Ectomycorrhizal fungi and exogenous auxins influence root and mycorrhiza formation of Scots pine hypocotyl cuttings in vitro.

We studied the ability of the ectomycorrhizal (ECM) fungi, Pisolithus tinctorius (Pers.) Coker and Couch and Paxillus involutus (Batsch) Fr. (Strain H), to produce indole-3-acetic acid (IAA) and to affect the formation and growth of roots on Scots pine (Pinus sylvestris L.) hypocotyl cuttings in vitro. Effects of indole-3-butyric acid (IBA) and the auxin transport inhibitor, 2,3,5-triiodobenzoic acid (TIBA), on rooting and the cutting-fungus interaction were also studied. Both fungi produced IAA in the absence of exogenous tryptophan, but the mycelium and culture filtrate of Pisolithus tinctorius contained higher concentrations of free and conjugated IAA than the mycelium and culture filtrate of Paxillus involutus. Inoculation with either fungus or short-term application of culture filtrate of either fungus to the base of hypocotyl cuttings enhanced root formation. Inoculation with either fungus was even more effective in enhancing root formation than treatment of the hypocotyl bases with IBA. Fungal IAA production was not directly correlated with root formation, because rooting was enhanced more by Paxillus involutus than by Pisolithus tinctorius. This suggests that, in addition to IAA, other fungal components play an important role in root formation. Treatment with 5 microM TIBA increased the rooting percentage of non-inoculated cuttings, as well as of cuttings inoculated with Pisolithus tinctorius, perhaps as a result of accumulation of IAA at the cutting base. However, the marked reduction in growth of Pisolithus tinctorius in the presence of TIBA suggests that the effects of TIBA on rooting are complicated and not solely related to IAA metabolism. The high IAA-producer, Pisolithus tinctorius, formed mycorrhizas, and the IBA treatment increased mycorrhizal frequency in this species, whereas TIBA decreased it. Paxillus involutus did not form mycorrhizas, indicating that a low concentration of IAA together with other fungal components were sufficient to stimulate formation and growth of the roots, but not the formation of ECM symbiosis.

[1]  T. Marks.  The role of the shoot apex in controlling rhizogenesis in vitro , 1996, Plant Growth Regulation.

[2]  G. Gay,et al.  Indole compounds released by the ectendomycorrhizal fungal strain MrgX isolated from a pine nursery , 1992, Mycorrhiza.

[3]  D. Blakesley,et al.  Endogeneous levels of indole-3-acetic acid and abscisic acid during the rooting of Cotinus coggygria cuttings taken at different times of the year , 1991, Plant Growth Regulation.

[4]  V. Pence,et al.  Effects of IAA and four IAA conjugates on morphogenesis and callus growth from tomato leaf discs , 1984, Plant Cell, Tissue and Organ Culture.

[5]  H. Häggman,et al.  Effects of exogenous diamines on the interaction between ectomycorrhizal fungi and adventitious root formation in Scots pine in vitro. , 2002, Tree physiology.

[6]  T. J. Cooke,et al.  Evolutionary Patterns in the Auxin Metabolism of Green Plants , 2000, International Journal of Plant Sciences.

[7]  F. Lapeyrie,et al.  Root hair elongation is inhibited by hypaphorine, the indole alkaloid from the ectomycorrhizal fungus Pisolithus tinctorius, and restored by indole-3-acetic acid , 2000, Planta.

[8]  H. Heinonen‐Tanski,et al.  Application of ectomycorrhizal fungi in rooting of Scots pine fascicular shoots , 2000 .

[9]  G. Gay,et al.  Dynamics of symbiotic establishment between an IAA-overproducing mutant of the ectomycorrhizal fungus Hebeloma cylindrosporum and Pinus pinaster. , 2000, Tree physiology.

[10]  J. Sánchez-Bravo,et al.  Influence of 2,3,5-Triiodobenzoic Acid and 1-N-Naphthylphthalamic Acid on Indoleacetic Acid Transport in Carnation Cuttings: Relationship with Rooting , 1999, Journal of Plant Growth Regulation.

[11]  D. D. Kaska,et al.  Auxin transport inhibitors act through ethylene to regulate dichotomous branching of lateral root meristems in pine , 1999 .

[12]  G. Gay,et al.  The auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) inhibits the stimulation of in vitro lateral root formation and the colonization of the tap-root cortex of Norway spruce (Picea abies) seedlings by the ectomycorrhizal fungus Laccaria bicolor. , 1998, The New phytologist.

