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.
Mode of action of thiocyanates and iodides in aminotriazole formulations
Ammonium thiocyanate (I) was shown to inhibit the oxidation of aminotriazole (3-amino-1,2,4-triazole) in two free-radical generating systems: (a) riboflavin photo-sensitised oxidation; and (b) oxidation by hydroxyl radicals. Evidence from in-vitro studies is presented to show that I could enhance aminotriazole performance by being preferentially oxidised within the leaf, thereby preventing aminotriazole free-radical formation and subsequent conjugation with amino acids and other compounds. This opens up the possibility of a whole new range of additives which could enhance translocation by inhibiting free-radical reactions. A comparison of possible inhibitors revealed that cyanides, iodides and perhaps bromides may be of use in this respect. In addition to inhibiting free-radical reactions, I and potassium iodide (II) were shown to have a considerable effect on the uptake of aminotriazole by bean leaves (Phaseolus vulgaris var. Canadian Wonder). In the absence of additives, uptake of aminotriazole was negligible (1.8%); in the presence of a 1:1 molar ratio of I or II, uptake of aminotriazole was increased to 36.6% and 54.2% respectively. At a 3:1 molar ratio of additive:aminotriazole, the respective figures were 63.5% and 81.0%. II appeared to be the more efficient of the two additives at higher humidity. However, the results and observations indicated that the situation may be reversed under low-humidity conditions.
INFRARED INTENSITY MEASUREMENTS APPLIED TO THE DETERMINATION OF MOLECULAR STRUCTURE
Chemists have been using absorption spectra for many years as aids to the interpretation of the molecular structure of complex organic compounds. The spectra studied in the ultraviolet and visible regions are almost invariably reported on an absolute intensity basis of molecular extinction coefficient (emax.). The E , , , ~ . values are a useful means of distinguishing between different ultraviolet chromophores that absorb in the same region of the spectrum, and they are also useful for evaluating purity, particularly in following the isolation of pure compounds from natural sources. A few infrared spectroscopists, including Rose,’ Anderson and Seyfried,2 Hampton and N e ~ e l l , ~ RicMurry and T h ~ r n t o n , ~ Cross and Rolfe,6 and Reggiani, Casu, and Caroti,E have used molecular extinction coefficients, but it is still the general practice to express infrared band intensities in arbitrary units of percentage absorbed or percentage transmitted. For spectra measured in the solid phase as Nujol mulls or halide disks, the extinction coefficients cannot be determined, as there are no adequate methods to correct for scattering errors or for the nonhomogeneous distribution of the sample. However, for spectra measured in solution the molecular extinction coefficients can be evaluated in the same way as in the visible and ultraviolet regions of the spectrum. It has been recognized for a long time that measurements of infrared intensity are liable to greater errors than similar measurements made at higher frequencies, and it is often stated that infrared molecular extinction coefficients are subject to such large errors that they cannot usefully be transferred from one spectrometer to another. I t is true that there are instrumental factors that make it advisable, for the present, to report infrared intensities in “apparent” units; nevertheless, if proper precautions are taken in setting up and operating the spectrometer these errors need not be excessive. Our laboratory has been looking into this problem with respect to the measurement of both molecular extinction coefficients and integrated absorption intensities, and the reproducibility of such measurements on various types of spectrometers has been examined. The conclusions of this study will be mentioned briefly below and described in more detail in a forthcoming publication.? I t should be emphasized a t the outset that with the instruments now available, the recording of absolute intensity measurements is slow and