Riboflavin Nullification of Inhibitory Actions of 3-Amino-1,2,4-Triazole on Seedling Growth.
The physiological mechanislmis involved in the toxic actions of 3-amino-1,2,4-triazole (amitrole) have been actively investigated since the chemical was first introduced as a potential herbicide in 1954 (2). Much of the research has been guided by hypotheses involving one of three major metabolic processes: A, porphyrin synthesis, B, cation functions, and more recently C, the metabolism of purines and their derivatives. The extensive literature associated with the first two categories will not be considered herein. Amitrole interferences in some of the biochemiiical processes of the third category now appear to be the actions of nmajor physiological importance in the response of plants to the herbicide. Much of the pertinent research deals with attempts to find physiological compounds capable of reducing the toxicity of amitrole to various organisms. The most effective conmpounds are purines (23, 24) or histidine (13, 23) for unicellular plants anid riboflavin or riboflavin derivatives (22, 24) for higher plants. The investigations reported herein Nwere initiated as a result of my observations that the riboflavin effect could not be denmonstrated with barley seedlings by tecliiques that had been used successfully with other herbicidemetabolite combinations (9, 14, 18). The objectives of this study were: A, to develop techniques by whiclh the riboflavin nullification of amitrole toxicity could be observed with higher plants, and to compare adenine and histidine with riboflavin by these techniques; BR, to consider the possibilitv that the riboflavin effect was the result of non-physiological processes: C, to compare the effectiveness of riboflavin in species of higher plants that differ in their response to amitrole, and D, to determine if certain other metabolites of theoretical interest might give additional reductionis in amitrole toxicity.
Beeinflussung der Amitroltoxizität durch Riboflavin in Haferkeimpflanzen
Summary The following parameters were determined to characterize the amitrole toxicity in oat seedlings: growth, wet and dry weight, content of pigments, and activity of catalase. Riboflavin reduces the inhibitory actions of amitrole only in plants, which have been treated with these substances in the light. In the dark riboflavin had no effect on amitrole toxicity. Riboflavin-14C is not translocated from the roots to the leaves, and this behaviour is not changed by amitrole. Riboflavin does not affect the uptake and the translocation of amitrole-14C. We suggest that in oat the effect of riboflavin in the light is exclusively due to the well-known riboflavin-mediated photodecomposition of amitrole but not to physiological processes within the plants. Furthermore we conclude from experiments with amitrole-[5-14C], which was supplied and metabolized in the dark, that the site of action of amitrole must be connected with light-independent reactions which are essential for subsequent light-dependent processes.
Investigations on the rôle of organic matter in plant nutrition
1. As the result of decomposition of green manure in a swamp soil, the coarse fractions (including coarse and fine sand) of the surface layer (first 3 inches) decreased by 11·2 per cent. while the fine ones (silt+clay) increased by 9·8 per cent. in the course of 43 days. The effect was less pronounced in the manured soil maintained at 60 per cent. saturation, while no alteration was to be noticed in the case of the unmanured specimens. 2. Treatment with dilute hydrochloric acid prior to dispersion had no appreciable effect on the estimates of mechanical composition obtained in the different cases. Loss in solution was also comparatively small. 3. The silica-sesquioxide ratio increased slightly as the result of decomposition of green manure in swamp soil. The composition of the fine fractions was also altered, the total percentages of the oxides of iron, aluminium and silicon increasing from 90·5 to 99·3 in the course of 71 days. 4. The practical significance of the above and related observations has been discussed.