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Photosynthetic Acclimation of Erythrophleum guineense and Dalbergia odorifera to Winter Low Temperature in a Marginal Tropical Area

几内亚格木和降香黄檀对热带北缘地区冬季低温的光合适应



全 文 :几内亚格木和降香黄檀对热带北缘地区冬季
低温的光合适应∗
黄  伟1ꎬ2ꎬ 曹坤芳2
(1 中国科学院昆明植物研究所资源植物与生物技术重点实验室ꎬ 云南 昆明  650201ꎻ 2 中国科学院
西双版纳热带植物园热带森林生态学重点实验室ꎬ 云南 勐腊  666303)
摘要: 在热带北缘地区ꎬ 冬季气温较夏季下降 10 ℃左右ꎬ 虽然热带植物对零上低温敏感ꎬ 但是大部分热
带树木能够适应热带北缘地区的冬季气温ꎬ 其光合生理机制并不清楚ꎮ 我们通过测定种植在热带北缘地区
(21°54′Nꎬ 101°46′E) 的两种热带树木 (几内亚格木和降香黄檀) 的光系统 I和 II活性以及光系统 I 和 II
的能量分配的季节变化ꎬ 发现这两个树种的光系统 I和 II活性在冬季并没有下降ꎮ 两个树种的光系统 II的
有效量子产额在冬季明显下降ꎬ 同时伴随着热耗散激发ꎮ 在冬季ꎬ 环式电子传递的激发与热耗散的激发呈
现显著的正相关ꎮ 环式电子传递的激发使得氧化态 P700比例的上升ꎬ 从而避免了光系统 I 受体端的过度
还原ꎮ 化学试剂抗霉素 A (PGR5途径环式电子传递的一种特异性抑制剂) 处理过的叶片较对照组表现出
更强光损伤程度ꎮ 这些结果表明环式电子传递的激发是热带树木适应热带北缘地区冬季低温的一个重要的
光合生理机制ꎮ
关键词: 适应ꎻ 环式电子传递ꎻ 冬季ꎻ 光系统 Iꎻ 光系统 IIꎻ 热带树木
中图分类号: Q 945            文献标识码: A                文章编号: 2095-0845(2014)03-310-11
Photosynthetic Acclimation of Erythrophleum guineense and
Dalbergia odorifera to Winter Low Temperature
in a Marginal Tropical Area
HUANG Wei1ꎬ2ꎬ CAO Kun ̄Fang2
(1 Key Laboratory of Economic Plants and Biotechnologyꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ
Kunming 650201ꎬ Chinaꎻ 2 Key Laboratory of Tropical Forest Ecologyꎬ Xishuangbanna Tropical
Botanical Gardenꎬ Chinese Academy of Sciencesꎬ Mengla 666303ꎬ China)
Abstract: In marginal tropical areasꎬ air temperature in winter usually decreases by 10 ℃ compared with summer at
night / day. Although tropical plants are sensitive to low temperatureꎬ the mechanism underlying photosynthetic accli ̄
mation of tropical trees to winter low temperature is unclear. To address this questionꎬ the photosystem I (PSI) and
photosystem II (PSII) activitiesꎬ and energy distribution in PSI and PSII were examined in summer and winter in
two tropical high ̄quality timber tree species Erythrophleum guineense and Dalbergia odorifera grown in a marginal
tropical area (21°54′Nꎬ 101°46′E). Our results indicated that the photosynthetic apparatus of E􀆰 guineense and
D􀆰 odorifera was maintained stable in winter. The effective quantum yield of PSII decreased significantly in winterꎬ
but non ̄photochemical quenching (NPQ) significantly increased. In winterꎬ cyclic electron flow (CEF) was signifi ̄
cantly stimulated in both speciesꎬ which was significantly and positively correlated with NPQ. Meanwhileꎬ the stimu ̄
lation of CEF led to an increase in P700 oxidation ratio and the over ̄reduction of PSI acceptor side was prevented.
