THE EFFECTS OF TEN PHENOLIC COMPOUNDS ON HYPOCOTYL GROWTH AND MITOCHONDRIAL METABOLISM OF MUNG BEAN

Secondary metabolites responses of plants exposed to ozone: an update

Tropospheric ozone (O3) is a secondary pollutant that causes oxidative stress in plants due to the generation of excess reactive oxygen species (ROS). Phenylpropanoid metabolism is induced as a usual response to stress in plants, and induction of key enzyme activities and accumulation of secondary metabolites occur, upon O3 exposure to provide resistance or tolerance. The phenylpropanoid, isoprenoid, and alkaloid pathways are the major secondary metabolic pathways from which plant defense metabolites emerge. Chronic exposure to O3 significantly accelerates the direction of carbon flows toward secondary metabolic pathways, resulting in a resource shift in favor of the synthesis of secondary products. Furthermore, since different cellular compartments have different levels of ROS sensitivity and metabolite sets, intracellular compartmentation of secondary antioxidative metabolites may play a role in O3-induced ROS detoxification. Plants' responses to resource partitioning often result in a trade-off between growth and defense under O3 stress. These metabolic adjustments help the plants to cope with the stress as well as for achieving new homeostasis. In this review, we discuss secondary metabolic pathways in response to O3 in plant species including crops, trees, and medicinal plants; and how the presence of this stressor affects their role as ROS scavengers and structural defense. Furthermore, we discussed how O3 affects key physiological traits in plants, foliar chemistry, and volatile emission, which affects plant-plant competition (allelopathy), and plant-insect interactions, along with an emphasis on soil dynamics, which affect the composition of soil communities via changing root exudation, litter decomposition, and other related processes.

Biochar for urban agriculture: Impacts on soil chemical characteristics and on Brassica rapa growth, nutrient content and metabolism over multiple growth cycles

With possible food crises looming in the near future, urban farming, including small-scale community and home gardens for home consumption, presents a promising option to improve food security in cities. These small-scale farms and gardens often use planter boxes and raised beds filled with lightweight soil or potting mixes. While previous studies on biochar focused on its application on large-scale contiguous farmlands, this study aimed to evaluate the suitability of biochar as a partial soil substitute to produce a durable and lightweight soil-biochar mix for small-scale urban farms. The effects of biochar on the chemical properties of the soil-biochar mix, crop yield and, particularly, crop nutrients and metabolic content were assessed. A germination test using pak choi seeds (Brassica rapa L. cultivar group Pak choi, Green-Petioled Form) showed that the biochar contained phytostimulants. Through a nursery pot experiment over four growth cycles, biochar treatments performed better than pure soil at retaining water-soluble NO₃^- and K⁺ ions, but were worse at retaining PO₄^3- ions. Nonetheless, despite its positive effect on soil NO₃^- retention, biochar application did not improve crop yield significantly when the application rate varied from 0% to 60% (v/v). Untargeted metabolomic analyses showed that biochar application may increase the production of carbohydrates and certain flavonoids and glucosinolates. The results of this study showed that biochar can potentially be used to improve pak choi nutritional values and applied in large quantity to obtain a lightweight soil mix for urban farming.

From sunscreens to medicines: Can a dissipation hypothesis explain the beneficial aspects of many plant compounds?

Medicine has utilised plant‐based treatments for millennia, but precisely how they work is unclear. One approach is to use a thermodynamic viewpoint that life arose by dissipating geothermal and/or solar potential. Hence, the ability to dissipate energy to maintain homeostasis is a fundamental principle in all life, which can be viewed as an accretion system where layers of complexity have built upon core abiotic molecules. Many of these compounds are chromophoric and are now involved in multiple pathways. Plants have further evolved a plethora of chromophoric compounds that can not only act as sunscreens and redox modifiers, but also have now become integrated into a generalised stress adaptive system. This could be an extension of the dissipative process. In animals, many of these compounds are hormetic, modulating mitochondria and calcium signalling. They can also display anti‐pathogen effects. They could therefore modulate bioenergetics across all life due to the conserved electron transport chain and proton gradient. In this review paper, we focus on well‐described medicinal compounds, such as salicylic acid and cannabidiol and suggest, at least in animals, their activity reflects their evolved function in plants in relation to stress adaptation, which itself evolved to maintain dissipative homeostasis.

