Les séminaires ont lieu sur le Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)
Jeudi 5 juin 2014
Salle 106 (Cœur d’école) à 14h
Metal-specific xylem loading mechanisms in Noccaea caerulescens: the roles for low-molecular weight chelators and vacuolar retention in root tissues
Department of Genetics, Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam, The Netherlands
Noccaea caerulescens is a facultative metallophyte, and a hyperaccumulator of Zn, Cd, or Ni. Its capacity to hyperaccumulate Zn is species-wide, although there is quantitative variation among populations. The Cd and Ni hyperaccumulation capacities are population-specific. Strongly enhanced rates of root-to-shoot translocation of all of these metals, in comparison with non-hyperaccumulators, are constitutive at species level, although there is quantitative variation among and within local populations.The high rates of metal xylem loading seem to be explained by a combination of an enhanced capacity to actively efflux metals from the surrounding tissues into the xylem, and a decreased capacity to retain metals within the vacuoles of peripheral root tissues, in particular the cortex, endodermis and pericycle.Free histidine concentrations in roots are about 10-fold enhanced, in comparison with non-hyperaccumulators, and exogenous histidine supply enhances the xylem loading of Ni and, particularly, Zn, but not Cd, in N. caerulescens, but does not so in the related non-hyperaccumulator, Thlaspi arvense. When supplied in combination with histidine, the uptake of Ni and Zn into energized tonoplast vesicles is inhibited in N. caerulescens, but not in T. arvense. It is suggested that histidine promotes Ni and Zn xylem loading through reducing these metals’vacuolar storage in peripheral root tissues, thus enhancing their radial transport across the root into the stele. Although Zn xylem loading is HMA4-dependent, but Ni xylem loading is not, segregating inter-population crosses revealed common genetic determinants for Zn and Ni hyperaccumulation. Since there is barely inter-population variation for root histidine concentrations and tonoplast transport capacities, it is likely that these common determinants are involved in root uptake, rather than translocation.Genetic analysis also revealed common determinants of inter-population variation for Zn and Cd hyperaccumulation capacity. Since this variation is uncorrelated with HMA4 expression, and root Cd is sulfur/oxygen-bound, rather than nitrogen/oxygen-bound, such as Ni and Zn, these common determinants are likewise involved in root uptake, rather than translocation.
Contact : Hatem Rouached