Maize Extracts Research Articles

IAA Oxidase Inhibitors from Normal and Mutant Maize Plants

Extracts of maize (Zea mays L.) plants contain substances which, in vitro, inhibit an indoleacetic acid (IAA) oxidase enzyme from maize. The extracts can be freed of inhibitors by dialysis or by passage through columns of polyvinylpyrrolidone powder. Inhibitor-free extracts contain an IAA oxidase enzyme which requires a phenolic co-factor and is stimulated by Mn(2+).IAA oxidase inhibitor and total phenol levels were compared for normal maize and for the maize mutant Knotted (Kn). In plants up to 18 days old the level of heat stable, water soluble IAA oxidase inhibitors increases with increasing dosage of the Kn allele. Increased inhibitor content is accompanied, but not paralleled, by increased content of total phenols. Although several inhibitors are present in crude extracts, most inhibition can be attributed to 1 compound. This compound is not destroyed by horseradish peroxidase in the absence of IAA. At pH 3.5 it is not extracted into ether, but it is rendered ether-extractable by incubation in 2 n KOH for 5 hr at room temperature. This compound is tentatively identified as an ester of ferulic acid and some unknown moiety.

Studies on the mechanism of activation and inactivation of pyruvate, phosphate dikinase. A possible regulatory role for the enzyme in the C4 dicarboxylic acid pathway of photosynthesis.

1. The activity of pyruvate,P(i) dikinase in leaves of maize and Amaranthus palmeri rapidly falls on transferring illuminated plants to darkness. Illumination of dark-treated plants results in an immediate rapid increase in activity of the enzyme, the final activity reached being dependent on the intensity of the incident light. 2. Activation of the enzyme in extracts of dark-treated maize leaves after gel filtration on Sephadex G-25 requires a thiol and P(i). The P(i) requirement for activation can be replaced by arsenate. Activation of the enzyme is inhibited by AMP and GMP and possibly also by ADP and ATP. Activation of the enzyme after gel filtration on Sephadex G-200 also requires a heat-labile component that is excluded by Sephadex G-25. 3. The active enzyme isolated from illuminated leaves is inactivated by ADP in the presence of a thiol, the rate of inactivation being very much faster in air than in an oxygen-free atmosphere. Reactivation of the ADP-inactivated enzyme requires a thiol, P(i) and a component excluded by Sephadex G-25 but considerably retarded by Sephadex G-200. 4. The active enzyme is rapidly and irreversibly inactivated in the absence of a thiol. Inactivation is accelerated by both sodium diethyldithiocarbamate and tetraethylthiuram disulphide, and the enzyme inactivated by these reagents is completely reactivated by incubation with dithiothreitol. This reactivation does not require P(i). The inactive enzyme from dark-treated leaves is stabilized by diethyldithiocarbamate and can be partially activated by dithiothreitol alone; complete reactivation requires both dithiothreitol and P(i). 5. The enzyme activity is markedly inhibited by the thiol reagents p-chloromercuribenzoate, gamma-(p-arsenophenyl)-n-butyrate and an equimolar mixture of arsenite and 2,3-dimercaptopropan-1-ol. 6. The processes of activation and inactivation observed in vitro are discussed in relation to the regulation of pyruvate,P(i) dikinase activity in the leaf.

Spectrophotofluorometric Determination of 6-Methoxy-2-benzoxazolinone, an Indicator of Resistance to European Corn Borer in Zea Mays12

By isotopic dilution Klun and Brindley (J. Econ. Entomol. 59: 711-8) showed the yield of 6-methoxy-2-benzoxazolinone (6MBOA) from maize at the whorl stage to be a reliable indicator of the plant’s resistance to the first-brood larvae of the European corn borer, Ostrinia nubilalis (Hubner). A spectrophotofluorometric method was devised to facilitate analysis of 6MBOA produced from the plant. Excitation of the compound at 292 mµ produced peak emission at 335 mµ the relative in tensity of the emission linear with concentrations of compound between 0.025 to 1.2 µg per ml. When 9 samples of maize, found to contain 234-1810 ppm of 6MBOA by isotopic dilution, were analyzed by the fluorometric procedure, results were in good agreement. Maize extracts contain a small amount of benzoxazolinone (BOA), which does not interfere with the 6MBOA analysis. 6MBOA and BOA in the µg range may be gas chromatographed, but the responses were not reliable for quantitative analysis.

On Oviposition, Olfactory Conditioning and Host Selection in Rhizopertha Dominica Fab. (Insecta, Coleoptera)

ABSTRACT The senses used in food finding and the factors inducing oviposition in Rhizo-pertha dominica (Fab.), a Bostrichid beetle pest of stored grain, were investigated. The sense of smell appears to be the most important in leading the animal to an environment where food is present. Responses were obtained in an olfactometer with maize, wheat, oats and barley and with different extracts of wheat and maize. The use of the sense of sight was also investigated. Once within an environment having the odour of food the sense of touch appears to be paramount in the selection of oviposition site. The influence of size, shape and texture were investigated. But in the absence of appropriate patterns of stimuli involving both olfactory and tactile sensations, restraint from ovippsition was exercised. No predilection was shown for oviposition or feeding in the food in which they were reared as larvae. Neither did the larvae especially choose for entry substances in which their parents have been reared. The animal can be made tolerant to the odour of peppermint instead of repelled by it in an olfactometer by exposing the adults to the odour of peppermint for a few weeks. The effect wears off after 10-14 days’ isolation from peppermint in wheat. Olfactory receptors which appear to be located on the antennae and legs were used in both food-finding and recognition of the opposite sex. A list is given of the substances in which the animal was reared. The bearing of these results on the problem of “gestalt” in conditioning, and on changes in habit in economic insects, is discussed.

Vitamin B2 and the Pellagra-like Dermatitis in Rats

IN our first experiments on the concentration and isolation1 of vitamin B2, we failed to observe definite changes in the skin and fur, such as those described by J. Goldberger and R. D. Lillie2, and by H. Chick and M. H. Roscoe3 and several other authors, in rats fed on diets containing the antineuritic vitamin in a purified form (for example, alcoholic extracts of wheat or maize, Peters's antineuritic concentrate from yeast, crystalline vitamin B1 preparations). The flavin pigment was identified by us with vitamin B2 by its growth-promoting properties. It was therefore a question for further investigation whether in these circumstances it was also identical with the anti-dermatitis factor and in particular with the pellagra preventing factor.