How to fire dropdownlist selectedindexchanged on edititemtemplate in gridview....pls help me to solve this

<asp:GridView ID="GridView1" runat="server"
OnRowCancelingEdit="GridView1_RowCancelingEdit" OnRowCommand="GridView1_RowCommand"
OnRowDataBound="GridView1_RowDataBound"
OnRowDeleting="GridView1_RowDeleting" OnRowEditing="GridView1_RowEditing"
OnRowUpdating="GridView1_RowUpdating";
<asp:TemplateField HeaderText="SNo" HeaderStyle-Width="10%">
<itemtemplate>
<asp:Label ID="lblName1" runat="server" Text='<%#Eval("SNo") %>'>
</itemtemplate>

<asp:TemplateField HeaderText="Compliance" HeaderStyle-Width="10%">
<itemtemplate>
<asp:Label ID="lblDepartment"   runat="server" Text='<%#Eval("Compliance") %>'>
</itemtemplate>
<edititemtemplate>
<asp:DropDownList ID="DropDownListDepartment" runat="server"
Width="60"  AutoPostBack="true" >
</edititemtemplate>
<footertemplate>
<asp:DropDownList ID="DropDownListAddDepartment" runat="server"
Width="60">
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ErrorMessage="*"
 ControlToValidate="DropDownListAddDepartment" 
ValidationGroup="valGrp">
</footertemplate>


<asp:TemplateField HeaderText="Marks Alloted" HeaderStyle-Width="10%">
<itemtemplate>
<asp:Label ID="lblMarks" runat="server" Width="50px" Text='<%#Eval("Marks") %>' >
</itemtemplate>
<footertemplate>
<asp:TextBox ID="txtAddMarks"  runat="server"  Width="50px">

private DataTable GetEmpDept()
{
    //Get Employee department
    DataTable dt = new DataTable();
    dt.Columns.Add("DepName");
    DataRow rw1 = dt.NewRow();
    rw1[0] = "Yes";
    dt.Rows.Add(rw1);
    DataRow rw2 = dt.NewRow();
    rw2[0] = "No";
    dt.Rows.Add(rw2);
    DataRow rw3 = dt.NewRow();
    rw3[0] = "NA";
    dt.Rows.Add(rw3);
    return dt;
}