الفهرس 
AcnoledgementOnly 14 pages are availabe for public view
 |  | from | 189 |  |  |
| | | from | 189 | | |
Abstract
Metribuzin (sencor), is a relatively new herbicide
introduced in A.R.E. The herbicide affected the vegetative
growth of faba bean plants. In the experiment that have
been carried out, in the present work, metribuzin was
applied as pre-emergence treatment. Consequently, experimental
work has extended to show the effects of different
rates of metribuzin on some physiological and biochemical
aspects of faba bean seedlings grown in hydroponic culture
containing 25% Hoagland nutrient solution. The results
obtained in the present work, can be briefly summarized
in the following:
1- The percentage of germination during five days was
not generally affected at the different rates of
metribuzin. In the treated seeds, germination was
accompanied by:
a. The lowest concentration of metribuzin (6.5 X 10-2
mM) stimulated the hydrolysis of carbohydrate
reserve, but the highest concentration (130 X
10-2 mM) retarded the hydrolysis of carbohydrate
reserve of faba bean seeds.
b. The stimulation and retardation of carbohydrate
hydrolysis in treated faba bean seeds with the
lowest and the highest concentrations were
accompanied by significant increase and decrease
in activities of amylases 0<. -and
-----~~~~~
-152-
f> -amylases).
c. The obvious increase or decrease of RNA and DNA
by lowest and highest concentrations of herbicide
compared to controls, coincides with its stimulatory
or inhibitory effect on protease enzyme
activity.
2- . DUring the growth period of faba bean seedlings in
hydroponic culture of 25% Hoagland solution, some
growth characteristics were affected as result of
exposure to different concentrations of metribuzin
for seven days. The results obtained, herein, for
growth characteristics, can be summerized in the
following:
a. Average growth rates especially length of faba
bean seedlings were significantly inhibited at
130 X 10-2 roM after four days of exposure. When
growth inhibition were examined across time at
relatively higher concentrations, the degree of
growth inhibition was a function of both concentration
and duration of treatment.
b. The shoot/root ratio in samples treated with concentrations
above 13 X 10-2 roM was decreased. This
could be explained by assuming that the shoot is
more sensitive to metribuzin than root especially
by increasing time of exposure.
-153-
c. The effects of metribuzin on growth of faba bean
seedlings grown in hydroponic culture can be significant
at ranges more than 32.5 X 10-
2
mM.
3- Some biochemical and physiological aspects were
affected in faba bean seedlings grown in hydroponic
culture of 25% Hoagland solution as result of exposure
to different levels of metribuzin. The results
obtained can be sumrnerized as follows:
a. Metribuzin induced significant inhibitory effect
on ;14C02 _ fixation, accumulation of soluble sugars,
biosynthesis of polysaccharides, and pigment
contentS.
b. The inhibitory effect was more pronounced in polysaccharide
and carotenoids.
c. Chlorophyll alb ratio was significantly decreased,
which means that chlorophyll ”a” was strongly
inhibited than ”b”.
d. Application of relatively low concentrations of
herbicides resulted in increase in protein content
which was accompanied by high rate of nitrate uptake
and stimulation in activity of nitrate reductase.
The relatively high concentrations of metribuzin
caused a decrease in protein biosynthesis
which was consistent with the rate of nitrate up-
154-
take and activity of nitrate reductase enzyme.
The stimulatory and inhibitory effects of metribuzin
were coinciding with the contents of nucleic
acids and activities of hydrolysing enzymes and
nitrate reductase enzyme.
4- The reduction in chlorophyll level in metribuzin
treated plants, because of an interference with its
formation, may be at least partially responsible for
inhibition of photosynthetic C02 - fixation, reduction
in total carbohydrate and hence the reduction in dry
weights of treated plants, an explanation which has
been provided for metribuzin action.
5- The stimulation in protein accumulation in treated
plants with sublethal concentrations of metribuzin
may be related to increased nutrient accumulation
or to stimulation of enzymes involved in nitrate
reduction and/or carbohydrate utilization for amino
acid and protein synthesis.
6- The action of herbicide might be partly attributed
to effects on nucleic acids and activities of certain
enzymeswhich underlay metabolic activity during plant
growth.
7- Interaction between the age of the plant and metribuzin
level occured at the highest, but not at the
-155-
lowest concentration.
8- The activities of metribuzin in faba bean plants
demonstrate conclusively that the modes of activity
are multiple and extent to include inhibition of
growth as well as the activities of amylases, protease
and nitrate reductase and biosynthesis of protein,
polysaccharides, pigments and nucleic acids, and that
primary mode of activity may depend upon metribuzin
concentration, mode of application and bioassay life
cycle stage.