Molecular Genetics and Plant Growth Hormone

Molecular genetics has advanced over the last three decades by leaps and bounds, providing knowledge regarding the control of developmental events nucleic acids and proteins. Further, scientists have perfected techniques in identification, isolation, sequencing of genes, their transplantation into new hosts, production of transgenic crops, so on so forth. It is no wondered that there is a temptation to make use of all this in plant hormone studies also. Following are the various aspects of these studies: a) Mutant varieties in various plant species which are identified for over production or under production of a given plant hormone are being isolated from nature or sometimes these mutants are produced through mutation breeding techniques.

Studies on phenotypic nature of these mutants would throw new light on the fact how far our earlier assumptions on the physiological responses of various plant hormones are correct or not. Mutants which are deficient in the production of particular hormone step in biosynthetic pathway are also found. Studies of these mutants are helping us in understanding the intricacies of biosynthetic pathways of hormones. Mutants which fail to show a particular physiological response to a given hormone (E.g. cytokinin retards leaf senescence, promotes leaf expansion, promotes chlorophyll biosynthesis etc., in wheat).

There can be one wheat mutant that shows all other responses except leaf senescence. Identification of genes that produce these hormones, cloning them and transplanting them in some other plants also helps us a good deal in knowing the interaction of hormones. Changes in the levels of molecules like m-RNA i.e. in terms of total quantity or quality i.e. how many new species of m - RNA etc. are being followed in cells exposed to hormones over the last two decades. These studies have given new information about hormonal effects at transcriptional and post-transcriptional levels. Observations have shown that polyribosomes formation is higher in cytokinin treated cells. Auxins stimulate both production of ribosomal RNA and m-RNA meant for ribosomal proteins. ABA has shown to cause deactivation of ribosomes. GA₃ treated cells show enhancement of ribosomal activity.