Frequency of resistance to Bacillus thuringiensis in field populations of pink bollworm

Strategies for delaying pest resistance to genetically modified crops that produce Bacillus thuringiensis (Bt) toxins are based primarily on theoretical models. One key assumption of such models is that genes conferring resistance are rare. Previous estimates for lepidopteran pests targeted by Bt crops seem to meet this assumption. We report here that the estimated frequency of a recessive allele conferring resistance to Bt toxin Cry1Ac was 0.16 (95% confidence interval = 0.05–0.26) in strains of pink bollworm (Pectinophora gossypiella) derived from 10 Arizona cotton fields during 1997. Unexpectedly, the estimated resistance allele frequency did not increase from 1997 to 1999 and Bt cotton remained extremely effective against pink bollworm. These results demonstrate that the assumptions and predictions of resistance management models must be reexamined.

Interactions between Senescence and Leaf Orientation Determine in Situ Patterns of Photosynthesis and Photoinhibition in Field-Grown Rice1

Photosynthesis and photoinhibition in field-grown rice (Oryza sativa L.) were examined in relation to leaf age and orientation. Two varieties (IR72 and IR65598-112-2 [BSI206]) were grown in the field in the Philippines during the dry season under highly irrigated, well-fertilized conditions. Flag leaves were examined 60 and 100 d after transplanting. Because of the upright nature of 60-d-old rice leaves, patterns of photosynthesis were determined by solar movements: light falling on the exposed surface in the morning, a low incident angle of irradiance at midday, and light striking the opposite side of the leaf blade in the afternoon. There was an early morning burst of CO2 assimilation and high levels of saturation of photosystem II electron transfer as incident irradiance reached a maximum level. However, by midday the photochemical efficiency increased again almost to maximum. Leaves that were 100 d old possessed a more horizontal orientation and were found to suffer greater levels of photoinhibition than younger leaves, and this was accompanied by increases in the de-epoxidation state of the xanthophyll cycle. Older leaves had significantly lower chlorophyll content but only slightly diminished photosynthesis capacity.

Nuclear magnetic dipole interactions in field-oriented proteins: information for structure determination in solution.

The measurement of dipolar contributions to the splitting of 15N resonances of 1H-15N amide pairs in multidimensional high-field NMR spectra of field-oriented cyanometmyoglobin is reported. The splittings appear as small field-dependent perturbations of normal scalar couplings. Assignment of more than 90 resonances to specific sequential sites in the protein allows correlation of the dipolar contributions with predictions based on the known susceptibility and known structure of the protein. Implications as an additional source of information for protein structure determination in solution are discussed.

Functional and physiological consequences of genetic variation at phosphoglucose isomerase: Heat shock protein expression is related to enzyme genotype in a montane beetle

Allele frequency variation at the phosphoglucose isomerase (PGI) locus in Californian populations of the beetle Chrysomela aeneicollis suggests that PGI may be undergoing natural selection. We quantified (i) apparent Michaelis-Menten constant (Km) of fructose 6-phosphate at different temperatures and (ii) thermal stability for three common PGI genotypes (1–1, 1–4, and 4–4). We also measured air temperature (Ta) and beetle body temperature (Tb) in three montane drainages in the Sierra Nevada, California. Finally, we measured 70-kDa heat shock protein (Hsp70) expression in field-collected and laboratory-acclimated beetles. We found that PGI allele 1 predominated in the northernmost drainage, Rock Creek (RC), which was also significantly cooler than the southernmost drainage, Big Pine Creek (BPC), where PGI allele 4 predominated. Allele frequencies and air temperatures were intermediate in the middle drainage, Bishop Creek (BC). Differences among genotypes in Km (1–1 > 1–4 > 4–4) and thermal stability (4–4 > 1–4 > 1–1) followed a pattern consistent with temperature adaptation. In nature, Tb was closely related to Ta. Hsp70 expression in adult beetles decreased with elevation and differed among drainages (BPC > BC > RC). After laboratory acclimation (8 days, 20°C day, 4°C night) and heat shock (4 h, 28–36°C), Hsp70 expression was greater for RC than BPC beetles. In RC, field-collected beetles homozygous for PGI 1–1 had higher Hsp70 levels than heterozygotes or a 4–4 homozygote. These results reveal functional and physiological differences among PGI genotypes, which suggest that montane populations of this beetle are locally adapted to temperature.

