Immunocytochemical localization of cytokinin in Azolla filiculoides

Abstract

In the small aquatic fern Azolla filiculoides, cytokinin immunolocalization was performed in longitudinal axial sections of plantlet shoots. The reaction was detected: (i) in the contiguous cell sheet which encircles vascular tissues, (ii) in shoot and root meristem target cells, and (iii) in the teat cells of the leaf cavity pore. Our results demonstrate, for the first time, that in ferns the cytokinin translocation pattern can be different to that described in seed plants. Thus, this class of hormones is translocated, via vascular tissues in seed plants, whereas in Azolla it depends upon a sheet layer of cells encircling the conducting tissues. In shoot and root meristems, cytokinin distribution widely differs; in fact, in the shoot apex, the signal is present only in a few target cells, whereas in the root the signal is localized in numerous contiguous cells. Another finding concerns the clear signal observed at the level of the teat cells delimiting the pore which connect the leaf cavity with the exterior. This result provides indication that cytokinins, which are known to be involved also in light perception, might play a key role in the control of Anabaena movement into and out of the leaf cavity. This is the first report concerning cytokinin distribution in fern cells and tissues. Our results suggest that these hormones are implicated in the different plant organs in very different and specific functions.

Key words:

• Cytokinin immunolocalization
• zeatin
• Azolla filiculoides
• leaf cavity pore

Acknowledgements

The authors thank Dr Federica Perri (Dept of Ecology, University of Calabria) for excellent technical support.