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1993 Special Awards Winners
State Science and Engineering Fair of Florida
April 14, 16, 1993
Central Florida Fairgrounds, Orlando
FDACS Senior / FDACS Junior / FAITC Senior / FAITC Junior
Awards Given By The Florida Department of Agriculture and Consumer Services
Neil A. Hattangadi
In Phase I, enzymatic incubation was the most effective wounding treatment, as it best dissolves pectins in the roots' cell walls allowing bacteria to enter the surface. Only rotten stone worked as a physical treatment since it is the only fine abrasive; the use of this wounding has never been documented before, from the literature surveyed by the experimenter, and represents a break-through from costly enzymes and extends the applicability of the procedure for practical agriculture. in Phase IA, barriers in symbiosis between unrelated clover and R. loti were overcome, showing the extension of cross-inoculation groups within the legume family through the elimination of the pectin proteins that bind to specific polysaccharides in the bacteria. Also, the synergistic effects of the bacterial mixture of R. loti and R. trifolii made it the best innoculant. Polyethylene glycol was found to be compulsory for non-legume nodulation, as it dissolves holes in the roots' cell walls, allowing for greater and faster bacterial uptake. After splitting the nodules, no leghemoglobin was detected through light microscopy, resulting from the non-legumes' lack of nodulin genes to stimulate rhizobial nitrogen fixation. Also, the non-legumes seemed to undergo the effects of nitrogen deprivation through chlorosis, demonstrating that no nitrogen compounds were provided for them. Thus, the nodules in non-legumes were both smaller and less numerous than those of the legumes, and were unable to function.
In Phase II, an alternative to the symbiotic nitrogen fixation for nonlegumes was found through free-living cyanobacteria. The original intent of the experimenter was to create various nitrogenase-derepressed mutants through ethyl methanesulfonate (EMS) mutagenesis of the strain Anabaena variabilis, to overcome nitrogenase repression resulting from a series of metabolic processes in ammonium assimilation; but due to the lack of resources he was forced to choose mutant strains already developed, through few of their properties in hydroponic systems were known. Based upon documented nitrite and nitrate reductase activity, a desirable nitrogenase-derepressed mutant strain was selected from about 10 mutants and obtained from the University of Florida in Gainesville. Hydroponic systems of the following variations were set up with rice and corn seedlings: 1 mg parent strain/100 mL medium, 1 mg mutant/100mL medium, 1 mg mutant/100 mL medium + 3mM (NH4)2SO4, 5mg mutant/100mL medium, 5mM (NH4)2SO4, and unamended. That mutant strain commenced nitrogenase activity at 6.444 ppm C2H4 hour -1).1 mg-1 as determined through acetylene reduction and a gas chromatograph versus 5.817 by the parent. In addition, it was found that the parent did not excrete ammonium, and when ammonium levels were detected with Nessler's reagent at the third and fourth weeks, it was due to their decomposition. The mutant did excrete NH4 and it did not show any assimilation until the concentration reached approximately 0.5mM, when 0.02umoler-glutamyl hydroxamate 15 min-1 1 mg-1 were detected, the limit of the assay procedure. The mutant strain's nitrogenase activity did decrease slightly as the NH4 levels increased, an undesirable characteristic attributed to an increase in the production of vegetative cells with a reduction in heterocysts. Since the mutant strain recorded little to no glutamine synthetase activity, it gradually reduced density to about 55% of the original, as measured by chlorophyll determination. It did show a statistically significant increase in plant biomass over the parent strain's and unamended systems, but less than that of the chemical (NH4)2SO4 supplements.
These results have a critical application in that they provide a low cost alternative to expensive, environmentally hazardous chemical fertilizers.