Lupine, acid phosphatase

In soil, the chances that any enzyme will retain its activity are very slim indeed, because inactivation can occur by denaturation, microbial degradation, and sorption (61,62), although it is possible that sorption may protect an enzyme from microbial degradation or chemical hydrolysis and retain its activity. The nature of most enzymes, particularly size and charge characteristics, is such that they would have very low mobility in soils, so that if a secreted enzyme is to have any effect, it must operate close to the point of secretion and its substrate must be able to diffuse to the enzyme. Secretory acid phosphatase was found to be produced in response to P-deficiency stress by epidermal cells of the main tap roots of white lupin and in the cell walls and intercellular spaces of lateral roots (63). Such apoplastic phosphatase is safe from soil but can be effective only when presented with soluble organophosphates, which are often present in the soil. solution (64). However, because the phosphatase activity in the rhizo-sphere originates from a number of sources (65), mostly microbial, and is much higher in the rhizosphere than in bulk soil (66), it seems curious that plants would have a need to secrete phosphatase at all. 

J. Wasaki, M. Ando, K. Ozawa, M. Omura, M. Osaki, H. Ito, H. Matsui, and T. Tadano, Properties of secretory acid phosphatase from lupin roots under phosphorus-deficient conditions, Plant Nutrition for Sustainable Food Production and Environment (T, Ando, K. Fujita, T. Mae, H. Matsumoto, S. Mori, and J. Sekiya, eds), Kluwer Academic Publishers, Dordrecht, 1997, p. 295. 

Figure 5 Model of phosphorus (P) deficiency-induced physiological changes associated with the release of P-mobilizing root exudates in cluster roots of white lupin. Solid lines indicate stimulation and dotted lines inhibition of biochemical reaction sequences or mclaholic pathways in response to P deliciency. For a detailed description see Sec. 4.1. Abbreviations SS = sucrose synthase FK = fructokinase PGM = phosphoglueomutase PEP = phosphoenol pyruvate PE PC = PEP-carboxylase MDH = malate dehydrogenase ME = malic enzyme CS = citrate synthase PDC = pyruvate decarboxylase ALDH — alcohol dehydrogenase E-4-P = erythrosc-4-phosphate DAMP = dihydraxyaceConephos-phate APase = acid phosphatase.

Seedlings are a rich source for nonspecific acid phosphatase. Newmark and Wenger (114) have reported on a 1000-fold purification from lupine seedlings. The purified enzyme hydrolyzes phosphate monoesters and pyrophosphate with p-nitrophenyl phosphate as substrate. The optimal activity was at pH 5.2-5.5, and Km was 3 X 10 4 M. Fluoride inhibition was noncompetitive. 

Gilbert, C.A., Knight, J.D., Vance, C.P. and Allan, D.L. (1999) Acid phosphatase activity in phosphorus-deficient white lupin roots. Plant, Cell and Environment 22, 801-810. 

Miller, S.S., Liu, J.Q., Allan, D.L., Menzhuber, C.J., Fedorova, M. and Vance, C.P. (2001) Molecular control of acid phosphatase secretion into the rhizosphere of proteoid roots from phosphorus-stressed white lupin. Plant Physiology 127, 594-606. 

Tadano, T., Ozawa, K., Sakai, H., Osaki, M. and Matsui, H. (1993) Secretion of acid phosphatase by the roots of crop plants under phosphorus-deficient conditions and some properties of the enzyme secreted by lupin roots. Plant and Soil 155/156, 95-98. 

Wasaki, j., Omura, M., Ando, M., Dateki, H., Shinano, T., Osaki, M., Ito, H., Matsui, H. and Tadano, T. (2000) Molecular cloning and root specific expression of secretory acid phosphatase from phosphate-deficient lupin (Lupinus albus L.). Soil Science and Plant Nutrition 46, 427-437. 

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