scholarly journals Ecological Implications of Organic Mulches in Arboriculture: A Mechanistic Pathway Connecting the Use of Organic Mulches with Tree Chemical Defenses

2009 ◽  
Vol 35 (4) ◽  
pp. 211-217
Author(s):  
Javier Lugo-Perez ◽  
John Lloyd
Keyword(s):  
Resource Availability ◽  
Urban Areas ◽  
Chemical Defenses ◽  
Plant Performance ◽  
Plant Chemical Defense ◽  
Experimental Conditions ◽  
Indirect Benefits ◽  
Plant Resource ◽  
Mechanistic Pathway ◽  
Plant Chemical

In addition to the aesthetic and practical benefits of mulching, studies have shown indirect benefits of organic mulches to tree establishment and growth. These indirect benefits are associated with direct improvements on soil water and nutrient availability by mulches. The generalization of the organic mulches benefit to soil and trees has been questioned by several studies showing contradictory results under different experimental conditions and mulching materials. In addition, overall benefits for trees may be overlooked by focusing studies on some aspects of plant performance (e.g., plant growing rate) while ignoring others (e.g., plant chemical defense). This paper reviews studies showing how organic mulches can directly affect plant resource availability in the soil, presenting evidence from the literature that illustrates the influence of organic mulches on plant resource availability can also affect tree photosynthate allocation dynamics with direct consequences on plant chemical defenses. Based on the reviewed literature, presented here is a mechanistic pathway to illustrate how organic mulches can influence plant resources in the soil, and in turn how that can affect tree physiology and tree-insect interactions in urban areas.

Controlled hydroxylations of diterpenoids allow for plant chemical defense without autotoxicity

Science ◽  
2021 ◽  
Vol 371 (6526) ◽  
pp. 255-260
Author(s):  
Jiancai Li ◽  
Rayko Halitschke ◽  
Dapeng Li ◽  
Christian Paetz ◽  
Haichao Su ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Chemical Defenses ◽  
Toxic Waste ◽  
Nicotiana Attenuata ◽  
Plant Chemical Defense ◽  
Herbivore Defense ◽  
Plant Chemical ◽  
In The Wild ◽  
Sphingolipid Biosynthesis ◽  
Diterpene Biosynthesis

Many plant specialized metabolites function in herbivore defense, and abrogating particular steps in their biosynthetic pathways frequently causes autotoxicity. However, the molecular mechanisms underlying their defense and autotoxicity remain unclear. Here, we show that silencing two cytochrome P450s involved in diterpene biosynthesis in the wild tobacco Nicotiana attenuata causes severe autotoxicity symptoms that result from the inhibition of sphingolipid biosynthesis by noncontrolled hydroxylated diterpene derivatives. Moreover, the diterpenes’ defensive function is achieved by inhibiting herbivore sphingolipid biosynthesis through postingestive backbone hydroxylation products. Thus, by regulating metabolic modifications, tobacco plants avoid autotoxicity and gain herbivore defense. The postdigestive duet that occurs between plants and their insect herbivores can reflect the plant’s solutions to the “toxic waste dump” problem of using potent chemical defenses.

Lack of rapid monoterpene turnover in rooted plants: implications for theories of plant chemical defense

Oecologia ◽  
1991 ◽  
Vol 87 (3) ◽  
pp. 373-376 ◽  
Author(s):  
Charles A. Mihaliak ◽  
Jonathan Gershenzon ◽  
Rodney Croteau
Keyword(s):  
Chemical Defense ◽  
Plant Chemical Defense ◽  
Plant Chemical

scholarly journals Cardenolides, toxicity, and the costs of sequestration in the coevolutionary interaction between monarchs and milkweeds

2021 ◽  
Vol 118 (16) ◽  
pp. e2024463118
Author(s):  
Anurag A. Agrawal ◽  
Katalin Böröczky ◽  
Meena Haribal ◽  
Amy P. Hastings ◽  
Ronald A. White ◽  
...  
Keyword(s):  
Danaus Plexippus ◽  
Monarch Butterfly ◽  
Chemical Defenses ◽  
Trade Off ◽  
Asclepias Curassavica ◽  
Plant Chemical ◽  
Whole Plants ◽  
Benefits And Costs

