PLANT PHYSIOLOGY , Vol 104, Issue 3 1051-1057, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Susceptibility of Tobacco Leaves to Photoinhibition following Infection with Two Strains of Tobacco Mosaic Virus under Different Light and Nitrogen Nutrition Regimes
S. Balachandran and C. B. Osmond
Department of Botany, Duke University, Durham, North Carolina 27708
Sensitivity to photoinhibition under high light stress (2000 [mu]mol
photons m-2 s-1 for 2 h in air) and recovery from this stress were examined
in leaves of control, uninfected tobacco (Nicotiana tabacum cv Xanthi)
leaves and in leaves in tobacco plants infected with tobacco mosaic virus
(TMV) when grown under low light (150-200 [mu]mol photons m-2 s-1) or high
light (1200 [mu]mol photons m-2 s-1) with high (8.0 mM) or low (0.5 mM)
nitrate supply. Photoinhibition was monitored using the dark-adapted
fluorescence parameters variable fluorescence/maximum fluorescence, an
indicator of photosynthetic efficiency that correlated well with the
quantum yield of photosynthetic oxygen evolution, and initial fluorescence,
potentially an indicator of photoinhibitory damage. Susceptibility to
photoinhibition was greater in low light- and low nitrogen-grown control
plants than in high light- or high nitrogen-treated plants. Compared with
uninfected controls, infection with the masked strain PV42 increased
susceptibility to photoinhibition only in plants grown under low light/low
nitrogen conditions. In expanding leaves, infection with severe strain TMV
PV230 markedly accelerated photoinhibition under these conditions and under
high light/low nitrogen conditions, even before visible symptoms were
evident. High nitrogen levels during growth protected against this
accelerated photoinhibitory response to virus infection during light stress
and generally promoted recovery, at least prior to symptom development. As
symptoms developed, the yellow regions provided evidence for chronic
photoinhibitory damage, prior to and during the stress treatment,
irrespective of growth conditions. Green regions of leaves showing visible
symptoms were generally indistinguishable from control, uninfected plants
during photoinhibitory stress and recovery. In developed leaves that
remained free of visible symptoms during the experiments, in spite of the
accumulation of about the same amounts of virus protein (S. Balachandran,
C.B. Osmond, A. Makino [1994] Plant Physiol 104: 1043-1050) infection led
to an acceleration of photoinhibition during stress treatments, especially
in low light/low nitrogen treatments, in which chronic photoinhibitory
damage was evident. These studies suggest a role for photoinhibitory damage
in the acceleration of visible symptom development following TMV PV230
infection of expanding leaves, as well as in acceleration of senescence in
developed leaves without visible symptoms.
