Roots nodules

EFFECT OF EXOGENOUSLY APPLIED AA ON NODULATION 1 1. Nodule Initiation 

AA treatment greatly enhanced nodule production. Application of 20 and 100 ppm AA resulted in a 2-3 fold Increase In nodule number of Clcer arletlnum CSwaraj and Garg, 1969  

Thirty to sixty percent Increase In the number of nodules was observed in lucerne and groundnut when the amount of AA applied ranging between 50 and 200 mg was split into three or four equal instalments. 

The Increase in nodule number with AA treatments was also accompanied by an increase in their fresh and dry weights. 

In Bengal gram, treatment with AA (20 and 100 ppm) resulted in a much higher nodule weight than that in the control (Swaraj and Garg, 1970). These authors (Swaraj and Garg, 

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Although root nodules are the most common sites of N2-fixiag symbioses, some tropical legumes like Sesbania produce stem nodules ia associatioa Jp rhi bium caulinodans (55). la coatrast to root aodules, some stem aodules are photosyathetic and contain, ia the case oiPieschjnomene indica rhizobia themselves capable of photosyathesis (56). This close relatioaship of photosyathesis to fixatioa may ease the eaergy supply demand of nodules. 

E. B. Fred, I. L. Baldwin, and E. McCoy, Root Nodule Bacteria andEeguminous Plants, Studies in Science No. 5, University of Wisconsin Press, Madison, Wis., 1932. 

Atmospheric N2 shown to be "fixed by organisms in certain root nodules. 

Legocki, R. P., Legocki, M., Baldwin, T. O., and Szalay, A. A. (1986). Bioluminescence in soybean root nodules demonstration of a general approach to assay gene expression in vivo by using bacterial luciferase. Proc. Natl. Acad. Sci. USA 83 9080-9084. 

A. L. Virtanen, S. Von Hausen, and T. Laine, Investigations on the root nodule bacteria of leguminous plants XIX. Influence of various factors on the excretion of nitrogenous compounds from nodules. Journal of Agricultural Science 27 332 (1937). 

N. P. J. Price and R. W. Carlson, Rhizobial lipo-oligosaccharide nodulation factors multidimensional chromatographic analysis of. symbiotic signals involved in the development of legume root nodules, Glycobiology 5 233 (1995). 

III. THE ROOT NODULE, A LEAFLESS STEM BORNE ON A ROOT... 

G. Truchet, P. Roche, P. Lerouge, J, Vasse, S. Camut. F. de Billy, J. C. Prome, and J. Denarie, Sulphated lipooligosaccharide signals of Rhizohiuni meliloli elicit root nodule organogenesis in alfalfa. Nature 351 670-673 (1991). 

L. Sk0t and H. Egsgaard, Identification of ononitol and O-methyl-scyllo-inositol in pea root nodules. Plania 161 32-36 (1984). 

E. A. Robleto, A. J. Scupham, and E. W. Triplett, Trifolitoxin production in Rhizohium eili strain CE3, increases competitiveness for rhizosphere colonization and root nodulation of pha.seolus vulgaris in soil. Mol. Plant Microbe Interact. 10 228-233 (1997). 

Two weeks after planting in the pipes, the plants were thinned to 35 pipe per pipe each and the cups to one plant each, and the treatments begun. Each first, third and fifth day of the week for twelve weeks the pipes were flushed with three liters of tap water poured in the elbow end. The water flowed past the plant root systems and drained out the screened end of the pipes into a flask. One hundred milliliter aliquots of this water ( root exudate ) were used to water the soybean plants in the cups three times weekly. After each flushing, two liters of a low nitrogen (50 ppm N) complete nutrient solution (Peter s Hydro-sol ) were added to each pipe. The soybean plants in cups were watered as needed at other times with tap water. On alternate weeks the soybean plants were fertilized with the complete nutrient solution. At 4, 8 and 12 weeks after the root exudate treatments started eighty soybean plants (10 treatments x 2 soybean varieties x 4 blocks) were randomly chosen for analysis. The soil was washed free of the plant roots and each soybean plant was divided into roots, nodules, stems, leaves and fruits. The plant parts were dried at 105°C for four days and weighed. 

Aliphatic acids such as butyric acid have been previously implicated as being allelopathic compounds (46, 47, 23). Chou and Patrick (23) isolated butyric acid from soil amended with rye and showed that it was phytotoxic. Hydroxy acids have also been shown to possess phytotoxic properties (48) but have not been implicated in any allelopathic associations. Since SHBA is a stereo isomer, and the enantiomer was not identified because of impurity, all bioassays were run using a racemic mixture. The D-(-) stereo isomer of SHBA has been isolated from both microorganisms and root nodules of legumes and is suspected to be a metabolic intermediate in these systems (49). It is likely that only one enantiomer was present in the extract therefore, the true phytotoxic potential of this compound awaits clarification of the phytotoxicity of the individual enantiomers. 

Robertson JG, Lyttleton P, Bullivant S, Grayston GF. Membranes in lupine root nodules. I. The role of Golgi bodies in the biogenesis of infection threads and peri-bacteroid membranes. J Cell Sci 1978 30 129-149. 

Some nitrogenases have been found to be unaffected by the presence of oxygen. However, if you do cut into the root nodules of a common legume like pea or bean, you will see that it has a blood-red colour due to the high levels of leghaemoglobin. 

Hoch, G.E., K.C. Schneider and R.H. Burris. Hydrogen evolution and exchange and conversion of N20 to N2 by soybean root nodules. Biochim. Biophys. Acta 37, 273-279 (1960). 

J.G. Torrey. Isolation and cultivation in vitro of the actinomycete causing root nodulation in Comptonia. Science 199,899-902 (1978). 

Figure 1.5 Bacteroids of Rhizobium leguminosarum in root nodules in the pea (Dr P. Poole, University of Reading).

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