الفهرس 
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Abstract
This study was carried out in the laboratories of the Genetics Dept., Fac. of Agric., Ain Shams Univ. during the period from 2013 to 2019. Stress is an environmental condition that threaten the survival of a cell, or at least prevent it from performing optimally, are commonly referred to as cell stress.
Five yeast strains (UQM 49, NRRL Y-17008, LBC 1208, LBC 254 and ATCC 58523) were used to assess the stress response among control and treatment yeast strains.
The aim of the research is to shed more light on the understanding of genetic changes at the level of genome structure or expression of genes in response to exposure to various environmental stresses (heat and salt) using yeast as a model organism.
The following results were obtained:
1. Dilution plating was used to count the number of colonies after exposed to heat or salt stresses and compared with control, the S1 strain was sensitive when exposed to 20°C while was tolerant at 40°C, 0.5 M and 1 M of NaCl difference with insignificant differences.
2. S2 strain showed the most significant difference when exposed to temperature of 20°C, 40°C and 1 M NaCl, while was tolerant with 0.5 M of NaCl.
3. S3 and S4 strains showed more tolerant at the heat and salt stresses where the difference between the control and the treatments was insignificant.
4. S5 strain wasn’t affected when exposed to 20°C and 40°C therefore the difference was insignificant while the difference was significant when exposed to 0.5 M and 1 M on NaCl.
5. SDS-PAGE showed heat shock protein bands 41.6 kDa that
disappeared after exposing to 20oC in the S1 strain, while S2 and S4 strains have the same bands between control and 20oC. A band of 17.5 kDa disappeared after exposing to 20oC in S3 strain. On the other hand, the same bands appeared after exposing to 20oC in the S5 strain.
6. New polypeptide bands of 73.7, 52.1, 43.5, 23, 19 and 10.5 kDa were expressed only at 40oC in S1 with excess band at 16.7 kDa in S2, S3, S4 and S5. On the other hand, some bands were repressed after exposing to heat stress. Bands of 83.2, 55.5, 47.4, 41.6, 25.3, 20.6, 17.5 and 11.2 kDa disappeared after exposing to 40oC in S1 strain. Otherwise, some bands were repressed after exposure to heat stress like 83.2, 55.5, 47.4, 41.6, 25.3, 20.6, 16.7 and 11.2 kDa which disappeared after exposing to 40oC in S2, S3, S4 and S5 strain.
7. New SDS-PAGE bands of 73.7, 52.1, 43.5, 23, 19, 16.7 and 10.5 kDa were expressed at 1 M of NaCl. Bands of 83.2, 55.5, 47.4, 41.6, 25.3, 20.6, 17.5 and 11.2 kDa disappeared after exposing to 1 M in the S1, S2, S3, S4 and S5 strains.
8. RAPD-PCR using five random primers was used to identify and characterize the five yeast strains. They showed highly polymorphism percentage more than 75%.
9. For S1 strain, polymorphism percentage ranged from 83.33% primer OPD-07 to 100% for primer OPF-05. Mean of band frequency ranged from 43.75% to 54.16%. RAPD primers differed in their amplified loci (band number) from just eight loci with OPF-05 primer to 14 different bands with OPM-01 primer.
10. For S2 strain, polymorphism percentage ranged from 75% primer OPF-06 to 100% for primer OPF-05. The mean of band frequency per primer ranged from 40.00% to 65.62%. RAPD primers differed in their amplified loci from just eight loci with OPF-06 primer to 15 different bands with OPM-01 primer.
11. For S3 strain, polymorphism percentage ranged from 78.57% primer OPD-07 to 100% for primers OPF-05 and OPM-01. The mean of band frequency per primer ranged from 40.00% to 56.81%. RAPD primers differed in their amplified loci from just ten loci with OPF-06 and OPM-01 primers to 14 different bands with OPD-07 primer.
12. For S4 strain, polymorphism percentage ranged from 50% primer OPF-06 to 100% for primers OPD-16 and OPF-05. The mean of band frequency % per primer ranged from 32.69% to 71.87%. RAPD primers differed in their amplified loci from just eight loci with OPF-06 primer to 14 different bands with OPF-05 primer.
13. For S5 strain, polymorphism percentage ranged from 71.41% primer OPF-06 to 100% for primer OPF-05. The mean of band frequency per primer ranged from 37.5% to 71.42%. RAPD primers differed in their amplified loci from seven loci with OPF-05 and OPF-06 primers to 11 different bands with OPD-16 primer.
14. The RAPD molecular marker confirmed a presence of a difference between the control and treatments.