Plant Cell Cancer: May Natural Phenolic Compounds Prevent Onset and Development of Plant Cell Malignancy? A Literature Review

Phenolic compounds (PCs) are known as a chemically diverse category of secondary and reactive metabolites which are produced in plants via the shikimate-phenylpropanoid pathways. These compounds-ubiquitous in plants-are an essential part of the human diet, and are of considerable interest due to their antioxidant properties. Phenolic compounds are essential for plant functions, because they are involved in oxidative stress reactions, defensive systems, growth, and development. A large body of cellular and animal evidence carried out in recent decades has confirmed the anticancer role of PCs. Phytohormones-especially auxins and cytokinins-are key contributors to uncontrolled growth and tumor formation. Phenolic compounds can prevent plant growth by the endogenous regulation of auxin transport and enzymatic performance, resulting in the prevention of tumorigenesis. To conclude, polyphenols can reduce plant over-growth rate and the development of tumors in plant cells by regulating phytohormones. Future mechanistic studies are necessary to reveal intracellular transcription and transduction agents associated with the preventive role of phenolics versus plant pathological malignancy cascades.

Effects of allelopathic compounds of corn pollen on respiration and cell division of watermelon

The effects of the allelopathic compounds of an "'ethanolic extract" of corn pollen on growth, respiration, and cellular division of watermelon (Citrullus lanatus, var. peacock improved) were studied. Bioassays with the ethanolic extract showed an inhibition of radicle and hypocotyl growth. The effects on respiration were observed in isolated watermelon hypocotyl mitochondria. The ethanolic extract acts as an inhibitor of the electron pathway, decreasing oxygen consumption in state 3, with malate and succinate substrates. The specific inhibition site probably is located before the cytochromec. Ascorbate-TMPD as substrate reversed the inhibitory effect of the ethanolic extract. An evaluation of the mitotic index was made in slide preparations of previously treated meristematic cells. A decrease in mitotic activity of more than 50% was found, as well as irregular and pycnotic nuclei. The data obtained from this study reflect an important mechanism of action of the allelopathic compounds of corn pollen.

Sorgoleone from root exudate inhibits mitochondrial functions

The aim of this investigation was to determine if sorgoleone (SGL), a hydrophobic compound inSorghum bicolor (L.) Moench root exudate, interferes with mitochondrial functions. Tests were conducted on mitochondria isolated from etiolated soybean [Glycine max (L.) Merr.] and corn (Zea mays L.) seedlings. The data show SGL is a potent inhibitor of state 3 and state 4 respiration rates in both soybean and corn. Using either NADH, succinate, or malate as substrate, the I50 was about 0.5μM SGL for state 3 and 5.0μM for state 4 based on 0.3-0.5 mg mitochondrial protein. Absorption spectra indicate SGL blocks electron transport at theb-c 1 complex. These data show that disruption of mitochondrial function may be a mechanism of SGL-mediated growth inhibition previously reported and demonstrate a probable role of SGL inSorghum allelopathy.

Effect of phytotoxic resin glycoside on activity of H(+)-ATPase from plasma membrane

A resin glycoside mixture isolated fromIpomoea tricolor inhibited radicle growth ofEchinochloa crusgalli. The effect of the resin was tested on the activity of the plasma membrane H(+)-ATPase fromE. crusgalli. For this purpose, plasma membrane vesicles were purified by the method of aqueous two-phase partitioning. The resin glycoside inhibited by 30% the activity of the plasma membrane ATPase. The same result was obtained with the purified main component of the resin. This indicates that the plasma membrane ATPase can be one of the cellular targets of the resin. Hence it is possible that the mechanism of action of the resin involves an inhibition of the plasma membrane ATPase.

