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Abstract Two experiments were designed to assess the effectiveness of exogenous ascorbate (Asc), salicylate (Sa), and silicate (Si) and /or nanosilicon to reduce the effect of water and salt stresses, on potato (Solanum tuberosum L.) and tomato (Solanum lycopersicum L.), respectively. The open field trial Forty days-old potato plants were exogenously applied with ascorbate (Asc) at (0, 0.25, 0.5 and 1.0 mM), salicylate (Sa) at (0, 0.25, 0.5 and 1.0 mM) , and silicate (Si) at (100, 250, and 500 ppm) to study its efficacy under water deficit regimes; i.e. three days interval (control) , four days interval (4DI), and five days interval (5DI) and their interaction. Leaf samples were collected to measure different biochemical parameters. Effect of applied treatments under studied stress on photosynthetic pigments Results of ascorbate treated group showed that ascorbate (0.25 mM) showed the highest values of Chl a and b contents compared with other concentrations at both 4DI and 5DI water regimes. In salicylatetreated group, the highest values of Chl a and b contents were recorded by Sa (1.0 mM), at the control water regime, also Sa (1.0 and 0.25 mM) increased Chl a and b contents at control and 4DI. In silicate-treated group, application of silicate (100 ppm) had the more pronounced effect compared with other concentration where it is improved Chl a the three water regimes and Chl b at 4DI and 5DI water regimes. Effect of applied treatments under water deficit stress on Carotenoids Data of ascorbate treated group showed that ascorbate (0.25 mM) represented the highest value of carotenoid content at 4DI water level. Regarding salicylate-treated group, Sa (0.5 mM) recorded the highest carotenoids content at 4DI and 5DI water levels. In silicate-treated group, Si (100 and 250 ppm) increased carotenoids content at 4DI and 5DI water levels. 139 SUMMARY Amal Abdelmonem Mostafa (2019), Ph.D., Fac. Agric., Ain Shams Univ. Effect of applied treatments under water deficit stress on free proline In ascorbate-treated group, at control water regime, Asc at (0.25, 0.5, and 1.0 mM) increased proline content compared to control, in contrast, these concentration led to reduction of the mean free proline content At 5D water level. Regarding salicylate application, Sa at (0.5 and 1.0 mM) decreased proline content compared to control at 4DI and 5DI water levels in addition to Sa (0.25mM) at 5DI. Concerning silicate-treated group, a reduction in free proline content was detected by; Si (100 and 250 ppm at control level of water, Si (100, 250 and 500 ppm) at 4DI water level and Si (100 and 500 ppm), at 5DI water level. Effect of applied treatments under water deficit stress on (MDA) In ascorbate-treated group, a reduction in MDA content was occurred by application of Asc 1.0 and Asc 0.25 under 4DI and 5DI water regime respectively. Concerning application with salicylate, the results showed that the increment in MDA content with water deficit was not affected significantly by application of salicylate, however, Sa (0.25 mM) increased MDA content at 4DI. Regarding silicate treatments, the results showed similar effect at control, 4DI and 5DI water regime, whereas Si 500 ppm slightly decreased MDA content by 2.48, 20.84 and 10.21%, respectively under the studied water regimes. Effect of applied treatments under water deficit stress on plant dry matter In ascorbate-treated group, Asc (0.5 mM) revealed the highest dry matter percentage under control water regime, while the same concentration detected the least dry matter at 5DI water regime. The result of salicylate-treated group showed, Sa (0.5 and 0.1 mM) improved plant dry matter by 17.83 and 10.05%, at control water regime, respectively. However Sa (0.5 and 0.25 mM) reduced the plant dry matter at 4DI and 140 SUMMARY Amal Abdelmonem Mostafa (2019), Ph.D., Fac. Agric., Ain Shams Univ. 5DI water regimes, respectively. Silicate application affected plant dry matter significantly, Si (250 ppm) increased plant dry matter percentage at control and 5DI water levels. Silicate at (100, 250, 500 ppm) increased plant dry matter by 25.52, 25.36 and 10.89 % at 4DI water level, respectively. Effect of applied treatments under water deficit stress on tuber dry matter Ascorbate application showed