Localization of enzymes in specific plant tissues is crucial to understanding their role in processes such as differentiation and disease resistance. The oxidative enzymes lipoxygenase (LOX; EC 220.127.116.11), peroxidase (PER, EC 18.104.22.168) and polyphenol oxidase (PPO; EC 22.214.171.124) have all been implicated as playing critical roles in plant disease resistance. The histochemical localization of all three enzymes in potato tuber slices was accomplished either directly on the tissue slices (for LOX) or by blotting of the tissue onto nitrocellulose membranes (for PER and PPO). LOX was visualized in specific tissues by the oxidation of KI to I2 via lipid peroxides and the subsequent reaction of I2 and endogenous starch to form a colored, insoluble complex. PER and PPO activities were visualized with 4-methoxy-α-naphthol and 3,4-dihydroxy-phenylalanine, respectively. Fractionation of the slices and determination of enzyme activities in the fractions confirmed the reliability of these techniques.
Steven F. Vaughn
The enzyme superoxide dismutase (SOD; EC 126.96.36.199) catalyzes the conversion of the superoxide radical (
Steven F. Vaughn and Gayland F. Spencer
The shelf-life of strawberries and raspberries is limited primarily due to losses from fungal decay. During ripening, these fruits release numerous volatile compounds, some of which have been shown to have antifungal activities. We examined fifteen volatiles released by both fruits for the prevention of postharvest fungal decay. Benzaldehyde, 1-hexanol and 2-nonanone completely inhibited all fungal growth on fruit at gas headspace concentrations of 0.1 μl/ml, while causing little damage to the fruit. However, greater levels of these compounds, although completely inhibiting fungi, generally caused some fruit damage. Headspace concentrations of these compounds at 0.04 μl/ml or greater completely inhibited the growth of Botrytis cinerea and Alternaria alternata in culture but higher levels were required to inhibit Colletotrichum gloeosporoides and Rhizopus stolonifer. These results suggest that these compounds could be used to effectively prevent fungal decay if constant, low levels could be maintained in the headspace surrounding the fruit.
Steven F. Vaughn and Fred J. Eller
Internal mold of sweet and hot peppers (Capsicum spp.) is caused by the pathogen Alternaria alternata. The pepper weevil, Anthomonus eugenii Cano (Coleoptera: Curculionidae), is an important pest of peppers in the southern U.S., Mexico, and Central America, and has been implicated in the transmission of the disease. We identified several volatiles released by pepper fruit during wounding by pepper weevils, including (E)-3-hexenyl acetate, linalool, beta-ocimene, and 3,7-dimethyl-1,3,6 octatriene (homoterpene). To study the roles of these volatiles in the interaction of the plant and fungus, we determined their effect on the growth of isolated cultures of A. alternata. Fungi were unaffected by any of the compounds when exposed to individual volatiles at 1 ppm; however, a 1 ppm mixture of the four compounds significantly reduced growth. All four compounds were inhibitory individually at 10 ppm, with linalool completely inhibiting fungal growth. These results indicate a role for these volatiles in the plant's response to infection by A. alternata.
Rick A. Boydston, Harold P. Collins, and Steven F. Vaughn
This research evaluated the use of dried distiller grains with solubles (DDGS) as a soil amendment to suppress weeds in container-grown ornamentals. DDGS is a byproduct of ethanol produced from corn, and developing new uses for DDGS could increase the profitability of ethanol production. Adding DDGS to a commercial pine bark potting mix reduced emergence and growth of common chickweed (Stellaria media) at concentrations of 5% (by weight) or greater and annual bluegrass (Poa annua) at concentrations of 10% (by weight) or more. Herbicidal activity of DDGS was maintained in methanol-extracted DDGS. Rosa hybrid ‘Red Sunblaze’, Phlox paniculata ‘Franz Schubert’, and Coreopsis auriculata ‘Nana’ transplanted into potting soil amended with 20% by weight DDGS were severely stunted and nearly all plants died. Plants survived when transplanted into potting soil containing 10% DDGS by weight, but growth was greatly stunted and flowering of rose and coreopsis was reduced. Addition of 20% DDGS decreased the C:N ratio from 90:1 to 24:1 for the potting mix and from 23:1 to 10:1 for a soil. The decrease in C:N ratio resulted in a twofold increase in microbial respiration at 3 d and 14 d of incubation for both the potting mix and soil. As a result of the phytotoxicity observed on ornamentals transplanted into DDGS-amended potting soil, subsequent studies evaluated surface-applied DDGS to suppress weeds. DDGS applied at 400 g·m−2 or less to the soil surface at transplanting did not reduce emergence or growth of common chickweed or annual bluegrass. DDGS applied at 800 and 1600 g·m−2 to the surface of transplanted ornamentals reduced number of annual bluegrass by 40% and 57% and common chickweed by 33% and 58%, respectively, without injury to transplanted ornamentals. DDGS may be useful for reducing weed emergence and growth in container-grown ornamentals applied to the soil surface at transplanting.
