PARENT SESSION
Contributed Oral Session 102: Herbivory: Effects of Photosynthesis; Nutrients
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal
Effects of herbivore feeding behavior on photosynthesis in Arabidopsis thaliana .
Tang, Jennie*,1, Zielinski, Raymond1, Zangerl, Arthur1, Crofts, Antony1, Berenbaum, May1, DeLucia, Evan1, 1 University of Illinois at Urbana-Champaign, Urbana, IL
ABSTRACT- The impact of herbivory on photosynthesis in the remaining leaf tissue may be as significant as the loss of photosynthetic tissue. An important factor that can influence how a damaged leaf responds to herbivory is the mode in which tissue was removed by the herbivore. We characterized how the different feeding behaviors of first and fourth instar Trichoplusia ni larvae affect photosynthesis in Arabidopsis thaliana and examined potential mechanisms by which they cause different effects. First instars make small holes and avoid veins, while fourth instars make large holes and consume veins. After larvae removed about 20 mm2 of leaf tissue, photosynthesis was measured by gas exchange and chlorophyll fluorescence imaging. To determine possible mechanisms of damage, we examined water loss from the cut edge with thermal imaging and the expression of a key photosynthetic gene, the Rubisco small subunit, with green fluorescent protein imaging. First instars reduced photosynthesis more than fourth instars: they decreased the assimilation rate by 16% and reduced the maximum quantum efficiency of Photosystem II photochemistry (Fv/Fm) by 4-8%. Fourth instars had no effect on either the assimilation rate or Fv/Fm. In leaves damaged by first instars, photosynthetic damage spread around holes that led to significant tissue desiccation in five of eight leaves; fourth instars caused little to no desiccation. The small holes produced by first instars may have isolated patches of tissue from the vascular system. First instars may have caused more water stress than fourth instars: water loss from cut edges produced by first instars persisted four days after herbivory, but ceased by day four for fourth instars. Since neither first nor fourth instar herbivory had a detectable effect on the expression of the Rubisco small subunit gene, we cannot attribute the difference in their effects to alternative changes in gene expression. The mode of feeding was important for determining the photosynthetic response to herbivory and appeared to be mediated by the level of water stress caused by the herbivore.
Key words: chlorophyll fluorescence imaging, thermal imaging, Rubisco small subunit gene, Trichoplusia ni