Ambient UV-B radiation causes deformities in amphibian embryos

There has been a great deal of recent attention on the suspected increase in amphibian deformities. However, most reports of amphibian deformities have been anecdotal, and no experiments in the field under natural conditions have been performed to investigate this phenomenon. Under laboratory conditions, a variety of agents can induce deformities in amphibians. We investigated one of these agents, UV-B radiation, in field experiments, as a cause for amphibian deformities. We monitored hatching success and development in long-toed salamanders under UV-B shields and in regimes that allowed UV-B radiation. Embryos under UV-B shields had a significantly higher hatching rate and fewer deformities, and developed more quickly than those exposed to UV-B. Deformities may contribute directly to embryo mortality, and they may affect an individual’s subsequent survival after hatching.

Methylation is not the main force repressing the retrotransposon MAGGY in Magnaporthe grisea

We have introduced the LTR-retrotransposon MAGGY into a naive genome of Magnaporthe grisea and estimated the copy number of MAGGY in a cell by serial isolation of fungal protoplasts at certain time intervals. The number of MAGGY elements rapidly increased for a short period following introduction. However, it did not increase geometrically and reached equilibrium at 20–30 copies per genome, indicating that MAGGY was repressed or silenced during proliferation. De novo methylation of MAGGY occurred immediately following invasion into the genome but the degree of methylation was constant and did not correlate with the repression of MAGGY. 5-Azacytidine treatment demethylated and transcriptionally activated the MAGGY element in regenerants but did not affect transpositional frequency, suggesting that post-transcriptional suppression, not methylation, is the main force that represses MAGGY proliferation in M.grisea. Support for this conclusion was also obtained by examining the methylation status of MAGGY sequences in field isolates of M.grisea with active or inactive MAGGY elements. Methylation of the MAGGY sequences was detected in some isolates but not in others. However, the methylation status did not correlate with the copy numbers and activity of the elements.

Hydroperoxide lyase depletion in transgenic potato plants leads to an increase in aphid performance

Hydroperoxide lyases (HPLs) catalyze the cleavage of fatty acid hydroperoxides to aldehydes and oxoacids. These volatile aldehydes play a major role in forming the aroma of many plant fruits and flowers. In addition, they have antimicrobial activity in vitro and thus are thought to be involved in the plant defense response against pest and pathogen attack. An HPL activity present in potato leaves has been characterized and shown to cleave specifically 13-hydroperoxides of both linoleic and linolenic acids to yield hexanal and 3-hexenal, respectively, and 12-oxo-dodecenoic acid. A cDNA encoding this HPL has been isolated and used to monitor gene expression in healthy and mechanically damaged potato plants. HPL gene expression is subject to developmental control, being high in young leaves and attenuated in older ones, and it is induced weakly by wounding. HPL enzymatic activity, nevertheless, remains constant in leaves of different ages and also after wounding, suggesting that posttranscriptional mechanisms may regulate its activity levels. Antisense-mediated HPL depletion in transgenic potato plants has identified this enzyme as a major route of 13-fatty acid hydroperoxide degradation in the leaves. Although these transgenic plants have highly reduced levels of both hexanal and 3-hexenal, they show no phenotypic differences compared with wild-type ones, particularly in regard to the expression of wound-induced genes. However, aphids feeding on the HPL-depleted plants display approximately a two-fold increase in fecundity above those feeding on nontransformed plants, consistent with the hypothesis that HPL-derived products have a negative impact on aphid performance. Thus, HPL-catalyzed production of C6 aldehydes may be a key step of a built-in resistance mechanism of plants against some sucking insect pests.