植 物 分 类 与 资 源 学 报  2014ꎬ 36 (3): 310~320
Plant Diversity and Resources                                    DOI: 10.7677 / ynzwyj201413157
∗ Funding: National Natural Science Foundation of China (grant 30900174)
Received date: 2013-07-29ꎬ Accepted date: 2013-09-16
作者简介: 黄  伟 (1986-) 男ꎬ 主要从事植物光合作用的研究ꎮ E ̄mail: huangwei@mail􀆰 kib􀆰 ac􀆰 cn
Antimycin A (a specific inhibitor of PGR5 ̄dependent CEF) significantly aggravated PSII photoinhibition under high
light in both species. These results suggested that stimulation of CEF is an important mechanism for photosynthetic
acclimation to winter low temperature in a marginal tropical area in the two tropical tree species.
Key words: Acclimationꎻ Cyclic electron flowꎻ Winterꎻ Photosystem Iꎻ Photosystem IIꎻ Tropical trees
  Tropical trees species are native to tropical are ̄
as in which the air temperature in winter is usually
high. Some of them produce high ̄quality timber. Due
to the exacerbation of fragmentation of tropical for ̄
ests and increasing demand for tropical hardwood
timberꎬ afforestation using tropical high ̄quality tim ̄
ber species in marginal tropical areas is presently
practiced. In Xishuangbanna Tropical Botanical Gar ̄
den (XTBGꎬ 21°54′Nꎬ 101°46′E)ꎬ air temperature
usually decreases to 12 / 25 ℃ at nigh / day during
winter. Because a lot of tropical trees showed large
decrease in photosynthetic rate in winter in XTBG
(Cao et al.ꎬ 2006ꎻ Jiangꎬ 2008)ꎬ the air tempera ̄
ture in winter in XTBG is regarded as relative low
temperature for tropical trees. Thereforeꎬ those tropi ̄
cal tree species that are able to survive in the low
winter temperature in XTBG should have feasible
mechanisms for protecting photosynthetic apparatus
from photoinhibition.
Light is the driving force of photosynthesisꎬ but
excess light could induce photoinhibition ( Barber
and Anderssonꎬ 1992ꎻ Aro et al.ꎬ 1993ꎻ Adir et
al.ꎬ 2005). Photoinhibition is regarded as a decline
of photochemistry efficiency under the conditions in
which the input of photons exceeds the requirement
for photosynthesis (Powlesꎬ 1984). Photoinhibition
of photosystem II (PSII) is caused probably by two
aspects: one is the damage to oxygen ̄evolving com ̄
plexes ( OEC) (Hakala et al.ꎬ 2005ꎻ Ohnishi et
al.ꎬ 2005ꎻ Takahashi et al.ꎬ 2009ꎻ Oguchi et al.ꎬ
2011ꎻ for a review on ROSꎬ see Danonꎬ 2012)ꎻ the
other one is the generation of reactive oxygen species
(ROS) which could be induced by excess light exci ̄
tation (Kornyeyev et al.ꎬ 2001ꎬ 2003aꎬ bꎻ Sainz et
al.ꎬ 2010). Recent studies have indicated that ROS
aggravate PSII photoinhibition primarily by inhibiting
the repair cycle of PSII photodamage by inhibition of
D1 protein synthesis but not by damaging PSII di ̄
rectly (Nishiyama et al.ꎬ 2001ꎬ 2004ꎬ 2005ꎬ 2006ꎬ
2011ꎻ Allakhverdiev and Murataꎬ 2004). Low tem ̄
perature depresses photosynthesis and increases ex ̄
cess light energyꎬ and then increase the risk of PSII
photoinhibition. Our previous studies indicated that
PSII in tropical trees is very sensitive to a chilling
temperature of 4 ℃ associated with moderate light
(Huang et al.ꎬ 2010aꎬ b). Howeverꎬ the mecha ̄
nism underlying photosynthetic acclimation of tropi ̄
cal tree species to relative winter low temperature of
12 / 25 ℃ at nigh / day it is unclear.
