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Resveratrol and its dimethoxylated derivative, pterostilbene, are produced by several plant species, including a few edible crops such as peanut (Arachis hypogaea L.), grapes (Vitis spp.), and blueberries (Vaccinium spp.), as well some plants used in traditional medicine. Both compounds are inducible, antimicrobial compounds with activity against both plant pathogenic bacteria and fungi, an activity apparently not directly related to their strong antioxidant activity. An amazing number of nutraceutical properties have been claimed for both compounds, including antioxidant, antiaging, anti-cholesterol, anticancer, antidiabetic and other beneficial activities. Most evidence supports the view that pterostilbene is more active for most of these effects, due in part to its greater biological availability. However, the amount of these compounds in most diets is insufficient to provide these health benefits. Dietary supplements of formulated pure compounds can now provide sufficient dietary levels for these effects, as transgenic crops in the future might also do.

Glyphosate is the most used herbicide worldwide, which has contributed to concerns about its environmental impact. Compared with most other herbicides, glyphosate has a half-life in soil and water that is relatively short (averaging about 30 d in temperate climates), mostly due to microbial degradation. Its primary microbial product, aminomethylphosphonic acid, is slightly more persistent than glyphosate. In soil, glyphosate is virtually biologically inactive due to its strong binding to soil components. Glyphosate does not bioaccumulate in organisms, largely due to its high water solubility. Glyphosate-resistant crops have greatly facilitated reduced-tillage agriculture, thereby reducing soil loss, soil compaction, carbon dioxide emissions, and fossil fuel use. Agricultural economists have projected that loss of glyphosate would result in increased cropping area, some gained by deforestation, and an increase in environmental impact quotient of weed management. Some drift doses of glyphosate to non-target plants can cause increased plant growth (hormesis) and/or increased susceptibility to plant pathogens, although these non-target effects are not well documented. The preponderance of evidence confirms that glyphosate does not harm plants by interfering with mineral nutrition and that it has no agriculturally significant effects on soil microbiota. Glyphosate has a lower environmental impact quotient than most synthetic herbicide alternatives.

Several grass and broadleaf weed species around the world have evolved multiple-herbicide resistance at alarmingly increasing rates. Research on the biochemical and molecular resistance mechanisms of multiple-resistant weed populations indicate a prevalence of herbicide metabolism catalyzed by enzyme systems such as cytochrome P450 monooxygenases and glutathione S-transferases and, to a lesser extent, by glucosyl transferases. A symposium was conducted to gain an understanding of the current state of research on metabolic resistance mechanisms in weed species that pose major management problems around the world. These topics, as well as future directions of investigations that were identified in the symposium, are summarized herein. In addition, the latest information on selected topics such as the role of safeners in inducing crop tolerance to herbicides, selectivity to clomazone, glyphosate metabolism in crops and weeds, and bioactivation of natural molecules is reviewed.

The identification of natural and environmentally friendly pesticides is a key area of interest for the agrochemical industry, with many potentially active compounds being sourced from numerous plant species. In this study, we report the bioassay-guided isolation and identification of phytotoxic and antifungal compounds from the ethyl acetate extract of Helietta parvifolia stems. We identified eight compounds, consisting of two coumarins and six alkaloids. Among these, a new alkaloid, 2-hydroxy-3,6,7-trimethoxyquinoline-4-carbaldehyde (6), was elucidated, along with seven known compounds. The phytotoxicity of purified compounds was evaluated, and chalepin (4) was active against Agrostis stolonifera at 1 mM with 50% inhibition of seed germination and it reduced Lemna pausicotata (duckweed) growth by 50% (IC50) at 168 μM. Additionally, we evaluated the antifungal activity against the fungal plant pathogen Colletotrichum fragariae using a thin-layer chromatography bioautography assay, which revealed that three isolated furoquinoline alkaloids (flindersiamine (3), kokusagenine (7), and maculine (8)) among the isolated compounds had the strongest inhibitory effects on the growth of C. fragariae at all tested concentrations. Our results indicate that these active natural compounds, i.e., (3), (4), (7), and (8), could be scaffolds for the production of more active pesticides with better physicochemical properties.

The herbicides used with crops that have been made resistant to them with transgenes are assumed to have no significant effects on these crops. Crops made resistant to glyphosate, glufosinate, dicamba, 2,4-D, mesotrione, and isoxaflutole are discussed in this paper. Most of the literature on this topic has been on glyphosate-resistant crops, as these have been the most successful of all herbicide-resistant crops. Reports of adverse effects, such as phytotoxicity symptoms, disrupted mineral nutrition, and reduced yield, caused by these herbicides on these crops are reviewed and critiqued herein. These reports are often conflicting, however, and there is no consistent evidence of any major adverse effects of these herbicides on these crops. Literature on the accumulation of residues of the intended herbicides in the parts of the plants that are used as food is also discussed. Reports of potential unintended beneficial effects, such as effects on crop pests and stimulation of crop growth and development are also critiqued.

