Regulation of nodulation in Alnus incana-Frankia symbiosis


  • Luis Gabriel Wall,

    Corresponding author
    1. Dept of Plant Physiology. Umeå Univ., S-901 87 Umeå, Sweden
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  • Kerstin Huss-Danell

    1. Dept of Plant Physiology, Umeå Univ., S-901 87 Umeå. Sweden, and Dept of Agricultural Research for Northern Sweden, Section for Crop Science. Swedish Univ. of Agricultural Sciences, Box 4097, S-904 03 Umeå, Sweden
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  • This paper is part of the contributions to the Tenth International Conference on Frankia and Actinorhizal Plants jointly sponsored by the College of Agricultural and Environmental Sciences at the University of California at Davis, and the National Science Foundation. held in Davis, CA, USA, 6–11 August, 1995.

L. G. Wall (corresponding author, e-mail; present address: Dept de Ciencia y Tecnologia, Univ. Nacional de Quilmes, R. Sáenz Peña 180. 1876 Bernal. Argentina).


We have studied regulation of nodulation in Alnus incana (L.) Moench using double inoculations in plastic pouches and a slide technique to observe root hair deformation. Initially, the distribution of nodules between main and lateral roots appeared quite constant, independent of the concentration of inoculum (1 to 250 μg of crushed nodules plant−1). Susceptibility to infection after the second inoculation was restricted to lateral roots after the initial infections developed. When pre-existing nodules were excised before the second inoculation, subsequent nodules appeared to arise where infections had arrested at stages earlier than actual nodule emergence. We observed that root hairs formed postinoculation were very crowded and short with a pronounced deformation. No nodules were found later on this region of the root, suggesting a loss of susceptibility in this region. Split-root experiments with delays between inoculation of the first and second side of the root system showed irreversible, systemic inhibition of nodulation on the second side starting between 3 and 6 days after the inoculation of the first side. Only when compatible, infective strains were used in the first inoculation, was nodule formation inhibited after the second inoculation. We conclude that autoregulation of nodulation operates in Alnus incana and on a time scale similar to what is found in some legumes.