Journal of Experimental Botany, Vol 49, 1671-1679, Copyright © 1998 by Oxford University Press
C Lu and J Zhang
Analyses of CO2 exchange and chlorophyll fluorescence were carried out to
assess photosynthetic performance during senescence of maize leaves.
Senescent leaves displayed a significant decrease in CO2 assimilatory
capacity accompanied by a decrease in stomatal conductance and an increase
in intercellular CO2 concentration. The analyses of fluorescence quenching
under steady-state photosynthesis showed that senescence resulted in an
increase in non-photochemical quenching and a decrease in photo-chemical
quenching. It also resulted in a decrease in the efficiency of excitation
energy capture by open PSII reaction centres and the quantum yield of PSII
electron transport, but had very little effect on the maximal efficiency of
PSII photochemistry. The results determined from the fast fluorescence
induction kinetics indicated an increase in the proportion of
QB-non-reducing PSII reaction centres and a decrease in the rate of QA
reduction in senescent leaves. Theoretical analyses of fluorescence
parameters under steady-state photosynthesis suggest that the increase in
the non-photochemical quenching was due to an increase in the rate constant
to thermal dissipation of excitation energy by PSII and that the decrease
in the quantum yield of PSII electron transport was associated with a
decrease in the rate constant of PSII photochemistry. Based on these
results, it is suggested that the decrease in the quantum yield of PSII
electron transport in senescent leaves was down-regulated by an increase in
the proportion of QB-non-reducing PSII reaction centres and in the
non-photochemical quenching. The photosynthetic electron transport would
thus match the decreased demand for ATP and NADPH in carbon assimilation
which was inhibited significantly in senescent leaves.Key words:
Chlorophyll fluorescence, gas exchange, maize (Zea
mays L.), photochemical and non-photochemical quenching,
photosystem II photochemistry.
ARTICLES
Modifications in photosystem II photochemistry in senescent leaves of maize plants
Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong; Corresponding author
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