Field performance of maize grown from Fusarium verticillioides-inoculated seed.

Fusarium verticillioides is an important fungus occupying dual roles in the maize plant. The fungus functions as an endophyte, a fungal/host interaction beneficial to the growth of some plants. At other times, the fungus may function as a mycotoxin producing pathogen. The advantages and/or disadvantages of the endophytic relationship must be established in order to target appropriate sites for controlling diseases and mycotoxins in maize. One possibility could be to ensure seed maize is fungal free prior to planting. Reciprocal inoculations were made with two fungal isolates on seed of two maize genotypes. Yield was measured at harvest by ear and seed characters and vegetative growth at one-month intervals for plant survival, height, weight and stem diameter. Yield and vegetative growth differed among mature plants only once based on seed inoculation status. In 1998, plant weight was reduced and seed weight per ear was increased for the dent maize, GT-MAS: gk, grown from F. verticillioides RRC 374-inoculated seed compared to other seed treatments. Most vegetative characters were reduced at the first collection for Silver Queen plants grown from F. verticillioides-inoculated seed in 1997 and 1999, but not in 1998. However, no significant differences occurred among mature Silver Queen plants during any of the three growing seasons. In conclusion, yield and vegetative growth of mature maize plants grown from F. verticillioides-inoculated seed were equal to or greater than plants grown from non-inoculated seed under south Georgia field conditions during 1997, 1998, and 1999.

Trichoderma viride suppresses fumonisin B1 production by Fusarium moniliforme.

Biocontrol activity against Fusarium moniliforme was analyzed for a Trichoderma viride strain isolated from root segments of corn plants grown in Piedmont Georgia. The isolate suppressed radial extension of F. moniliforme colonies during cocultivation on potato dextrose agar and fumonisin B1 (FB1) production during incubation of both fungi on corn kernels. T. viride decreased radial extension of F. moniliforme by 46% after 6 days and by 90% after 14 days. Furthermore, the colony diameter of F. moniliforme was less at 14 days than at 5 days, suggesting that F. moniliforme mycelia were undergoing lysis. FB1 production by F. moniliforme on corn kernels decreased by 85% when both organisms were inoculated the same day onto corn kernels and by 72% when inoculation of T. viride was delayed by 7 days after F. moniliforme inoculation. These results are the first to demonstrate that T. viride can suppress FB1 production by F. moniliforme, thereby functioning to control mycotoxin production. Thus, this isolate may be useful in biological control to inhibit F. moniliforme growth as a preharvest agent to prevent disease during plant development and/or as a postharvest agent during seed storage to suppress FB1 accumulation when kernels are dried inadequately.

Decreased activity of Blastocladiella emersonii zoospore ribosomes: correlation with developmental changes in ribosome-associated proteins.

Ribosomal proteins isolated from dormant zoospores were compared to the ribosomal proteins found in the active growth phase by two-dimensional polyacrylamide gel electrophoresis. Zoospore ribosomes were found to contain a set of five proteins, designated Z1 to Z5, which were not present in growth phase ribosomes. The Z1-Z5 proteins were not removed by high-salt washes using either 1 M KCl or 1 M NH4 Cl. The Z1 protein is found associated with zoospore 60 S subunits while Z2-Z5 are bound to 40 S subunits. Zoospore monoribosomes and polyribosomes contain comparable levels of each of the five proteins. Approximately 60 min. after sporulation is induced, the Z1-Z5 proteins begin to accumulate on the ribosomes with the highest levels of these proteins found associated with ribosomes at the zoospore stage. During germination, the proteins gradually disappear and are not detectable on the ribosomes after 4 hr of germination. The presence of the Z1-Z5 proteins correlates with a decrease in in vitro protein synthetic activity of the fungal ribosomes. The data are consistent with the hypothesis that the proteins regulate translation by completely blocking protein synthesis on a subset of ribosomes while the remainder of the ribosomes function at normal rates.

Amiodarone-induced pulmonary toxicity in the rat.

A rat model of amiodarone-induced pulmonary toxicity is described. The rats were fed, by gavage, 175 mg/kg/day of amiodarone hydrochloride suspended in methyl cellulose. Controls received methyl cellulose alone. Groups of rats were examined after 1, 3, 6, 9, and 12 weeks of feeding. We found that drug-fed rats had significantly more macrophages, neutrophils, and lymphocytes in the bronchoalveolar lavage (BAL). The early increase in cellularity was due to an increase in macrophages, and the macrophage count peaked after 6 weeks of drug treatment. The number of neutrophils in the experimental animals remained high throughout the course of the experiment. An increasing number of lymphocytes was seen in the BAL between 6 and 12 weeks of drug treatment. Protein in the lavage fluid was significantly elevated after 12 weeks of amiodarone exposure. Histologic sections were abnormal after 3 weeks of drug treatment, characterized by interstitial thickening with accumulation of mononuclear cells and alveoli packed with large foamy macrophages. There was only minimal evidence of fibrosis. This model appears to be very similar to human amiodarone-induced pulmonary toxicity and should be useful for the study of the pathogenesis of amiodarone-induced toxicity.

Stage-specific synthesis of proteins complexed to ribonucleoprotein particles and ribosomes in zoospores of Blastocladiella emersonii.

In Blastocladiella emersonii zoospores, a set of proteins was found associated with the ribosomes and free ribonucleoprotein particles distinct from the ribosomes and polyribosomes. These proteins were designated P120, P105, P64, P56, and P42 based on their molecular weights determined by gel electrophoresis. Synthesis of these proteins was detected only during late sporulation just before the time polyadenylated ribonucleic acid accumulates in the sporangia. These proteins banded in isopycnic metrizamide gradients at densities of 1.31 and 1.27 g/cm3, which corresponded to the densities of the ribosomes and free ribonucleoprotein particles, respectively. Comparison of the distribution of the proteins in sucrose versus metrizamide gradients suggested that P105 was removed from the free ribonucleoprotein particles before complexing with the ribosomes. During germination, these proteins disappeared from the ribosomal fractions, with kinetics corresponding to the resumption of protein synthesis. Another protein (P178) was observed to bind to the ribosomes before the onset of protein synthesis during germination. Cycloheximide did not block the addition of this protein to the monoribosomes.

Characteration of RNA synthesized during germination of Blastocladia ramosa Zoospores.

The synthesis of RNA was studied during the synchronous germination of Blastocladia ramosa zoospores. Comparison of RNA synthesis during germination of B. ramosa and Blastocladiella emersonii zoospores revealed that B. ramosa has a longer lag time before RNA synthesis is initiated and, in addition, the rate of RNA synthesis is ten-fold lower in B. ramosa. Zoospores of B. ramosa were shown to contain pre-formed messenger RNA but this messenger RNA directs only a portion of the protein synthesis which occurs during early germination. The conclusion that the remainder of the protein synthetic activity of the germinating spores is due to new message synthesis was supported by demonstrating that the timing of the initation of protein synthesis on new messages correlates with the time RNA synthesis is initiated. New message synthesis was also demonstrated by the incorporation of label into RNA which contains a poly (A) fragment. Synthesis of all classes of RNA including ribosomal, messenger, and transfer RNA was shown to be initiated at the same time. The implications of this observation are discussed.