Autoinactivation of xanthine oxidase: the role of superoxide radical and hydrogen peroxide.

Xanthine oxidase suffers autoinactivation in the course of catalyzing the oxidation of acetaldehyde. When no special efforts were made to maintain a high pO2 in these reaction mixtures catalase protected the xanthine oxidase, but superoxide dismutase did not. However, when oxygen depletion was slowed or prevented by working at lower concentrations of xanthine oxidase, at lower temperatures or by vigorous agitation under an atmosphere of 100% oxygen, superoxide dismutase or catalase protected markedly when added separately and protected almost completely when added together. This result correlates with the greater production of O2-, relative to H2O2, by xanthine oxidase, at elevated pO2. Since histidine also provided some protection and the high levels of acetaldehyde used would have precluded any significant effect of OH., we conclude that singlet oxygen, or something with similar reactivity, was generated from O2- plus H2O2 and contributed significantly to the observed autoinactivation.

Expression of transfected human CuZn superoxide dismutase gene in mouse L cells and NS20Y neuroblastoma cells induces enhancement of glutathione peroxidase activity.

The human CuZn superoxide dismutase (superoxide dismutase 1) a key enzyme in the metabolism of oxygen free-radicals, is encoded by a gene located on chromosome 21 in the region 21 q 22.1 known to be involved in Down's syndrome. A gene dosage effect for this enzyme has been reported in trisomy 21. To assess the biological consequences of superoxide dismutase 1 overproduction within cells, the human superoxide dismutase 1 gene and a human superoxide dismutase 1 cDNA were introduced into mouse L cells and NS20Y neuroblastoma cells. Both cell types expressed elevated levels (up to 3-fold) of enzymatically active human superoxide dismutase 1. These human superoxide dismutase 1 overproducers, especially neuronal cell lines, showed an increased activity in the selenodependent glutathione peroxidase. These data are consistent with the possibility that gene dosage of superoxide dismutase 1 contributes to oxygen metabolism modifications previously described in Down's syndrome.

beta-1,3-Glucanase Activity in Peanut Seed (Arachis hypogaea) is Induced by Inoculation with Aspergillus flavus and Copurifies with a Conglutin-Like Protein.

ABSTRACT Infection of peanut (Arachis hypogaea) seed by Aspergillus flavus and A. parasiticus is a serious problem that can result in aflatoxin contamination in the seed. Breeding resistant cultivars would be an effective approach to reduce aflatoxin accumulation. The objective of this study was to investigate the expression of the pathogenesis-related (PR) protein beta-1,3-glucanase and the isoform patterns in peanut seed inoculated with A. flavus. Peanut genotypes GT-YY9 and GT-YY20 (both resistant to A. flavus infection) and Georgia Green and A100 (both susceptible to A. flavus infection) were used in this study. The activities of beta-1,3-glucanase were similar in the uninfected seed of all genotypes, but increased significantly in the resistant genotypes after inoculation in comparison with the susceptible genotypes. An in-gel (native polyacrylamide gel electrophoresis [PAGE]) enzymatic activity assay of beta-1,3-glucanase revealed that there were more protein bands corresponding to beta-1,3-glucanase isoforms in the infected seed of resistant genotypes than in the infected seed of susceptible genotypes. Both acidic and basic beta-1,3-glucanase isoforms were detected in the isoelectric focusing gels. Thin-layer chromatography analysis of the hydrolytic products from the reaction mixtures of the substrate with the total protein extract or individual band of native PAGE revealed the presence of enzymatic hydrolytic oligomer products. The individual bands corresponding to the bands of beta-1,3-glucanase isoforms Glu 1 to 5 were separated on the sodium dodecyl sulfate-PAGE, resulting in two bands of 10 and 13 kDa, respectively. The sequences of fragments of the 13-kDa major protein band showed a high degree of homology to conglutin, a storage protein in peanut seed. Conglutin is reported as a peanut allergen, Ara h2. Our data provide the first evidences for peanut having beta-1,3-glucanase activities and the association with the resistance to A. flavus colonization in peanut seed. We have not directly demonstrated that conglutin has beta-1,3-glucanase activity.

Identification of Transcripts Involved in Resistance Responses to Leaf Spot Disease Caused by Cercosporidium personatum in Peanut (Arachis hypogaea).

