ORIGINAL PAPER Genetic Engineering of Glycine Betaine Biosynthesis Reduces Heat-Enhanced Photoinhibition by Enhancing Antioxidative Defense and Alleviating Lipid Peroxidation in Tomato Meifang Li & Zhimei Li & Shufen Li & Shangjing Guo & Qingwmeng Meng & Gang Li & Xinghong Yang # Springer Science+Business Media New York 2013 Abstract Glycine betaine (GB) is a compatible solute that accumulates rapidly to enhance heat tolerance in many plants grown under heat stress. In this study, a BADH gene (betaine aldehyde dehydrogenase) from spinach was intro- duced into tomato (Lycopersicon esculentum cv. ‘Money- maker ’ ) via Agrobacterium-mediated transformation. Transgenic tomato lines expressing BADH exhibited higher capabilities for GB accumulation. Chlorophyll fluorescence analysis of wild type (WT) and transgenic plants exposed to heat treatment (42 °C) showed that transgenic plants exhibited higher photosynthetic capacities than WT plants. This finding suggests that GB accumulation increases toler- ance to heat-enhanced photoinhibition. This increased toler- ance was associated with an improvement in D1 protein content, which accelerated the repair of photosystem II (PSII) following heat-enhanced photoinhibition. Significant accumulations of hydrogen peroxide (H 2 O 2 ) and superoxide radical (O 2 - ) were observed in WT plants under heat stress. However, these accumulations were much less for the trans- genic plants. An important finding reported herein is that exogenous GB cannot directly reduce the content of reactive oxygen species (ROS). In accordance with a lower relative electrolyte conductivity and malondialdehyde content, the activities of antioxidant enzymes were higher in transgenic lines than in WT plants, indicating that the degree of mem- brane injury in the transgenic plants was lower compared to the WT plants. These results suggest that GB accumulation in vivo cannot directly eliminate ROS. Rather, higher anti- oxidant enzyme activities must be maintained to lessen the accumulation of ROS in transgenic plants and to decrease the degree of membrane injury. Keywords Glycine betaine . Photoinhibition . Tomato . Reactive oxygen species . Antioxidant enzyme activities Introduction Glycine betaine (GB) is a compatible solute that accumu- lates rapidly in several plants under various environmental stresses (Chen and Murata 2011). Two biosynthetic path- ways lead to the generation of GB (Chen and Murata 2002; Rasheed et al. 2011). In the majority of plants, GB is synthesized from choline by a two-step oxidation reaction: choline is oxidized to betaine aldehyde, which is dehydrogenated to yield GB. The first oxidation step is catalyzed by choline monooxygenase (CMO), and the sec- ond by betaine aldehyde dehydrogenase (BADH) (Chen and Murata 2002; Takabe et al. 2006). In the soil bacterium Arthrobacter sp., GB is synthesized from choline by a single enzyme, choline oxidase, which is encoded by the codA gene (Chen and Murata 2002). The enhancement of heat tolerance upon genetic transformation with GB synthesis was previously studied in Arabidopsis (Alia et al. 1998). GB accumulation in vivo as a result of the introduction of the BADH gene into tobacco enhances both growth and photosynthesis tolerance to high temperature in transgenic plants (Yang et al. 2005, 2007; Li et al. 2011). In vivo studies on the accumulation of GB via genetic engineering have demonstrated that GB maintains functional membranes under cold (Deshnium et al. 1997; Zhang et al. 2012) and freezing (Sakamoto and Murata 2000) stresses. The accu- mulated GB stabilizes quaternary structures and stimulates Meifang Li, Zhimei Li, and Shufen Li contributed equally to this work M. Li : Z. Li : S. Li : Q. Meng : G. Li : X. Yang (*) State Key Laboratory of Crop Biology, Shandong Key Laboratory of Crop Biology, Shandong Agricultural University, Taian 271018, China e-mail: xhyang@sdau.edu.cn M. Li : S. Guo College of Life Science, Liaocheng University, Liaocheng 252000, China Plant Mol Biol Rep DOI 10.1007/s11105-013-0594-z