Changes of phenolic metabolism and oxidative status in nitrogen-deficient Matricaria chamomilla plants

The effects of nitrogen deficiency on selected physiological attributes, phenylalanine ammonia-lyase (PAL, EC. 4.3.1.5) activity, phenolic contents, peroxidase (EC. 1.11.1.7) and catalase (EC. 1.11.1.6) activities, lipid peroxidation status and H₂O₂ accumulation were studied in N-deficient Matricaria chamomilla (L.) over 12 days. N deficiency enhanced root growth and inhibited shoot growth. Chlorophyll composition and F _v/F _m were not affected by N stress, but nitrogen and soluble proteins decreased in both the rosettes and the roots. PAL activity, expressed per mg protein, was enhanced in N-deficient rosettes and tended to decrease by the end of the experiment, while in the roots PAL activity was maintained. Total phenolic contents increased in both rosettes and roots. Peroxidase and catalase activities in N-deficient rosettes tended to decrease by the end of the experiment, while in the roots they increased on the 12th day of deficiency. Furthermore, lipid peroxidation status increased in N-deficient roots on the 12th day, indicating that antioxidative protection was insufficient to scavenge reactive oxygen species being generated. Surprisingly, H₂O₂ content was even lower in N-deficient roots by the end of the experiment, while in the leaves increased. This observation in correlation to lipid peroxidation and H₂O₂ degradation is discussed. The importance of PAL activity and phenolic metabolites in combination with antioxidative enzymes for plant protection against oxidative stress and the significance of PAL activity for the mobilization of N availability in N-deficient tissue are also discussed in view of existing information.