J. Brad Murphy

Herbivory: caterpillar saliva beats plant defences.

Blood-feeding arthropods secrete special salivary proteins that suppress the defensive reaction they induce in their hosts. This is in contrast to herbivores, which are thought to be helpless victims of plant defences elicited by their oral secretions. On the basis of the finding that caterpillar regurgitant can reduce the amount of toxic nicotine released by the tobacco plant Nicotiana tabacum, we investigate here whether specific salivary components from the caterpillar Helicoverpa zea might be responsible for this suppression. We find that the enzyme glucose oxidase counteracts the production of nicotine induced by the caterpillar feeding on the plant.

Salivary Glucose Oxidase: Multifunctional Roles for Helicoverpa zea?

Labial glands of Helicoverpa zea produced a glucose oxidase (GOX), which was present in the saliva and midgut lumen. We purified GOX 23-fold by isoelectric focusing of labial gland homogenates and investigated physical and kinetic properties of the enzyme. D-glucose and 6-deoxy-D-glucose were the optimal substrates of 22 carbohydrates tested with GOX. The enzyme was not inhibited by several inhibitors of fungal GOX but was sensitive to HgCl(2). Labial gland GOX activities varied daily during larval development with highest activities found when larvae were actively feeding. Based on pH optimum, pI, molecular weight estimate and K(m(glucose)), the insect enzyme is not derived from fungal GOXs but appears to have similar kinetic and physical attributes to other insect GOXs. Some possible functions are discussed, including antimicrobial properties, manipulating midgut O(2) levels, altering host plant defense responses, and metabolizing carbohydrates. Arch. Copyright 1999 Wiley-Liss, Inc.

Analysis for substituted benzoic and cinnamic acids using high-pressure liquid chromatography.

Abstract A high-pressure liquid chromatographic (HPLC) technique for separating the 11 most common substituted benzoic and cinnamic acids occurring naturally in plants, and both parent acids, has been developed. Separation was by reversephase adsorption chromatography, based upon differential polarity of the investigated compounds. True polar mobility was obtained by the addition of ammonium acetate to inhibit intramolecular hydrogen bonding of the phenolic hydroxy groups. Optimum separation was obtained using a combination of isocratic and linear gradient elution. The HPLC technique offers excellent resolution, reproducibility, and an analysis time of 25 min. When coupled with a computing integrator, divergence from expected relative peak areas was less than 2% for all but four of the investigated compounds.

Polyethylene glycol and maltose enhance somatic embryo maturation in loblolly pine (Pinus taeda L.)

SummaryA culture medium that can efficiently produce mature somatic embryos was developed for loblolly pine (Pinus taeda L.). The medium contained maltose as a carbohydrate source and polyethylene glycol as an osmoticum. This medium formulation significantly enhanced embryo maturation efficiency compared to a medium with only maltose, or with sucrose combined with polyethylene glycol. Maltose at 4% and polyethylene glycol at 6% resulted in the highest embryo maturation efficiency; an average of around 100 cotyledonary embryos were produced from 1 g of embryogenic tissue. These results suggested that previous ineffective embryo maturation in loblolly pine may be due to the lack of the proper combination of osmoticum and carbohydrate source. This embryo maturation method also improved morphology of cotyledonary embryos of loblolly pine.

Medicago truncatula (E)-β-ocimene synthase is induced by insect herbivory with corresponding increases in emission of volatile ocimene

Virtually all plants are able to recognize attack by herbivorous insects and release volatile organic compounds (VOC) in response. Terpenes are the most abundant and varied class of insect-induced VOC from plants. Four genes encoding putative terpene synthases (MtTps1, MtTps2, MtTps3 and MtTps4) were shown to accumulate in Medicago truncatula Gaertn. in response to Spodoptera exigua (Hübner) feeding and methyl jasmonate treatment in a previous study [S.K. Gomez, M.M. Cox, J.C. Bede, K.K. Inoue, H.T. Alborn, J.H. Tumlinson, K.L. Korth, Lepidopteran herbivory and oral factors induce transcripts encoding novel terpene synthases in Medicago truncatula, Arch. Insect Biochem. Physiol. 58 (2005) 114-127.] The focus of the current study is the functional characterization of one (MtTps4) of these four genes. Using an M. truncatula cDNA clone, the insect-inducible putative terpene synthase was expressed in Escherichiacoli and shown to convert geranyl diphosphate (GPP) into the monoterpene (E)-beta-ocimene as the major product. The clone was therefore designated M. truncatula (E)-beta-ocimene synthase (MtEBOS). Transcripts encoding this enzyme accumulate in M. truncatula leaves in response to exogenous jasmonic acid treatments, lepidopteran herbivory, and lepidopteran oral secretions. Treatment with the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) did not cause an increase in MtEBOS transcripts. The volatile (E)-beta-ocimene was released from leaves of both undamaged and insect-damaged plants, but at levels two-fold higher in insect-damaged M. truncatula. Although leaves have low constitutive levels of MtEBOS transcripts, RNA blot analysis indicates no constitutive expression in flowers, stems or roots. The strong insect-induced expression of this gene, and its correspondence with release of volatile ocimene, suggest that it plays an active role in indirect insect defenses in M. truncatula.

Protein Synthesis and Aminopeptidase Activity in Dormant Sugar Pine Seeds During Stratification and Warm Incubation

Summary The capacity for protein synthesis, the activity of leucine-tyrosine aminopeptidase, and the pattern of soluble native proteins were determined for embryos and megagametophyte tissue from dormant sugar pine ( Pinus lambertiana Dougl.) seeds during 90 d of 25 °C warm, moist incubation or 5 °C stratification. The capacity for protein synthesis increased rapidly during the first 7 d in 25 °C embryos and megagametophytes and then decreased gradually through the rest of the 90-d treatment period. However, this protein synthesis at 25 °C occurred independently of germination, as these seeds maintained their dormancy. The capacity for protein synthesis in the 5 °C embryos eventually surpassed the capacity in 25 °C embryos after 60 d but remained significantly lower in the 5 °C than the 25 °C megagametophytes throughout the 90-d period. The pattern of increase in the capacity for protein synthesis in the 5 °C embryos generally paralleled increases in germinability. After about 14 d, the rate of leucine-tyrosine aminopeptidase activity remained higher in both embryos and megagametophytes at 5 °C than at 25 °C. A decline in activity occurred towards the end of the 90-d period. Patterns of native protein bands, as determined by polyacrylamide gel electrophoresis, remained the same in 5 °C and 25 °C embryos and megagametophytes throughout the 90-d period. However, the staining intensity of several individual bands appeared greater in 25 °C embryos than in 5 °C embryos.