ABSTRACT Late leaf spot disease caused by Cercosporidium personatum is one of the most destructive foliar diseases of peanut (Arachis hypogaea) worldwide. The objective of this research was to identify resistance genes in response to leaf spot disease using microarray and real-time polymerase chain reaction (PCR). To identify transcripts involved in disease resistance, we studied the gene expression profiles in two peanut genotypes, resistant or susceptible to leaf spot disease, using cDNA microarray containing 384 unigenes selected from two expressed sequenced tag (EST) cDNA libraries challenged by abiotic and biotic stresses. A total of 112 spots representing 56 genes in several functional categories were detected as up-regulated genes (log(2) ratio > 1). Seventeen of the top 20 genes, each matching gene with known function in GenBank, were selected for validation of their expression levels using real-time PCR. The two peanut genotypes were also used to study the functional analysis of these genes and the possible link of these genes to the disease resistance trait. Microarray technology and real-time PCR were used for comparison of gene expression. The selected genes identified by microarray analysis were validated by real-time PCR. These genes were more greatly expressed in the resistant genotype as a result of response to the challenge of C. personatum than in the susceptible genotype. Further investigations are needed to characterize each of these genes in disease resistance. Gene probes could then be developed for application in breeding programs for marker-assisted selection.

Porphyria cutanea tarda associated with disinfectant misuse.

Porphyria cutanea tarda was detected in a 44-year-old janitress. The illness was probably caused by the unintentional synthesis of a polychlorinated phenol as a result of mixing commonly available household ingredients in toilet bowls and shower stalls. Although the evidence for this hypothesis is circumstantial, its likelihood and the wide-spread household use of these reagents justify calling attention to the innovative misuse of disinfectants as a potential source of toxic exposure.

Uptake of gallium-67 in transfected cells and tumors absent or enriched in the transferrin receptor.

UNLABELLED: Gallium-67 has been a controversial tumor-imaging agent in nuclear medicine for decades. This controversy centers on why tumors are variable in gallium-avidity, whether 67Ga uptake is a transferrin-independent or dependent process, and whether tumors and normal tissues differ in mechanism of uptake. If the factors that control uptake of 67Ga were understood better, then efforts to improve oncologic imaging with 67Ga by increasing the tumor activity, or by decreasing the background, may be warranted. METHODS: Conventional systems for evaluating the mechanism and control of 67Ga uptake have significant limitations. We have endeavored to circumvent these by developing a pair of transfected cell lines. One cell line has no transferrin receptor. In the other, the human transferrin receptor has been restored by transfection and is over-expressed constitutively, without the necessity to manipulate factors such as cell growth or iron content. The uptake of 67Ga, both as a citrate salt and as a gallium-transferrin complex, was examined in these pairs of cells in vitro. The effect of calcium and of soluble (ionic) iron concentration on 67Ga uptake also was determined. Tumors were grown as explants of these cells in nude mice and comparisons of uptake of 67Ga by these tumors in vivo were made. RESULTS: The in vivo uptake of 67Ga is significantly increased in tumors in which the transferrin receptor is overexpressed, compared to those without a functional transferrin receptor. However, a notable amount of accumulation of 67Ga also occurs, both in vitro and in vivo, by a transferrin-independent route. In vitro experiments demonstrate that the uptake of 67Ga by the transferrin-independent route can be enhanced further to levels that equal or exceed those achieved by the transferrin-dependent route by increasing the content of calcium or iron salts in the incubation medium. CONCLUSION: Significant transferrin-independent uptake of 67Ga occurs both in vitro and in vivo. This uptake can be stimulated further in vitro, suggesting that in vivo enhancement might also be possible to enhance the utility of the radiometal for tumor imaging.

Distribution of gallium-67 in normal and hypotransferrinemic tumor-bearing mice.

The mechanism by which 67Ga accumulates in tumors is controversial. The most popular theory is that 67Ga binds to transferrin and gains access to cells by the transferrin receptor. However, substantial evidence suggests that uptake of 67Ga may not be universally mediated by transferrin in tumors. To determine whether transferrin is required for uptake of 67Ga in vivo, we compared the uptake of 67Ga by two types of implanted tumors and by normal tissues in normal and severely hypotransferrinemic strains of Balb/C mice. One type of tumor was strongly gallium-avid in normal mice; the other was not. Uptake of 67Ga by normal soft tissues was markedly less in hypotransferrinemic than in normal mice. Uptake of 67Ga by bone was equivalent in the two types of mice. For the more gallium-avid tumor, uptake of 67Ga was similar and the ratio of tumor-to-background activity was substantially higher in the hypotransferrinemic than in the normal mice. For the less gallium-avid tumor, uptake was significantly less in hypotransferrinemic than in normal mice. These data suggest that uptake of 67Ga by bone and by some tumors may be a transferrin-independent process.

