Poster: Intercellular Signaling

Abs # 800: An Apoplastic Mechanism for Short¨CTerm Effects of Rare Earth Elements at Lower Concentrations

Presenter:	Sun, Ying , sunying100@etang.com
Authors	Sun, Ying  (A) (B)  Liu, Delong  (A) (B)  Yu, Zhengquan  (A) (B)  Zhang, Qian  (A) (B)  Bai, Juan  (A) (B)  Sun, Daye  (A) (B)
Affiliations:	(A): Institute of Molecular Cell Biology (B): Hebei Normal University

The capacity of rare earth elements (REEs) to promote plant growth has long been realized. But the exact mechanism underlying their effects on plant tissue and cells is far from clear. Here we tested short-term effects of Lanthanum (La ³⁺ ), one of important REEs on pollen germination and tube growth at lower concentration, trying to understand the mechanism of REEs action by using simple cell system. The results showed that 2.5¡«20¦ÌM La ³⁺ increased pollen germination and pollen tube growth. The most effective concentration shifted from 10¦ÌM to 40¦ÌM, depending on the Ca ²⁺ concentration in the medium. Calmodulin (CaM) antagonist W7-agarose and anti-CaM antibody which specially inhibit apoplastic CaM due to impermeable to membrane, depressed La ³⁺ -promoted pollen germination and tube growth. La ³⁺ -CaM complexes (La ³⁺ -CaM) increased pollen germination and tube growth more greatly than CaM or La ³⁺ alone did. Pertussis toxin inhibited La ³⁺ -promoted pollen germination and tube growth. Cholera toxin partially recovered the inhibition of the above La ³⁺ -promoted process by the anti-CaM antibody. 10 ^-7 ~10 ^-9 M La ³⁺ -CaM increased GTPase activity inside plasma membrane vesicles of the pollen tube, but apo-CaM or La ³⁺ alone had no positive effects. All the results suggest that apoplastic CaM may be involved in the promotion effects of lower concentrations of La ³⁺ on pollen germination and tube growth, and the heterotrimeric G-protein on the plasma membrane may transduce La ³⁺ activated CaM signaling. Our studies provide an apoplastic mechanism for short-term effects of REEs at lower concentrations.