Subcellular localization of calcium in the incompatible and compatible interactions of wheat and Puccinia striiformis f. sp. tritici.

Ca(2+) is an ubiquitous intracellular molecule which is used as a second messenger to control many physiological activities in plant cells. In the present work, the relationship between calcium localization and the hypersensitive response (HR)one of the most crucial and indispensable pathway to resist a pathogenwas studied in the wheat-wheat strip rust system using cytochemical technique. Our results show that calcium is involved in the interaction between wheat and wheat stripe rust. In the incompatible interaction associated with necrosis of host mesophyll cells, an influx of Ca(2+) from the intercellular space to the cytoplasm and finally an efflux to the intercellular space again was detected in an incompatible interaction. Calcium precipitates were also observed in mesophyll cells adjacent to necrotic cells. On the contrary, calcium flow was not significantly altered in a compatible interaction. These results suggest that calcium might induce HR as a secondary messenger in the incompatible interaction of wheat and wheat stripe rust.