Fig. 4.

Responses induced by ZmPep3 are effective direct defenses against Spodoptora exigua herbivory. (A) Relative expression of genes encoding proteinase inhibitors and (B) genes encoding biosynthetic enzymes for benzoxazinoid defense metabolites associated with direct defense against herbivores 12 h posttreatment with water (yellow), ZmPep3 (dark blue), or Gln-18:3 (light blue). (C) Accumulation of the highly reactive benzoxazinoid precursor 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc) 48 h posttreatment in scratch-wounded intact leaves. Statistics were used to compare plant tissues that were damaged and treated with either water, ZmPep3, or Gln-18:3 each applied at 2 nmol⋅g⁻¹ FW. Within each plot, different letters (a–c) represent significant differences between mean values (n = 4, ± SEM; all ANOVAs, P < 0.005; Tukey test corrections for multiple comparisons, P < 0.05). (D) Fold change in S. exigua larval mass after 18 h on leaves that were either untreated (black) or pretreated for 48 h with water, ZmPep3, or Gln-18:3. Within each plot, different letters (a and b) represent significant differences between mean values (n = 24, ± SEM; ANOVA, P < 0.015; Tukey test corrections for multiple comparisons, P < 0.05).