root growth. To confirm this hypothesis, we evaluated the effects of cinnamic, p-coumaric, caffeic, ferulic and sinapic acids on soybean root growth, lignin and the composition of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) monomers. To this end, three-day-old seedlings were cultivated in nutrient solution with or without allelochemical (or selective enzymatic inhibitors of the phenylpropanoid pathway) in a growth chamber for 24 h. In general, the results showed that 1) cinnamic, p-coumaric, caffeic and ferulic acids reduced root growth and increased lignin content; 2) cinnamic and p-coumaric acids increased p-hydroxyphenyl (H) monomer content, whereas p-coumaric, caffeic and ferulic acids increased guaiacyl (G) content, and sinapic acid increased sinapyl (S) content; 3) when applied in conjunction with piperonylic acid (PIP, an inhibitor of the cinnamate 4-hydroxylase, C4H), cinnamic acid reduced H, G and S contents; and 4) when applied in conjunction with 3,4-(methylenedioxy)cinnamic acid (MDCA, an inhibitor of the 4-coumarate:CoA ligase, 4CL), p-coumaric acid reduced H, G and S contents, whereas caffeic, ferulic and sinapic acids reduced G and S contents. These results confirm our hypothesis that exogenously applied allelochemicals are channeled into the phenylpropanoid pathway causing excessive production of lignin and its main monomers. By consequence, an enhanced stiffening of the cell wall restricts soybean root growth.

Exogenous caffeic acid inhibits the growth and enhances the lignification of the roots of soybean (Glycine max)

The allelopathic effect of caffeic acid was tested on root growth, phenylalanine ammonia-lyase (PAL) and peroxidase (POD) activities, hydrogen peroxide (H(2)O(2)) accumulation, lignin content and monomeric composition of soybean (Glycine max) roots. We found that exogenously applied caffeic acid inhibited root growth, decreased the PAL activity and H(2)O(2) content and increased the soluble and cell wall-bound POD activities. The p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) monomers and total lignin (H+G+S) increased in the caffeic acid-exposed roots. When applied in conjunction with piperonylic acid (PIP, an inhibitor of the cinnamate 4-hydroxylase, C4H), caffeic acid equalized the inhibitory effect of PIP, whereas the application of methylene dioxocinnamic acid (MDCA, an inhibitor of the 4-coumarate:CoA ligase, 4CL) plus caffeic acid decreased lignin production. These results indicate that exogenously applied caffeic acid can be channeled into the phenylpropanoid pathway via the 4CL reaction, resulting in an increase of lignin monomers that solidify the cell wall and inhibit root growth.