Phytotoxic activity

The cytolytic agent termed aponin has been characterized in terms of biological activity, and the results to date indicate a material that does not adversely affect the organisms tested. Material isolated from cultures of Nannochloris sp. also has some phytotoxic activity as evidenced by the assays with lettuce seeds, and some antifungal activity. The materials elaborated by Nannochloris sp. thus have environmental significance, but it must be admitted that the full significance of these materials, like others, remains to be fully appreciated. 

In cooperation with USDA-ARS, isolated compounds demonstrating phytotoxic activity will be synthesized and tested to determine lethal concentrations, mode of action, and mechanism of action. 

Chou CH, Patrick ZA (1976) Identification and phytotoxic activity of compounds produced during decomposition of com and rye residues in soil. J Chem Ecol 2 369-387 Christians NE (1993) The use of com gluten meal as a natural preemergence weed control in turf. Int Turfgrass Society Res J 7 284—290... 

Next, the studies were extended to evaluate the effect of the compounds on duckweed which is one of the best characterized models for assessing phytotoxic activity. The duckweed assay system makes it possible to study the toxic effects throughout the plant life cycle, as well as to plant specific toxic effects which target photosynthesis. Of all the isolates, only 12 and 13 showed significant phytotoxicity on duckweed at concentrations of 100 xM and 200 xM inhibiting plant growth by 80% and 100%, respectively and chlorophyll production by 40% and 84%, respectively. ... 

Table 1. Effect of Bibenzyls 19,20,23-28 on Duckweed Cultures at 72 Hours. (Reprinted from J Agric Food Chem, 53, Hernandez-Romero Y, Acevedo L, Sanchez MD, Shier WT, Abbas HK and Mata R, Phytotoxic activity of bibenzyl derivatives from the orchid Epidendrum rigidum, 2005, 6276-6280 with permission from ACS.)...

Rajan, A. "Phytotoxic Activity of Imperata cylindrica (L.) Beauv." Ph.D. Thesis, Univ. New Eng., Armidale, 1984. 

The objective of this study was to develop an efficient whole plant bloassay that would identify diverse types of compounds that cause phytotoxic activity. 

Then standard isolation and structure determination techniques were used to identify the compound(s) responsible for the phytotoxic activity. 

The objectives of this paper are broad. Our first objective is to describe the primary mechanism of action of usnic acid on plants as ascertained by our laboratory.33 A second objective is to describe the phytotoxic activity of selected lichen anthraquinone analogues. In addition to the phytotoxic activity, we describe the effects of these secondary metabolites on phloem-feeding insects. Finally, we provide a hypothesis to explain the functional roles of these metabolites in the ecosystem. 

Lichens containing usnic acid may exhibit phytotoxic activity. In nature, (-)-usnic acid may decrease interspecific competition by inhibiting growth of seedlings in the canopy. Since it is primarily an HPPD inhibitor and secondarily inhibits Protox, there may be a decreased chance for resistance in those competing species. 

Rhodocladonic acid is an anthraquinone that occurs in several lichen species, especially in the family Roccellaceae).20 Little research has been done documenting bioactivity, particularly phytotoxic activity. Similar to emodin, we tested two sets of analogues (Fig. 1.10). Series 1 consisted of a group of compounds with aliphatic R-groups ending in a terminal hydroxyl. Series 2 had a terminal methyl. The R-group substitutions were identical to those of emodin. 

Unlike the emodin analogues, rhodocladonic acid analogues exhibited different phytotoxic effects for similar substitutions. There was no dose-dependent bleaching associated with any of these compounds. In addition, there was no selectivity in phytotoxic activity between monocots and dicots. Despite the lack of bleaching, structure-activity relationships would suggest the potential for PS II inhibition. Both series of Rhodocladonic acid analogues, those with terminal -CH3 and those with a terminal - OH (Fig. 1.11 A B, respectively), caused an increase in PSII activity with regard to controls. 

Quassinoids are bitter components produced by members of the Simaroubaceae. They exhibit diverse biological activities including anticancer, antimalarial, insecticidal, and phytotoxic activities. Ailanthone (26), chaparrinone (27), and other quassinoids, along with indole alkaloids, contribute to the invasiveness of the Chinese tree tree-of-heaven Alianthus altissima Swingle), in Europe.15... 

Many other phytotoxins not presented here have been structurally characterized and tested In some plant bioassay systems. Numerous other reported phytotoxin studies are In the "active fraction" stage and structure elucidation of the active components has not been achieved. Nevertheless, from the data presented. It can generally be concluded that diverse microbes produce a broad range of chemistries with phytotoxic activities chemical and biochemical synthesis of almost all of these compounds Is unknown (but derivitizatlon studies to alter phytotoxic activity have been used In a few Instances) knowledge of the spectrum of species susceptible to these compounds Is Incomplete (many weed and crop species have not been tested some compounds are toxic to organisms other than plants) and the molecular mode of phytotoxin action Is unstudied or unknown for most. The major exception Is the vast amount of data on blalaphos, phosalacine, and phosphinothricin, which have achieved commercial status. 

Phytotoxins from nonpathogenic organisms also have potential as weed-control agents. Numerous phytotoxic compounds have been isolated and bioassayed for phytotoxic activity, and their chemical structures have been determined. Generally, these naturally occurring compounds have unique chemistries that differ from those of commercial synthetic herbicides. Some of these compounds—or others yet to be discovered—may be used directly as herbicides or provide templates for the development of new, efficacious weed control agents that are less persistent and more environmentally compatible than some compounds currently being used. 

Alternaria species are associated with several leaf-spot diseases of plants. Alternaric acid (8.10), produced by A. solani, which is the cause of early blight on potatoes and tomatoes, has a marked phytotoxic activity and may be responsible for many of the symptoms of the plant disease caused by the fungus. It also shows a specific anti-fungal activity. The branched chain structure is biosynthesized from nine acetate units and three Ci units derived from formate. The solanopyrones are another group of phytotoxic metabolites of A. solani. Solanopyrone A (8.11) induced necrotic lesions on the leaves of potatoes typical of this fungal infection. The structures of the solanopyrones were established by... 

The technical products is not a uniform compound. Intensive investigations showed it to be actually a mixture of 6 isomeric compounds. According to Kirby et al. (1964 and 1966), 2,4-dinitro-6-isooctylphenyl crotonate is the carrier of acaricidic and phytotoxic activity, while 2,6-dinitro-4-isooctylphenyl crotonate is the most effective component against powdery mildew (Pianka and Sweet, 1968). Both derivatives may have 3 isomers, depending on the nature of the isooctyl chain ... 

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