Imaging of total calcium in urediospore germlings of Uromyces by ion microscopy

Calcium has been implicated in growth and appressorium formation of uredios pore germlings of the bean rust fungus, Uromyces appendiculatus. Using ion microscopy, a mass spectrometry-based imaging technique, intracellular stor es of calcium were analyzed by direct imaging of total calcium in frozen fr eeze-dried germlings. Calcium concentration was calculated by ratioing and spatially registering Ca-40 to C-12 signals. Intracellular distributions of total potassium, sodium, magnesium, and carbon were similarly imaged in th e same germlings for a direct comparison of their localizations to total ca lcium, Calcium was remarkably heterogeneous with highest concentrations (2 to 10 mM) in the mid-region of the germling between the nuclei and the apex . A similar distribution of Ca2+ (assessed using Fluo-3) was also noted seq uestered in organelles in live germlings, Distributions of remaining elemen ts (K, Na, Mg, and C) were mostly homogeneous throughout the cytoplasm and nuclei of the fungal cell. The K/Na ratio ranged from 17 to 31. (C) 1999 Ac ademic Press.