Arbuscules of vesicular-arbuscular mycorrhizal fungi inhabit an acidic compartment within plant roots

Abstract. The most widespread type of mycorrhiza is the so-called vesicular-arbuscular mycorrhiza. In this endomycorrhiza, fungal hyphae penetrate plant cell walls in the root cortex. There they form densely branched arbuscules. Fungus and plant plasma membrane are separated by a common interfacial apoplast. The pH of the compartment between the symbionts is of pivotal importance for nutrient transfer. Histochemical experiments were conducted to check for an acidic nature of the interface in the model system Glomus versiforme (Karst.) Berch-Allium porrum L. Two chemically different acidotropic dyes (neutral red and LysoSensor Green DND-189) stained the arbuscules intensely. The staining of arbuscules could be eliminated by addition of the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP) or treatments leading to membrane rupture. Therefore, the staining of the arbuscules was based on the ion-trap mechanism, which indicates acidic, membrane-bound compartments. Microscopic examination of stained arbuscules at high optical resolution revealed a peripheral accumulation of the dye. Since plasmolysis rapidly destained the arbuscules, it is concluded that the dyes accumulate in the arbuscular interface, indicating the highly acidic nature of this compartment. The findings are discussed with respect to their relevance for the nutrient transfer in mycorrhizas. In addition, evidence for a discontinuity in the arbuscular interface between the stem and the branches of the arbuscule is given.

[1]  Tom Alexander,et al.  Dynamics of arbuscule development and degeneration in mycorrhizas of Triticum aestivum L. and Avena sativa L. with reference to Zea mays L , 1988 .

[2]  M. Boutry,et al.  The Plasma Membrane H+-ATPase (A Highly Regulated Enzyme with Multiple Physiological Functions) , 1995, Plant physiology.

[3]  Y. Piché,et al.  A developmental study of the early stages in vesicular-arbuscular mycorrhiza formation , 1985 .

[4]  Tom Alexander,et al.  Dynamics of arbuscule development and degeneration in onion, bean, and tomato with reference to vesicular–arbuscular mycorrhizae in grasses , 1989 .

[5]  T. Boller,et al.  Dynamics of Vacuolar Compartmentation , 1986 .

[6]  V. Gianinazzi-Pearson,et al.  Plant Cell Responses to Arbuscular Mycorrhizal Fungi: Getting to the Roots of the Symbiosis. , 1996, The Plant cell.

[7]  M. C. Heath Ultrastructural and functional similarity of the haustorial neckband of rust fungi and the Casparian strip of vascular plants , 1976 .

[8]  M. J. Harrison,et al.  A phosphate transporter from the mycorrhizal fungus Glomus versiforme , 1995, Nature.

[9]  D. H. Jennings The Physiology of Fungal Nutrition , 1995 .

[10]  J. Guern,et al.  Intracellular pH: Measurement and Importance in Cell Activity , 1989 .

[11]  R. Peterson,et al.  Development of a vesicular-arbuscular mycorrhiza in bean roots. , 1979 .

[12]  H. Sentenac,et al.  Effect of pH on Orthophosphate Uptake by Corn Roots. , 1985, Plant physiology.

[13]  G. Azzone,et al.  The Membrane Structure Studied with Cationic Dyes , 1972 .

[14]  G. Azzone,et al.  The membrane structure studied with cationic dyes. 2. Aggregation, metachromatic effects and pK a shifts. , 1972, European journal of biochemistry.

[15]  F. A. Smith,et al.  Structure and function of the interfaces in biotrophic symbioses as they relate to nutrient transport. , 1990, The New phytologist.

[16]  N. Nelson,et al.  The evolution of H+-ATPases. , 1989, Trends in biochemical sciences.

[17]  Sally E. Smith,et al.  Enzymatic studies on the metabolism of vesicular-arbuscular mycorrhizas. V, Is H+-ATPase a component of ATP-hydrolysing enzyme activities in plant-fungus interfaces ? , 1991 .

[18]  J. Fraymouth Haustoria of the Peronosporales , 1956 .

[19]  C. Marx,et al.  ENZYMATIC STUDIES ON THE METABOLISM OF VESICULAR–ARBUSCULAR MYCORRHIZAS , 1982 .

[20]  V. M. Emmel,et al.  Biological Stains, a Handbook on the Nature and Uses of the Dyes Employed in the Biological Laboratory , 2015 .

[21]  M. Canny Locating active proton extrusion pumps in leaves , 1987 .

[22]  R. Santus,et al.  Solvent Polarity and pH Effects on the Spectroscopic Properties of Neutral Red: Application to Lysosomal Microenvironment Probing in Living Cells , 1996, Photochemistry and photobiology.

[23]  J. LaManna,et al.  The use of neutral red as an intracellular pH indicator in rat brain cortex in vivo. , 1984, Analytical biochemistry.

[24]  B. M. McDougall MOVEMENT OF 14C‐PHOTOSYNTHATE INTO THE ROOTS OF WHEAT SEEDLINGS AND EXUDATION OF 14C FROM INTACT ROOTS , 1970 .

[25]  C. Overly,et al.  Quantitative measurement of intraorganelle pH in the endosomal-lysosomal pathway in neurons by using ratiometric imaging with pyranine. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[26]  S. Perotto,et al.  Tansley Review No. 82. Strategies of arbuscular mycorrhizal fungi when infecting host plants , 1995 .