No abstract

Patatin, the nonspecific lipid acyl hydrolase from potato (Solanum tuberosum L.) tubers, dose-dependently inhibits the growth of southern corn rootworm (SCR) and western corn rootworm when fed to them on artificial diet. The 50% growth reduction levels are somewhat cultivar dependent, ranging from 60 to 150 pg/g diet for neonate SCR larvae. A single patatin isoform also inhibits larval growth. Neonate SCR continuously exposed to patatin are halted in larval development. Treatment with di-isopropylfluorophosphate essentially eliminates patatin's phospholipase, galactolipase, and acyl hydrolase activities. SCR growth inhibition is eliminated also, indicating that patatin's serine hydrolase activity is responsible for the observed activities. Patatin-mediated phospholipolysis is highly pH and cultivar dependent, with specific activities up to 300-fold less at pH 5.5 than at pH 8.5. Esterase or phospholipase activities do not correlate with insect growth inhibition. Calactolipase activity, being cultivar and pH independent, correlates significantly with SCR growth inhibition. Insect-growth inhibition of patatin is significantly reduced with increased dietary cholesterol levels. In conclusion, patatin represents a new class of insect-control proteins with a novel mode of action possibly involving lipid metabolism.

SummaryIrradiation of 4‐day‐old dark‐grown seedlings of Cuscuta campestris Yuncker and Cusctira indecara Choisy with I min of red light stimulated coiling and prehaustoria formation in excised upper 4‐cm segments of seedlings during a 48‐h dark period in which zeatin was applied. Coiling and prehaustoria development were completely reversed when irradiated with 2 min of far‐red light applied directly after red light. When deetiolated segments were subjected to prolonged exposure of pure blue light, or mixtures of ultraviolet‐A/far‐red, blue/far‐red or red/far‐red light, coiling and prehaustona development were induced. Blue light at photon fluxes lower than 1 μmol m‐2 s‐1 did not promote coiling and formation of prehaustoria. Mechanical stimulation caused tendrils to coil and form prehaustona in biue and blue/far‐red light, but not in darkness. Zeatin substituted for high irradiance blue light and mechanical stimulation caused coiling and prehaustoria formation.

Both the bacterium Photorhabdus luminescens alone and its symbiotic Photorhabdus-nematode complex are known to be highly pathogenic to insects. The nature of the insecticidal activity of Photorhabdus bacteria was investigated for its potential application as an insect control agent. It was found that in the fermentation broth of P. luminescens strain W-14, at least two proteins, toxin A and toxin B, independently contributed to the oral insecticidal activity against Southern corn rootworm. Purified toxin A and toxin B exhibited single bands on native polyacrylamide gel electrophoresis and two peptides of 208 and 63 kDa on SDS-polyacrylamide gel electrophoresis. The native molecular weight of both the toxin A and toxin B was determined to be approximately 860 kDa, suggesting that they are tetrameric. NH 2 -terminal amino acid sequencing and Western analysis using monospecific antibodies to each toxin demonstrated that the two toxins were distinct but homologous. The oral potency (LD 50 ) of toxin A and toxin B against Southern corn rootworm larvae was determined to be similar to that observed with highly potent Bt toxins against lepidopteran pests. In addition, it was found that the two peptides present in toxin B could be processed in vitro from a 281-kDa protoxin by endogenous P. luminescens proteases. Proteolytic processing was shown to enhance insecticidal activity.

White light-grown seedlings of smallseed dodder were (a) provided with unilateral far-red (700 to 800 nm) at photon irradiances ranging from 20 to 110 μmol m−2 s−1 against a background of cool white light (400 to 700 nm) from above at 77 μmol m−2 s−1, or (b) transferred to darkness and provided with unilateral white light at 20 μmol m−2 s−1, unilateral blue light (400 to 500 nm) at 10 μmol m−2 s−1, unilateral red light (600 to 700 nm) at 10 μmol m−2 s−1, unilateral far-red at 50 μmol m−2 s−1, or (c) in experiments utilizing bilateral irradiations, provided with unilateral far-red perpendicular to unilateral white light. Positive phototropic curvature was induced by unilateral white light and by unilateral blue light in otherwise darkness and by unilateral far-red in a background of cool white light. Seedling vines were also phototropic toward unilateral far-red when provided with unilateral white light perpendicular to unilateral far-red. Phototropism to unilateral white light was inhibited in seedlings treated with 200 μM norflurazon and 50 mM potassium iodide. Norflurazon- and potassium iodide-treated seedlings remained phototropic toward unilateral far-red when provided with unilateral white light perpendicular to unilateral far-red. Seedling vines were not phototropic to unilateral red or to unilateral far-red in otherwise darkness, and seedlings in cool white light were neither skototropic (i.e., tropic toward unilateral darkness) nor tropic to or from infra-red (radiation with wavelengths greater than 900 nm). Phototropism toward regions of lowered red:far-red may aid smallseed dodder in chlorophyllous host location and attachment.