Flavonoids Affect the Light Reaction of Photosynthesis in Vitro and in Vivo as Well as the Growth of Plants

Flavonoids retusin (5-hydroxy-3,7,3′,4′-tetramethoxyflavone)
(1) and pachypodol (5,4′-dihydroxy-3,7,3′-trimethoxyflavone)
(2) were isolated from Croton ciliatoglanduliferus Ort. Pachypodol acts as a Hill reaction inhibitor with its target
on the water splitting enzyme located in PSII. In the search for new
herbicides from natural compounds, flavonoids 1 and 2 and flavonoid analogues quercetin (3), apigenin
(4), genistein (5), and eupatorin (6) were assessed for their effect in vitro on the photosynthetic
electron transport chain and in vivo on the germination and growth
of the plants Physalis ixocarpa, Trifolium alexandrinum and Lolium perenne. Flavonoid 3 was
the most active inhibitor of the photosynthetic uncoupled electron
flow (I50 = 114 μM) with a lower
log P value (1.37). Results in vivo suggest that 1, 2, 3, and 5 behave
as pre- and postemergent herbicides, with 3 and 5 being more active.