(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.
