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Abstract
0SUMMARY
Part I
This study was carried to examine the effect of cadmium on the growth and metabolic contents of Ambrosia maritima. L.
The main experimental results can be briefly summarized in the following:
1- All morphological features of Ambrosia maritima. L plant were affected by the increase of cadmium concentration from 0.0 (mM) to 3.0 (mM), since all measured growth parameters (shoot length, number of nodes, number of lateral branches and buds, number and area of leaves, root length, number of lateral root, fresh and dry weight of leaves, stems, roots and intact plant, flowering date, number of flowers (male, female), starting, date of fruiting and number of fruits were significantly decreased by Cd treatments.
2- The pigment content of Ambrosia maritima. L leaves was significantly decreased with cadmium treatments, throughout the four stages of plant growth.
3- The obtained results showed that disaccharides as well as polysaccharides were significantly decreased with cadmium treatments, while monosaccharides showed insignificantly increase due to the effect of cadmium on enzyme activities.
4- Protein- nitrogen and total- nitrogen were significantly decreased by the increase of cadmium in the soil, but the soluble-nitrogen showed insignificantly increase with the increase of cadmium concentrations in the soil throughout the four stages of plant growth.
5- Increasing of cadmium concentrations in the soil led to a decrease in amino acids content in leaves of Ambrosia maritima. L plants amino acid proline was increased in damsissa leaves with cadmium treatments throughout the four stages of plant growth.
6- Increasing of cadmium concentrations in the soil induced insignificant decrease in nucleic acids (RNA, DNA) content in Ambrosia maritimal. L leaves throughout the four stages of plant growth.
7- Active ingreadients in Ambrosia maritima. L Leaves (sesquiterpene lactones “Ambrosin, damsin”) showed significant decrease with cadmium treatments throughout the four stages of plant growth.
8- On estimation of the growth regulators content in fractionated shoot and root extract of Ambrosia maritima. L Plants throughout the four stages of plant growth, the obtained results showed that abscisic acid (ABA) content in shoot and root extracts was significantly increased while auxins content showed significant decrease with the increase in cadmium concentration in the soil.
Part II
This investigation was planned to study the effect of soil treatment with cadmium chloride on the prevailence of rhizosphere fungal flora of Ambrosia miritima (Damssisa) plant. It is also tended to find out possible explanation for the observed variations in microflora in terms of sensitivity or resistance of the microorganisms to cadmium ion. Inocula of the selected fungi were grown on elevated Cd-concentrations to denote the level of resistance of each fungus in the light of its biochemical and physiological changes. The possible antagonistic or synergistic interactions of both cadmium and -radiation on the test fungi was also studied.
The results obtained could be summarized in the following points:
1- 6600 fungal colony belonging to 24 genera and 42 species, were isolated and identified from samples collected from untreated soil with cadmium chloride.
2- The total number of fungal genera and species, isolated and identified from samples collected from treated soils with different concentrations of cadmium chloride was found to be lower than that isolated from samples collected from cadmium free soil;
i- At 0.5 mM Cd-concentration, 5364 fungal colony belonging to 18 genera and 36 fungal species were isolated and identified. It is the most favourable concentration for attaining maximum fungal counts.
ii- At 1.5 mM Cd-concentration, 3786 fungal colony belonging to 11 genera and 26 fungal species were isolated and identified. This concentration was suitable for achieving moderate occurrence and moderate fungal counts.
iii- At 3.0 mM Cd-concentration, 1137 fungal colony belonging to 3 genera and 5 fungal species were isolated and identified, an observation which indicates the unsuitability of that concentration for survival of fungal population.
3- Aspergilli represented the group of fungi of highest frequency of occurrence under the different experimental conditions. This group represented 51.9%, 58.3%, 61.5% and 93.0% of the total count at 0.0, 0.5, 1.5 and 3.0 mM Cd-concentrations.
4- The remaining isolated groups can be arranged in the following descending order according to their frequent occurrence, Dematiaceae > Moniliaceae (excluding Aspergillus and Penicillium) > Penicillium spp. > Phycomycetes > Ascomycetes > Fusarium spp. > Mycelia sterilia.
5- With respect to the frequency of occurrence of fungal species in the field at 3.0 mMCd, the following sequence of decreasing tolerance to CdCl2 was obtained, A.tamarii > A.sydowi > A.niger > Stemphylium herbarum > Thysanophora penicillioides.
