Isolation and Characterization of Cyclotides from Brazilian <i>Psychotria</i>: Significance in Plant Defense and Co-occurrence with Antioxidant Alkaloids

Plants from the genus <i>Psychotria</i> include species bearing cyclotides and/or alkaloids. The elucidation of factors affecting the metabolism of these molecules as well as their activities may help to understand their ecological function. In the present study, high concentrations of antioxidant indole alkaloids were found to co-occur with cyclotides in <i>Psychotria leiocarpa</i> and <i>P. brachyceras</i>. The concentrations of the major cyclotides and alkaloids in <i>P. leiocarpa</i> and <i>P. brachyceras</i> were monitored following herbivore- and pathogen-associated challenges, revealing a constitutive, phytoanticipin-like accumulation pattern. Psyleio A, the most abundant cyclotide found in the leaves of <i>P. leiocarpa</i>, and also found in <i>P. brachyceras</i> leaves, exhibited insecticidal activity against <i>Helicoverpa armigera</i> larvae. Addition of ethanol in the vehicle for peptide solubilization in larval feeding trials proved deleterious to insecticidal activity and resulted in increased rates of larval survival in treatments containing indole alkaloids. This suggests that plant alkaloids ingested by larvae might contribute to herbivore oxidative stress detoxification, corroborating, in a heterologous system with artificial oxidative stress stimulation, the antioxidant efficiency of <i>Psychotria</i> alkaloids previously observed <i>in planta</i>. Overall, the present study reports data for eight novel cyclotides, the identification of <i>P. leiocarpa</i> as a cyclotide-bearing species, and the absence of these peptides in <i>P. umbellata