5 CONCLUSION
Redroot pigweed allelopathy leads to alteration in photosynthetic gas
exchange parameters of studied plants and the suppression of
photosynthetic electron transfer chain. In addition, increasing electron
leakage due to decline in reduced coenzymes utilization and increasing
free radicals in the photosynthetic space has been observed. The partial
return of emitted electrons to the photosystem II reaction centers along
with the cyclic electron transfer chain results in the continuation of
ATP production without NADPH/H+ production. Free
radicals’ presence in the photosynthetic space as well as the constant
return of electrons to photosystem II reaction centers make the
structure of this photosystem vulnerable, causing subunits to be
destroyed, especially D1 subunits. In addition to the indirect effect,
some allelochemicals present in the amaranth leachate, are also able to
directly bind to D1 subunits and destroy its structure. Finally, redroot
pigweed allelopathy can affect the expression of photosynthetic genes in
the treated plants and the quantity and quality of these effects are
dependent on studied plant species.