Leaves position in Populus alba Villafranca clone reveals a strategy towards cadmium uptake response

Abstract: The aim of this study was to investigate Cd uptake of Populus alba Villafranca clone applying 0, 0.5 and 1 mg kg−1 soil DW of Cd (Cdc, Cdl and Cdh respectively) for 6 weeks. Cd allocation in the leaves, as a function of their position along the stem, was studied before its toxicity may alter physiological, biochemical and molecular biology of plants. Significant growth stimulation of roots (2.5 and 2.2 times more than control at Cdl and Cdh, respectively) and basal leaves (+79 and +55 % at Cdl and Cdh, respectively) was recorded when Cd was accumulated in a relatively higher concentration compared to other organs. In these experimental conditions, Villafranca clone can be considered a ‘‘root accumulator’’; in fact Translocation factor (Tf) calculated at leaves and stem levels were below 1. Even if Cd distribution among leaves did not change in function of their position, only apical leaves of Villafranca clone didn’t show changes in AsA and GSH concentration after Cd exposure as indication of different mechanism of Cd scavenge ability. A different expression of the genes related to antioxidant machinery such as GST, GPX and cAPX was observed in apical leaves, indicating that a strict regulation of the antioxidant defence system is required by poplar plant under Cd. All these energy consuming mechanisms were not found in more aged median and basal leaves. This could be a strategy adopted by Villafranca clone to avoid Cd effect in apical leaves, allowing plants to continue their growth without damages. Graphical Abstract: [Figure not available: see fulltext.

Expression of specific genes involved in Cd uptake, translocation, vacuolar compartmentalisation and recycling in Populus alba Villafranca clone

Cadmium (Cd) is a heavy metal toxic to humans and its occurrence in soils represents a significant environmental problem. Poplar trees may provide one possible option to help remove Cd contamination from soil. However, before this is practicable, the ability of poplar to accumulate Cd needs to be enhanced. A better understanding of the genes involved in Cd accumulation in poplar would help to achieve this goal. Here, we monitored the expression of genes known to be involved in Cd uptake, accumulation and translocation from other species, in order to provide information on their potential role in Cd accumulation in poplar. Cd concentration in poplar was significantly higher in roots than in stem and leaves in Cd treated plants. Expression of the poplar homologues of IRT1, NRAMP and OPT3 was initially increased after exposure to Cd but reduced after longer term Cd exposure. Exposure to Cd also influenced the accumulation of Fe, Ca, Cu, Mg and Mn in poplar. In particular, Cd treated plants had a higher concentration of Fe, Ca, Cu, and Mg in leaves and stem compared to control plants after one day and one week of experiment; while in roots after one month Cd treated plants had a lower concentration of Mn, Fe, Cu, Co, and Mg