Comparative effects of glycinebetaine on the thermotolerance incodA- andBADH-transgenic tomato plants under high temperature stress

Key message We propose thatcodAtomato plants exhibited higher degrees of enhanced thermotolerance thanBADHtomato plants, and H(2)O(2)as a signaling molecule also plays an important role in heat resistance. Betaine aldehyde dehydrogenase (BADH) and choline oxidase (COD) are key enzymes in glycinebetaine (GB) synthesis. In this study, two kinds of transgenic tomato plants, which were transformed withBADHgene andcodAgene, respectively, were used to explore their thermotolerance. Our results showed that the levels of GB in leaves of the fourteen independent transgenic lines ranged from 1.9 mu mol g(-1)fresh weight to 3.4 mu mol g(-1)fresh weight, while GB was almost undetectable in leaves of WT plants. CO(2)assimilation and photosystem II (PSII) photochemical activity in transgenic plants were more thermotolerant than WT plants, especially thecodA-transgenic plants showed the most. Significant accumulation of hydrogen peroxide (H2O2), superoxide anion radical (O-2 center dot(-)), and malondialdehyde (MDA) were more in WT plants than transgenic plants, while this accumulation incodA-transgenic plant was the least. Furthermore, the expression of the heat response genes and the accumulation of heat shock protein 70 (HSP70) were found to be more in transgenic plants than that in WT plants during heat stress, as well as showing the most expression and accumulation of HSP70 in thecodA-transgenic plants. Taken together, our results suggest that the enhanced thermotolerance in transgenic plants is due to the positive role of GB in response to heat stress. And interestingly, in addition to the major role of GB incodA-transgenic plants, H(2)O(2)as a signaling molecule may also play an important role in heat resistance, leading to higher thermotolerance compared toBADH-transgenic plants.