Role of cysteine proteinase inhibitors in preference of Japanese beetles (Popillia japonica) for soybean (Glycine max) leaves of different ages and grown under elevated CO2.

ZAVALA, J.A.; NABITI, P.; CASTEEL, C.L.; BERENBAUM, M.R.; DE LUCIA, E.H.

OECOLOGIA

SPRINGER

Año: 2009 vol. 161 p. 35 - 41

0029-8549

The concentration of CO2 is rising and produces chemical changes in plant tissues that affect plant-insect interactions. In a previous study we demonstrated that elevated CO2 increased susceptibility of soybeans by down-regulating the expression of genes related to the defense hormones jasmonic acid and ethylene, which in turn decreased gene expression and activity levels of cysteine proteinase inhibitors (CystPIs) in soybean foliage, and increased digestive cysteines in the gut of the herbivore Japanese beetles (JB; Popillia japonica). To examine the effects of elevated CO2 on JB preference within the plant, soybeans were grown at the SoyFACE facility established at the University of Illinois at Urbana–Champaign. Here we demonstrated that CystPI activity modulates JB attack and preference within the plant by changing the digestive cysteine proteinase activity in their guts. The higher the CystPI activity in the foliage, the lower the damage produced by JB on soybean leaves. Typically, younger leaves with higher CystPI activity and photosynthetic rates are more important to support fitness and are more protected against herbivore attack. Although many defense traits are elicited after herbivore attack and younger leaves with higher fitness value are more protected than older leaves, our survey in the soybean field showed that elevated CO2 disrupted plant defenses increasing herbivore attack on younger leaves. The higher insect damage on younger leaves of plants grown under elevated CO2 found in FACE experiments may contribute to the offset of the predicted increases in agricultural productivity associated with greater levels of CO2 in the atmosphere.