Maize organic acid

The role of the secretion from the root apex of organic acids such as citric and malic in the resistance of maize and wheat, respectively, to Al toxicity (81,82) has emerged recently as one with plausibility (83). These studies have been carried out in solution cultures, but how does the suggestion hold up in soil The first and probably greatest difficulty is that the toxic species of Al, probably hydrated Al ", must diffuse to some site in the root apex and stimulate the produc-... 

D. M. Pellet, D. L. Grimes, and L. V. Kochian, Organic acid exudation as an aluminium-tolerance mechanism in maize Zea mays L.). Planta 796 788 (1995). 

W. Petersen and M. Bottger, Contribution of organic acids to the acidification in the rhizosphere of maize seedlings. Plant Soil 132A59 (1992). 

Jorge RA., Arrunda P. Aluminium induced organic acids exudation by roots of aluminium tolerant maize. Phytochemistry 1997 45 675-681. 

Strom, L., Owen, A. G., Godbold, D. L., and Jones. D. L. (2002). Organic acid P mobilization in the rhizosphere and uptake by maize roots. Soil Biol. Biochem. 34, 703-710. 

Gaume, A., Machler, F., De Leon, C., Narro, L., and Frossard, E., Low P tolerance by maize Zea mays L.) genotypes signiflcance of root growth, and organic acids and acid phosphatase root exudation. Plant Soil, 228, 253-264, 2001. 

Release of organic acids for complexing ions outside the root apoplast plays a role in Ah" -tolerant cultivars of maize and wheat. The excreted (or exuded) malic and/or citric acid incorporates Ah" into negatively charged stable anion complexes which are harmless for roots and which are not taken up (Jones etal. 1996). 

George, T.S., Gregory, P.J., Wood, M., Read, D. and Buresh, R.J. (2002b) Phosphatase activity and organic acids in the rhizosphere of potential agroforestry species and maize. Soil Biology and Biochemistry 34, 1487-1494. 

Maize juice produced from com starch, which has received considerable attention as a sucrose source, has been snccessfully deionized by conventional treatment with the result that improved sugar recoveries are possible. In the manufacture of dextrose, the organic acids and colored substances produced as degradation products during starch hydrolysis were eliminated economically by the use of the ion-exchange process to produce a high-quality sugar. 

This biorefinery processes starch crops (see Figure 17.2), such as wheat, maize and potatoes, or sugar crops (see Figure 17.3), such as sugar beet or sugar cane. Its most important output is glucose, which can be further used for the production of ethanol and organic acids. 

In plants, acetyl-CoA carboxylase levels seem to play an important role in the overall rates of fatty acid synthesis de novo. The purified enzyme is unaffected by citrate or a whole range of organic acids. There is evidence that in vivo it may be controlled by a combination of factors. Thus, the change in chloroplast pH, Mg ", ATP and ADP levels which occur during illumination have been shown by Hawke to cause an increase of about 24-fold in the activity of the maize enzyme in vitro. This is almost exactly the same as the observed increase in fatty acid synthesis in vivo when leaves are illuminated. 

In the presence of air, the roots, coleoptile, mesocotyl, endosperm, scutellum, and anther wall of maize synthesise a tissue-specific spectrum of polypeptides. The scutellum and endosperm of the immature kernel synthesise many or all of the ANPs constitutively, along with many other proteins under aerobic conditions. Under anaerobic conditions all of the above organs selectively synthesise only the ANPs. Moreover, except for a few characteristic qualitative and quantitative differences, the patterns of anaerobic protein synthesis in these diverse organs are remarkably similar (Okimoto et al., 1980). On the other hand, maize leaves, which have emerged from the coleoptile, do not incorporate labelled amino acids under anaerobic conditions and do not survive even a brief exposure to anaerobiosis (Okimoto et al., 1980). 

Diets of corn (maize) and soybean meal are usually fortified with sulfur amino acids for pigs and chickens. Sometimes fishmeal, a good source of sulfur amino acids, is added to die diets, or sulfur amino acids synthesized by organic chemical processes may be used,... 

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