Photosynthetic response to dehydration and high temperature in trehalose-producing transgenic tobacco

Abstract

Transgenic tobacco plants harboring E. coli TPS (trehalose-6-phosphate synthase) gene (ots A) were generated by leaf disc transformation. Transgenic plants were identified by PCR, Northern hybridization, and trehalose synthesis. All lines of transgenic plants manifested stunted growth and extended generation time in varying degree. Transgenic plants typically exhibited some morphological changes in leaf shape and branching pattern. The stunted growth was not accompanied with early senescence or necrosis. Homozygous plants obtained in F2 generation were used to examine their photosynthetic responses to dehydration and high temperature. All transgenic plants showed enhanced tolerance against dehydration as shown by improved retention in fresh weight after PEG-treatment. However, decreases in water potential by dehydration through PEG-treatment were in parallel phase in both nontransformants and transgenic plants although the initial water potential was observed higher in all transgenic plants. Upon dehydration, decrease in Pmax occurred in similar phase in both nontransformants and transgenic plants, but no significant changes in Chl fluorescence parameters were observed in both nontransformants and transgenic plants. It appears that trehalose confers transgenic plants improved water retaining ability against dehydration, but without keeping their photosynthetic capacity. On the other hand, trehalose-producing plants showed improved ability of holding photosynthetic activity after heating at 40° ~ 45°C. Both Pmax and Chl fluorescence parameters (Fo and Fv/Fm) remained more favorable in transgenic plants after heat treatment than nontransformants. The results suggest that engineering trehalose-producing plants would be more effective in conferring enhanced tolerance against high temperature than dehydration in term of maintaining photosynthetic productivity.