Hi ,
In event handler of Data_changed write this code.
LOOP AT er_data_changed->mt_good_cells INTO ls_good.
CASE ls_good-fieldname.
when <material decrption filed>.
Get row_id using method get_cell_value
Read <internal table > into wa index ro_id.
Get <material description >by using wa-matnr
modify cell value by
CALL METHOD pr_data_changed->modify_cell
EXPORTING
i_row_id = row_id
i_fieldname = 'material description field'
i_value = <material description >
for more details http://wiki.sdn.sap.com/wiki/display/ABAP/Get+Changed+Value+In+ALV+Grid+Dynamically.
Regards,
Sreenivas.