Studies Of Ca～(2+) Dependence Of Abscisic Acid-regulated Inward K～+ Current Of Guard Cells In Arabidopsis Thaliana Wild-type And Los5-1 Mutant

Environmental stress, such as drought,salinity and low temperture all can result in osmotic stress, and affect the normal developmental process of plants. As one of the stress-stimulated phytohomone, ABA promotes the special signal transduction networks and affects many physiological or biochemical course for adapting to environmental stress. The typital biological process of regulation of abscisic acid (ABA) on plants may be cause stomata closing, and inhibit the opening of stomata. Its mechanism probably may be ABA enhancing [Ca²⁺]i and cytosolic pH in guard cells. A series of signal transduction pathways induced by enhancement of [Ca²⁺]i could regulate the activity of inward K⁺ channel. But the results often obtained by effect of extrogenous ABA. The regulation of endogenous ABA and extrogenous ABA on inward K⁺ channel in the plasma membrane of guard cells remains incompletely understood. The los5-1 is an ABA biosynthesis deficient mutant, and mape-based cloning reveals that los5 is allelic to aba3. los5/aba3 encodes a putative molybdenum cofactor (Mo-Co) sulfurase that catalyzes the sulfuration of the desulfo form MoCo. Sulfurylated MoCo is a cofactor of ABA-aldehyde oxidase that function in the last step of ABA biosynthesis. Comparing with wild-type, mutant can't biosynthesize ABA. The mutant provided a good genetic material for synthetical analysis of ABA regulation on activity of K⁺ channel in electrophysiology. Using patch-clamp techniques, after the treatment of LaCl₃ (inhibitor of Ca²⁺ channels in the plasma membrane of guard cells) and EGTA (chelator of cytosolic Ca²⁺), we examined the effect of Ca²⁺ on inward K⁺ channel activity which regulated by ABA in the plasma membrane of guard cells from Arabidopsis thaliana (wild-type C₂₄ and ABA deficient mutant los5-1 ) . The data showed that the inward whole cell K⁺ current in the guard cell protoplasts of both nutant (los5-1) and wild type (C₂₄) significantly decreased 20 mins after added 10μmol/L ABA into the bath solution. The level of suppressed by ABA in mutant (los5-1) is significantly higer than wild-type (C₂₄). Whereas there was virtuallly no effect on ABA-induced decreasing of inward K⁺ current in mutant under ABA (10μmol/L )+LaCl₃ (10μmol/L) or ABA(10μmol/L )+EGTA (2mmol/L) treatment together , though the inward K⁺ current regulated by ABA was significantly impaired in wild-type plant. These results suggested that Ca²⁺ involved in ABA-regulated inward K⁺ channel in wild type guard cells, while in los5-1 mutant this process is Ca²⁺ -independence. These results indicated that the Ca²⁺ dependence of ABA-regulated inward K⁺ current in Arabidopsis wild-type and mutant los5-1 guard cells is different, and ABA-regulated inward K⁺ current in guard cell may be mediated by different transduction pathways in Arabidopsis wild-type and mutant.