الفهرس 
Identification of some salinity tolerance-specific genes in tomato hybridsOnly 14 pages are availabe for public view
 |  | from | 64 |  |  |
| | | from | 64 | | |
Abstract
This study was carried out at Sabaheya Station of the Agricultural Research center. Hybridization carried out between salt tolerant cultivar Edkawy with salt sensitive cultivar Castle rock and Budai torpe cultivar (its tolerance is not known), resulted Edkawy x Castle rock (ExC) and Edkawy x Budai torpe (ExB) F1 hybrids. The two hybrids and their three parents were used in salt treatment experiment to evaluate their response to salt stress by measuring some parameters. Salinity treatments started seven days after transplanting by irrigated plants with half strength Hoagland solution supplemented by NaCl in four salinity levels 2, 5, 10, 15 dS/m beside control tap water.
The main objectives of this study:
1- Investigation the effect of salt stress with three cultivars of tomato and their two hybrids.
2- Studying some physiological and biochemical traits which related by salt stress response of plants.
3- Using real-time PCR (rt-PCR) to investigate the expression of LeNHX1 gene.
The obtained important results can be summarized as follows:
1- Salt stress negatively affected vegetative plant growth by the increase the level of salinity in all tomato plants under study after three weeks of salt treatment.
2- The proline content in leaves of the three cultivars Edkawy, Castle Rock and Budai Torpe beside their two hybrids ExB and ExC showed significant rise with increased of salinity levels.
3- Castle Rock, cultivar responded more significantly to salinity than other genotypes. Two hybrids ExB and ExC have the highest proline content, after Castle Rock cultivar, ExC hybrid has a higher mean (14.09μmole) than ExB hybrid (11.95μmole). The Edkawy cultivar has the lowest mean (11.19μmole) followed by Budai Torpe (9.76μmole).
4- Genotypes were classified to two groups’ significantly different (P ≤ 0.0001) in their chlorophyll a contents, the two hybrids ExB and ExC have the highest means (23.29μg/ml and 24.32μg/ml respectively). Second group contained Edkawy and Budai Torpe cultivars with overall means 18.87μg/ml and 18.00μg/ml respectively (Figure 6a, Table 3). Castle Rock cultivar found in the first group with the two hybrids because its plants died in the fourth and fifth treatments subsequently its average was higher than in fact. There is non-significant difference among cultivars on their contents of chlorophyll b. There is no significant difference was found between the two hybrids (ExB and ExC) in total chlorophyll content and they have the highest average values 42.74μg/ml and 43.00μg/ml respectively. The hybrids is different significantly from the Edkawy and Budai Torpe cultivars, they have overall means 35.40 μg/ml and 35.26μg/ml respectively. from the previous results, we found that the two hybrids have better performance than their parents. Also, chlorophyll level was higher in salt-tolerant (Edkawy) cultivar than the salt-sensitive one (Castle Rock) in the three salinity levels 0, 2, 5dS/m. The chlorophyll a affected more with increasing salt stress. We may consider the chlorophyll a as an indicator for salt tolerance than chlorophyll b in our study.
5- Results indicated that Na+ ion increase with salinity increase, despite K+ ion amount decreases. Regarding to the main effects of genotypes, there is a significant difference between genotypes. ExB hybrid has the highest overall mean, followed by edkawy cultivar, ExC hybrid and Budai Torpe. We detected significant interaction between genotypes and stages of stress on its Na+ content in leaf tissue. In unstressed conditions (T1), the tolerant Edkawy cultivar has the highest Na+ concentration in leaf tissue (19.00 mg/L) and there is non-significant difference between Budai Torpe, Castle Rock cultivars and ExB hybrid. Results from statistical analysis indicated that levels of salinity (P ≤0.0001) and genotypes (P ≤0.0001) had a significant overall effect on K+ concentration in leaf tissues. ExC hybrid has the lowest overalls mean. We detected significant genotypes x salinity levels interaction for K+ concentration in leaves. Edkawy cultivar has the highest mean followed by Budai Torpe. We mention that there is no significant difference between Budai Torpe and Castle Rock in their K+ concentration in leaf of unstressed plants. By increasing salinity, K+ concentration slightly decreased in all genotypes. By treatment T3 (5dS/m), K+ decreased to the half (comparing with control plants..T1). There is no significant difference between Edkawy, Budai Torpe, Castle Rock cultivars and ExB hybrid. ExC hybrid has the lowest mean of K+ concentration in leaf. The highest mean in the fourth treatment (10dS/m) was for ExB hybrid which non-significantly different from Edkawy and Budai Torpe cultivars. The last treatment recorded non-significant difference between four genotypes. Na+/K+ ratio increases with salinity level increase as a result for increasing of Na+ concentration in tomato leaves in this study.
6- A significant interaction was found between genotypes x levels of salinity on Na+ concentration of roots. Na+ concentration in Edkawy cultivar increased non- significantly from T1 to T2. Also, it increased non-significantly from T2 to T3. Then it increased significantly at salinity level 10dS/m (T4) .finally, Edkawy plants increases non-significantly in their concentration of Na+ at the highest salinity level 15dS/m There are no a significant difference between genotypes under the control conditions (T5). The significance increase (29.33mg/L) in ExB hybrid occurs at the 5dS/m salinity level. Similar result with second hybrid ExC (22mg/L) occurred at 5dS/m. The significant increase of Na+ concentration for Budai Torpe cultivar occurred at T2 (18.33 mg/L). We found from statistical analysis that there is no significant interaction between salinity levels and genotypes on K+ concentration in root tissue. the ExB hybrid and Edkawy cultivar have the highest overall means 23.66mg/L and 22.73mg/L respectively, followed by Budai Torpe 17.33mg/L , ExC 16.66mg/L and Castle Rock 14.66mg/L (Figure 15). K+ concentration in root tissue decreased significantly with increasing salt stress. from our results we recorded that there is a significant increase in Na+/K+ ratio in roots with increasing of salt stress in all five genotypes. The two hybrids (ExB and ExC) have the highest overall means (1.76 and 1.69 mg/L), followed by the three cultivars (Budai Torpe, Castle Rock and Edkawy) (1.30, 1.22 and 1.04mg/L respectively).
7- The results of rt-PCR showed that the relative gene expression of LeNHX1 stress related gene was increased when the plants were treated with NaCl at concentrations (0, 5, 10 dS/m). However, the gene expression level was found to be concentration-dependant and tissue dependant, when it was determined in both leaf and root tissues using RT-quantitative PCR technique. In Edkawy and the two hybrids leaf tissues, it was found that the (T3) treatment showed enhanced the expression of LeNHX1 up to 4 fold increase, while T4 which is a harsh treatment caused increase in the expression level up to 2.5 fold. This fold change increase is in agreement with the previously published data indicating that the gene expression level was associated with salt tolerance traits. In addition, the gene expression level in the root tissues was up to 3 fold increase, particularly, in the two hybrid tissues followed by the Edkawy variety with 2.6 fold increase in the gene expression level. The two other cultivars Budai Torpe and Castle Rock showed marginal fold change increase (1.2) which is of a non-significant effect. It is noteworthy that however the gene expression level in the root tissues was dropped in Edkawy plants but it was still higher than the control plants, but the plants begin deteriorating.
This study revealed to that the two fybrids have the best performance than their parents. Additionly they need more molecular and breeding studies to prove their salt tolerance from all aspects.