Transgenes that confer tolerance to abiotic stress may permanently transfer from transgenic crops to the nuclear genome of their weedy relatives which may result in drought tolerant superweeds [92] when the gene is inserted into the nuclear genome and the transgenic plant outcross with relative weeds. There is a great potential, therefore, for the genetic manipulation of key enzymes involved in stress metabolism in plants within plastids. Because plastid genomes of major crops including cotton and soybean have been Nicotiana tabacum nptII [153] Nicotiana tabacum uidA [154] Nicotiana tabacum Human somatotropin (hST) [155] Nicotiana tabacum cry [88] Nicotiana tabacum cry9Aa2 [84] Nicotiana tabacum Bar & aadA [156] Nicotiana tabacum Cor 15a-FAD7 [157] Nicotiana tabacum rbcL [55] Nicotiana tabacum DXR [158] Nicotiana tabacum aadA & gfp [60] Nicotiana tabacum Delta(9) desaturase [159] Nicotiana tabacum AsA2 [160] Nicotiana tabacum PhaG & PhaC [161] Nicotiana tabacum gfp [4] Nicotiana tabacum A1AT [162] Arabidopsis thaliana aadA [39] Solanum tuberosum aadA & gfp [40] Oryza sativa aadA & gfp [50] Solanum lycopersicon aadA [1] Solanum lycopersicon Lyc [42] Brassica napus aadA & cry1Aa10 [44] Brassica napus aadA [38] Lesquerella fendleri aadA & gfp [43] Daucus carota dehydrogenase (badh) [48] Gossypium hirsutum aphA-6 [49] Glycine max aadA [47] Petunia hybrida aadA & gusA [45] Lactuca sativa gfp [46] Brassica oleracea gus & aadA [163] Lettuce gfp [164] Populus alba gfp [51] Brassica oleracea aadA & uidA [74] Beta vulgaris aadA & uidA [165] Crocus sativus CstLcyB1& CstLcyB2a [166] Solanum melongena aadA [26] Arabidopsis thaliana pre-Tic40-His [167] Zea mays ManA [168] successfully transformed, this offers an exciting new approach to create transgenic plants with abiotic stress tolerance [93] . Therefore, the authors believe that there appears to be tremendous potential for increasing tolerance in plants to a number of stresses by expression of appropriate genes within plastids due to the maternal inheritance of transgenes that confer tolerance to abiotic stress. Plastid engineering had been successfully applied for the development of plants with tolerance to salt, drought [94] and low temperature [reviewed in 3]. Djilianov et al. [95] demonstrated that enhanced tolerance to abiotic stresses has been achieved when the gene was directed to plastid genome.