no significant differences on tuber dry matter percentage. Regarding salicylate application, the data showed the same rank however, almost all salicylate concentrations tended to enhance tuber dry matter percentage under all water regimes. In the case of Si-treated plants, application with silicate under water deficit conditions showed no marked differences on tuber dry matter percentages. Effect of applied treatments under water deficit stress on tuber yield Ascorbate-treated group showed that Asc at (0.25 mM) improved tuber yield by 50.32%, 25.79% and 73.38% respectively under control, 4DI and 5DI water levels,. Ascorbate at (0.5 mM) increased tuber yield by 19.95 and 50.44%, under both control and 5DI water regimes. In addition, (Asc 1.0 mM) enhanced plant tuber yield by 6.7 and 24.46% under 4DI and 5DI, compared to its control. In silicate-treated group the effect of silicate was fluctuating between increment and decrement at both control and 4DI water level. However, all silicate concentration (0.25, 0.5 and 1.0 mM) improved tuber yield at 5DI water regime by 65.61, 21.8 and 33.33 % compared to its control, respectively. The greenhouse trial The experiment was carried out to study the effect of silicon in nano particle form (Si NPs) on transgenic tomato lines expressing CaMV35S-ySpdSyn; i.e. C4 and C15, along with their azygous control 141 SUMMARY Amal Abdelmonem Mostafa (2019), Ph.D., Fac. Agric., Ain Shams Univ. (L5) under 200 mM NaCl stress. Leaf samples were collected at three time points; before starting salt (Zero), 14 day after starting salt (14 DAS), and 14 days after recovery with tap water (Recovery). Effect of Si NPs on chlorophyll content in tomato genotypes under salt stress Effect of Si NPs on total chlorophyll content (SPAD), showed that L5 represented more chlorophyll compared with C4 and C15 lines. Salt stress tended to increase the level of chlorophyll, whereas Si NPs did not show significant differences at zero and 14 DAS whoever, it significantly increased chlorophyll content in C4 line at recovery phase in unstressed plants. Effect of Si NPs on free proline in tomato genotypes under salt stress Effect of Si NPs on free proline exhibited that L5 has more proline content compared with C4 and C15 transgenic lines. At zero time, Application with Si NPs enhanced proline content significantly in both L5 and C15. At 14 DAS, salt exposure resulted in a dramatic enhancement in proline content, proline increment was more pronounced in C4 and C15 lines compared with L5, however, application with Si NPs decreased proline content in these lines. At recovery phase, a sharp reduction in proline has been occurred compared with the previous phase (14 DAS), Si NPs reduced proline in C4 and C15 in unstressed and C4 in salt stressed plants. Effect of Si NPs on malonaldehyde (MDA) in tomato genotypes under salt stress The result indicated that at zero time point, Si NPs tended to reduce MDA content in all tested lines. At 14 DAS, salt applied plants accumulated more MDA content, whereas C4 and C15 slightly accumulated more MDA compared with L5. Also, Si NPs lead to a slight reduction in MDA content in C4 line. At recovery phase, in unstressed 142 SUMMARY Amal Abdelmonem Mostafa (2019), Ph.D., Fac. Agric., Ain Shams Univ. plants no significant differences was observed between treatments. In stress recovered plants Si NPs cause a reduction in C4 by 26 %. Effect of Si NPs on hydrogen peroxide (H2O2) in tomato genotypes under salt stress Effect of Si NPs on hydrogen peroxide (H2O2) showed that data of zero and 14 DAS confirmed that L5 had more H2O2 compared with the transgenic lines. At 14 DAS, salt addition resulted in an increment in H2O2 content ranging from 1.5 to 3.6 folds. Si NPs application reduced H2O2 in C4 subjected to salt. At recovery phase, in unstressed plants no significant differences was observed between treatments, while in the stress-recovered plants C4 + Si recorded the lowest value, however L5 + Si recorded the highest. Looking at the three points together, it is noticeable that, Si NPs reduced H2O2 in C4 line started at 24 h after applying Si NPs (Zero time) and continued after applying salt and at recovery period. Effect of Si NPs on electrolyte leakage EL% in tomato genotypes under salt stress Electrolyte leakage EL % at 14 DAS