Carnitine-induced physio-biochemical and molecular alterations in maize seedlings in response to cold stress

This study was conducted for the purpose of identifying the physio-biochemical and molecular basis of effects of carnitine on the growth and defence strategies of maize seedlings grown in optimum and cold conditions. While carnitine alone resulted in an effective increment in seedling growth compared to control, in combination with cold stress it alleviated the negative effect of cold stress leading to growth retardation. Similarly, cold-induced reductions in photosynthetic parameters (leaf surface area, stoma aperture, chlorophyll content, and activity and gene expression of Rubisco) and nitrogen assimilation pathway (activities and gene expressions of nitrate reductase, glutamine synthase, and glutamate synthase) were declined by carnitine application. Carnitine was also found to reduce level of oxidants (superoxide anion and hydrogen peroxide) and oxidative damage parameters (lipid peroxidation, protein oxidation and freezing injury) by stimulating activities of antioxidant enzymes (superoxide dismutase, guaiacol peroxidase, catalase, ascorbate peroxidase and glutathione reductase). Carnitine also altered ratio of saturated and unsaturated fatty acids in membranes in favour of unsaturated fatty acids to protect cellular membranes from damage caused by cold stress. In conclusion, carnitine improved plant growth and cold tolerance by modulating photosynthesis and nitrogen assimilation at physio-biochemical and molecular level and by improving antioxidant defence system.