Abstract
Plant latex is widely found in plant species (ca. 12,000-35,000 species). We here show two novel examples from our studies where latex ingredients, proteins and chemicals, play crucial roles in plant defense against insect herbivory.
Leaves of the Papaya tree (Carica papaya) showed strong toxicities against lepidopteran larvae such as Samia ricini, Mamestra brassicae, and Spodoptera litura, though no apparent toxic factors from these species had been reported. Our results suggested that cysteine proteases in latex, papain, is responsible for the defense activity.
Mulberry leaves (Morus spp.) showed strong toxicities to lepidopteran larvae other than the silkworm, Bombyx mori, (such as S. ricini and M. brassicae). The high concentrations (1.5-2.5% to wet latex, 8-18% to dried latex) of anti-diabetic sugar-mimic alkaloids that we found in mulberry latex, such as 1,4-dideoxy-1,4-imino-D-arabinitol (D-AB1), 1-deoxy nojirimycin (DNJ), and 1,4-dideoxy -1,4-imino-D-ribitol, accounted for the defense activities of mulberry leaves against insect herbivory.
