Papain protects papaya trees from herbivorous insects: role of cysteine proteases in latex
Article first published online: 11 DEC 2003
The Plant Journal
Volume 37, Issue 3, pages 370–378, February 2004
How to Cite
Konno, K., Hirayama, C., Nakamura, M., Tateishi, K., Tamura, Y., Hattori, M. and Kohno, K. (2004), Papain protects papaya trees from herbivorous insects: role of cysteine proteases in latex. The Plant Journal, 37: 370–378. doi: 10.1046/j.1365-313X.2003.01968.x
- Issue published online: 9 JAN 2004
- Article first published online: 11 DEC 2003
- Received 22 August 2003; revised 10 October 2003; accepted 20 October 2003.
- plant latex;
- cysteine protease;
- Eri silkmoth;
- plant defense;
- plant–herbivore interactions
Many plants contain latex that exudes when leaves are damaged, and a number of proteins and enzymes have been found in it. The roles of those latex proteins and enzymes are as yet poorly understood. We found that papain, a cysteine protease in latex of the Papaya tree (Carica papaya, Caricaceae), is a crucial factor in the defense of the papaya tree against lepidopteran larvae such as oligophagous Samia ricini (Saturniidae) and two notorious polyphagous pests, Mamestra brassicae (Noctuidae) and Spodoptera litura (Noctuidae). Leaves of a number of laticiferous plants, including papaya and a wild fig, Ficus virgata (Moraceae), showed strong toxicity and growth inhibition against lepidopteran larvae, though no apparent toxic factors from these species have been reported. When the latex was washed off, the leaves of these lactiferous plants lost toxicity. Latexes of both papaya and the wild fig were rich in cysteine-protease activity. E-64, a cysteine protease-specific inhibitor, completely deprived the leaves of toxicity when painted on the surface of papaya and fig leaves. Cysteine proteases, such as papain, ficin, and bromelain, all showed toxicity. The results suggest that plant latex and the proteins in it, cysteine proteases in particular, provide plants with a general defense mechanism against herbivorous insects.