Changes in photosynthesis, mesophyll conductance to CO2, and isoprenoid emissions in Populus nigra plants exposed to excess nickel

Poplar (Populus nigra) plants were grown hydroponically with 30 and 200 μM Ni (Ni30 and Ni200). Photosynthesis limitations and isoprenoid emissions were investigated in two leaf types (mature and developing). Ni stress significantly decreased photosynthesis, and this effect depended on the leaf Ni content, which was lower in mature than in developing leaves. The main limitations to photosynthesis were attributed to mesophyll conductance and metabolism impairment. In Ni-stressed developing leaves, isoprene emission was significantly stimulated. We attribute such stimulation to the lower chloroplastic [CO2] than in control leaves. However chloroplastic [CO2] did not control isoprene emission in mature leaves. Ni stress induced the emission of cis-β-ocimene in mature leaves, and of linalool in both leaf types. Induced biosynthesis and emission of isoprenoids reveal the onset of antioxidant processes that may also contribute to reduce Ni stress, especially in mature poplar leaves.

Graphical abstractVisible damage caused by Ni treatment. 1 – Ni0 (control plants); 2 – Ni200; M = mature and D = developing Populus nigra leaves.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We study the effect of Ni pollution on photosynthesis and isoprenoid emissions. ► Ni stress significantly decreases photosynthesis. The main limitations are attributed to mesophyll conductance and metabolism impairment. ► Constitutive isoprene emission was significantly stimulated in Ni-stressed leaves. Exposure to enhanced Ni concentration induces cis-beta-ocimene and linalool emissions.