Peroxidase activity and phenolic compounds content in maize root and leaf apoplast, and their association with growth

Apoplastic fluid originated from maize (Zea mays L.) leaf and root growing and non-growing regions were analyzed for peroxidase (POD) activities and phenols content. The samples were obtained by two different methods, as apoplastic washing fluid (AWF) from excised leaf and root segments, and as root apoplastic fluid (RAF) collected from the surface of intact roots by filter papers. AWF and RAF were tested for peroxidative and oxidative activity of POD, being lowest in the growing zones and gradually increasing toward root base and leaf tip. Isoelectric focusing of AWF and RAF revealed the differences pronounced in cationic group of peroxidases. Quantitative and qualitative analyzes of phenolic compounds from root and leaf apoplastic fluid was performed by HPLC. The increase of peroxidase activities was parallel to the increase of coniferyl alcohol, as well as other phenolic compound concentrations with root and leaf age, indicating that increased phenolic concentrations reflect increased lignin production during maturation. The data presented in this paper indicate that the method for getting RAF using filter papers is a more reliable procedure than infiltration/centrifugation method for studying processes which take place in root and leaf apoplastic fluid.