Cytochemical gradients and mitochondrial exclusion in the apices of vegetative hyphae

Summary Apical maximal acidity (shown by subapically increasing pH) and maximal concentration of inorganic phosphate (shown by a subapically decreasing gradient of yellow phosphomolybdate) contrast with the subapical, mainly mitochondrial sequestration of calcium ions. Such gradiential control of calcium concentration appears to be the requisite for the Ca⁺⁺ sensitive gelation of the apical hyaloplasm preventing the mitochondria from entering into this continuosly elongating zone of growing hyphae.The support of the founds National Suisse de la Recherche Scientifique is acknowledged and we thank Miss E. Herz for her technical assistance.