Targeting prokaryotic choline oxidase into chloroplasts enhance the potential of photosynthetic machinery of plants to withstand oxidative damage

Chloroplasts from plants of transgenic lines expressing prokaryotic choline oxidase gene (the codAps gene; GenBank accession number-AY589052) and wild-type of chickpea and Indian mustard were evaluated for their efficacy to withstand photoinhibitory damage, by exposing them to high light intensity (∼1200 μmol m−2 s−1 photon flux density) at 10 and 25 °C. Western analysis confirmed presence of choline oxidase in chloroplasts of only transgenic lines. The loss in PS II activity in chloroplasts of wild-type exposed to high light intensity was significantly higher than that in chloroplasts of transgenic chickpea as well as Indian mustard. Although, chloroplasts of both wild-type and transgenic chickpea as well as Indian mustard were more sensitive to photoinhibitory damage at 10 than at 25 °C, the damage recorded in chloroplasts harboring choline oxidase was significantly lower than those of wild-type. High light promotes H2O2 production in chloroplasts more significantly at low temperature (10 °C) than at 25 °C. We compared low temperature accelerated photoinhibition of chloroplasts with that caused due to exogenously applied H2O2. Although exogenous H2O2 accelerated high light intensity induced loss in PS II activity of chloroplasts of wild-type, it caused only a little alteration in PS II activity of chloroplasts from transgenic lines of both chickpea and Indian mustard, demonstrating that the chloroplasts harboring choline oxidase are better equipped to resist photoinhibition. We hypothesize that H2O2 produced by choline oxidase as a byproduct during synthesis of glycinebetaine is responsible for building stronger antioxidant system in chloroplasts of transgenic lines compared to that of wild-type.