Poster: Plant Pathogen/Symbiont Interactions

Abs # 716: Involvement of Ca²⁺ and K⁺ influxes in the early signaling of Nod factor-induced root hair deformation in Medicago sativa.

Presenter:	Wu, Wei-Hua , wuwh@public3.bta.net.cn
Authors	Wu, Wei-Hua  (A)   Fan, Ling-Wen  (A)   Wang, An-Zhao  (A)
Affiliations:	(A): College of Biol. Sci., State Key Lab of Plant Phys. & Biochem., China Agric. Univ.

Nod factor-induced [Ca²⁺]_cyt increase in legume root hairs (RH) is an essential signaling step for the later root hair deformation (HAD). However, the proposed Ca²⁺ -channels that facilitate Ca²⁺ influx in the PM of legume RHs have not been identified and characterized so far. In addition, K⁺ ions may play critical roles in NF-induced rapid PM depolarization and osmotic regulation in legume RHs. The focus of this study is to demonstrate whether Ca²⁺ - and K⁺ -channel-mediated ion influxes is involved in NF-induced early signaling in legume RHs. Our results showed that the root nodulation of M. sativa upon the infection with S. meliloti was external Ca²⁺ - and K⁺ -dependent. Ca²⁺ - or K⁺ -channel blockers significantly inhibited NF-induced HAD, and high Ca²⁺ or K⁺ can mimic NF-induced HAD. By application of patch clamp techniques, the inward Ca2+-channels in RH protoplasts of M. sativa were first identified. NFs significantly stimulated the whole-cell Ca²⁺ currents and strongly inhibited the whole-cell K⁺in currents of RH protoplasts, while NFs had no effect on the open probability of the K⁺ in channels in the membrane patches. The results suggest the possible involvement of cytoplasmic factors in regulation of the inward K⁺ channels by NFs. The inward K⁺ -channels were also sensitive to changes in either external or internal Ca²⁺. It is concluded that the Ca²⁺ -channel- and K⁺ -channel-mediated ion influxes are involved in NF-induced early signaling in legume RHs.