Annexin Is Involved In Salt Stress Induced Ca²⁺ Influx In Epidermal Root Cells Of Oryza Sativa L.

Annexins are widely found in animal and plant kingdoms. They play an important role in cell growth, development and adaptability. The annexin of plants are mainly present in cytosol, plasma membrane, endometrial, and a variety of organelles. Annexins are involved in plant tolerance to abiotic stress. They form hyperpolarization-activated calcium channels and participate in the generation of calcium signals in the cytoplasm.In order to explore the physiological mechanism of Osannx induced resistance, we used wild type, Osannex mutants and overexpression strains as experimental material, and patch clamp technique as main method, the effect of NaCl stimulating on activity of calcium channels in the plasma membrane of rice root epidermal cell was investigated. The function of annexin in salt stress inducing calcium influx was investigated by comparing different response of materials.First, by using whole-cell step voltage clamping hyperpolarization-activated calcium channels were recored in plasma membrane of rice root epidermal cells. When the membrane voltage was hyperpolarized up-120mV the calcium channel was activated, and then the calcium current increased gradually with increasing hyperpolarization. After adding calcium channel blocker Gd3+, the inward current was strongly inhibited. In tail current experiment, the reversal potential was20mV, confirming that the cuttent we detected is Ca2+channel. The result of ramp voltage clamping was consistent with step-voltage clamping result.To verify whether annexin is the calcium channel who mediate Ca2+signal. Under salt stress, the effect of salt-strees on calcium channel in wild-type, Osannx overexpression strains: Osannx-OXl, Osannx-OX2, Osannx-OX3, Osannx-OX4, Osannx lost-of-function mutant: Osannx-1, Osannx-2and Osannx-3was measured. The basic calcium currents were not different among the three materials. After adding100mmol/L NaCl, the currents of wild type were not markedly affected, the currents in Osannx overexpression strains were significantly increased, while in the lost-of-function mutants were significantly decreased. The results indicated that annexin may play important role in salt-stress induced Ca2+signal in rice root epidermal cells. Based on our results, we suggest that annexin of rice may regulate Ca2+in the cytoplasm as hyperpolarization-actived calcium channel and may be involved in salt stress induced calcium influx, which induces resistance to salt stress.