الفهرس 
IntroductionOnly 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, experi¬mental 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 ( α –and β-amylases).
c. The obvious increase or decrease of RNA and DNA by lowest and highest concentrations of herbicide compared to controls, coincides with its stimul¬atory 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 mM 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 concent¬ration and duration of treatment.
b. The shoot/root ratio in samples treated with con¬centrations above 13 X 10-2 mM was decreased. This could be explained by assuming that the shoot is more sensitive to metribuzin than root especially by increasing, time of exposure.
c. The effects of metribuzlin on growth of faba bean seedlings grown in hydroponic culture can be signi¬ficant 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 summerized 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 poly¬saccharide and carotenoids.
c. Chlorophyll a/b 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 up¬take and stimulation in activity of nitrate reduct¬ase. The relatively high concentrations of metri¬buzin caused a decrease in protein biosynthesis which was consistent with the rate of nitrate up-take and activity of nitrate reductase enzyme. The stimulatory and inhibitory effects of metri-buzin 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 CO2 - 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 enzymes which underlay metabolic activity during plant growth.
7- Interaction between the age of the plant and metri¬buzin level occured at the highest, but not at the 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.