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Abstract:
Poplar (Populus spp.) trees are widely distributed and play an important role in ecological
communities and in forestry. Moreover, by releasing high amounts of isoprene, these
trees impact global atmospheric chemistry. One of the most devastating diseases
for poplar is leaf rust, caused by fungi of the genus Melampsora. Despite the wide
distribution of these biotrophic pathogens, very little is known about their effects on
isoprene biosynthesis and emission. We therefore infected black poplar (P. nigra) trees
with the rust fungus M. larici-populina and monitored isoprene emission and other
physiological parameters over the course of infection to determine the underlying
mechanisms. We found an immediate and persistent decrease in photosynthesis
during infection, presumably caused by decreased stomatal conductance mediated
by increased ABA levels. At the same time, isoprene emission remained stable during
the time course of infection, consistent with the stability of its biosynthesis. There
was no detectable change in the levels of intermediates or gene transcripts of the
methylerythritol 4-phosphate (MEP) pathway in infected compared to control leaves.
Rust infection thus does not affect isoprene emission, but may still influence the
atmosphere via decreased fixation of CO2.
