Effect of TiO2 nanoparticles on metabolic limitations to photosynthesis under cold in chickpea

We evaluated the effect of TiO2 nanoparticles (NPs) on metabolic and molecular traits involved in photosynthesis of two chickpea (Cicer arietinum L.) genotypes (Sel96Th11439, cold tolerant genotype, and ILC533, cold susceptible one) during cold stress (4°C). The data analysis showed that hydrogen peroxide (H2O2) content increased more extremely under cold in susceptible plants than in tolerant ones. TiO2 NPs caused a significant decrease in H2O2 content so that tolerant plants showed lower H2O2 content than susceptible ones. This decrease often was accompanied with higher metabolic potential for photosynthesis particularly in tolerant plants. Under thermal treatments, TiO2 NPs significantly increased the activity of Rubisco compared to control plants although its activity decreased significantly under cold comparison with optimum temperature. Along with a decreasing in H2O2 content, more photosynthetic activity at the transcription levels of CaLRubisco, CaSRubisco and Cachlorophyll a/b-binding protein genes in a simultaneous manner particularly in plants treated with TiO2 NPs ensure the acclimation of plants to survival or recovery. Under such status, phosphoenolpyruvate carboxylase (PEPC) activity increased particularly in tolerant plants compared to susceptible ones as well as in plants treated with TiO2 NPs compared to control plants, indicating probably an increase in energy efficiency through different mechanisms like malate. Thus, chickpea tolerance responses to cold stress may occur after TiO2 NPs application on plants through managing the pressure of temperature decline damage and altered metabolism for plant growth.