represented that, in unstressed plants, EL% was in normal level ranging from 8-11 % with no marked differences between genotypes or Si NPs treatment. In the saltstressed plants, salt application caused increment in EL% by 2.7- 4.1 folds between treatments. C4 and C15 lines without Si NPs had more leakage compared with L5, while Si NPs application promoted reduction in the leakage by 4.8, 19.77 and 15.6 % in L5, C4 and C15, respectively. Effect of Si NPs on minerals in tomato genotypes under salt stress Sodium content At zero time, no significant difference was observed among different treatments. At 14 DAS, in the unstressed plants no significant differences was observed. Meanwhile, in salt stressed plants, salt addition resulted in a sharp accumulation of Na+ in the leaves of all tested lines. In 143 SUMMARY Amal Abdelmonem Mostafa (2019), Ph.D., Fac. Agric., Ain Shams Univ. addition, C4 and C15 significantly accumulated more Na+ compared with L5. At recovery, in the unstressed plants, L5 showed less Na+ content compared with C4 and C15 lines, while Si NPs treatment did not show significant influence. In stress recovered plants, the transgenic lines along with Si NPs treatment were not associated with significant differences in Na+ content, however the transgenic lines still showed more Na+ content compared with L5. In conclusion, from the three time points, L5 accumulated less Na + compared with the transgenic lines, in addition the effect of Si NPs was not significant at the three time points. Potassium content At zero time, C15 showed less K+ compared with C4 and L5, however C4 plants recorded the highest values. At 14 DAS phase, in the unstressed plants, C4 and C15 showed higher K+ content compared with L5. In the salt stressed plants, K+ content decreased with salt addition. Also, no significant differences were obvious among different treatments; however C15 exhibited the highest K+ content compared with other lines. At recovery, both unstressed plants as well as stress recovered plants showed the same rank regarding K+ content. Calcium content No significant influence, at zero time, on Ca++ content was observed regarding transgenic lines along with Si NPs treatment and their interaction. At 14 DAS, L5 had more calcium content compared with transgenic lines. Also, existence of salt caused enhancement in calcium content compared with unstressed ones. The effect of Si NPs was not significant on Ca++ content. At recovery, in both unstressed and stressrecovered plants, transgenic lines showed higher Ca++ content compared with L5. 144 SUMMARY Amal Abdelmonem Mostafa (2019), Ph.D., Fac. Agric., Ain Shams Univ. In conclusion, transgenic lines represented less Ca++ at 14 DAS, while at recovery these lines accumulated more Ca++ than L5, furthermore salt stress resulted in accumulation of Ca++ in salt stressed plants. Magnesium content At zero time, C15 line exceeded other lines in Mg++ content, whereas Si NPs did not show significant influence on magnesium content. At 14 DAS, L5 showed higher Mg++ content compared with transgenic lines. Applied Si NPs decreased Mg++ content in all lines in the unstressed plants, however increased Mg++ content in L5 and C15 lines in the salt stressed plants. an enhancement in Mg++ content was observed by applying salt. At recovery phase, in the unstressed plants, there was no significant influence on Mg++ content between different treatments. However, in the stress-recovered plants, an obvious reduction on Mg++ content was recorded in plants after using tap water for recovery. Phosphorous content At zero time, no significant differences among lines were detected, while applied Si NPs reduced phosphorous content in case of L5 and C15 lines. At 14 DAS, in the unstressed plants, the differences in phosphorous content among different treatments were not obvious at this point. In salt stressed plants, NaCl addition caused reduction in phosphorous content. At recovery, unstressed plants, showed the same rank in P content. Stress recovered plants showed that higher phosphorous content, compared with unstressed ones. C15 line had more phosphorous content compared with other lines. Within transgenic lines Si NPs resulted in significant reductions in phosphorous content, whereas its effect on L5 resulted in increase in phosphorous content |