For highly specialized insect herbivores, plant chemical defenses are often co-opted as cues for oviposition and sequestration. In such interactions, can plants evolve novel defenses, pushing herbivores to trade off benefits of specialization with costs of coping with toxins? We tested how variation in milkweed toxins (cardenolides) impacted monarch butterfly (Danaus plexippus) growth, sequestration, and oviposition when consuming tropical milkweed (Asclepias curassavica), one of two critical host plants worldwide. The most abundant leaf toxin, highly apolar and thiazolidine ring–containing voruscharin, accounted for 40% of leaf cardenolides, negatively predicted caterpillar growth, and was not sequestered. Using whole plants and purified voruscharin, we show that monarch caterpillars convert voruscharin to calotropin and calactin in vivo, imposing a burden on growth. As shown by in vitro experiments, this conversion is facilitated by temperature and alkaline pH. We next employed toxin-target site experiments with isolated cardenolides and the monarch’s neural Na+/K+-ATPase, revealing that voruscharin is highly inhibitory compared with several standards and sequestered cardenolides. The monarch’s typical >50-fold enhanced resistance to cardenolides compared with sensitive animals was absent for voruscharin, suggesting highly specific plant defense. Finally, oviposition was greatest on intermediate cardenolide plants, supporting the notion of a trade-off between benefits and costs of sequestration for this highly specialized herbivore. There is apparently ample opportunity for continued coevolution between monarchs and milkweeds, although the diffuse nature of the interaction, due to migration and interaction with multiple milkweeds, may limit the ability of monarchs to counteradapt.

scholarly journals Evaluation of the chemical composition of gas- and particle-phase products of aromatic oxidation

2020 ◽  
Vol 20 (16) ◽  
pp. 9783-9803
Author(s):  
Archit Mehra ◽  
Yuwei Wang ◽  
Jordan E. Krechmer ◽  
Andrew Lambe ◽  
Francesca Majluf ◽  
...  
Keyword(s):  
Gas Phase ◽  
Mass Spectrometer ◽  
Urban Areas ◽  
Minor Component ◽  
Proton Transfer Reaction ◽  
Chemical Mechanism ◽  
Particle Phase ◽  
Experimental Conditions ◽  
Radical Oxidation ◽  
Product Ions

Abstract. Aromatic volatile organic compounds (VOCs) are key anthropogenic pollutants emitted to the atmosphere and are important for both ozone and secondary organic aerosol (SOA) formation in urban areas. Recent studies have indicated that aromatic hydrocarbons may follow previously unknown oxidation chemistry pathways, including autoxidation that can lead to the formation of highly oxidised products. In this study we evaluate the gas- and particle-phase ions measured by online mass spectrometry during the hydroxyl radical oxidation of substituted C9-aromatic isomers (1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, propylbenzene and isopropylbenzene) and a substituted polyaromatic hydrocarbon (1-methylnaphthalene) under low- and medium-NOx conditions. A time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) with iodide–anion ionisation was used with a filter inlet for gases and aerosols (FIGAERO) for the detection of products in the particle phase, while a Vocus proton-transfer-reaction mass spectrometer (Vocus-PTR-MS) was used for the detection of products in the gas phase. The signal of product ions observed in the mass spectra were compared for the different precursors and experimental conditions. The majority of mass spectral product signal in both the gas and particle phases comes from ions which are common to all precursors, though signal distributions are distinct for different VOCs. Gas- and particle-phase composition are distinct from one another. Ions corresponding to products contained in the near-explicit gas phase Master Chemical Mechanism (MCM version 3.3.1) are utilised as a benchmark of current scientific understanding, and a comparison of these with observations shows that the MCM is missing a range of highly oxidised products from its mechanism. In the particle phase, the bulk of the product signal from all precursors comes from ring scission ions, a large proportion of which are more oxidised than previously reported and have undergone further oxidation to form highly oxygenated organic molecules (HOMs). Under the perturbation of OH oxidation with increased NOx, the contribution of HOM-ion signals to the particle-phase signal remains elevated for more substituted aromatic precursors. Up to 43 % of product signal comes from ring-retaining ions including HOMs; this is most important for the more substituted aromatics. Unique products are a minor component in these systems, and many of the dominant ions have ion formulae concurrent with other systems, highlighting the challenges in utilising marker ions for SOA.

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