A light and scanning-electron microscopic study of infection of tomato plants by virulent and avirulent races of Cladosporium fulvum

Infection of tomato plants byCladosporium fulvum Cooke was studied using light and scanning-electron microscopy. Races 1.2.3 and 4 ofCladosporium fulvum were used, whereas tomato cultivars, carrying the Cf2 gene (susceptible to race 1.2.3 and immune to race 4) and the Cf4 gene (immune to race 1.2.3 and susceptible to race 4) served as differentials. No differences were observed in growth between compatible and incompatible combinations during germination, subsequent formation of runner hyphae and stomatal penetration. Runner hyphae did not show directional growth towards stomata. Penetration usually occurred on the third or fourth day after inoculation. In compatible combinations the fungus grew intercellularly, often in close contact with spongy mesophyll cells. Under optimal conditions it did not cause visible damage to plant cells during early stages of infection. Under suboptimal conditions in winter, the host cells often reacted with callose deposition, but growth of the fungus did not appear to be inhibited. Ten to twelve days after inoculation conidiophores emerged through the stomata and produced conidia. In incompatible combinations fungal growth was arrested one to two days after penetration and confined to stomata and surrounding cells. Very soon the host cells, in contact with the fungus, deposited extensive amounts of callose. Later these cells turned brown and collapsed. At the surface of the host cells, contacted by fungal hyphae, abundant extracellular material could be observed by scanning-electron microscopy. Removing the epidermis of leaves before inoculation delayed the resistant response. On stripped leaves the rate of fungal growth was equal for both interactions up to ten days after inoculation, but the incompatible combination lacked sporulation.     

Induction of acquired cellular resistance in mice with viable and macrophage-processed Listeria monocytogenes

Intracutaneous immunization of mice with 10(5) or 10(6) viable listeria resulted in acquired cellular resistance (ACR) of short duration (7 days). The period during which viable Listeria monocytogenes had to be present in order to induce ACR was estimated by killing the listeria at different times after immunization by injecting the bactericidal antibiotic amoxycillin. The killing of listeria within 6 h after injection prevented the induction of A CR completely, between 6 and 12 h partially, while survival of listeria within animals for at least 18 h was required for the induction of complete protection. To determine whether multiplication of viable listeria was a prerequisite for the induction of ACR, the bacteriostatic antibiotic minocycline was injected for four days after immunization. Induction of ACR was only possible if the dose of viable listeria was large enough to permit a proportion of the listeria to escape bacteriostasis. Interaction of peritoneal macrophages of normal mice and viable listeria yielded a supernatant which induced specific ACR in normal recipient mice. No ACR could be induced with supernatant obtained from normal macrophages after digestion of killed listeria. A reduced level of ACR was obtained with supernatant collected after interaction of macrophages from immune mice and viable listeria. The immunogenic material present in the supernatant of normal macrophages after interaction with viable listeria is thermolabile, has a molecular weight of over 300,000, and is not affected by treatment with DNase, RNase, or trypsin.     

A note on the amino acid composition of the Turkey

1. The amino acid composition of the whole body protein of 28‐ and 56‐d‐old turkeys is reported.

2. There were some differences between the two ages; these could largely be reconciled by considering the likely differences in the proportion of feather protein.

3. The results were compared with similar values for the chicken and goose; overall there is a striking similarity, both in absolute concentrations and relative proportions of amino acids.     

Influence of ascorbic acid on the adverse effect of feeding a diet containing excess tyrosine to chicks

1. The effects of dietary or parenteral administration of ascorbic acid on the adverse effects of excess dietary tyrosine were investigated with young male White Leghorn chicks in a 2‐week experiment.

2. Addition of 10 g ascorbic acid/kg to the control diet (without excess tyrosine) produced no beneficial effects on performance. Excess dietary tyrosine caused depressions in all measures of performance.

3. Adding 0.1, 1, 10 or 20 g ascorbic acid/kg to the diet containing excess tyrosine tended to improve performance.

4. Subcutaneous injection of 50 mg ascorbic acid/bird d to chicks receiving excess tyrosine brought about a significant improvement in body‐weight gain.

5. The elevation of plasma free tyrosine caused by excess dietary tyrosine decreased as dietary ascorbic acid increased.

6. Ascorbic acid can alleviate, though not completely counteract, the adverse effect of excess dietary tyrosine.