Betanin-Mediated Antiherbivore Defense: Functional Significance of Red Pigmentation in Epidermal Salt Bladders of Chenopodium album Leaves.

Plant coloration, predominantly regulated by various natural plant pigments, has been hypothesized to serve crucial ecological functions in plant-animal interactions. Betalains are a rare class of plant pigments synthesized exclusively in specific families within the Caryophyllales order. Their biosynthesis is restricted by the availability of nitrogen. Betalains exhibit significant functions like protecting plants against abiotic stresses, pathogen, and virus; however, their role in plant-herbivore interactions remains largely unknown. In the current study, binary feeding assays revealed that the red leaves of Chenopodium album and the epidermal red salt bladders isolated from the leaves showed defensive effects against Peridroma saucia larvae. Subsequent LC-MS/MS analysis identified betanin as the primary pigment in the red salt bladders, while HPLC quantification revealed a betanin concentration of 0.121 mg/cm on leaf surface. Bioassays with purified betanin showed dose-dependent defensive efficacy against P. saucia larvae, establishing a direct link between pigment concentration and anti-herbivore activity. This study elucidated the chemical defense function of betanin, discussed the growth-defense trade-off in C. album leaves, and explored its potential coevolutionary dynamics with herbivores, providing novel insights into pigment-driven ecological adaptations.