Application of Indole-Alkaloid Harmaline Induces Physical Damage to Photosystem II Antenna Complexes in Adult Plants of Arabidopsis thaliana (L.) Heynh

Finding herbicides with new and multiple modes of action
is a solution
to stop the increase in resistant weed species. Harmaline, a natural
alkaloid with proven phytotoxic potential, was tested on Arabidopsis adult plants by watering and spraying; watering resulted as the
more effective treatment. Harmaline altered several photosynthetic
parameters, reducing the efficiency of the light- (ΦII) and dark-adapted (Fv/Fm) PSII, suggesting physical damages in photosystem
II, although dissipation of the energy in excess under the form of
heat was not compromised as demonstrated by the significant increase
in ΦNPQ. Metabolomic alterations, such as osmoprotectant
accumulation and reduction in sugars’ content, also indicate
a reduction of photosynthetic efficiency and suggest early senescence
and water status alteration induced by harmaline. Data suggest that
harmaline might be considered a new phytotoxic molecule interesting
for further studies.