This study describes the impact of sorbitol on plantlets regeneration frequency (PRF) of four rice cultivars (japonica, Oryza sativa L.) both of which mature and immature embryo-derived calli were investigated. The variance analysis results showed that PRF of the three elite upland rice cultivars, Handao297 (HD297), Handao502 (HD502), Handao65 (HD65) and one lowland rice cultivar Zhongzuo93 (ZZ93) were significantly increased with addition of appropriate amount of sorbitol in culture media. Supplementing appropriate sorbitol in the media of a continous culture from induction and maintenance to regeneration for mature embryo-derived calli could improve PRF dramatically, originally from 27.6% up to a maximum of 71.8%. Especially to low regenerative capacity (LRC) cultivar HD65, the PRF was increased over 7-fold (from 9.7% to 74.0%). The optimum concentrations of sorbitol for calli induction, subculture and differentiation were 5, 20 and 40 g/l, respectively. Adding sorbitol, only in maintenance media at concentration of 20 g/l, also enhanced the PRF greatly in all the cultivars from 27.6% to 43.3%. Similar results were observed when incorporating with maltose in regenerating media both in immature and mature embryo-derived calli. The optimal concentration was 25 g/l sorbitol + 20 g/l maltose and 20 g/l sorbitol + 25 g/l maltose, respectively. HD297 appeared to be the most responsive genotype compared to other cultivars in PRF, 99.2% in immature embryoderived calli and 76.8% in mature embryo-derived calli. The results and relevant conclusions might be valuable to establish an efficient plant regeneration system from somatic embryogenesis culture in upland rice.
In this study, Chinese upland rice cultivars including Handao297 and Handao502 were transformed with the anti-herbicide bar gene in order to achieve efficient weed control. PCR amplification, Southern blot analysis and field Basta resistance identification in early T 0 , T 1 , and late generation T 6 and T 11 -T 13 illustrated that the exogenous bar gene had been integrated into the genome of the upland rice varieties with stable expression in successive generations. Different transformants had a different gene copy numbers, which was not related to Basta resistance. Some of the transgenic lines showed gene silencing, whereas multiple copies of the bar gene were observed in other late generation transgenic lines. Basta resistance can thus be inherited stably among generations, and an optimal Basta concentration and selective pressure are suitable for resistance segregation and breeding of homozygous progenies with high resistance. After three generations of successive Basta resistance selection in 207 T 0 plants, we obtained 555 T 3 lines. Comprehensive identification and selection for Basta resistance, drought resistance, yield, and other agronomic traits in nine generations yielded two promising transgenic lines, HD297T-31 and HD297T-523. Although both varieties were resistant to 0.1 % Basta, HD297T-31 possessed high (100 %) resistance to Basta while HD297T-523 showed moderate (95 %) resistance. Moreover, during the reproductive stage, the stems, sheaths, leaves, and panicles of HD297T-31 were immune-highly resistant to highly-moderately resistant to 0.5 % Basta, whereas, they were highly resistantmoderately resistant to 1 % Basta. HD297T-523 was immune-highly resistant and immune-highly resistant to 0.5 and 1 % Basta respectively. The plant and stem percentage sensitive to 0.5 % Basta was lower than 1 and 3 % respectively. Since HD297T-31 showed isozygosity, it could be used as a new variety in production.
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