Herbicide resistant transgenic plants

Due to increasing concern about contamination of environment by herbicides, new herbicides are being developed that are safer and biodegradable. This has necessitated the development of resistance in crop plants against these new and safer herbicides.

Herbicides, normally affect processes like photosynthesis or biosynthesis of essential amino acids. Two approaches have, therefore, been used for the development of herbicide resistant plants: (i) In the first approach, we try that either the target molecules should become insensitive to herbicide or the target protein should be overproduced. (ii) In the second approach, a pathway is introduced that will detoxify the herbicide.

Another class of herbicides includes sulphonylurea compounds (active ingredients of Glean and Qust herbicide) and imidazolinones that inhibit the enzyme acetolactate synthase (ALS), which is involved in the bisoynthesis of branched chain amino acids like leucine, isoleucine and valine. Transgenic tobacco plants expressing a mutant ALS gene from tobacco or Arabidopsis, were produced that were tolerant to sulphonylurea herbicides.

Similarly transgenic tobacco plants were produced by incorporation of genes for resistance against (i) L-phosphinothricin (PPT), which is the active ingredient of herbicide 'Basta' and inhibits glutamine synthase (GS), and (ii) atrazine which inhibits photosynthesis. These genes were isolated from Medicago sativa and Amaranthus hybrids respectively.