A plant cell which is resistant to a herbicidal glutamine synthetase (GS) inhibitor, wherein the resistance is caused by levels of GS activity which, when present in an otherwise herbicidal GS inhibitor senstive plant cell, render the cell substantially resistant to the herbicidal GS-inhibitor. The plant cell may, for example, carry a genetic sequence combination comprising a first genetic sequence coding for genomic GS functional in the plant cell operably linked to a second genetic sequence capable of increasing the levels of expression of the first genetic sequence, thereby increasing the levels of GS activity within the cell.
