• transporters PaHMA2-3-4
• transporters PaABCC1-2
• populus alba
• poplar
• phytochelatins
• heavy metals
• Cadmium

Photoautotrophic organisms are faced with the complex regulation of metal homeostasis. Some metals (iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn)) are essential micronutrients for many physiological processes, but at high levels they interfere with metabolic reactions. Other metals (lead (Pb), cadmium (Cd), mercury (Hg), chromium (Cr), uranium (Ur), selenium (Se), silver (Ag), gold (Au), and nickel (Ni)), instead, are toxic even at low concentrations and are not beneficial to plants, causing reduced growth due to reduced photosynthetic activity and activity of many enzymes. Some of these metals are defined as heavy, and among them cadmium (Cd) is one of the most dangerous, and its presence in the soil is an environmental problem. Several evidences indicate that Cd uptake in plants occurs via divalent cation transporters, such as those for Zn, Ca, Mn, and Mg.
Among the heavy metal detoxification mechanisms present in most plants are phytochelatins (PCn), small peptides with a general structure of (gamma-glutamyl-cysteinyl)n-glycine ranging from 2 to 5. The biosynthesis of phytochelatins starts from glutathione (GSH) in a transpeptidase reaction catalyzed by phytochelatin synthase (PCS), a gamma-glutamylcysteine-dipeptidyl-(trans) peptidase belonging to the "CA clan" of "papain-like" cysteine proteases. PCS genes are constitutively expressed and phytochelatin accumulation is activated upon exposure to heavy metals. Phytochelatins chelate heavy metals, forming complexes that are sequestered in the vacuole through ATP-dependent transporters. Sequestration in the vacuole of phytochelatin-heavy metal complexes prevents ion accumulation in the cytosol.
Poplar can be used in the phytoextraction of Cd and other heavy metals from soil because of its high transpiration level, huge root system and high growth rate. Poplar can be considered as a tolerant non-hyper-accumulator because the heavy metals that have been absorbed by it generally remain at root level preventing or limiting toxic effects
This is the context for this master's thesis work, which aims to go and analyze in Populus alba the presence of phytochelatins, as well as some ecophysiological parameters in response to the presence of Cd. Finally, the expression levels of the enzyme PCS and the transporters PaABCC1-2 and PaHMA2-3-4 were evaluated by quantitative PCR.
Overall, the data collected and analyzed provided important insights into the defense and detoxification mechanisms involved in the response to Cd in P. alba.