全 文 ：Received 8 Sept. 2003 Accepted 7 Jan. 2004
Supported by the National Natural Science Foundation of China (30200021).
* Author for correspondence. E-mail: .
http://www.chineseplantscience.com
Acta Botanica Sinica
植 物 学 报 2004, 46 (5): 552-559
Diurnal Photosynthesis and Photoinhibition of Rice Leaves
with Chlorophyll Fluorescence
LIU Ji-Yong1, QIU Bao-Sheng1, 2* , LIU Zhi-Li2, YANG Wan-Nian1
(1. College of Life Sciences, Central China Normal University, Wuhan 430079, China;
2. College of Life Sciences, Nanjing University, Nanjing 210093, China)
Abstract : The diurnal photosynthesis and photoinhibition in the photoper iod-sensit ive genic
male-sterile rice (Oryza sativa L.), Nongken 58S (NK58S), were investigated. From 06:00 to 09:00, no
remarkable photoinhibition occurred, and the down-regulation of photosynthesis might be due to the
running of xanthophylls cycle. From 10:00 to 12:00, the specific energy flux for dissipation (DIo/RC) and
the net rate of reaction centers (RCs) closure (dV/dto) were increased, while the probability of electron
transport at the acceptor side (yo) and the density of active RCs (Do) were decreased. These indicated
that the photoinhibition of NK58S was exacerbated with the inactivation of PSⅡ RCs. Fluorescence dark
relaxation analysis and inhibitor treatment suggested that all of state transition, xanthophyll cycle and
inactivation of PSⅡ RCs could contribute to protect NK58S against photodamage. Compared with the
inactivation of PSⅡRCs, xanthophyll cycle had an immediate response to high light stress, wh ich
functioned mainly in the period of relatively low light intensity. However, the inactivation of PSⅡ RCs
played an important role in protecting the remaining active RCs when xanthophyll cycle was saturated.
Key words: photoperiod-sensitive genic male-sterile rice; Nongken 58S; JIP test; photoinhibition;
reaction center inactivation; D1 protein turnover; xanthophylls cycle
Higher plants are usually encountered with light stress
in their habitats. Strong irradiance will inevitably induce
photoinhibit ion with the decrease of photochemical effi-
ciency when the absorbed energy is much higher than that
utilized by the photosynthetic organs (Long et al., 1994).
The photoinhibition will occur much frequently when strong
irradiance is combined with high temperature, drought or
o ther s t ress es in s ummer midday . Furthermore, the
photoinhibition could result in photooxidative damage, pig-
ment bleaching and even irreversible damage to the photo-
syn thetic apparatus. Numerous p rotective mechanisms
have been developed to minimize the sunlight absorption
in long-term evolu tionary history, such as alterat ion in
leaves ang le, chloroplast movement and reflective cuticle
covering. Alternatively, state transition, xanthophylls cycle
and PSⅡ repair cycle contribute internally to avoiding the
damage to the photosynthetic apparatus (Long et al., 1994;
Horton et al., 1996). However, various species might differ
in their protective mechanisms for photoinhibition.
Photoinhibition is characterized by the decline of pho-
tos ynthet ic quan tum efficiency and pho tochemical
efficiency, and Fv/Fm value is widely used as an index to
evaluate the extent o f photoinhibit ion (Krause and Weis,
1991; Govindjee, 1995; Maxwell and Johnson, 2000).
Nevertheles s, many processes includ ing PSⅡ reaction
center repair cycle and thermal dissipation associated with
xan thophylls cycle could lead to the decrease o f Fv/Fm
(Long et a l ., 1994). In add it ion , the locat ion o f
pho to inh ib it ion varies with the s pecific inh ib itory
mechanisms, donor side or acceptor side of PSⅡ reaction
center (Long et al., 1994; Andersson and Aro, 2001). These
could not be distinguished just by evaluating the changes
of Fv/Fm. Then, a thorough investigation on the primary
photochemical reactions as well as the whole electron trans-
port chain by the fluorescence techniques is required. This
is the story of “JIP test”.