Comparison of methods for calculating glomerular filtration rate: technetium-99m-DTPA scintigraphic analysis, protein-free and whole-plasma clearance of technetium-99m-DTPA and iodine-125-iothalamate clearance.

True glomerular filtration rate (GFR) was measured in normal volunteers and in patients with normal and impaired renal function by the iothalamate clearance (IC) method of Sigman. Within 24 hr, GFR was also determined by two other methods: technetium-99m- (99mTc) DTPA scintigraphic analysis (SA) utilizing a modification of the Gates computer program, and by measuring disappearance of 99mTc-DTPA from whole plasma (WPC) and from protein-free ultrafiltered plasma (PFPC). Determinations of GFR by IC and by PFPC methods were virtually identical (mean absolute error 5.36 ml/min, r = 0.99, p greater than 0.05). GFRs measured in protein-free, ultrafiltered plasma differed significantly from those obtained from whole plasma only in sicker patients and in those taking multiple medications (in whom alterations in protein-binding of DTPA may be seen). The SA method correlated less well with the iodine-125-(125I) IC method than did either the protein-free or whole-plasma clearance methods (mean absolute error 32.36 ml/min, r = 0.74, p less than 0.05). However, the SA method provided useful information with respect to differential (split) renal function.

Efficacy of IV theophylline in children with severe status asthmaticus.

STUDY OBJECTIVE: To determine whether adding IV theophylline to an aggressive regimen of inhaled and IV beta-agonists, inhaled ipratropium, and IV methylprednisolone would enhance the recovery of children with severe status asthmaticus admitted to the pediatric ICU (PICU). DESIGN: A prospective, randomized, controlled trial. Asthma scoring was performed by investigators not involved in treatment decisions and blinded to group assignment. SETTING: The PICU of an urban, university-affiliated, tertiary-care children's hospital. PATIENTS: Children with a diagnosis of status asthmaticus who were admitted to the PICU for < or = 2 h and who were in severe distress, as indicated by a modified Wood-Downes clinical asthma score (CAS) of > or = 5. INTERVENTIONS: All subjects initially received continuous albuterol nebulizations; intermittent, inhaled ipratropium; and IV methylprednisolone. The theophylline group was also administered infusions of IV theophylline to achieve serum concentrations of 12 to 17 microg/mL. A CAS was tabulated twice daily. MEASUREMENTS AND RESULTS: Forty-seven children (median age, 8.3 years; range, 13 months to 17 years) completed the study. Twenty-three children received theophylline. The baseline CASs of both groups were similar and included three subjects receiving mechanical ventilation in each group. All subjects receiving mechanical ventilation and theophylline were intubated before drug infusion. Among the 41 subjects who were not receiving mechanical ventilation, those receiving theophylline achieved a CAS of < or = 3 sooner than control subjects (18.6 +/- 2.7 h vs 31.1 +/- 4.5 h; p < 0.05). Theophylline had no effect on the length of PICU stay or the total incidence of side effects. Subjects receiving theophylline had more emesis (p < 0.05), and control patients had more tremor (p < 0.05). CONCLUSIONS: Theophylline safely hastened the recovery of children in severe status asthmaticus who were also receiving albuterol, ipratropium, and methylprednisolone. The role of theophylline in the management of asthmatic children in impending respiratory failure should be reexamined.

Uptake of cadmium-109, a metallothionein-binding radiometal, by tumors in mice as a function of the transformed phenotype.

Metallothionein (MT) is an intracellular protein that binds many metals with isotopes having imaging or radiotherapeutic potential. To determine whether uptake of radioisotopes that bind to MT is increased in tumors, we measured the uptake of cadmium-109 (Cd-109) in tumors and in normal tissues of mice. Tumors were grown in Balb/C mice from cultured Balb/3T3 cells transformed by the Moloney murine sarcoma virus (MMSV). Uptake of Cd-109 by MMSV tumors exceeded that by normal tissues examined, with the exception of liver and kidney (the organs known to be richest in metallothionein). The MMSV tumor:background ratios of activity were greater for Cd-109 than for gallium-67 for many of the normal tissues examined. The magnitude of uptake of Cd-109 by tumors from four related cell lines paralleled their degree of expression of two indices of the transformed, or malignant, phenotype. We conclude that metals that bind to MT may be useful for imaging or radiotherapy of cancer.

