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Nitrogenous constituents in forage crops with particular reference to grasses

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AgizaAH_1951redux.pdf (43.16Mb)
Date
1951
Author
Agiza, Aly Hassan
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Abstract
 
 
(The aim of the present work was to study the changes which may take place in the nitrogenous compounds, especially the amino acids of the protein; of different species of forage crops. Such factors as stage of growth, nitrogenous fertilizers, date of sowing and different conditions of growth were taken into consideration.
 
She plan and material examined are given on P. (150).
 
A detailed review of the literature on the chemistry of protein, nitrogen metabolism and protein formation in the plants, and the biological value,of proteins has been written and the results and hypothesis of different investigators have been stated and commented upon.
 
A review of the methods for the extraction of protein from the aerial parts of the plants and for the determination of amino acids has also been made; the advantages and disadvantages of these methods have been mentioned. Some of these methods were tried experimentally and modifications with respect to the reagents or the apparatus were devised and tested.
 
The extraction of protein from plant material by means of a formic acid - ethanol mixture was considered to be an effective method of obtaining a representative sample of protein from plants of economic importance (grasses and other forage crops) whether they were fresh, air dried or oven dried. An exception to this was found with mature aftermath of Timothy (untreated with nitrogen) from which practically no protein could he extracted.
 
A modified technique for the separation of the different amino acids in a protein hydrolysate by means of filter paper chromatography was adopted and a colorimetric method for determination of amino acids by ninhydrin was used after a study of its accuracy. Samples were taken from the plants under investigation at frequent intervals ( 3-4 days) in order to follow the changes in the total nitrogen, true protein and non - protein nitrogen of the plants and in the amino acid contents of the proteins at different stages of growth} the influence of nitrogenous fertilisers and farm yard manure was also examined. Other samples of plants were taken to supplement and Gonfirm these observations.
 
The results for the total, true protein and non-protein nitrogen extracted and nitrogen remaining in the residues after extraction have been presented in Tables a (Appendix) and shown graphically in plates ( included in the text;. The results show a decline in the total* true protein and non-protein nitrogen (on dry matter basis) with age. The application of nitrogen fertilisers either in the form of nitrate or ammonium sulphate increased the amounts of these fractions in grasses whether the fertilisers were added at an early or late stage of growth; the increase was larger 'when nitrogen was applied early, during the active vegetative growth. In the case of clover, the addition of nitrogen was not as effective as it was with the grasses; it reduced the population of clover when this was grown in association with the grasses Ammonium sulphate increased the nitrogen content of the first growth of Italian rye grass more than did farm yard manure, hut the opposite was found in the second growth; the reasons are discussed.
 
The figures for the amino acid constituents of proteins have been presented in Tables b and a (Appendix). These tables show that aspartic acid and glutamic acid increased while serine, the leucines, lysine, arginine, tyrosine and tryptophane decreased with the age of the plant.
 
The changes were significant in grasses, barley and oats but slight in clover and lucerne. This has been explained on the grounds that grasses and similar species absorb the major part of their nitrogen in the first few weeks of their growth while clover and lucerne have a continuous source of nitrogen in the presenoe of symbiotic bacteria; and that the young grasses have a lower carbon/ nitrogen ratio than the older grasses.
 
No differences were observed between the amino acids of proteins extracted from different strains . of clover. Very slight differences were obtained between amino acids of the proteins of lucerne and clover
 
She differences between the proteins of grasses and clover were small, especially when the grasses were young.
 
She nitrogen fertilisers did not have much effect on the composition of the proteins of clover. However, they had a significant effect if they were applied to grasses at the early stage of growth? aspartic acid and glutamic acid decreased whereas the leucines, lysine, arginine, tyrosine and tryptophans increased. No changes in amino acids occurred as a result of a nitrogen top-dressing at a late stage of growth of either clover or grasses.
 
The d&te of sowing had no effect on the composition of the protein of grasses, if comparison was carried out on grasses of the same age. With successive growths, no changes took place in the proteins of clover or lucerne, and with grasses the changes were due mainly to the rapid development and the presence of flowering plants even in the early stages of growth. However, the amounts of amino acids were found to come into the same range for both first and second growth.
 
URI
http://hdl.handle.net/1842/29981
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