PLANT PHYSIOLOGY , Vol 104, Issue 3 1059-1065, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Diagnosis of the Earliest Strain-Specific Interactions between Tobacco Mosaic Virus and Chloroplasts of Tobacco Leaves in Vivo by Means of Chlorophyll Fluorescence Imaging
S. Balachandran, C. B. Osmond and P. F. Daley
Department of Botany, Duke University, Durham, North Carolina 27708
Fluorescence imaging was used to diagnose early stages of the
strain-specific interactions between tobacco mosaic virus (strain PV230)
and chloroplasts following infection of tobacco leaves (Nicotiana tabacum
cv Xanthi). The earliest indication of interaction in tissues that
ultimately become chlorotic was a reduction in chlorophyll fluorescence,
and there was little fluorescence quenching compared with adjacent healthy
tissues. Subsequently, fluorescence increased but remained unquenched. In
the late stages fluorescence declined again in chlorotic regions as the
chloroticmosaic symptoms developed. These in vivo data showing altered
fluorescence yields confirm strain-specific interaction of virus coat
protein with photosystem II (PSII) components in vitro, leading to
photoinhibition and photooxidation of chlorophyll in infected cells and the
development of visible chlorotic-mosaic symptoms. Although mechanisms
leading to the low, unquenched fluorescence condition are not known, the
intermediate high, unquenched fluorescence condition is consistent with
impaired PSII electron transport as measured in vitro. Fluorescence lesions
appear more rapidly and develop more extensively in high light, consistent
with the faster and larger extent of symptom formation in high-light-grown
leaves than in low-light-grown leaves.
