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.