Hi Abhinav,
Since the Plant field is second in the itab, you can't use AT END OF in this case. Declare a work area like WA_PREVIOUS of same type as your itab. As the last statement in your loop, copy the current table row into WA_PREVIOUS. Prior to that, use IF itab-plant <> wa_previous_plant to call the BAPI. After the loop you need to handle the last plant in the itab by testing IF wa_previous_plant IS NOT INITIAL then call the BAPI.
Make sure the itab is sorted by plant.
Jim