An apoplastic mechanism for short-term effects of rare earth elements at lower concentrations.
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.
Sun
Y.
Y
Institute of Molecular Cell Biology, Institute of Molecular Cell Biology, College of Life Science, Hebei Normal University, Shijiazhuang, Hebei 050016, P. R. China.
Liu
D. L.
DL
Yu
Z. Q.
ZQ
Zhang
Q.
Q
Bai
J.
J
Sun
D. Y.
DY