TRANSLOCATION AND TRANSFER OF NUTRIENTS IN VESICULAR‐ARBUSCULAR MYCORRHIZAS

Abstract

SUMMARY This paper reports the effects of environmental variables on the movement of phosphate by external hyphae of the mycorrhizal fungus Glomus mosseae , infecting Trifolium repens (white clover), across a barrier in soil‐agar/agar split‐plate cultures. Increasing the transpiration rate of the host increased the total P translocated by the fungus: the maximum rate obtained at full transpiration was 2·3 times that at low transpiration. Temperature also affected P transport, which was at a maximum at 15 to 25°C, but at 5°C only a small amount of P was transported. The maximum P flux in the hyphae, calculated for 20 to 25°C and a moderate host transpiration rate, was 2 × 10 ‐9 mol cm ‐2 s ‐1 . A cytoplasmic streaming inhibitor (cytochalasin B) prevented detectable movement of P across the barrier by the fungus and consequently had inhibited either the uptake or translocation of P by the fungus. Osmotic potentials of 1 or 2 bars in the medium from which 32 P was being absorbed did not appreciably alter the rate of transport of P. The results support the general conclusion that translocation of P in the hyphae occurs normally by protoplasmic streaming but there may also be a‘bulk flow’of hyphal contents under a water potential gradient.