Gastric emptying after gastric interposition for cancer of the esophagus or hypopharynx.

Transhiatal esophagectomy with primary anastomosis to the stomach (gastric pull-up) is an attractive surgical alternative to colic interposition in patients with cancer of the esophagus and hypopharynx. However, the lack of intrinsic gastric peristalsis and complaints by patients of postprandial regurgitation prompted us to measure the effect of body posture on the rates of gastric emptying in these patients. The rates of solid and liquid gastric emptying were measured in 14 patients who had undergone gastric interposition for esophageal and hypopharyngeal carcinoma. Rates of emptying were measured in both the supine and upright position using a dual-isotope radiolabeling technique. In these patients, the rate of gastric emptying of both solids and liquids was significantly slower in the supine position than in the upright position. Emptying in supine patients was also prolonged when compared with supine normal volunteers. Conversely, the upright rate of solid and liquid emptying in the patients was accelerated when compared with published values for upright normal volunteers. We conclude that gastric emptying after gastric interposition is dependent on upright posture after meals.

Ionized calcium: pediatric perspective.

Ionized calcium is a physiologically critical calcium pool. It is easily determined, although accuracy depends on sample handling. As a clinical parameter, directly measured ionized calcium has particular import in the care of neonates, patients with sepsis or other cardiovascular instability, massively transfused patients, and those undergoing cardiopulmonary bypass or liver transplantation. Disturbances of calcium occur in many other settings, however, and accurate diagnosis and research conclusions may depend on using the best measurement available. Clinical and investigational use of ionized calcium determinations represent appropriate applications of current proven technology. In the future, clinical calcium manipulation may include modifying specific transmembrane transport processes and intracellular calcium pools and movements. At the current time we are largely restricted to studies of extracellular calcium concentration and its interactions. Much is known, but Mother Nature still has too many secrets. The interested reader is referred to discussions of ionized calcium and hemodynamics, reviews of the endocrine disturbances of calcium and phosphorus, textbook discussions pertinent to general calcium disturbances, and critical care issues.

Restriction fragment length polymorphism assessment of the heterogeneous nature of maize population GT-MAS:gk and field evaluation of resistance to aflatoxin production by Aspergillus flavus.

Aflatoxin, produced by Aspergillus flavus, is one of the most toxic and carcinogenic substances known and contaminates many agricultural commodities such as corn, peanuts, cottonseed, and tree nuts. The challenge to breeders/plant pathologists is to identify lines that have resistance to aflatoxin production. Maize population GT-MAS:gk has been identified and released as a germplasm with resistance to aflatoxin contamination. In the present study, we assessed genetic divergence in the GT-MAS:gk population using restriction fragment length polymorphism (RFLP) DNA markers to survey 11 selfed inbred lines and conducted field evaluations for the dissimilarities in aflatoxin production among these inbred lines in comparison with a sister population, GT-MAS:pw.nf. The 11 selfed inbred lines were assayed for DNA polymorphism using 113 RFLP markers in 10 linkage groups covering 1,518.2 centimorgans (cM; unit of gene or chromosome size). Considerable variation among the inbreds was detected with RFLP markers, of which 42 probe-enzyme combinations gave 102 polymorphic bands. Cluster analysis based on genetic similarities revealed associations and variations among the tested lines. Three polymorphic groups were distinguished by cluster analysis. Two years of field evaluation data showed that aflatoxin concentrations among the lines were significantly different in both years (P < 0.001). Maturity data were also different. Thus, this study demonstrates that the maize population GT-MAS:gk is heterogeneous and that individuals may be different in resistance to A. flavus infection and aflatoxin production. Therefore, the most resistant lines should be inbred to increase homogeneity, and resistance should be confirmed through progeny testing.

Distribution of antifungal proteins in maize kernel tissues using immunochemistry.

This study examined the distribution of two antifungal proteins, ribosome-inactivating protein (RIP) and zeamatin, in maize kernel tissues. Proteins were extracted from endosperm (including aleurone layer) and embryo tissues of imbibed maize kernels. Western blot analyses revealed that RIP-like protein was present at higher levels in endosperm than in embryo tissues, whereas zeamatin-like protein was more concentrated in embryo tissues than in endosperm tissues. However, there were three protein bands in the endosperm and two bands in the embryo that reacted to anti-RIP antibody in Western blot analyses. Tissue prints were conducted to localize the antifungal proteins. Imbibed kernels were cut longitudinally and transversely and blotted onto nitrocellulose membranes. Using antibodies against maize RIP and zeamatin, RIP was found primarily in the aleurone layer of the endosperm and glandular layer of scutellum, whereas zeamatin was located mainly in the kernel embryo. These results provide insight into the potential functions of these antifungal proteins, especially since the presence of RIP and zeamatin within maize kernels uniquely protects kernels from pathogens.