Fast fluorescence rise of dark-adapted leaves recorded
with high time-resolution fluorimeters such as PEA shows
a polyphasic O-J-I-P transient. The polyphasic O-J-I-P rise
reflects the kinetic process of PSⅡ closure and has also
been found to be very sensit ive to s tres ses caused by
changes in different environmental conditions, such as light
intensity, temperature, drought, atmospheric CO2 or ozone
elevation and chemical in fluences (Strasser and Tsimilli-
Michael, 2001). But it is hard to evaluate the PSⅡ pho to-
chemical behav iors just from its shape change. The JIP-
tes t has been in troduced and further developed for the
quantitative analysis of O-J-I-P transient (St rass er and
Strasser, 1995). It translates the shape changes of O-J-I-P
transient to quantitative changes of various parameters and





Acta Botanica Sinica 植物学报 Vol.46 No.5 2004558
down-regulation o f photosynthetic activity in NK58S.
Nevertheless, each mechanism plays different roles to dis-
sipate excess excitation energy and protects NK58S against
photodamage. It has been suggested that state transition
is much important only in low light (Krause and Weis, 1991).
Thus, we have not paid much attention to it in this paper.
The xanthophyll cycle was initiated immediately in the first
hour when NK58S was exposed to strong irradiance in-
doors (Fig.6). Thereafter, certain amounts of PSⅡ RC were
inactivated. The inactivation of PSⅡ RC is inevitable when
the fully operation of xanthophyll cycle could not dissipate
excess excitation energy effectively. This is consistent with
the suggestion that xanthophyll cycle is the firs t line of
defense against PSⅡ over-excitat ion (Long et a l., 1994).
The JIP test has also shown that the photoinhibition of
NK58S is not marked from 06:00 to 09:00 and the down-
regulation of photosynthetic activity is mainly related with
the xanthophyll cycle (Fig .4). The inactivation of PSⅡ
RC occurs when ligh t intensity is increased to 1 200
mmol·m-2·s-1 at 10:00, and both Do and yo values started to
decrease (Fig.4). This is also consistent with Quick and
Stitt (1989). They had suggested that the fast component
of fluorescence quenching was not well suited to dissipate
light energy at super-saturating intensities.
Our resu lts sugges t that the damage-repair cycle of
PSⅡ RCs could contribute to protecting NK58S against
photodamage. The inactivation of PSⅡ RC has ever been
regarded simply as damage to plants. Its protective effects
against photodamage have been known gradually. The
accumulated inactivated RCs could act as potent quenchers,
convert absorbed excitation energy to heat, and protect
the remaining centers against further damage (Long et al.,
1994). However, the exact mechanism for inactivated RCs
to dissipate excess excitation energy is still uncertain. The
repair of photodamaged PSⅡ requires a number of p ro-
cesses including the dephosphorylation of D1 protein, its
degradation, de novo synthesis, and reassembly into func-
tional PSⅡ complexes (Zhang et al., 2000; Andersson and
Aro, 2001). The damaged D1 protein is t riggered to be
degraded via a multistep proteolytic reaction requiring GTP
and ATP and catalyzed by proteases Deg P2 and FtsH
(Goldberg, 1992; Spetea et a l., 1999; Andersson and Aro,
2001). It is uncertain whether the s peedup of ATP con-
sumption in the damage-repair cycle of PSⅡ RC could con-
tribute NK58S to dissipating excess excitation energy.
It has been s uggested that the net degradation of D1
protein may res ult from the strong irradiance used indoor
which the field grown p lants seldom encounter in their
habitats. The indoor treatment of strong irradiance is 1 200
µmol·m-2·s-1 in this study and is far below the maximal
light intensity in the field (2 000 µmol·m-2·s-1). This sug-
gests that the inactivation of PSⅡ RCs in NK58S is not due
to the difference of light intensities indoor and outdoor.
In this study, we have investigated the photoinhibition
of field grown NK58S with JIP test, from which the conclu-
sion is well in accordance with that of laboratory experi-
ment with the utilization of inhibitor. The JIP-test has been
proved to be a very useful tool for the in vivo investigation
of the adaptive behavior of the photosynthetic apparatus
and, especially, of PSⅡ to a wide variety and combination
of stressors owing to its convenient, rapid and non-inva-
sive features (Lu and Vonshak, 1999; Strasser and Tsimilli-
Michael, 2001). However, the recorded fluorescence tran-
sients carry much more information than those used by the
JIP test. The more powerful methods of numerical simula-
tions utilizing the rich in formation are expected. This is
dependent on our profound understanding to the fluores-
cence signal and the appearance of more powerful fluorim-
eters in the future.
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