Mitigative Effect Of Exogenous Carbon Monoxide On Cell Death In Rice Suspension-Cultured Cells Under Salt Stress

Salt injury is one of the most serious abiotic stress in agricultural production. It is significance to clarify the mechanism of plant response to salt stress and its salt resistance. Rice is one of the four major food crops in the world, and an important model organism with clear genetic background. Suspension cell culture has so many advantages, such as propagation speed fast, culture easily, less interference by environmental factors, uniformity of stress treat, no seasonal restrictions, and so on, that it is regarded as an ideal experiment system.In this study, the role of carbon monoxide (CO) on reducing cell death rate of rice suspension-cultured cells was investigated under salt stess. The cell death rate rised with the rincreasing of NaCl concentration (0～400 mmol·L-1) and time (3,6,12 and 24 h),in which 400 mmol·L-1 treatment for 24 h resulted in the cell death rate as high as 55.2%. Pretreatment with different saturation exogenous carbon monoxide(CO) aqueous solutions for 3 h was able to alleviate the elevating cell death rate induced by further 200 mmol·L-1 NaCl treatment.50% saturation of exogenous CO aqueous solution pretreatment for 3 h was optimum and was significantly different(P<0.05)in various time points(3h,6h). The cell death rate induced by further 200 mmol·L-1 NaCl treatment for 3h and 6h increased 67.7% and 34.2% by pretreating with 50% CO aqueous solution combined with 1.5g·L-1 hemoglobin (Hb, a scavenger of CO) (CO50+Hb→S200) than that by pretreating with 50% CO aqueous solution (CO50→S200).Hb pretreatment(Hb→S200)significantly increased cell death rate(P<0.05)also. The results indicate that the cytoprotective effect of CO could be reversed by the addition of Hb.50% saturation of exogenous CO aqueous solution pretreatment increased in various degrees superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) activity of the rice suspension cell treated with 200 mmol·L-1 NaCl.More than others, APX activity was significantly different (P<0.05). Besides, the trend of enzyme activity increasing was consistent with the effect of CO alleviate cell death under NaCl stress. RT-RCR results shows that, pretreatment with 50% CO for 3h could not modify Fe-SOD and APX1 gene transcripts, while Cn/Zn-SOD-1 gene transcripts were down regulation. Under NaCl stress, pretreatment with 50% CO increased Fe-SOD and APX1 gene transcripts in different degrees, yet Cu/Zn-SOD-1 gene transcripts were not significantly different.