Developmental and induced responses of nickel-based and organic defenses of the nickel-hyperaccumulating shrub, psychotria douarrei
2001
Davis, Michael A. | Pritchard, Seth C. | Boyd, Robert S. | Prior, Stephen A.
Developmental and inducible changes in metal-based (nickel (Ni)) and organic defenses (phenolics) are compared in the Ni-hyperaccumulating shrub, Psychotria douarrei. Young and old leaves of P. douarrei shrubs, subjected to different degrees of simulated herbivory, were analyzed for metals, tannins, macronutrients and total carbon, and compared with a co- occurring nonhyperaccumulator shrub, Ficus webbiana. Leaf age affected bot nickel Ni-based and organic defenses in P. dourarrei; foliar metal concentrations were higher in mature leaves, whereas organic defenses were higher in young leaves. Neither metal-based nor organic defenses were increased by simulated herbivore damage, implying noninducibility, although some organic defense compounds were significantly reduced. P. dourarrei had a greater percentage of total phenolics, condensed tannins and protein precipitation ability than F. webbianai. Since total carbon content did not tdiffer between species, Psychotria invests more of its leaf carbon budget in organic defenses than does Ficus. Data suggest that P. dourarrei foliage is well protected by Ni, but tannins have multiple functions. The high concentrations of tannins in Psychotria leaves might function as a detoxification mechanism for elevated cytoplasmic metal concentrations, in addition to providing defensive benefits.
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