Biosynthesis of secondary metabolites in sugarcane

Bioactive compounds as an alternative for the sugarcane industry: Towards an integrative approach

Here, a comprehensive review of sugarcane industrialization and its relationship with bioactive compounds (BCs) detected in various products and by-products generated during its processing is presented. Furthermore, it is discussed how these compounds have revealed important antioxidant, antineoplastic, antidiabetic, and antimicrobial activities. From this bibliographic research highlights the significance of two types of BCs of natural origin (phenolic compounds (PCs) and terpenoids) and a group of compounds synthesized during industrial transformation processes (Maillard reaction products (MRPs)). It was found that most of the studies about the BCs from sugarcane have been conducted by identifying, isolating, and analyzing ones or a few compounds at a specific period, this being a conventional approach. However, given the complexity of the synthesis processes of all these BCs and the biological activities they can manifest in a specific biological context, novel approaches are needed to address these analyses holistically. To overcome this challenge, integrating massive and multiscale methods, such as omics sciences, seems necessary to enrich these studies. This work is intended to contribute to the state of the art that could support future research about the exploration, characterization, or evaluation of different bioactive molecules from sugarcane and its derivatives.

Phenolic Compounds of Soybean Seeds from Two European Countries and Their Antioxidant Properties

There is only a small acreage of planted soybeans in northern Europe, as the global production of this crop is mainly dictated by the warmer temperatures needed for bountiful yields. The defense response of soybean plants to a cold climate entails the secretion of specific compounds which help mitigate oxidative stress, i.e., antioxidants, including phenolic compounds. The objective of this study was to examine differences in the concentrations of phenolic compounds, their antioxidant properties, and the concentration of key isoflavones (namely genistein, daidzein, malonyl daidzein, malonyl genistein, and daidzin) in the seeds of six soybean cultivars from two different regions of Europe, namely Poland and France. The total phenolic contents, isoflavone levels, and in vitro antioxidant capacities of soybean seeds from most of the investigated cultivars of northeast Europe were found to be greater than those from southwest Europe. The phenolic compounds of seed extracts are primarily responsible for the free-radical scavenging of soybeans. Factors regulating the production of phenolic compounds in the seeds have not been thoroughly elucidated. Hence, the results presented in this paper can be useful in the selection of soybean cultivars with higher levels of seed phenolics, because of their beneficial impact on human health and on the soybean's defense mechanism against plant stresses.

Increase in cytotoxic lignans production after smut infection in sugar cane plants

Smut infection alters the transcription of dirigent proteins (DIR) by sugarcane plants. Here, we show that these alterations are associated to an elevated production of cytotoxic lignans. Smut-resistant sugarcane varieties display a fivefold increase in pinoresinol and also produce elevated amounts of secoisolariciresinol. Conversely, smut-sensitive varieties do not produce pinoresinol or secoisolariciresinol upon infection, synthesizing instead small amounts of matairesinol. Our data indicate that commercial pinoresinol and secoisolariciresinol seem to prevent smut teliospore germination and sporidia release from sprouted teliospores. Consistently, we observed abundant morphological alterations of sporidia incubated in the presence of these lignans. However, commercial lignans do not block the development of the pathogen in a definitive way. Additional experiments demonstrate that only the extracts from healthy or smut-exposed resistant plants inhibit sporidia growth in vitro, indicating that a specific mixture of lignans from resistant plants is necessary to constitute an effective defense mechanism.

Defense potential of secondary metabolites in medicinal plants under UV-B stress

Ultraviolet-B (UV-B) radiation has, for many decades now, been widely studied with respect to its consequences on plant and animal health. Though according to NASA, the ozone hole is on its way to recovery, it will still be a considerable time before UV-B levels reach pre-industrial limits. Thus, for the present, excessive UV-B reaching the Earth is a cause for concern, and UV-B related human ailments are on the rise. Plants produce various secondary metabolites as one of the defense strategies under UV-B. They provide photoprotection via their UV-B screening effects and by quenching the reactive oxygen- and nitrogen species produced under UV-B influence. These properties of plant secondary metabolites (PSMs) are being increasingly recognized and made use of in sunscreens and cosmetics, and pharma- and nutraceuticals are gradually becoming a part of the regular diet. Secondary metabolites derived from medicinal plants (alkaloids, terpenoids, and phenolics) are a source of pharmaceuticals, nutraceuticals, as well as more rigorously tested and regulated drugs. These metabolites have been implicated in providing protection not only to plants under the influence of UV-B, but also to animals/animal cell lines, when the innate defenses in the latter are not adequate under UV-B-induced damage. The present review focuses on the defense potential of secondary metabolites derived from medicinal plants in both plants and animals. In plants, the concentrations of the alkaloids, terpenes/terpenoids, and phenolics have been discussed under UV-B irradiation as well as the fate of the genes and enzymes involved in their biosynthetic pathways. Their role in providing protection to animal models subjected to UV-B has been subsequently elucidated. Finally, we discuss the possible futuristic scenarios and implications for plant, animal, and human health pertaining to the defense potential of these secondary metabolites under UV-B radiation-mediated damages.