[13]  P. Frey-Klett,et al.  In vitro effects of Laccaria bicolor S238 N and Pseudomonas fluorescens strain BBc6 on rooting of de-rooted shoot hypocotyls of Norway spruce. , 1998, Tree physiology.

[14]  Sally E Smith and David J Read.  Mycorrhizal Symbiosis 2nd ed , 1997 .

[15]  M. Rudawska,et al.  Mycorrhizal formation by Paxillus involutus strains in relation to their IAA-synthesizing activity. , 1997, The New phytologist.

[16]  F. Lapeyrie,et al.  Host plant stimulates hypaphorine accumulation in Pisolithus tinctorius hyphae during ectomycorrhizal infection while excreted fungal hypaphorine controls root hair development. , 1997, The New phytologist.

[17]  J. Hausman,et al.  Internal Controls of Root Induction in Poplar Shoots Raised in Vitro , 1997 .

[18]  J. Debaud,et al.  Rooting and acclimatization of micropropagated cuttings of Pinus pinaster and Pinus sylvestris are enhanced by the ectomycorrhizal fungus Hebeloma cylindrosporum , 1996 .

[19]  J. Harbage,et al.  Ethylene Does Not Promote Adventitious Root Initiation on Apple Microcuttings , 1996 .

[20]  B. Goldfarb,et al.  Maturation‐related loss in rooting competence by loblolly pine stem cuttings: The role of auxin transport, metabolism and tissue sensitivity , 1996 .

[21]  C. Kevers,et al.  Changes in the concentrations of auxins and polyamines during rooting of in-vitro-propagated walnut shoots. , 1996, Tree physiology.

[22]  M. Greenwood,et al.  Genetic variation in rooting ability of loblolly pine cuttings: effects of auxin and family on rooting by hypocotyl cuttings. , 1995, Tree physiology.

[23]  J. Debaud,et al.  Auxin overproducer mutants of Hebeloma cylindrosporum Romagnesi have increased mycorrhizal activity , 1994 .

[24]  Supriyanto,et al.  In vitro regeneration of plantlets of Scots pine (Pinus sylvestris) with mycorrhizal roots from subcultured callus initiated from needle adventitious buds , 1994 .

[25]  A. Heredia,et al.  Levels of endogenous indole-3-acetic acid and indole-3-acetyl-aspartic acid during adventitious rooting in avocado microcuttings , 1994 .

[26]  J. Ludwig-Müller,et al.  Indole-3-butyric acid in plants : occurrence, synthesis, metabolism and transport , 1993 .

[27]  E. Strzelczyk,et al.  The Effect of pH on Production of Plant Growth Regulators by Mycorrhizal Fungi , 1993 .

[28]  A. Varma,et al.  Techniques for the study of mycorrhiza , 1991 .

[29]  Douglas G. Altman,et al.  Practical statistics for medical research , 1990 .

[30]  B. Lyon.  Effect of the ectomycorrhizal fungus Hebeloma hiemale on adventitious root formation in derooted Pinus halepensis shoot hypocotyls , 1990 .

[31]  F. Negm,et al.  Involvement of ethylene in ectomycorrhiza formation and dichotomous branching of roots of mugo pine seedlings , 1989 .

[32]  S. Arnold,et al.  Initiation of roots on hypocotyl cuttings of Pinus sylvestris with emphasis on direct rooting, root elongation growth and auxin uptake , 1988 .

[33]  I. Ho.  Comparison of eight Pisolithustinctorius isolates for growth rate, enzyme activity, and phytohormone production , 1987 .

[34]  D. Read,et al.  THE DEVELOPMENT AND ULTRASTRUCTURE OF ECTOMYCORRHIZAS , 1984 .

[35]  M. Ek,et al.  INDOLE‐3‐ACETIC ACID PRODUCTION BY MYCORRHIZAL FUNGI DETERMINED BY GAS CHROMATOGRAPHY‐MASS SPECTROMETRY , 1983 .

[36]  D. Batten,et al.  Auxin Transport Inhibitors and the Rooting of Hypocotyl Cuttings from Etiolated Mung-bean Vigna radiata (L.) Wilczek Seedlings , 1981 .

[37]  L. Jacobson,et al.  Inhibitory effects of 2,3,5-triiodobenzoic Acid on ion absorption, respiration, and carbon metabolism in excised barley roots. , 1981, Plant physiology.

[38]  D. Marx.  The influence of ectotrophic mycorrhizal fungi on the resistance of pine roots to pathogenic infections. I. Antagonism of mycorrhizal fungi to root pathogenic fungi and soil bacteria , 1969 .