In cases of mortgaged real estate, the mortgagor, for the purposes of taxation, shall be deemed the owner, until the mortgagee takes possession, after which the mortgagee shall be deemed the owner. Any mortgagee of real estate, on which any taxes remain unpaid for a period of 8 months after the taxes are assessed, may pay such taxes, and the amount so paid together with interest and costs thereon shall become a part of the mortgage debt and shall bear interest at the same rate as the lowest rate of interest provided for in any of the notes secured by any mortgage on that real estate held by such mortgagee.