Changes in metabolic profiling of sugarcane leaves induced by endophytic diazotrophic bacteria and humic acids

Plant growth-promoting bacteria (PGPB) and humic acids (HA) have been used as biostimulants in field conditions. The complete genomic and proteomic transcription of Herbaspirillum seropedicae and Gluconacetobacter diazotrophicus is available but interpreting and utilizing this information in the field to increase crop performance is challenging. The identification and characterization of metabolites that are induced by genomic changes may be used to improve plant responses to inoculation. The objective of this study was to describe changes in sugarcane metabolic profile that occur when HA and PGPB are used as biostimulants. Inoculum was applied to soil containing 45-day old sugarcane stalks. One week after inoculation, the methanolic extracts from leaves were obtained and analyzed by gas chromatography coupled to time-of-flight mass spectrometry; a total of 1,880 compounds were observed and 280 were identified in all samples. The application of HA significantly decreased the concentration of 15 metabolites, which generally included amino acids. HA increased the levels of 40 compounds, and these included metabolites linked to the stress response (shikimic, caffeic, hydroxycinnamic acids, putrescine, behenic acid, quinoline xylulose, galactose, lactose proline, oxyproline and valeric acid) and cellular growth (adenine and adenosine derivatives, ribose, ribonic acid and citric acid). Similarly, PGPB enhanced the level of metabolites identified in HA-treated soils; e.g., 48 metabolites were elevated and included amino acids, nucleic acids, organic acids, and lipids. Co-inoculation (HA+PGPB) boosted the level of 110 metabolites with respect to non-inoculated controls; these included amino acids, lipids and nitrogenous compounds. Changes in the metabolic profile induced by HA+PGPB influenced both glucose and pentose pathways and resulted in the accumulation of heptuloses and riboses, which are substrates in the nucleoside biosynthesis and shikimic acid pathways. The mevalonate pathway was also activated, thus increasing phytosterol synthesis. The improvement in cellular metabolism observed with PGPB+HA was compatible with high levels of vitamins. Glucuronate and amino sugars were stimulated in addition to the products and intermediary compounds of tricarboxylic acid metabolism. Lipids and amino acids were the main compounds induced by co-inoculation in addition to antioxidants, stress-related metabolites, and compounds involved in cellular redox. The primary compounds observed in each treatment were identified, and the effect of co-inoculation (HA+PGPB) on metabolite levels was discussed.

The effects of cold stress on the phenolic compounds and antioxidant capacity of grapevine (Vitis vinifera L.) leaves

According to some estimates, a 70% increase in crop yield could be achieved if the environmental conditions were close to the optimum ones for a given plant, which is why the identification and control of adverse environmental effects is a top priority in many countries worldwide. This paper contains a discussion of the changes in selected elements of the secondary metabolism in the leaves of two grapevine varieties (Vitis vinifera L.) with a different degree of tolerance to cold stress during prolonged and constant low temperature stress. The analyses have shown that the more-tolerant variety was characterized by a higher content of phenolic compounds, better radical-scavenging capacity and stronger reducing power. However, the cold stress caused a decrease in the concentration of the phenolics and decreased the scavenging capacity in the leaves of both varieties. Four phenolic acids have been identified in the extracts from the leaves of both grapevines: caffeic acid, p-coumaric acid, ferulic acid and a caffeic acid derivative. Caffeic acid appeared in the highest concentrations in all the leaf extracts. Additionally, it has been noted that in the leaves of the varieties susceptible and tolerant to cold stress, the prolonged exposure to low temperature caused a considerable reduction of the content of all identified phenolic acids. The results of the analyses have demonstrated large differences in the functioning of the secondary metabolism in response to the same stressor.