Bioassay-guided fractionation of an EtOAc extract of the broth of the endophytic fungus Nemania sp. UM10M (Xylariaceae) isolated from a diseased Torreya taxifolia leaf afforded three known cytochalasins, 19,20-epoxycytochalasins C (1) and D (2), and 18-deoxy-19,20-epoxy-cytochalasin C (3). All three compounds showed potent in vitro antiplasmodial activity and phytotoxicity with no cytotoxicity to Vero cells. These compounds exhibited moderate to weak cytotoxicity to some of the cell lines of a panel of solid tumor (SK-MEL, KB, BT-549, and SK-OV-3) and kidney epithelial cells (LLC-PK11). Evaluation of in vivo antimalarial activity of 19,20-epoxycytochalasin C (1) in a mouse model at 100 mg/kg dose showed that this compound had weak suppressive antiplasmodial activity and was toxic to animals.

Natural products are a main source of new chemical entities for use in drug and pesticide discovery. In order to discover lead compounds with high herbicidal activity, a series of new pyrido[2,3-d] pyrimidine derivatives were designed and synthesized using 2-chloronicotinic acid as the starting material. Their structures were characterized with 1H NMR, 13C NMR and HRMS, and the herbicidal activities against dicotyledonous lettuce (Lactuca sativa), field mustard (Brassica campestris), monocotyledonous bentgrass (Agrostis stolonifera) and wheat (Triticum aestivum) were determined. The results indicated that most of the pyrido[2,3-d] pyrimidine derivatives had no marked inhibitory effect on lettuce at 1 mM. However, most of the pyrido[2,3-d] pyrimidine derivatives possessed good activity against bentgrass at 1 mM. Among them, the most active compound, 3-methyl-1-(2,3,4-trifluorophenyl)pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (2o), was as active as the positive controls, the commercial herbicides clomazone and flumioxazin. Molecular simulation was performed with molecular docking and DFT calculations. The docking studies provided strong evidence that 2o acts as an herbicide by inhibition of protoporphyrinogen oxidase. However, the physiological results indicate that it does not act on this target in vivo, implying that it could be metabolically converted to a compound with a different molecular target.

Knowledge of the mode of action of an allelochemical can be valuable for several reasons, such as proving and elucidating the role of the compound in nature and evaluating its potential utility as a pesticide. However, discovery of the molecular target site of a natural phytotoxin can be challenging. Because of this, we know little about the molecular targets of relatively few allelochemicals. It is much simpler to describe the secondary effects of these compounds, and, as a result, there is much information about these effects, which usually tell us little about the mode of action. This review describes the many approaches to molecular target site discovery, with an attempt to point out the pitfalls of each approach. Clues from molecular structure, phenotypic effects, physiological effects, omics studies, genetic approaches, and use of artificial intelligence are discussed. All these approaches can be confounded if the phytotoxin has more than one molecular target at similar concentrations or is a prophytotoxin, requiring structural alteration to create an active compound. Unequivocal determination of the molecular target site requires proof of activity on the function of the target protein and proof that a resistant form of the target protein confers resistance to the target organism.

Sorgoleone, a major component of the hydrophobic root exudates of Sorghum spp., is probably responsible for many of the allelopathic properties attributed to members of this genus. Much of the biosynthetic pathway for this compound has been elucidated, with the exception of the enzyme responsible for the catalysis of the addition of two hydroxyl groups to the resorcinol ring. A library prepared from isolated Sorghum bicolor root hair cells was first mined for P450-like sequences, which were then analyzed by quantitative reverse transcription-polymerase chain reaction (RT-qPCR) to identify those preferentially expressed in root hairs. Full-length open reading frames for each candidate were generated, and then analyzed biochemically using both a yeast expression system and transient expression in Nicotiana benthamiana leaves. RNA interference (RNAi)-mediated repression in transgenic S. bicolor was used to confirm the roles of these candidates in the biosynthesis of sorgoleone in planta. A P450 enzyme, designated CYP71AM1, was found to be capable of catalyzing the formation of dihydrosorgoleone using 5-pentadecatrienyl resorcinol-3-methyl ether as substrate, as determined by gas chromatography-mass spectroscopy (GC-MS). RNAi-mediated repression of CYP71AM1 in S. bicolor resulted in decreased sorgoleone contents in multiple independent transformant events. Our results strongly suggest that CYP71AM1 participates in the biosynthetic pathway of the allelochemical sorgoleone.