L-GLUTAMINASE ACTIVITY IN SOILS - ASSAY, DISTRIBUTION, KINETICS AND THE EFFECT OF CROP COVER ON ITS ACTIVITY
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Date
2015
Authors
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PROFESSOR JAYASHANKAR TELANGANA STATE AGRICULTURAL UNIVERSITY, RAJENDRANAGAR, HYDERABAD
Abstract
Present research work entitled “L-GLUTAMINASE ACTIVITY IN SOILS -
ASSAY, DISTRIBUTION, KINETICS AND THE EFFECT OF CROP COVER ON ITS
ACTIVITY” has been carried out with several objectives viz: to have a basic
understanding of the activity and characteristics of L-glutaminase in the heterogeneous
soil matrix, then to determine the influence of pH, moisture, temperature and kinetics
with a view to determine its involvement in soil nitrogen transformation.
Thirty soil samples collected from different parts of Rangareddy district of
Telangana state were assayed using standard procedure. L-Glutaminase activity of
surface soils were expressed as μg of NH4
+ released g-1 soil 2h-1 and ranged from 2.1 to
13.6 with an average value of 6.42 with the pH 8 buffer solution and with the pH 10
buffer solution the values ranged from 2.3 to 11.5 with an average value of 5.6. A
simple correlation was carried out between the levels of L-glutaminase activity with
physico-chemical and chemical characteristics of soil. The correlation analysis showed
that L-glutaminase activity was positively and significantly correlated with organic
carbon content (0.86**) and has shown no correlation with pH, EC and silt.
Soil L-glutaminase activity increased with an increase in substrate concentration
i.e from 2 to 30 mM and with further increase in substrate concentration, minimal
change in the enzyme activity was observed. Characteristics of enzyme activities like
maximum enzyme reaction velocity and Michaelis constant were determined using
Michaelis Menten equation, Vmax values varied with the type of soil from 12.65 to
58.82 and the Km values varied from 8.21 to 82.41 μg of L-glutamine hydrolyzed g-1
soil 2h-1 for soil L-glutaminase. Effect of temperature on L-glutaminase activity was studied by incubating the
soil samples from 20 to 80oC. Increase in temperature increased L-glutaminase activity
from 20oC to 50oC, but decreased sharply with further increase in temperature.
Temperature coefficient (Q10) values were also calculated and found to be less than 1
when the temperature exceeds 50oC indicating the deactivation of enzymes.
L-glutaminase activity increased with increase in pH from 2 to 8 and thereafter
a decrease in enzyme activity was observed with further increase in pH. The activity of
L- glutaminase increased with increase in moisture levels from 30% to 100% but a
sharp increase was observed up to 50% moisture and there after it levels down.
A pot culture experiment was conducted with one Alfisol in the Vegetable
Production Unit of Department of Horticulture, to study the influence of crop cover on
soil enzyme activity. The experiment was undertaken with three cereals - rice, sorghum
and maize, two oilseeds - groundnut and sesamum, two legumes - blackgram and
greengram, two vegetables - spinach and bhendi. The experiment was conducted using
crops as treatments in Completely Randomized Block design with three replications
along with uncropped control. The effect of plant cover on L-glutaminase activity
showed that there was increase in L-glutaminase activity with age of crop and it varied
with the plant species grown. The increase in L-glutaminase activity (μg of NH4
+
released g-1 soil 2h-1 ) ranged in groundnut from 5.7 to 13.4, blackgram from 5.7 to
12.9, greengram 5.6 to 12.7, sesamum from 4.8 to 11.8, rice from 4.7 to 11.3, maize
from 4.3 to 10.2, sorghum from 3.1 to 10.7, spinach 3.8 to 9.5, bhendi from 2.4 to 8.4.
The activity of L-glutaminase, acid and alkaline phosphatases under different crop
coverages followed the order groundnut> black gram> greengram> sesamum> rice
>maize> sorghum> spinach > Bhendi. The presence of plants and the type of plants
grown on soil have shown a marked effect on enzyme activities.
Description
Keywords
enzymes, crops, planting, acidity, nitrogen, amino acids, aromatic compounds, concentrates, inorganic acid salts, economic resources