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The role of endogenously induced higher level of cytokinins and exogenously applied kinetin in relation to the development of barley leaf spot caused by Bipolaris sorokiniana (Sacc.) Shoemaker (syn. Helminthosporium sativum Pammel, King and Bakke) was studied. Spraying barley leaves with kinetin suppressed the number and the size of necrotic spots caused by the fungus. Inoculation of the lower leaves of barley by a spore suspension of the fungus B. sorokiniana induced resistance on the upper leaves against a subsequent challenge inoculation by the same pathogen 10 days later. An increase in the level of cytokinins was observed in these resistant leaves. Elevated levels of cytokinins may cause a type of juvenility in leaf tissues. The juvenile state could be in a causal relationship with the suppression of necrotic spots caused by the fungus. [ABSTRACT FROM AUTHOR]

Wheat leaves infected by stem rust exhibit a high respiratory rate and accumulate ammonia, glutamine and asparagine. Feeding of ammonium salts to healthy tissues led to metabolic alterations which are highly similar to those elicited by rust infection: the respiratory rate was enhanced and glutamine accumulated. The response of rusted leaves to treatment with ammonia was less. The extent of parasitically increased glutamine accumulation is dependent on the reaction type of the tissues. Less glutamine is synthesized by resistant combinations. The mechanism of the parasitically stimulated glutamine synthesis was studied. It has been found that in addition to the increased ammonia production by infected leaves the parasitically enhanced activity of glutamine synthetase also contributes to the accumulation of glutamine. Strangely enough, parallel with glutamine and asparagine accumulation the ability of infected tissues to deamidate externally supplied amides is enormously increased. Slight activation of some deaminases was also observed. Germinating stem rust uredospores exhibited a high deamidase activity. Therefore, the enhanced deamidase activity of the infected tissues might be attributed to the developing fungus. The problem of simultaneous activation of amide synthesis from endogenous sources or from externally supplied ammonium salts and the enormous stimulation of deamidase activity in rusted tissues is discussed and as an explanation the compartmentization of the processes of nitrogen metabolism is offered. [ABSTRACT FROM AUTHOR]

1. It has been shown that the respiration of etiolated wheat seedlings is more resistant to malonate than the O2-uptake of green controls. 2. The illumination of etiolated seedlings by direct daylight enhances their sensitivity to malonate. UV radiation has the same effect. 3. There is no parallelism between the greening of the etiolated plants and the rise in the malonate sensitivity of their respiration. Root tissues are equally influenced by light. 4. The light-induced malonate-sensitivity is a fairly constant property of the cells since it will not readily be abolished by replacing the plants in the dark. 5. It has been shown using the paper chromatographic technique that the results cannot be explained by an increased permeability induced by illumination. 6. Green seedlings grown in the greenhouse show an increased respiratory rate if previously exposed to direct illumination by daylight. The enhanced respiration is more resistant to malonate than the original O2-uptake. UV radiation induces in green seedlings the same effect as natural daylight. 7. The results are discussed from the point of view of light activation of enzyme systems and the tentative explanation is offered that the succinic oxidase-cytochrome system is activated in etiolated tissues when exposed to illumination. As to the nature of the entirely opposite reaction in green tissues we can hardly give an explanation at present. [ABSTRACT FROM AUTHOR]

1. The respiration of wheat seedlings infected with stem rust and powdery mildew is considerably augmented. 2. By the use of various inhibitors it has been found that the parasitically increased respiration involves also qualitative changes in comparison with the normal respiration. 3. The respiration of healthy plants is malonate-sensitive but on the contrary that of the infected tissues is highly insensitive to malonate. 4. The glycolysis inhibitors (fluoride, iodoacetate) are equally influencing the respiration of healthy and diseased plants. 5. The respiration of both control and infected plants is highly sensitive to azide. The O2-uptake of healthy tissues is totally resistant to cyanide. However, the infection is correlated with the development of a cyanide- sensitive fraction, 6. R.Q. in both healthy and diseased plants is around 1.0. In malonate treated tissues the R.Q. rises over 2.0. 7. Contrary to expectations, the presence of toxin could not be detected. 8. The results seem to substantiate the fact that the respiratory changes are taking place in the tissues of host and cannot be explained by the additive effect of fungus respiration. 9. An attempt has been made to interprete the parasitically stimulated respiration in biochemical terms. As a theory of the possible mechanisms the proposed views about the abolishing of Pasteur effect have the greatest possibility at present. [ABSTRACT FROM AUTHOR]