Phenotypic plasticity with respect to salt stress response by Lotus glaber: the role of its AM fungal and rhizobial symbionts

ECHEVERRÍA, M, SCAMBATO, A., SANNAZZARO A., MAIALE S., RUIZ O. A. & MENÉNDEZ A.

MYCORRHIZA

SPRINGER

Año: 2008 vol. 18 p. 317 - 329

0940-6360

Our hypothesis is that Lotus glaber (a glycophytic species, highly tolerant to saline-alkaline soils) displays a plastic root phenotypic response to soil salinity that may be influenced by mycorrhizal and rhizobial microorganisms. Uninoculated plants and plants colonized by Glomus intraradices or Mesorhizobium loti were exposed to either 150 or 0 mM NaCl.  General plant growth and root architectural parameters (morphology and topology) were measured and phenotypic plasticity determined at the end of the salt treatment period. Two genotypes differing in their salt tolerance capacity were used in this study.  G. intraradices and M. loti reduced the total biomass of non-salinized, sensitive plants but they did not affect that of corresponding tolerant ones. Root morphology of sensitive plants was greatly affected by salinity, whereas the fungus counteracted salinity effects. Under both saline conditions, the external link length (ELL) and the internal link length (ILL) of mycorrhizal salt-sensitive plants were higher than those of uninoculated control and rhizobial treatments. The topological trend (TT) was strongly influenced by genotype x symbiosis interaction. Under non-saline conditions, rhizobial roots of the sensitive genotype were more herringbone than the corresponding uninoculated ones. At 150 mM NaCl, roots of rhizobial tolerant plants were more “dichotomous”, and those of the corresponding sensitive genotype more “herringbone”. Notwithstanding the absence of results linking observed TTs and variations in plant growth, it is possible to predict a dissimilar adaptation of plants with different TTs. Both root colonizers reduced the level of root phenotypic plasticity in the sensitive genotype. We conclude that root plasticity could be part of the general mechanism of L. glaber salt tolerance only in the case of non-symbiotic plants.