Leafy spurge

The Role of Phytochemistry in Attacking the Leafy Spurge Euphorbia esula) Problem... 

While leafy spurge can be controlled by herbicides ( ) or vigorous cultivation, the cost of control is continuous since current chemical means do not eradicate this weed. More than 20 million dollars a year is spent for the control of this plant, and its agro-economic impact is greater than 12 million dollars per year in the state of North Dakota alone ( ). Recent research efforts on the leafy spurge problem have concentrated on Increased herbicide efficiency and the successful application of insect biological control methods. 

This paper summarizes the results of phytochemical examinations of plant-plant and plant-insect interactions Involving leafy spurge... 

Scheme I. The Chemical Separation of Leafy Spurge Plant Material...

Table I. The Effect of Small Everlasting Extracts on the Growth of Lettuce Roots and the Elongation of Leafy Spurge Roots...

Isolated, crystallized and characterized. Pure commercial samples of each of the three phenols and p-benzoqulnone (VIII), the oxidation product of hydroqulnone (Included to evaluate the possible vivo oxidation of hydroqulnone), were tested In lettuce and leafy spurge root elongation tests and In leafy spurge cell cultures (Table II). 

Table II. The Effect of Chemical Constituents Occurring In Small Everlasting on the Growth of Lettuce Roots, Root Elongation and Cell Culture Growth of Leafy Spurge...

This study showed that hydroquinone was glycosated by the barley to form arbutln and was therefore effectively detoxified. If the equilibrium of the detoxification mechanism of a plant is sensitive to an oversupply of the toxic and detoxified compound, an oversupply of a detoxified compound could produce equilibrium amounts of the toxic compound. Cell culture bloassay (Table II) showed that hydroquinone is not significantly detoxified in vivo in leafy spurge, indicating the succeptiblllty of the plant to low levels of hydroquinone which could originate from an oversupply of arbutln. The observed toxicity of -benzoquinone in the cell cultures and seed bloassays also indicates that oxidation processes affecting hydroquinone will not detoxify the compound vivo. 

This investigation has shown hydroquinone to be a potent phytotoxin toward developing leafy spurge roots. Hydroquinone, originating from a chronic oversupply of arbutln, is considered to play a significant role in the observed allelopathy of small everlasting toward leafy spurge. 

Leafy Spurge Wax. Leaves of four North American accessions and one European accession of Euphorbia esula were dipped in chloroform (30 sec.) to obtain leaf wax samples for analytical gas chromato-graphy/mass spectrometry (GC/MS) analysis (28). The wax samples were partitioned into acetone soluble and acetone-insoluble fractions. 

Leafy Spurge Root Extractives. Prior chemical examinations of leafy spurge have considered only aerial portions of the plant. Our recent chemical examination of root material relative to mammalian toxicity and/or allelopathy (29) resulted in the isolation and characterization of two new jatrophane diterpenes (esulone A (IX) and esulone B (X)) from the ether extract of the roots. Biological assay of esulone A showed it to be moderately phytotoxic (29% root length reduction (lettuce seeds) at 250 ppm), moderately toxic (LD50 78 23 mg/kg) and mildly Inflammatory (10 5 to 10 M, dermal) to mammals with no hyperplasia. 

Barkosky RR, Einhellig FA, Butler JL. 2000. Caffeic acid induced changes in plant-water relationships and photosynthesis in leafy spurge (Euphorbia esula). J Chem Ecol 26 2095-2109. 

Brinkman, M.A., Clay, S.A., Kremer, R.J. Influence of deleterious rhizobacteria on leafy spurge (Euphorbia esula) roots. Weed Technol 1999 13 835-839. 

Souissi, T., Kremer, R, J., White, J.A. Scanning and transmission electron microscopy of root colonization of leafy spurge (Euphorbia esula L.) seedlings by rhizobacteria. Phytomorphology 1997 47 177-193. 

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