Stephen O. Duke

Bio: Stephen O. Duke is an academic researcher from University of Arkansas. The author has contributed to research in topics: Cropping & Genus. The author has an hindex of 4, co-authored 4 publications receiving 111 citations.

Phytochrome Control of Longitudinal Growth and Phytochrome Synthesis in Maize Seedlings

Abstract: The active, far-red light absorbing, form of phytochrome was found to inhibit growth and phytochrome levels in the mesocotyl and coleoptile of 4- to 5.5-day-old seedlings of Zea mays L. Short, low-irradiance red or far-red light treatments were used to produce different proportions of active phytochrome at the end of highdirradiance white-light periods, which left different levels of total phytochrome in the plants. After light treatments which left relatively high levels of spectrophotometrically assayable phytochrome in the seedlings, apparent phytochrome synthesis in the subsequent dark period was low regardless of the proportions of each form of the pigment present at the beginning of the dark period. In light treatments producing relatively low levels of assayable phytochrome, levels of apparent phytochrome synthesis in both red and far-red treatments and differences between apparent synthesis in red and far-red treatments were maximal. No simple correlation was found between growth and apparent phytochrome synthesis. However, growth and total phytochrome levels were positively correlated in both organs. Using a subtractive method of correlation, in which only phytochrome effects were plotted, strong linear relationships between phytochrome levels or longitudinal growth and Pfr levels were found in those light treatments leaving greater than 8% of dark control levels of phytochrome in the tissues. Using this technique non-linear, inverse relationships between Pfr and apparent phytochrome synthesis was found, indicating that modes of phytochrome control over phytochrome synthesis and growth differ. Our results are consistent with the view that in vivo assays of “bulk’ phytochrome reflect levels and states of the physiologically active phytochrome fraction under our experimental conditions in maize.

Tentoxin effects on infrastructure and greening of ivyleaf morningglory (Ipomoea hederacea var. hederacea) cotyledons

Abstract: The effects of 20 μM tentoxin on mesophyll chloroplast ultra-structural development, chlorophyll organization and accumulation, and pigment transformations in cotyledons of dark-grown, 4-day-old ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. var. hederacea]were monitored. After 6 h of white light (200 μEm−2T.s−1), many plastids of tentoxin-treated tissues contained prolamellar bodies or inconsistent internal membrane orientation in contrast to the uniform internal membrane orientation and absence of prolamellar bodies in controls. Grana stacking did not progress beyond three to four disc loculi in tentoxin-treatments, and fret membranes were usually discontinuous and reduced. Cylindrical or cupped grana appeared in many chloroplasts after 3 days of light, while other chloroplasts in which disruption was more pronounced had few grana except for remnants, but usually did possess vesicles or structures resembling prolamellar bodies. Tentoxin had no apparent effect on stroma density or plastoglobuli size and number. No starch grains appeared in any of the tentoxin treatments, whereas they appeared after 24 h in controls. Initial protochlorophyllide content and its photoconversion to chlorophyllide and subsequent Shibata shift were not affected by tentoxin. Chlorophyll accumulation rates in tentoxin-treated cotyledons were about 10% of control rates during the first 24 h of greening and about 20% of controls from 48 to 72 h of greening. Chlorophyll alb ratio and PSU size (total Chl/P700) were not significantly affected by tentoxin.

Weed and Crop Allelopathy

Abstract: Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization, and root exudation. Allelochemical structures and modes of action are diverse and may offer potential for the development of future herbicides. We have focused our review on a variety of weed and crop species that establish some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are ...

Development and Fine Structure of the Glandular Trichomes of Artemisia annua L.

Abstract: Development of capitate glands on the leaves of annual wormwood (Artemisia annua L.) was monitored with scanning and transmission electron microscopy. Differentiation of foliar cells into gland cells began in the youngest leaf primordia. After differentiation into a 10-celled biseriate structure of two stalk cells, two basal cells, and three pairs of secretory cells, the cuticle of the six secretory cells separated from the cell walls to form a bilobed sac that eventually splits to release its contents. At every developmental stage, the cells of the the gland contained relatively little vacuolar volume. The secretory cells contained extensive endoplasmic reticulum. The plastids of each cell pair were different. At maturity, the apical cells contained proplastids or leucoplasts with only occasional thylakoids. The cell pair below the apical cell pair contained amorphous chloroplasts without starch grains. The basal cell pair contained proplastids or leucoplasts and the stalk cells contained chloroplasts. T...

Localization of artemisinin and artemisitene in foliar tissues of glanded and glandless biotypes of artemisia annua l.

Abstract: The tissue localization of the antimalarial sesquiterpenoid compound artemisinin in annual wormwood (Artemisia annua L.) was determined by differential extraction of a glanded biotype and through the use of a glandless biotype. A 5-s dip in chloroform extracted 97% of the artemisinin from glanded A. annua leaf tissue. In addition, all of the detectable artemisitene, an artemisinin analog, was extracted. This extraction method caused collapse of the subcuticular space of the capitate glands on the leaf surface, whereas no other damage to the leaf surface was observed with SEM. Light microscopy and TEM revealed that this extraction method, despite causing some organelle structural changes, did not disrupt cell membranes. An A. annua biotype without glands contained neither artemisinin nor artemisitene. These results indicate that artemisinin and artemisitene present in foliar tissue are localized entirely in the subcuticular space of capitate glands of A. annua.

Acaricidal properties of Artemisia absinthium and Tanacetum vulgare (Asteraceae) essential oils obtained by three methods of extraction.

Abstract: Essential oils of Artemisia absinthium L. and Tanacetum vulgare L. were extracted by three methods, a microwave assisted process (MAP), distillation in water (DW) and direct steam distillation (DSD), and tested for their relative toxicity as contact acaricides to the twospotted spider mite, Tetranychus urticae Koch. All three extracts of A. absinthium and of T. vulgare were lethal to the spider mite but to variable degrees. The LC50 obtained from the DSD oil of A. absinthium was significantly lower (0.04 mg/cm2) than that of the MAP (0.13 mg/cm2) and DW (0.13 mg/cm2) oil of this plant species. DSD and DW extracts of T. vulgare were more toxic (75.6 and 60.4% mite mortality, respectively, at 4% concentration) to the spider mite than the MAP extract (16.7% mite mortality at 4% concentration). Chromatographic analysis indicated differences in composition between the more toxic DSD oil of A. absinthium and the other two extracts of this plant, indicating that a sesquiterpene (C15H24) compound present in the DSD oil and absent in the other two may enhance the toxicity of the DSD oil. Chemical analysis of the T. vulgare extracts indicated that β-thujone is by far the major compound of the oil (>87.6%) and probably contributes significantly to the acaricidal activity of the oil.