Kidney transplants in patients over 50.

Patients with end-stage renal failure shouldn't be denied the only possibility of cure just because they're old or have other chronic diseases. In this study of 69 patients over age 50-the largest series reported from a single medical center-kidney transplants from related donors had the same high rate of success as in younger patients. Over 80 percent of the patients who received kidneys from their children or siblings are still alive, in contrast to 52 percent of those who had to settle for a cadaver kidney. Infection posed the most serious hazard after surgery. Late complications, particularly hypertension and diabetes, were easily controoled and by no means debilitating. Four of the survivors still need hemodialysis, but over two-thirds have recovered completely.

Complications of nasogastric and gastrostomy tube feedings in children with end stage renal disease.

Twelve children with end stage renal disease requiring dialysis received enteral feedings via nasogastric (NG) or gastrostomy (G) tube between 1984 and 1989 for provision of adequate nutrition. Records were reviewed for frequency and types of complications seen. Six patients, ages 1 week to 16 months received NG feedings for a total of 32 months. Complications included persistent vomiting with recurrent aspiration (2), persistent vomiting with peritoneal dialysis (PD) exit site leak (1), sinusitis (1), and refusal to continue NG feeds because of patient/parental anxiety (1). Three of the 6 were changed to G tube feedings after 2 days to 3 months. The complication rate was 1 per 6.4 patient months. Nine patients, ages 4 days to 11 years, received G tube feedings for 64 months. The complication rate was similar, 1 per 7.1 months. Complications were PD fluid leak around G tube exit site (1), G tube infection (2), G tube obstruction requiring tube replacement (3), tube migration producing intestinal obstruction (1), and gastrocutaneous fistula (2). Both methods were associated with similar complication rates, although somewhat different types of complications were seen. The young dialysis patient may have certain unique risks in addition to the complications generally associated with enteral feedings.

Ultrafiltration using low volume peritoneal dialysis in critically ill infants and children.

Ultrafiltration (UF) using dialysate volumes of less than 20 ml/kg was assessed in 12 critically ill infants and children with hypervolemia as the primary indication for dialysis. Ten of the 12 required mechanical ventilation (O2 requirements 45-100%). Seven, all infants, received at least one pressor intravenously in attempts to maintain systolic blood pressure of 60. Age was 22 +/- 11.5 mos. (mean +/- SE) with weight of 11.1 +/- 4.3 kg (range 2.4-50 kg). Dialysis prescription was as follows: Volume of 10.1 +/- 1.3 ml/kg/exchange; dwell time 30-45 minutes; drain time 15-20 minutes. Glucose concentration ranged from 1.5-4.25%. Drained dialysate volume expressed as a percent of volume instilled was 133.5 +/- 3.4%. When calculated for body weight and time, UF was 3.0 +/- 0.3 ml/kg/hour. UF was not significantly different in patients requiring pressors versus those not requiring blood pressure support. Although minor ventilatory changes were required, significant deterioration of blood gases did not occur during the first 3-6 hours of PD, nor did significant changes in blood pressure develop. Hyperkalemia, present in 1 patient prior to PD, resolved using this regimen. Low volume PD was a viable alternative to hemodialysis or hemofiltration for control of hypervolemia in this small group of very ill infants and children.

Evaluation of transgenic sweet corn hybrids expressing CryIA (b) toxin for resistance to corn earworm and fall armyworm (Lepidoptera: Noctuidae).