6- On studying the effect of six different Cd-concnetrations (0.0-2000 M) in vitro culture on the dry mass of 18 selected fungi, the following sequence in order of descending resistance can be recorded; A.tamarii > A. terreus > A. sydowi > A. niger > G. lujikuroi > F.oxysporum > A. subolivaceus, B. piluliferum > P. corylophilum, C.echinulata > A. carneus > A. ellipticus > A. flavus > S. atra corda > A. ochraceous > P. islandicum > P.variotii > A. caespitosus.
7- On studying the effect of different concentrations of CdCl2 (0.0-4000 M) in vitro culture on the growth parameters (dry weight and mycelial linear growth) of the three selected Aspergillus species; the following sequence of decreasing resistance can be obtained;
A. tamarii > A. sydowi > A. niger.
8- At 3.0 mMCd A. tamarii was the most dominant species in the field, appeared to be the most resistant in the in vitro study. A. niger the most sensitive in the field, was also sensitive to Cd in the vitro study.
So, the observed resistance or sensitivity of the three fungi to cadmium were inherent to the organism itself and not due to other coherent factors such as nature of the soil and type of its tolerance as clay and/or organic matter.
9- Amino acids analysis at 2000 M CdCl2 revealed that the total free amino acids content in the untreated samples of both A. tamarii and A. niger was collectively higher than that recorded in the comparable sample of A. sydowi, while the total free amino acids content of both A. tamarii and A. sydowi was appreciably increased followed Cd-supplementation. Cd-administration was accompanied with reduction in the amount of total free amino acids content in A. niger compared to the untreated cells.
10- With respect to A. tamarii, it accumulates; proline, glycine, cysteine, aspartic acid, serine, threonien and glutamic acid, while A. sydowi accumulates, proline, glycine, cysteine, aspartic acid, valine, serine and glutamic acid. A. niger accumulates proline, cysteine, alanine and serine.
11- Accumulation of free amino acids by the two Cd-resistant fungi, A. tamarii and A. sydowi compared to the sensitive strain A. niger indicates that amino acids may have an important role in fungal resistance to Cd, or probably may increased the fungal mechanism of resistance to this heavy metal.
12- Nucleic acids analysis of the mycelial mats of the three test fungi A. tamarii, A. sydowi and A. niger indicated that Cd-treatment (2000 M) reduced the level of both DNA and RNA contents, an observation which more pronounced in the most sensitive strain A. niger. This feature may be due to the dramatic effect of Cd on cell division more than a result of metabolic disorder.
13- Sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) indicated relatively high content of protein under Cd-stress (2000 M) compared to non treated culture of both A. tamarii and A. sydowi. In contrast, a decrease in protein content in Cd-treated cells of A. niger was observed.
14- SDS-PAGE revealed that Cd-treated fungal cells of A. tamarii synthesized new three stress proteins (hsp’s) of molecular weights; (151.74, 121.63, 109.15 KDa). A. sydowi senthesized new four stress proteins (hsp’s) of molecular weights; (181.19, 158.89, 145.57, 40.911 KDa). In cell culture of A. niger, cadmium induced new four stress proteins (hsp’s) with the following molecular weights; (182.87, 139.02, 76.987, 61.951 KDa).
Stress proteins may be play an important role in the detoxification of Cd+2 in both resistant fungi A. tamarii and A. sydowi.
15- Finally, an experiment was carried out to investigate the possible antagonistic or synergestic interaction between Cd and -radiation.
a) It was found that Cd--radiation combination acted synergistically on the growth of both A. tamarii and A. sydowi at the low doses of -radiation leading to a significant drop in the dry weight more than in the presence of radiation separately.
b) At high doses of -radiation, the mycelial dry weight of both organisms was increased than in the presence of radiation alone, indicating that the two treatments together antagonised the toxicity of each other.
c) With respect to A. niger the combination of Cd and -radiation acted synergistically on the growth of this organism leading to a significantly drop in the dry mass more than in the presence of -radiation separately.
16- The previous observation confirmed the tendency that the effect of antagonistic effect of cadmium--radiation combination may be, to some extent, due to competition between Cd and radiation for senthesizing a set of specific proteins, the so called heat shock proteins (hsp’s) which may protect the organism from the deleterious effect of both stresses.