Boyd, Robert .
Exploring Plant Elemental Defenses: Conceptual Models of the Defensive Enhancement and Joint Effects Hypotheses.
The concept of plant elemental defenses originated as an explanation for extremely elevated concentrations of some elements (termed hyperaccumulation) in tissues of some plant species (called hyperaccumulators). Here I further develop elemental plant defense by presenting conceptual modelsof two new related hypotheses. The Defensive Enhancement Hypothesis (DEH) suggests that hyperaccumulation evolved from relatively low levels of elements that provided plants with defensive benefits against their natural enemies. In this scenario, after an initial defensive benefit accrued from a relatively low initial concentration, increased concentration of an element provided increased plant fitness. This in turn allowed natural selection to favor greater and greater elemental concentrations, until hyperaccumulation levels were achieved. Critical to the DEH is occurrence of defensive effects of elements at relatively low concentrations: this has been demonstrated in recent experiments against some plant natural enemies. The second new hypothesis (Joint Effects Hypothesis) postulates that additive or synergistic effects between more than one elemental defense, or between an elemental and an organic chemical defense, may have contributed to the evolution of hyperaccumulation. By lessening the concentration of an element necessary to provide an initial defensive benefit to a plant, joint effects could decrease the level of an element that provides an initial defensive benefit and so allow defensive enhancement to take effect. Recent experimental tests, of both element/element and element/organic compound combinations, have shown joint effects that support this hypothesis. Together, these hypotheses suggest how hyperaccumulator plants may have evolved in response to plant-natural enemy interactions. They also illustrate the potential importance of elemental defenses to plant ecology and evolution by suggesting that elemental levels below those used to define hyperaccumulation may be ecologically effective.
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1 - Auburn University, Department Of Biological Sciences, 101 LIFE SCIENCES BLDG, AUBURN UNIVERSITY, AL, 36849-5407, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Franklin B/Hyatt
Date: Wednesday, July 11th, 2012
Time: 10:30 AM