Herbivory induces both direct and indirect defenses in plants; however, some combinations of these defenses may not be compatible. The jasmonate signal cascade activated both direct (nicotine accumulations) and indirect (mono- and sesquiterpene emissions) whole-plant defense responses in the native tobacco Nicotiana attenuata Torr. Ex Wats. Nicotine accumulations were proportional to the amount of leaf wounding and the resulting increases in jasmonic acid (JA) concentrations. However, when larvae of the nicotine-tolerant herbivore, Manduca sexta, fed on plants or their oral secretions were applied to leaf punctures, the normal wound response was dramatically altered, as evidenced by large (4- to 10-fold) increases in the release of (i) volatile terpenoids and (ii) ethylene, (iii) increased (4- to 30-fold) accumulations of endogenous JA pools, but (iv) decreased or unchanged nicotine accumulations. The ethylene release, which was insensitive to inhibitors of induced JA accumulation, was sufficient to account for the attenuated nicotine response. Applications of ethylene and ethephon suppressed the induced nicotine response and pre-treatment of plants with a competitive inhibitor of ethylene receptors, 1-methylcyclopropene, restored the full nicotine response. This ethylene burst, however, did not inhibit the release of volatile terpenoids. Because parasitoids of Manduca larvae are sensitive to the dietary intake of nicotine by their hosts, this ethylene-mediated switching from direct to a putative indirect defense may represent an adaptive tailoring of a plant's defense response.

No abstract

Ethylene emission from wild‐type Agrobacterium tumefaciens (C58)‐induced stem tumours of Ricinus communis was continuously measured with two different methods, process gas chromatography and photo‐acoustic spectrometry. Ethylene production was as high as 700 pmol g FW–1 h–1, namely 140 times greater than emitted by non‐tumourized control stems. It was highest in 5‐week‐old tumours, independent of light, depressed by anoxia and, during water deficit it was stimulated by rewatering. A remarkable concomitant CO‐production was discovered. Accumulation of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), the substrate of ACC‐oxidase, preceded ethylene emission with a maximum 2 weeks after tumour induction. Simultaneously, the xylem in the tumour‐adjacent host stem underwent drastic changes: it increased two to three times in thickness, vessel diameters decreased, the rays remained unlignified and became multiseriate. With increasing emission of ethylene aerenchyma developed in the non‐transformed, tumour‐surrounding tissue that formerly was stem cortex. Cotyledons reacted with epinastic symptoms indicating induction of senescence. The present results reveal an important role of ethylene, in addition to cytokinin and auxin, for the differentiation and physiology of A. tumefaciens‐induced tumours.

No abstract

Using an optical beating technique, the diffusion coefficients and relative scattered intensity of Escherichia coli 70S, 50S, and 30S ribosomes are measured as a function of temperature and Mg(2+) concentration. For solutions at 10 mM Mg(2+) and between 0 degrees C and about 40 degrees C, the values of D(20,w) obtained are 1.7, 1.9, and approximately 2.1 x 10(-7) cm(2)/s, respectively. Preparative procedures drastically affect these values and equivalent hydrodynamic ellipsoids of revolution models give large axial ratios indicating extensive hydration or a deviation from the assumed shape. Calculations also indicate that the subunits expand upon dissociation. Measurements of D(20,w) vs. temperature indicate that 70S particles undergo a conformational change prior to dissociation and can be heat dissociated at 30-32 degrees C at low concentrations. Treatment of 70S ribosomes with EDTA causes a biphasic dissociation reaction. Addition of Mg(2+) after dissociation with EDTA shows that longer waiting times yield fewer 70S particles and that even short waiting times may yield ribosomes differing from the native conformation. Addition of p-chloromercuribenzoic acid (PCMB) is shown to dissociate 70S particles, but to a lesser extent than ethylenediaminetetraacetic acid (EDTA).