A potential role for sinapyl p-coumarate as a radical transfer mechanism in grass lignin formation

Grass lignins are differentiated from other lignin types by containing relatively large amounts of p-coumaric acid (pCA) acylating the C-9 position of lignin subunits. In the case of a mature corn (Zea mays L.) stems, pCA constitutes 15-18% of a dioxane soluble enzyme lignin. The major portion of the pCA is specifically attached to syringyl residues. Studies with isolated corn wall peroxidases show that pCA readily undergoes radical coupling in the presence of hydrogen peroxide, whereas sinapyl alcohol radical coupling proceeds more slowly. Analysis of corn wall peroxidases did not reveal specific enzymes that would lead to the preferred incorporation of sinapyl alcohol as seen in other plants. The addition of ethyl ferulate, methyl p-coumarate, or sinapyl p-coumarate conjugates to a reaction mixture containing peroxidase, sinapyl alcohol, and hydrogen peroxide stimulated the rate of sinapyl alcohol radical coupling by 10-20-fold. Based on spectral analysis it appears that pCA and ferulate radicals form rapidly, but the radical is readily transferred to sinapyl alcohol. The newly formed sinapyl alcohol radicals undergo coupling and cross-coupling reactions. However, sinapyl alcohol radicals do not cross-couple with pCA radicals. As long as hydrogen peroxide is limiting pCA remains uncoupled. Ferulates have similar reaction patterns in terms of radical transfer though they appear to cross-couple in the reaction mixture more readily then pCA. The role of pCA may be to internally provide a radical transfer mechanism for optimizing radical coupling of sinapyl alcohol into the growing lignin polymer. Attachment of some pCA to sinapyl alcohol ensures localization of the radical transfer mechanism in areas where sinapyl alcohol is being incorporated into lignin.

Allelopathic effects of phenolic acids on nucleic acid and protein levels in soybean seedlings

Experiments were carried out, in a controlled environment during a 4-h incubation period, to examine the effects of phenolic acids on uptake by soybean (Glycine max (L.) Merr cv. Maple Bell) roots of phosphate and methionine and their incorporation into nucleic acids and proteins, respectively. Benzoic, p-hydroxy benzoic, vanillic, cinnamic, p-coumaric, and ferulic acids were used in the study. Nucleic acid and protein synthesis were assayed by the incorporation of 32P and 35S-methionine into soybean root. The uptake of 32P was reduced by benzoic, cinnamic, vanillic, and ferulic acids, while p-hydroxybenzoic and p-coumaric acids increased slightly its absorption. At 250 μM, all allelochemicals tested reduced the incorporation of 32P into DNA and RNA. Benzoic, cinnamic, ferulic, and vanillic acids reduced the uptake of 32S-methionine, whereas p-hydroxybenzoic and p-coumaric acids increased its uptake. The methionine incorporation into proteins was reduced by all phenolic acids, except for p-coumaric acid and vanillic acid at 125 μM. These results suggest that interference with nucleic acid and protein metabolism by the phenolic acids is one of the main mechanisms by which they influence plant growth. Key words: Allelochemicals, mechanism of action, phenolic acids, phosphorus, proteins, methionine, ion uptake.

5-O-β-D-galactopyranosyl-7-methoxy-3',4'-dihydroxy-4-phenylcoumarin, an inhibitor of photophosphorylation in spinach chloroplasts

5-O-β-D-galactopyranosyl-7-methoxy-3',4'-dihydroxy-4-phenylcoumarin isolated from Exostema caribaeum (Rubiaceae) has been found to act as an energy-transfer inhibitor in spinach chloroplasts. ATP synthesis and phosphorylating (coupled) electron flow were inhibited by 89 and 72%, respectively, at a concentration of 400 μM. H(+)-uptake, basal and uncoupled electron transport were not affected by the coumarin. The light-activated Mg(+2)-ATPase activity from bound membrane thylakoid chloroplasts was slightly inhibited by the coumarin. Also, the heat-activated Ca(+2)-ATPase activity of the isolated coupling factor protein was insensitive to this compound. In chloroplasts partially stripped of coupling factor 1 by an EDTA treatment, the coumarin showed a restoration of the proton uptake process. These results suggest that the 4-phenylcoumarin under investigation inhibited phosphorylation in chloroplasts by specifically blocking the transport of protons through a membrane-bound component or a carrier channel (CFO) located in a hydrophobic region at or near the functional binding site for the coupling factor 1.