Many of the lepidopterous insects which attack sweet corn, Zea mays L., are susceptible to insecticidal proteins produced by Bacillus thuringiensis ssp. kurstaki (Berliner) (Btk). Transgenic sweet corn expressing a synthetic cry gene for production of a Btk-insecticidal protein may provide a more environmentally acceptable means of sweet corn production. Eight transgenic sweet corn hybrids containing a synthetic gene for CryIA(b) protein production (BT11 event) were evaluated for resistance to the corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J. E. Smith). Laboratory tests revealed that all Btk sweet corn hybrids were highly resistant to leaf and silk feeding by neonate 3 and 6 d old corn earworm larvae. Ear damage in the field to the Btk sweet corn hybrids caused by corn earworm was negligible. All Btk sweet corn hybrids, except Btk 95-0901, were moderately resistant to leaf and silk feeding by the fall armyworm. Survival and weight gain were reduced when neonates were fed excised whorl leaves of the Btk plants. Weight gain, but not survival, was reduced when 3- and 6-d-old fall armyworm larvae were fed excised whorl leaves of the Btk plants. Btk sweet corn hybrids appear to be ideal candidates for use in integrated pest management (IPM) programs for both the fresh and processing sweet corn markets, and their use should drastically reduce the quantity of insecticides currently used to control these pests in sweet corn. With appropriate cultural practices, it is highly unlikely that Btk sweet corn will contribute to the development of resistance to Btk proteins in these insects because of the high toxicity of the Cry proteins expressed in these sweet corn hybrids and the harvest of sweet corn ears from fields before larvae can complete development.

Restriction fragment length polymorphism markers associated with silk maysin, antibiosis to corn earworm (Lepidoptera: Noctuidae) larvae, in a dent and sweet corn cross.

Maysin, a C-glycosylflavone in maize silk, has insecticidal activity against corn earworm, Helicoverpa zea (Boddie), larvae. Sweet corn, Zea mays L., is a vulnerable crop to ear-feeding insects and requires pesticide protection from ear damage. This study was conducted to identify maize chromosome regions associated with silk maysin concentration and eventually to transfer and develop high silk maysin sweet corn lines with marker-assisted selection (MAS). Using an F2 population derived from SC102 (high maysin dent corn) and B31857 (low maysin sh2 sweet corn), we detected two major quantitative trait loci (QTL). It was estimated that 25.6% of the silk maysin variance was associated with segregation in the genomic region of npi286 (flanking to p1) on chromosome 1S. We also demonstrated that a1 on chromosome 3L had major contribution to silk maysin (accounted for 15.7% of the variance). Locus a1 has a recessive gene action for high maysin with the presence of functional p1 allele. Markers umc66a (near c2) and umc105a on chromosome 9S also were detected in this analysis with minor contribution. A multiple-locus model, which included npi286, a1, csu3 (Bin 1.05), umc245 (Bin 7.05), agrr21 (Bin 8.09), umc105a, and the epistatic interactions npi286 x a1, a1 x agrr21, csu3 x umc245, and umc105a x umc245, accounted for 76.3% of the total silk maysin variance. Tester crosses showed that at the a1 locus, SC102 has functional A1 alleles and B31857 has homozygous recessive a1 alleles. Individuals of (SC102 x B31857) x B31857 were examined with MAS and plants with p1 allele from SC102 and homozygous a1 alleles from B31857 had consistent high silk maysin. Marker-assisted selection seems to be a suitable method to transfer silk maysin to sweet corn lines to reduce pesticide application.

Lost P1 allele in sh2 sweet corn: quantitative effects of p1 and a1 genes on concentrations of maysin, apimaysin, methoxymaysin, and chlorogenic acid in maize silk.

In the United States, insecticide is used extensively in the production of sweet corn due to consumer demand for zero damage to ears and to a sweet corn genetic base with little or no resistance to ear-feeding insects. Growers in the southern United States depend on scheduled pesticide applications to control ear-feeding insects. In a study of quantitative genetic control over silk maysin, AM-maysin (apimaysin and methoxymaysin), and chlorogenic acid contents in an F2 population derived from GE37 (dent corn, P1A1) and 565 (sh2 sweet corn, p1a1), we demonstrate that the P1 allele from field corn, which was selected against in the development of sweet corn, has a strong epistatic interaction with the a1 allele in sh2 sweet corn. We detected that the p1 gene has significant effects (P < 0.0001) not only on silk maysin concentrations but also on AM-maysin, and chlorogenic acid concentrations. The a1 gene also has significant (P < 0.0005) effects on these silk antibiotic chemicals. Successful selection from the fourth and fifth selfed backcrosses for high-maysin individuals of sweet corn homozygous for the recessive a1 allele (tightly linked to sh2) and the dominant P1 allele has been demonstrated. These selected lines have much higher (2 to 3 times) concentrations of silk maysin and other chemicals (AM-maysin and chlorogenic acid) than the donor parent GE37 and could enhance sweet corn resistance to corn earworm and reduce the number of applications of insecticide required to produce sweet corn.