| The plants will encounter many obstacles in the process of growth, such as drought, salinization, and pollution of heavy metal.At present, there are many ways to alleviate the pollution of heavy metal in soil, mainly including chemical, physical and biological.And biological repairs were considered as the most effective methods. Bacillus subtilis which were the dominant species in plant and soil, it has promoting effect on the growth of plants which under heavy metal stress. In this study, we used wheat seeds from Shanxi province as experiment material. The external stress was Pb heavy metal, and B. subtilis QM3 as the mitigation bacterial strain. Under this circumstance, we studied the effect of B. subtilis QM3 on wheat leaves that under lead stress from different aspects. The following were the main conclusions of the study:(1)The effect of heavy metal Pb on the leaves morphology of wheat was first promoted and then inhibited. Low concentration of lead can promote the growth of Wheat, including the leaves length,number, surface, biomass accumulation. But with the lead concentration increased, these indicators were suppressed. But the leaves width were not seriously affected by heavy metals. It wasshown that B. Subtilis QM3 prevented decline in the leaves length,number, biomass accumulation. Under the same concentration of lead, the leaves length, leaves area respectively increased by33.1-78% and 17.2-89%, while the number of leaves increased by3.3-10% compared to the control group(P < 0.05), which soaked with B1, B2, B3.(2)The effect of heavy metal Pb on the leaves photosynthetic system of wheat was first promoted and then inhibited. When stressed by lead, the indicators include chlorophyll a, chlorophyll b, total chlorophyll content, Fv/Fm, Fv/F0, q P, Y were increased first and then decreased. But q N was just the opposite.However this stress can be alleviated by B. Subtilis QM3. When the lead concentration was 0.5g/kg, soaked with B1, B2, B3, the chlorophyll a, chlorophyll b, total chlorophyll content, Fv/Fm, Fv/F0,q P and Y respectively increased by 3.4%-16%, 6.7%-14.7%,1.3%-6.3%, 5.7%-29%, 5.2%-77%, 42%-90%, while q P reduced by4.4%-14.2% compared to the control group(P < 0.05).(3)The content of MDA, souble sugar, soluble protein and proline were increased in wheat leaves that under lead stress. When the lead concentration were 0.5-3.0g/kg, there was a significant difference between the content of MDA, souble sugar, soluble protein, proline and those of control group. When the lead concentration were 3.0g/kg, the content of MDA, souble sugar,soluble protein and proline increased by 51.6%, 111.5%, 61%,145.8% compared to the control group(P <0.05). Experiment results showed that B. Subtilis QM3 could reduced the content of MDA,souble sugar, soluble protein and proline Significantly.(4)The effect of heavy metal Pb on the leaves antioxidant enzyme system of wheat leaves was first promoted and then inhibited. The antioxidant enzyme system includes SOD, POD, CAT,APX. When the lead concentration were 2.5 g/kg, the activity of SOD,POD, CAT and APX had a significant difference between Pb treatment and control group, and the activity of them increased by52.9%, 159.4%, 133.4%, 61.5% compared to the control group(p <0.05). Under the same concentration of Pb, the activity of SOD, POD,CAT and APX were reduced by soaked with B. Subtilis QM3.(5)The effect of heavy metal Pb on the leaves ultrastructural of wheat leaves was first promoted and then inhibited. The number of mesophyll cell reduced significantly after heavy metal stress and even occurred collapse and disintegrated. When the lead concentration were 0.5-3.0g/kg, indexes of leaves thickness,diameter of inner and outer bundle sheath had a significant difference between Pb treatment group and control group. The indexes of wheat leaves reached the maximum when lead concentration was 0.5g/kg. Our results showed that B. Subtilis QM3 prevented decline in the thickness, diameter of inner and outer bundle sheath of leaves under Pb stress. When the lead concentration was 0.5g/kg, wheat soaked with B1, B2, B3,, the leaves thickness, diameter of inner and outer bundle sheath increased by 11.6%-21.3%, 64%-71.6%, 33%-81% compared to the control group(p < 0.05).In summary, lead stress were affected the growth of plants leaves in different degrees. From the composition, we can known that the chlorophyll content in wheat leaves(a, b, total content)were decreased, and the photosynthesis was severely affected by the lead stress; at the same time, it can enhance the resistance of wheat to heavy metal stress, mainly by increased the content of osmotic adjustment and the activities of antioxidant enzyme. From the structure, the lead stress have changed the leaves thickness,the diameter of the inner and outer bundle sheath. However, B.Subtilis QM3 as a mitigation bacterial strain, it can promote the growth of wheat, such as increased the amount of chlorophyll, the content of osmotic adjustment and the activity of antioxidant enzyme. Therefore, we can say that B. subtilis QM3 can relieved lead stress on the plant effectively. That is to say, it can enhanced the adaptability of wheat to lead stress. |
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