| Under environmental stress, plant cells usually accumulates some compatible solutes(also regarded as osmotin) in order to alleviate the injury derived from environmental stress. Glycine betaine (GB) is regarded as an extremely effective compatible solute, therefore researchers pay much attention to the bio-engineering of GB. The BADH encoding BADH which catalyzes betaine aldehyde (BA) into GB stands the essential position in the synthesis of GB. Firstly, we determined the OA and photosynthesis of flag leaves in strong and weak drought resistant wheat varieties, and then analyzed the expression level of BADH, BADH activity and GB content of flag leaves in two wheat varieties at different stage under drought stress and dissertated the physiological function of GB in molecular biology. Secondly, some physiological parameters such as the BADH activity, GB content and photosynthesis of transformed wheat plants with BADH from spinach under drought stress were studied; Finally, we cloned complete sequence of the BADH cDNA from the leaves of strong drought resistant cultivar Hanfeng9703, constructed the expression vector and acquired transgenic tobacco plants. The results are followed:1. Two winter wheat(Triticum aestivum L.)varieties( Drought-resistant cultivar Hanfeng 9703 and Drought-sensitive cultivar Shannong 215953) were used to study the OA, Pn and photochemical activity of PSII complex as well as the expression level of BADH and GB content in flag leaves at different stage under long-term field drought stress. OA and RWC of Hanfeng 9703 were higher than those of Shannong 215953 at three stages, OA atseed filling stage was the highest which increased 0.058and 0.284MPa comparing to that of flowering stage and milk ripening stage respectively. Drought stress resulted in the decrease of Pn, Fv/Fm and φPSII of two wheat varieties at three different stage; But Pn, Fv/Fm, φPSII of Hanfeng 9703 were higher than those of Shannong 215953 under drought stress. Drought stress aggravated the depression of Pn in midday in leaves of two wheat varieties at milk ripening stage, PSII photochemical activity of leaves of Hanfeng 9703 were higher than those of Shannong 215953; Higher osmotic adjustment of Hanfeng 9703 maintained Pn and PSII photochemical activity which were beneficial for the higher production, it was concluded that the higher GB content in Hanfeng9703 might play pivotal role in enhancement of stress resistance. Northern blot results showed that continuous drought stress leads to the increase of the BADH expression at seed filling stage in two varieties, severe drought stress results in the decline of expression level at milk ripening stage, the BADH expression level of flag leaves in Hanfeng 9703 were obviously higher than that in Shannong 215953. The changes of BADH activity and GB content was similar to the change of BADH expression in two varieties. After moderate drought stress at seed filling stage, the higher BADH expression of leaves in Hanfeng 9703 leaded to the higher GB content in comparason to Shannong 215953 which was one of the major reasons of keeping stronger PSII photochemical efficiency in Hanfeng 9703 under drought stress. It can be concluded that the GB content and BADH activity in flag leaves could be used as the reference criterion for resistance appraisal of crop germplasm. The tolerance to the low temperature, drought and anti-photoxidation stress in transgenic wheat plants (line-99T1,99T4,99T6) transformed with BADH from Atriplex hortensis were higher comparing to those of wild-type plants(4185); The stronger OA, higher anti-oxidation enzymes activity and faster turnover of D1 protein were main protective mechanism in 99T4 and 99T6, Furthermore, the higher GB content in leaves may play important role in the enhancement of stress tolerance.. The leaf electrolyte leakage in 99T4 and 99T6 were lower than those in 4185 and 99T1.Under low temperature conditions, compared to the wild-type plants, the osmotic adjustment in 99T4 and 99T6 were 17.3% and 8.2% h...
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