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We
have developed an instrument to spatially map chlorophyll fluorescence
from intact leaves. Our instrument
extends the capabilities of previous instruments by (1) measuring Fo
in addition to other steady-state fluorescence parameters Fm, Fm’, F’;
(2) imaging both rapid fluorescence induction kinetics and electron
transfer in the two-electron gate of photosystem II; (3) allowing for
imaged areas ranging from 4 mm2
to 6 cm2;
and (4) allowing leaves to be free, attached to the plant, or held in a
cuvette that allows for environmental control and simultaneous measurement
of gas exchange parameters. Illumination
is provided by a combination of 1200 red and blue LEDs that deliver
measuring pulses, an over-saturation pulse, or continuous actinic light.
Measurement of fluorescence yield is achieved by detection of
fluorescence during short (typically <100 msec),
weak (<1% actinic) pulses of blue light. The instrument’s electronics
currently support a JAI progressive scan CCD camera (659 x 494; 8-bit; 10
Hz) but allow for easy upgrade to more sensitive or higher speed cameras.
All instrument parameters (timing, intensities, LED color ratio,
shuttering times) can be varied independently to provide flexibility for
different experimental protocols. Control
of the instrument, image capture, manipulation, analysis, and presentation
are executed through a program developed specifically for the task.
We are using this instrument to study how herbivory by insects
affects the photosynthetic competence of the remaining leaf tissues.
Initial results indicate that apparent rates of electron transport
in linden bean are reduced by 40% at >5 mm from the point of herbivory
by corn earworm. The ability to
reduce photosynthesis away from the initial region of damage suggests that
the effects of herbivory on plant production may have been greatly
underestimated in the past. We are
in process of modifying the instrument to simultaneously map chlorophyll
fluorescence and gene transcription by fluorescence from green-fluorescent
protein.
Tim
Miller and Antony Crofts
, Department of
Biochemistry, University of Illinois
; Kevin
Oxborough
, Department
of Biological Sciences, University of Essex
; Jason
Hamilton and Evan DeLucia
, Department
of Plant Biology, University of Illinois
We gratefully acknowledge
the Competitive Research Initiative at the University of Illinois for
providing the funding for this project. |
