Identification and characterization of organic and glycosidic acids in the crude resin glycoside fraction of Ipomoea lacunosa seeds

Resin glycosides are commonly found in plants belonging to the Convolvulaceae family. Ipomoea lacunosa L. (Convolvulaceae) is an herbaceous vine native to the United States. The resin glycosides of this plant have not been studied in detail. In this study, the components of the crude resin glycoside fraction extracted from the seeds of I. lacunosa are characterized. Alkaline hydrolysis of the crude resin glycoside fraction obtained from methanolic extract of the seeds yielded three organic acids, namely, 2S-methylbutyric, (E)-2-methylbut-2-enoic, and 2R-methyl-3R-hydroxybutyric acids, and a glycosidic acid fraction. Acidic hydrolysis of the glycosidic acid fraction yielded hydroxyl fatty acid components, including 7S-hydroxydecanoic, 11S-hydroxytetradecanoic, 11S-hydroxyhexadecanoic, 3S,11S-dihydroxytetradecanoic, 3S,11S-dihydroxyhexadecanoic, and 3S,12S-dihydroxyhexadecanoic acids, as well as monosaccharide components, including d-glucose, d-quinovose, d-fucose, and l-rhamnose. Trimethylsilyldiazomethane-hexane treatment of the glycosidic acid fraction further yielded eleven previously undescribed glycosidic acid methyl esters and two known glycosidic acid methyl esters. The structures of the obtained compounds were characterized using various spectral techniques. Four of the undescribed compounds were hexaglycosides, five were heptaglycosides, and two were octaglycosides. The aglycone of these compounds was either methyl 11S-hydroxytetradecanoate, methyl 3S,11S-dihydroxytetradecanoate, or methyl 3S,11S-dihydroxyhexadecanoate. Among the undescribed compounds identified, eight contained novel glycans, and three were rare bisdesmosides with sugar linkages at the C-3 and C-11 positions of methyl 3S,11S-dihydroxytetradecanoate.

Comparative Metabolomic Analyses of Ipomoea lacunosa Biotypes with Contrasting Glyphosate Tolerance Captures Herbicide-Induced Differential Perturbations in Cellular Physiology

Glyphosate-tolerant Ipomoea lacunosa is emerging as a problematic weed in the southeastern United States. Metabolomic profiling was conducted to examine the innate physiology and the glyphosate induced perturbations in two biotypes of I. lacunosa (WAS and QUI) that had contrasting glyphosate tolerance. Compared to the less tolerant QUI-biotype, the innate metabolism of the more tolerant WAS-biotype was characterized by a higher abundance of amino acids, and pyruvate; whereas the sugar profile of the QUI biotype was dominated by the transport sugar sucrose. Glyphosate application (80 g ae/ha) caused similar shikimate accumulation in both biotypes. Compared to QUI, in WAS, the content of aromatic amino acids was less affected by glyphosate treatment, and the content of Ala, Val, Ile, and Pro increased. However, the total sugars decreased by ∼75% in WAS, compared to ∼50% decrease in QUI. The innate, higher proportional abundance, of the transport-sugar sucrose in QUI coud partly explain the higher translocation and greater sensitivity of this biotype to glyphosate. The decrease in sugars, accompanied by an increase in amino acids could delay feedback regulation of upstream enzymes of the shikimate acid pathway in WAS, which could contribute to a greater glyphosate tolerance. Our study, through a metabolomics approach, provides complementary data that elucidates the cellular physiology of herbicide tolerance in Ipomoea lacunosa biotypes.

Possible glyphosate tolerance mechanism in pitted morningglory (Ipomoea lacunosa L.)

Natural tolerance of Ipomoea lacunosa to glyphosate has made it problematic in the southeastern U.S. since the adoption of glyphosate-resistant crops. Experiments were conducted to determine (i) the variability in tolerance to glyphosate among accessions, (ii) if there is any correlation between metabolism of glyphosate to aminomethylphosponic acid (AMPA) or sarcosine and the level of tolerance, and (iii) the involvement of differential translocation in tolerance to glyphosate. Fourteen I. lacunosa accessions had GR50 values ranging from 58 to 151 grams of acid equivalent per hectare (ae/ha) glyphosate, a 2.6-fold variability in tolerance to glyphosate. There was no evidence of the most tolerant (MT) accession metabolizing glyphosate to AMPA more rapidly than the least tolerant (LT) accession. Metabolism to sarcosine was not found. (14)C-glyphosate absorption was similar in the two accessions. LT accession translocated more (14)C-glyphosate than MT accession at 24 and 48 h after treatment. Differential translocation partly explains glyphosate tolerance in MT accession.

Evolution of the selfing syndrome in Ipomoea

Plants that are highly selfing typically exhibit a suite of morphological traits termed a "selfing syndrome," including reduced corollas and reproductive structures, loss of corolla pigmentation, little anther-stigma separation, and a lower pollen/ovule (P/O) ratio. While it is typically assumed that these changes are adaptive, few attempts have been made to determine whether they result from the operation of natural selection or genetic drift. In the southeastern United States, Ipomoea lacunosa has evolved a typical selfing syndrome compared to its close relative, Ipomoea cordatotriloba. Microsatellite markers confirmed that selfing rates are substantially higher in I. lacunosa. Furthermore, using a standard QST - FST comparison, we evaluated the relative importance of selection and drift in the evolution of selfing syndrome traits in I. lacunosa. The analysis demonstrated that natural selection is responsible for the evolution of reduced corolla size, anther-stigma distance, and style length in this species. By contrast, leaf characteristics unrelated to selfing were found to have diverged largely by genetic drift. Our study provides one of the first confirmations that natural selection drives the evolution of selfing-syndrome traits.

Interaction Among a Nematode (Heterodera glycines), an Insect, and Three Weeds in Soybean

A 2 x 3 x 4 factorial field experiment was established to determine the interaction among a nematode, an insect, and three weed species on soybean in 1983-86. Low (nematicide treated) or high (untreated) population densities of the soybean cyst nematode (SCN), Heterodera glycines, and 0, 30, or 70% main stem girdling by the threecornered alfalfa hopper (TCAH), Spissistilus festinus, were combined with no weeds, one common cocklebur (CC), Xanthium strumarium, one sicklepod (SP), Cassia obtusifolia, or one pitted morningglory (PMG), Ipomoea lacunosa, per meter of row in all possible combinations. Most of the losses from the pests were significant (P </= 0.05) and additive. The high population density of SCN suppressed soybean seed yield by 14%. Girdling of 30 and 70% by TCAH suppressed yields by 10 and 25%, respectively. One CC, SP, or PMG per meter of row suppressed yield by 22, 14, and 12%, respectively. The addition of loss predictions for each pest was approximately the actual treatment losses recorded. The pests did not have an evident interactive effect on yield losses; however, the losses attributed to each pest were additive.