title: An apoplastic mechanism for short-term effects of rare earth elements at lower concentrations.
abstract: The short-term effects of rare earth elements on pollen germination and tube growth were tested. Concentrations of 2.5 approximately 20 micro m lanthanum(La3+) or cerium (Ce3+)increased pollen germination and pollen tube growth, whereas concentrations higher than 40 micro m La3+ and Ce3+ inhibited this process. The most effective concentration of La3+ needed for promotion shifted from 10 to 40 micro m, depending on the Ca2+ concentration in the medium. Calmodulin (CaM) antagonist W7-agarose and anti-CaM antibody depressed La3+-promoted pollen germination and tube growth in a dose-dependent manner. La3+-CaM complexes (La3+-CaM) increased pollen germination and tube growth more than CaM or La3+ alone. Pertussis toxin (PTX) inhibited La3+-promoted pollen germination and tube growth. Cholera toxin (CTX) partially recovered the inhibition of the above La3+-promoted process by the anti-CaM antibody. Concentrations of 10-7 approximately 10-9 m La3+-CaM increased GTPase activity inside plasma membrane vesicles of the pollen tube, but apo-CaM or La3+ alone had no positive effects. The results suggest that apoplastic CaM may be involved in the promotion effects of lower concentrations of La3+ on pollen germination and tube growth, and the heterotrimeric G-protein on the plasma membrane may transduce La3+-activated CaM signalling. The present studies provide an apoplastic mechanism for short-term effects of rare earth elements at lower concentrations in the pollen system.
authors.affiliation: Institute of Molecular Cell Biology, Institute of Molecular Cell Biology, College of Life Science, Hebei Normal University, Shijiazhuang, Hebei 050016, P. R. China.
authors.forename: Y.
authors.initials: Y
authors.lastname: Sun
authors.forename: D. L.
authors.initials: DL
authors.lastname: Liu
authors.forename: Z. Q.
authors.initials: ZQ
authors.lastname: Yu
authors.forename: Q.
authors.initials: Q
authors.lastname: Zhang
authors.forename: J.
authors.initials: J
authors.lastname: Bai
authors.forename: D. Y.
authors.initials: DY
authors.lastname: Sun