Steven F. Vaughn, Mark A. Berhow, and Brent Tisserat
Meadowfoam (Limnanthes alba Hartweg ex. Benth.) seedmeal, a coproduct of oil extraction from meadowfoam seeds, has been found to increase the growth of greenhouse plants when added to the growing medium. (3-Methoxyphenyl)acetonitrile (3-MPAN) is a biologically active glucosinolate degradation compound previously identified at high levels in meadowfoam seedmeal. 3-MPAN was tested as a foliar spray at several concentrations (0 μm, 0.18 mm, 0.37 mm, 0.73 mm, 2.2 mm, and 7.3 mm) on lime basil (Ocimum basilicum L.), spearmint (Mentha spicata L.), cuphea (Cuphea lanceolata L.), and French marigold (Tagetes patula L.) seedlings grown in the greenhouse. 3-MPAN increased the fresh and dry weights of all four species tested. However, this effect was dose-dependent among species with spearmint growth higher at all 3-MPAN application rates, whereas basil growth was promoted at only the 2.2-mm rate. 3-MPAN increased the tissue concentrations of the secondary compound (−)-carvone at the 7.3-mm application rate. In addition, 3-MPAN added to sterile nutrient media stimulated the growth of spearmint plants in vitro. These results indicate that 3-MPAN may have applicability as a postemergent growth stimulant for a wide variety of plants.
Rick A. Boydston, Treva Anderson, and Steven F. Vaughn
Mustard seed meal is a byproduct of mustard (Sinapis alba L.) grown for oil production. Developing new uses for mustard seed meal could increase the profitability of growing mustard. Seed meal of mustard, var. ‘IdaGold’, was applied to the soil surface to evaluate its effect on several common weeds in container-grown ornamentals. Mustard seed meal applied to the soil surface of containers at 113, 225, and 450 g·m−2 reduced the number of annual bluegrass (Poa annua L.) seedlings by 60%, 86%, and 98%, respectively, and the number of common chickweed (Stellaria media L.) seedlings by 61%, 74%, and 73%, respectively, at 8 weeks after treatment (WAT). Mustard seed meal applied to the soil surface after transplanting Rosa L. hybrid, var. ‘Red Sunblaze’, Phlox paniculata L., var. ‘Franz Schubert’, and Coreopsis auriculata L., var. ‘Nana’ did not injure or affect the flowering or growth of ornamentals. In separate experiments, mustard seed meal applied at 225 g·m−2 to the soil surface reduced the number of emerged seedlings and fresh weight of creeping woodsorrel (Oxalis corniculata) 90% and 95%, respectively, at 8 WAT. Mustard seed meal applied at 450 g·m−2 completely prevented woodsorrel emergence at 8 WAT. Mustard seed meal applied postemergence to established liverwort (Marchantia polymorpha L.) at 113, 225, and 450 g·m−2 did not injure container-grown Pulsatilla vulgaris Mill., var. ‘Heiler Hybrids Mixed’ up to 6 WAT and controlled liverwort from 83% to 97% at 6 WAT. Weed suppression with mustard seed meal generally increased as rate increased from 113 to 450 g·m−2. Mustard seed meal may be useful for selective suppression of annual weeds when applied to the soil surface of container-grown transplanted ornamentals.