| Because of the poor root regeneration ability of Upland Cotton (Gossypium hirsutum L.) and the difficulty in keeping the plants lively after transplantation, we often adopt the nourishment pot transplanting and the soil protecting membrane techniques to resolve the problem and make the growth and developmental period be earlier during the cotton growing season in the central area of China. Even so, the recovery period of the transplanted young plants still at least lasts 15 days, hence not only affecting the earlier ripening of cotton, also affecting the ratio of the three kinds of bolls (bolls set before hot summer days, bolls set during hot summer days, and the bolls set during Autumn). Therefore breeding new cotton varieties with the strong rooting ability is an important way to overcome the barrier that we meet at the early stage of cotton production.The Ri plasmid of Agribacterium rhizogens contains a region called rooting loci (rol genes) that can induce adventitious root formation at the site of the bacterium infection. Inducing of one or several rol genes to plant genome demonstrated that the rooting ability of transgenic plants was greatly improved. Transgenic cotton lines transformed with artificially reconstructed rol genes expressed strong rooting ability both in laboratory and in field. In this study, molecular analysis, drought tolerance and seed dormancy of the transgenic cotton lines, which we obtained previously, were carried out to evaluate the stability of the transgene expression and the performs of the transgenic lines against abiotic stress. The main research results were as followings:1. Total DNA was prepared from the leaf extracts of the rol transgenic lines and the control by modified CTAB method. PCR experiments were carried out with the specific primers designed in accordance with rolB and NPTll sequences to prove the existence of the transgenes in cotton genome. The result showed that all the samples taken from the transgenic lines presented anticipated fragments of target genes, indicating that the rolB genes had stably integrated into the genomes of all the transgenic lines.2. RNA was also isolated from the leaf extracts of the rolB transgenic lines and the control. The results of RNA/DNA hybridizations presented that all the samples, excepting the control, showed two bands of positive signals probed with the PCR fragments of rolB and one band while probed with that of NPTII, demonstrating that both of the transgenes expressed stably at RNA level in the genome of transgenic lines.3. Results from the investigation of drought tolerance of transgenic cotton lines presented that: (1) the transgenic lines 7343,7346,7342 and 7351 did not show significant difference from the check test variety 4105 in seedling mortality after one month of transplantation, young leaf sizes, praline content and water pressure of leaf cells during the period of florescence. (2) Survival percentages of seedlings of four transgenic lines varied from 50% to 75% under the conditions of drought stress, these lines fell in the category of drought tolerance, whereas that of the control variety 4105 is 45%. (3) No significant differences for the diameter at the base of stems were detected between 7343 and 4105, 7346 and 4105, 7342 and 7351; but stem diameter of 7343 was larger than that of 7346, 7342 and 7351; that of 7343 was wider than those of 7351 and 7342. (4) Dry weight ratio of root/shoot of 7343,7342 and 7351 were higher than those of 7342 and the control 4105, the differences reached significant levels. Together with all these results manifested that the rolB transgenic lines were stronger than the control variety 4105 in the development of root systems, and thus expressed an expanded capacity in drought tolerance.4. Two trials were designed to investigate the seed dormancy of the transgenic lines. Trial A was that the seeds were germinated under the condition of 25℃in a incubator, without taking any measure to relieve the seed dormancy. Trial B is that the seeds were placed under the condition of 40℃for 24 hours to get rid off the dormancy before germination under a normal temperature. The germination capacities of the seeds from 4 transgenic lines 7351,7342,7343 and 7347 together with the control 4105 in trial A were higher than those of all the seeds in trial B, but the percentages of seed germination in trial A were lower than those in trial B. The germination capacities and the germination percentages of the seeds from four transgenic lines in trial A were lower than that of the control 4105, indicating that the seed dormancy of all four transgenic lines were higher than that of the control. The seed germination percentages of 7351,7342,7343 and 4105 varied from 30% to 50% , fell in the category of moderate dormancy. The germination percentages of the line 7347 varied from 5% to 30%, it belongs to a strong dormant line. The seed germination percentage of the line 7351 was highest in trial B, but the seed germination capacities of four transgenic lines were lower than that of the control. The differences of the transgenic lines in germination capacity and percentage possibly attributed to the results of that the rolB gene integrated into the different sites of the cotton genome.
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