Chilling-induced changes in membrane fluidity and antioxidant enzyme activities in Coffea arabica L. roots

Exposure of coffee to low temperatures caused growth inhibition, changes in metabolic rates, and membrane alterations. Root tissue exposed to 10 degrees C evolved significantly lower rates of metabolic heat compared with controls grown at 25 degrees C, and the values were closely associated with the observed root growth inhibition. Electron paramagnetic resonance spectra of intact tissues showed that the spin probe 5-doxylstearic acid was capable to intercalate within the cellular membrane lipids. Indeed, at the depth of the 5(th) carbon atoms of the alkyl chains, the nitroxide radical detected more rigid membranes in seedlings exposed to 10 degrees C compared with 25 degrees C treated samples. Ascorbate peroxidase and catalase activities did not show appreciable changes under chilling conditions, while guaiacol peroxidase activity increased 55 % compared to the control. On the other hand, glutathione reductase activity decreased, in parallel to a significant decline in the capacity to reduce triphenyl-tetrazolium. Our results showed a marked correlation between lipid peroxidation and root tissue damage, which seemed to be associated with increased membrane rigidity.