Male-fertility genes expressed in male flower buds of Silene latifolia include homologs of anther-specific genes

When the female plant of Silene latifolia is infected with the smut fungus Microbotryum violaceum, its rudimentary stamens develop into anthers which contain fungus teliospores instead of pollen. To identify genes required for maturation of anthers in S. latifolia, we performed a cDNA subtraction approach with healthy male buds and female buds infected with M. violaceum. We isolated five cDNA clones, which were preferentially expressed in healthy male buds during stages associated with a burst in tapetal activity. These five cDNAs are predicted to encode a mandelonitrile lyase protein (SlMDL1), a strictosidine synthase protein (SlSs), a glycosyl hydrolase 17 protein (SlGh17), a proline-rich protein APG precursor (SlAPG), and a chalcone-synthase-like protein (SlChs). All five genes showed expression in both healthy and fungus-infected male buds, but not expressed in either healthy or infected female buds. The first three genes were highly expressed in both tapetum and pollen grains while the last two genes were expressed only inside the tapetum of male flower buds. Phylogenetic analysis results showed that SlChs and SlGh17 belong to anther-specific subgroups of chalcone-synthase-like genes and glycosyl hydrolase 17 family genes, respectively. Our results suggest that the isolated five genes are related to the fertility of the anther leading to the development of fertile pollen. The smut fungus was not able to induce the expression of the five genes in the infected female buds. This raises the possibility that these genes are under the control of master gene(s) on the Y chromosome.

Physiological implications of metabolite biosynthesis for net assimilation and heat-stress tolerance of sugarcane (Saccharum officinarum) sprouts

Global increase in ambient temperature is a critical factor for plant growth. In order to study the changes in growth over short intervals, various primary and secondary metabolites, and their relationships with thermotolerance, 1-month-old sugarcane (Saccharum officinarum) sprouts were grown under control conditions (28 degrees C) or under heat-stress conditions (40 degrees C), and measurements were made at six 12-h intervals. Heat stress greatly reduced dry matter and leaf area of sprouts initially but only nominally later on. Changes in the rates of relative growth and net assimilation were greater than relative leaf expansion, indicating an adverse effect of heat on assimilation of nutrients and CO(2) in producing dry matter. Although reduction in leaf water potential was an immediate response to heat, this effect was offset by early synthesis of free proline, glycinebetaine and soluble sugars (primary metabolites). Among secondary metabolites, anthocyanin synthesis was similar to primary metabolites; carotenoids and soluble phenolics accumulated later while chlorophyll remained unaffected. Relationships of growth attributes and metabolite levels, not seen in the controls, were evident under heat stress. In summary, observed changes in metabolite levels were spread over time and space and were crucial in improving net assimilation and heat tolerance of sugarcane.

Possible involvement of some secondary metabolites in salt tolerance of sugarcane

Accumulation of toxic ions in plant tissues modulates the levels of primary and secondary metabolites, which may be related to salinity tolerance. In this study two sugarcane clones, CP-4333 (tolerant) and HSF-240 (sensitive), were exposed to salinity levels at the formative stage, and evaluated three times at 10-day intervals. Although net rate of photosynthesis (Pn), leaf area, length and dry weight of shoots were decreased in both clones, the CP-4333 showed less reduction compared to HSF-240. Both clones displayed a general tendency to accumulate Na+ and Cl- and little K+, though CP-4333 accumulated less Na+ and more K+ compared to HSF-240, and thus showed a higher K+:Na+ ratio. The carotenoid (CAR) content remained steady, while total chlorophyll (CHL) was slightly reduced in the tolerant clone and significantly reduced in HSF-240. In contrast, soluble phenolics (PHE), anthocyanins (ANT) and flavones (FLA) levels were 2.5, 2.8 and 3.0 times greater in CP-4333 in comparison with HSF-240. The decrease in Pn and most secondary metabolites demonstrated by the sensitive clone, but not evidenced in the tolerant clones, suggest that the presence of those metabolites is related to increased salt tolerance of sugarcane. The increased synthesis of PHE, ANT and FLA seems to protect sugarcane from ion-induced oxidative stress, probably due to a common structural skeleton, the phenyl group, of those metabolites. CAR, as components of the light harvesting center (LHC) and biosynthesized in chloroplasts, may confer resistance to this organelle. The PHE, ANT and FLA synthesized in the cytosol may protect cells from ion-induced oxidative damage by binding the ions and thereby showing reduced toxicity on cytoplasmic structures.

Isolation and Structure Determination of Bioactive Isoflavones from Callus Culture of Dipteryx odorata

Crude extracts of callus and roots of Dipteryx odorata were analyzed by HPLC to detect and quantify isoflavone contents. Based on spectroscopic and X-ray crystallography data the structures of two isoflavones were elucidated as 7-hydroxy-4',6-dimethoxyisoflavone and 3',7-dihydroxy-4',6-dimethoxyisoflavone. The production of dry biomass of 7-hydroxy-4',6-dimethoxyisoflavone in cultured callus was 4.12 mg/g, approximately eleven fold higher than the amount accumulated in roots of D. odorata wild-growing plants. The 7-hydroxy-4',6-dimethoxyisoflavone was effective against glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma cruzi. This is the first report on those bioactive isoflavones accumulated in callus of D. odorata.