Browsing by Subject "Xylem production"

After Prokaryotes, plants have the largest biomass on Earth. Xylem, commonly known as wood, represents most of this biomass. Like any other organism, plants have stem cells – meristems – that are responsible for the formation of new tissues. Regarding xylem formation, the responsible meristem is called vascular cambium, and it is found in the root and shoot of plants. Still today, the regulation of the vascular cambium is not well-characterized. The main objective of the Plant Growth Dynamics group is to understand how the vascular cambium is regulated. For that, we were interested in finding the organizing center, a group of cells in contact with the meristem and key regulators of stem cell activity, which happens to be unidentified in the vascular cambium. The Plant Growth Dynamics group had reasons to believe that xylem committed cells can be this missing organizing center. Therefore, this thesis research was focused on testing the validity of this hypothesis. We approached this research in two different ways; first, to induce xylem committed cells with GA treatment, and later on to observe the vascular formation with Paclobutrazol (PAC), a GA biosynthesis inhibitor. Second, to inhibit HD Zips III family of transcription factors, involved in vascular patterning and xylem identity, and this way block the formation of new xylem committed cells. In addition, we were also interested in the molecular regulation of GA and HD Zips III on xylem production. Our different approaches shed some light on the molecular and hormonal regulation of the vascular cambium and xylem production. We have observed the positive role of GA on PIN stability, polar auxin transport and xylem expansion and confirmed the contrary effects of PAC in the root, reducing auxin responses and xylem area. Further, we described the role of HD Zips III in defining the auxin maxima by controlling PIN polarity, crucial for xylem specification. Together, our results strongly suggest that xylem-committed cells can act as the organizing center for the vascular cambium, since both induction and inhibition of xylem-committed cells can induce meristematic changes and vast misregulation of the vascular cambium activity. However, further research is needed to fully understand the regulation of the vascular cambium.