Agrobacterium mediated transformation has been widely used for research in plant molecular biology and for genetic improvement of crops exploiting its tremendous ability to transfer foreign DNA to plants. In this study, the transformation efficiency of five Agrobacterium tumefaciens strains GV2260, LBA4404, AGL1, EHA105, and C58C1 was evaluated in Nicotiana tabacum L. cultivar Samsun. The Agrobacterium strains contained the recombinant binary vector pBin19 harboring beta-glucuronidase uidA gene under 35S promoter. Neomycin phosphotransferase (nptII) gene was used as a selectable marker at a concentration of 100 mg L-1 kanamycin. The expression of uidA gene in regenerated T0 plants was firstly analyzed by GUS histochemical analyses and later on confirmation of presence of the nptII and uidA genes in regenerated plants was determined by PCR. The highest transformation rate (20%) was obtained with the Agrobacterium strain LBA4404, followed by EHA105, GV2260, C58C1 and AGL1. The higher transformation efficiency achieved in our studies make LBA4404 Agrobacterium strain optimal for functional genomics and biotechnological applications in tobacco plants.

Most of the commercialized Bt crops express cry genes under 35S promoter that induces strong gene expression in all plant parts. However, targeted foreign gene expression in plants is esteemed more important as public may be likely to accept 'less intrusive' expression of transgene. We developed plant expression constructs harboring cry1Ac gene under control of wound-inducible promoter (AoPR1) to confine Bt gene expression in insect wounding parts of the plants in comparison with cry1Ac gene under the control of 35S promoter. The constructs were used to transform four Turkish cotton cultivars (GSN-12, STN-468, Ozbek-100 and Ayhan-107) through Agrobacterium tumefaciens strains GV2260 containing binary vectors p35SAcBAR.101 and AoPR1AcBAR.101 harboring cry1Ac gene under control of 35S and AoPR1, respectively. Phosphinothricin (PPT) was used at concentration of 5 mg L-1 for selection of primary transformants. The primary transformants were analyzed for transgene presence and expression standard molecular techniques. The transformants exhibited appreciable mortality rates against larvae of Spodoptera exigua and S. littoralis. It was found that mechanical wounding of T 1 transgenic plants was effective in inducing expression of cry1Ac protein as accumulated levels of cry1Ac protein increased during post-wounding period. We conclude that use of woundinducible promoter to drive insecticidal gene(s) can be regarded as a valuable insect-resistant management strategy since the promoter activity is limited to insect biting sites of plant. There is no Bt toxin accumulation in unwounded plant organs, seed and crop residues, cotton products and by-products, thus minimizing food and environmental concerns.

Cotton (Gossypium hirsutum L.) is the most significant cash crop and backbone of global textile industry. The importance of cotton can hardly be over emphasized in the economy of cotton-growing countries as cotton and cotton products contribute significantly to the foreign exchange earnings. Cotton breeders have continuously sought to improve cotton's quality through conventional breeding in the past centuries; however, due to limited availability of germplasm with resistant to particular insects, pests and diseases, further advancements in cotton breeding have been challenging. The progress in transformation systems in cotton paved the way for the genetic improvement by enabling the researchers to transfer specific genes among the species and to incorporate them in cotton genome. With the development of first genetically engineered cotton plant in 1987, several characteristics such as biotic (insects, viruses, bacteria and fungi) resistance, abiotic (drought, chilling, heat, salt), herbicide tolerance, manipulation of oil and fiber traits have been reported to date. Genetic engineering has emerged as a necessary tool in cotton breeding programs, strengthening classical strategies to improve yield and yield contributing factors. The current review highlights the advances and endeavors in cotton genetic engineering achieved by researchers worldwide utilizing modern biotechnological approaches. Future prospects of the transgenic cotton are also discussed.

In order to address biosafety concerns regarding the constitutive expression of foreign genes in crops, we applied a strategy aimed at confining foreign gene expression in insect wounding sites of cotton. For this purpose, a plant expression construct was designed by cloning the AoPR1 promoter (pathogenesis-related protein gene isolated from Asparagus officinalis) upstream from the insecticidal gene cry1Ac. The Turkish cotton cultivar cv. STN-468 was transformed using the Agrobacterium tumefaciens strain LBA4404 containing the recombinant binary vector pRD400 harboring cry1Ac under a wound-inducible promoter. The neomycin phosphotransferase (nptII) gene was used as a selectable marker at a concentration of 100 mg/L. The primary transformants were analyzed for T-DNA integration and expression using standard molecular approaches. The efficacy of insecticidal gene control of the AoPR1 promoter was investigated using leaf bioassays with 2 nd instar larvae of Helicoverpa armigera and Spodoptera littoralis. Positive primary transformants from T 0 progeny were further raised under greenhouse conditions to obtain progeny (T 1 ). The introduced gene was properly inherited and expressed in T 1 progeny. The mechanical wounding of plants resulted in increased cry1Ac protein levels during 0-48 h of the wounding period. The transgenic lines exhibited appreciable levels of resistance against targeted insect pests in the leaf bioassays. The use of a wound-inducible promoter to drive insecticidal gene expression is a valuable insect resistant management strategy as gene expression will remain limited to the insect biting sites of plant and crop, food and environmental concerns can be minimized.

To date, there are few reports on the signaling and metabolic pathways of carbohydrates during cell culture (Huang and Liu, 2002;Huang et al., 2006). In addition to serving as an energy source, sucrose acts as a hypotonic and hypertonic osmotic agent in tissue