Occurrence and Localization of Apocarotenoids in Arbuscular Mycorrhizal Plant Roots

Abstract

The core structure of the yellow pigment from arbuscular mycorrhizal (AM) maize roots contains the apocarotenoids mycorradicin (an acyclic C14 polyene) and blumenol C cellobioside (a C13 cyclohexenone diglucoside). The pigment seems to be a mixture of different esterification products of these apocarotenoids. It is insoluble in water and accumulates as hydrophobic droplets in the vacuoles of root cortical cells. Screening 58 species from 36 different plant families, we detected mycorradicin in mycorrhizal roots of all Liliopsida analyzed and of a considerable number of Rosopsida, but also species were found in which mycorradicin was undetectable in mycorrhizal roots. Kinetic experiments and microscopic analyses indicate that accumulation of the yellow pigment is correlated with the concomitant degradation of arbuscules and the extensive plastid network covering these haustorium-like fungal structures. The role of the apocarotenoids in mycorrhizal roots is still unknown. The potential C40 carotenoid precursors, however, are more likely to be of functional importance in the development and functioning of arbuscules.

Cloning, Characterization, and Immunolocalization of a Mycorrhiza-Inducible 1-Deoxy-D-Xylulose 5-Phosphate Reductoisomerase in Arbuscule-Containing Cells of Maize

“…Subsequently, (oxo) carotenoids (xanthophylls) are synthesized and cleaved to lead to C 13 cyclohexenone derivatives (R 1 ϭ glycosyl residues) and C 14 mycorradicin (R 2 ϭ H). Mycorradicin is presumably esterified to cyclohexenone glycosides, forming an insoluble complex (Fester et al, 2002a).…”

“…It is still an open question whether carotenoids or their apocarotenoid cleavage products are the functional molecules. A functional significance for the accumulating end products seems rather unlikely because they are found in osmiophilic droplets in the cytoplasm or in the vacuole of cells harboring degenerating or collapsed arbuscules (Fester et al, 2002a). During attempts to detect and identify carotenoids in mycorrhizal roots, only very low levels of -carotene could be found (Fester et al, 2002a(Fester et al, , 2002b, suggesting a high flux rate in the carotenoid pathway.…”

“…A functional significance for the accumulating end products seems rather unlikely because they are found in osmiophilic droplets in the cytoplasm or in the vacuole of cells harboring degenerating or collapsed arbuscules (Fester et al, 2002a). During attempts to detect and identify carotenoids in mycorrhizal roots, only very low levels of -carotene could be found (Fester et al, 2002a(Fester et al, , 2002b, suggesting a high flux rate in the carotenoid pathway. Only upon blocking the PDS reaction with norflurazone, could measurable levels of phytoene be identified in several plant species (Fester et al, 2002b).…”

“…A long-known phenomenon is the accumulation of yellow compounds in the roots of many plants upon mycorrhization (Jones, 1924;Fester et al, 2002a). The respective chromophore component of this so-called "yellow pigment" was isolated and identified as a linear C 14 polyenic acid of putative carotenoid origin called mycorradicin (Klingner et al, 1995).…”

Chemical Identification and Functional Analysis of Apocarotenoids Involved in the Development of Arbuscular Mycorrhizal Symbiosis

“…3) was found to be the chromophore of the yellow pigments that were eluted as a single broad peak in HPLC. 39,40) It was assumed that mycorradicin is esterified to as yet unknown compounds, 41) or bound in oligo-or polyesters to cyclohexenone derivatives in the case of Zea mays. 40) Free mycorradicin is liberated and detected only after mild alkaline hydrolysis of the yellow complex, although a trace amount of free mycorradicin, along with a series of its derivatives, was recently found for the first time in mycorrhizal roots of Ornithogalum umbellatum.…”