Master of Science

In this experimental study, the effects of the application of plant growth regulators on flavonoid biosynthesis pathway were examined using transgenic red tobacco plants. The ectopic expression of the Myeloblastosis (MYB) transcription factor, production of anthocyanin pigment l (PAPI) fiom Arabidopsis had been strongly enhanced in these transgenic red tobacco plants. Controlled transcription of biosynthetic genes is one way to regulate secondary metabolite production like, anthocyanin pigments in plant cells. It is known that transcription factor affects several metabolic steps at the lower end of the flavonoid biosynthetic pathway, by reducing mRNA levels of genes encoding enzymes involved in anthocyanin and flavonol biosynthesis. In this study, it was found that the exogenous application of the growth regulator, trinexapac-ethyl (PrimoB) caused a decrease in the anthocyanin content in the transgenic plants. On the other hand, the anthocyanin content in these transgenic red tobacco plants was further enhanced by the application of methyl jasmonate (MeJA). Lastly, it was also observed in this study that the developmental stage of the plants could affect the anthocyanin accumulation by these plant growth regulators as well. It was found that the application of MeJA influences and increases the accumulation of anthocyanin especially at the newly expanded older leaves. Therefore, these older leaves tend to benefit more with this exogenous application of MeJA. On the other hand, the application of primoB affects the accumulation of anthocyanin in newly expanded younger leaves to a greater extent. This is consistent with the fact that anthocyanin usually accumulates at the young leaves for the function of photo-protection. Thus the anthocyanin content is more likely to be negatively affected at the younger leaves under the effect of exogenous retardant.