الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 186 |  |  |
| | | from | 186 | | |
Abstract
Stevia rebaudiana is a medicinal plant, a perennial herb that belongs to the family Asteraceae widely used as a sweetener from ancient times in South American. The sweetening power of the leaves comes from the diterpenoid glycoside generally known as steviol glycosides, which are about 200 times sweeter but much less calorific than sugar. The problem with this plant is related to the poor germination of seeds causing scarce and high cost of plant materials. Endophytes being a part of the plant-associated microorganisms, endophytic bacteria live intercellular spaces or inside the plant cells at least part of their lifetime without causing visibly harmful effects on the host. Four endophytic bacterial isolates from Stevia leaves were tested for ability of plant growth promoting traits and were applied for the biopriming seeds and plantlets with gibberellin and Azosperillium brasilense to test their effect on developing stevioside content, other bioactive compound and the expression of genes responsible for stevioside production. The aim of this study is the isolation of endophytic bacteria from Stevia leaves, test their ability for plant growth promoting traits and apply on other group of Stevia plant and seed biopriming to enhance germination. The results were shown that treatments were effect significantly on bioactive compounds, stevioside content and the expression of genes. The best result in seed biopriming was B. cereus SA1 + B. paralicheniformis SA3 and in plantlet treatments were T10 B. paramycoids SA4 + A. brasilense and T15 B. cereus SA1+ B.licheniformis SA2 + B. paralicheniformis SA3+ B. paramycoids SA4+ A.brasilense + Gibberellin. During this study, the obtained results were summarized in the following items: 1- Endophytic bacteria isolated from Stevia leaves on LB agar media, tested for plant growth promoting traits and molecularly identified by 16srRNA. 2- The isolates applied for plantlets to increase stevioside contents. Plant growth parameters, carbohydrates, protein, antioxidants assay, antioxidants enzymatic assay were determined physiologically and HPLC analysis of stevioside content. The expression of genes responsible for stevioside production were determined by quantitative real time PCR. 3- Four endophytic bacteria isolated from Stevia leaves give positive results of the most plant growth promoting traits tests. 4- Applied for plantlets and seeds as a bioprimer. 5- Results proved that treatments effect on stevioside contents and bioactive compounds, these results were significantly agreed with gene expression assay as the gene expression increase compared with control. 6- The best result in seed biopriming was B. cereus SA1 + B. paralicheniformis SA3 7- Plantlet treatments results showed that treatment effect on morphological parameters (shoot length, root length, plant length, water content, fresh and dry weight) and the biochemical tests of plant such (total carbohydrates, total soluble sugars), pigments(chlorophyll a, chlorophyll b, carotenoids and total pigments), enzymatic antioxidants( polyphenol oxidase, peroxidase and catalase), non-enzymatic antioxidant (phenolics, flavonoids, total antioxidant activity DPPH and total antioxidant capacity). 8- The biochemical results and morphological results supported by HPLC results of stevioside content and the genes responsible for synthesis of steviols. 9- The best treatments results were T10 B. paramycoids SA4 + A. brasilense and T15 B. cereus SA1+ B.licheniformis SA2 + B. paralicheniformis SA3+ B. paramycoids SA4+ A.brasilense + Gibberellin. 10- Four isolated endophytic bacteria from S.rebaudiana were tested for their plant growth promoting traits and results was that isolates had the ability for production of most traits and identified by 16s rRNA and submitted on gene bank. 11- Applied for two applications: Seed biopriming by endophytic bacterial isolates in single strain and co-culture between strains results were significant as the germination percentage increased from 5% to 40%. 12- The treatments showed effective results in growth parameters and biochemical tests because of plant growth promoting hormones secreted by PGPB and GA3 significantly increased the stem length, stem dry weight in Stevia and total soluble sugar content increased. 13- Gene expression showed significant results; the results were agreed with most of biochemical test, which prove that all treatments had a great effect and can be used for promoting S.rebaudiana, increasing their bioactive compound content and its expression of genes.