Localization of ornithine decarboxylase and changes in polyamine content in root meristems of Zea mays

Polyamine content and the activity of arginine decarboxylase (EC 4.1.1.19) and ornithine decarboxylase (EC 4.1.1.17) were studied with respect to meristematic activity in primary roots and in developing lateral roots of Zea mays L.(cv. Neve Ya'ar 170) seedlings. Comparative localization of active ornithine decarboxylase and of meristematic activity were determined by labelling roots either with α‐[5‐¹⁴C]‐difluoromethyl ornithine or with [³H]‐thymidine, respectively. Lateral roots were formed during the 72 h post‐decapitation period, accompanied by an initial decline in putrescine content and by a significant increase in spennidine con‐tent at 48–72 h. High levels of spermidine and lower levels of putrescine were found in the primary root apex as well. A marked increase in ornithine and arginine decarboxylase activity, as measured by ¹⁴CO₂ release, was found during the 72 h post‐decapitation period of lateral root development. This increase in ornithine decarboxylase activity was confirmed also by a parallel rise in the incorporation of α‐[5‐¹⁴C]‐difluoromethyl ornithine into trichloroacetic acid‐insoluble fractions. Microautoradiographs of longitudinal and cross sections of roots, labelled with α‐[5‐¹⁴C]‐difluoromethyl ornithine, showed that ornithine decarboxylase is localized mainly in the meristematic zones, as evidenced by [³H]‐thymidine incorporation. A close correlation between meristematic activity and polyamines was demonstrated in situ, suggesting that polyamine content and biosynthesis may have a role in meristematic activity in corn roots.