Plants have the ability to dissipate excitation
energy harmlessly as heat in the antenna proteins of
PSII (Demmig ̄Adamsꎬ 1990ꎻ Asadaꎬ 1999ꎻ Niyo ̄
giꎬ 1999ꎬ 2000ꎻ Takahashi et al.ꎬ 2009)ꎬ which is
called qE and is measured as a component of non ̄
photochemical quenching of chlorophyll fluorescence
(NPQ). The activation of NPQ is regulated by low
lumenal pHꎬ which is accompanied by the genera ̄
tion of proton gradient across the thylakoid mem ̄
brane (ΔpH) (Gilmore et al.ꎬ 1998). Cyclic elec ̄
tron flow (CEF) helps the generation of ΔpHꎬ and
further favors the activation of NPQ (Munekage et
al.ꎬ 2002ꎬ 2004ꎻ Takahashi et al.ꎬ 2009). Further ̄
moreꎬ the activation of NPQ is dependent on xantho ̄
phyll cycle. The size of xanthophylls pool is positive ̄
ly correlated the capacity of NPQ. In previous stu ̄
dies on acclimation of photosynthesis to low tempera ̄
tureꎬ it is clearly documented that the up ̄regulation
of NPQ is an important mechanism for affording pho ̄
toprotection for PSII ( Krivosheeva et al.ꎬ 1996ꎻ
Verhoeven et al.ꎬ 1999ꎻ Hormaetxe et al.ꎬ 2004ꎻ
Ballottari et al.ꎬ 2007). Howeverꎬ little studies fo ̄
cus on the role of CEF in acclimation of PSII activity
to natural low temperature in winter. Previous studies
indicated that NPQ was enhanced in tropical trees in
1133期      HUANG and CAO: Photosynthetic Acclimation of Erythrophleum guineense and Dalbergia odorifera to 􀆺     
winter in marginal tropical areas ( Elsheery et al.ꎬ
2007ꎻ Zhu et al.ꎬ 2009). We speculate that the en ̄
hancement of NPQ in tropical tree species in winter
is due to the stimulation of CEF.
When the PSI acceptor side is over ̄reducedꎬ
the recombination between the radical pairs P700+ /
A0- or P700+ / A1- can generate the triplet state of
P700 (Shuvalov et al.ꎬ 1986ꎻ Golbeckꎬ 1987ꎻ Gol ̄
beck and Bryantꎬ 1991). Chlorophyll triplets can re ̄
act with molecular oxygen to produce very toxic sin ̄
glet oxygen that could cause photoinhibitory damage
to PSI. Thereforeꎬ there are two main mechanisms
for the PSI photodamage: the accumulation of hy ̄
droxyl radicals at PSI acceptor side and the over ̄re ̄
duction of the PSI acceptor side. It has been repor ̄
ted that CEF is essential for photoprotection of PSI
in Arabidopsis (Munekage et al.ꎬ 2002ꎬ 2004ꎻ Joliot
and Johnsonꎬ 2011) and tropical tree species (Huang
et al.ꎬ 2011). CEF is regarded as a mechanism that
maintains high P700 oxidation ratio and alleviates o ̄
ver ̄reduction of the acceptor side of PSI (Munekage
et al.ꎬ 2002ꎬ 2004ꎬ 2008). Oxidized P700 (P700+)
can harmlessly quench excess excitation energy as
heat and thereby efficiently ameliorating the deleteri ̄
ous effects of excess light (Nuijs et al.ꎬ 1986). The
metal centers in the PSI acceptor side (FX and FA /
FB) of Arabidopsis mutant plants pgr5 is over ̄re ̄
duced under high light (Munekage et al.ꎬ 2008).
The over ̄reduced PSI acceptors react with superox ̄
ideꎬ generating hydroxyl radicals which damage PSI
reaction centers. Previous studies indicated that PSI
is insusceptible to chilling and light stress in tropical
trees grown under high light (Huang et al.ꎬ 2010aꎬ
b). Howeverꎬ the response of PSI activity in tropical
trees to natural low winter temperature in marginal
tropical areas is unknown.
1  Materials and methods
1􀆰 1  Plant materials and growth conditions
The following two tropical evergreen tree species
were chosen for the study. Erythrophleum guineense
G. Don (Fabaceae) is a large canopy species native
to west coast of Africa and mainly distribute in
Guinea and Senegambia. Dalbergia odorifera T.
Chen (Fabaceae) is native to the Hainan island of
China ( yearly average air temperature 23 - 25 ℃)
and a light ̄demanding tree species that inhabits sec ̄
ondary forests. These two species produce high ̄quali ̄
ty timber and their adult plants exhibit good growth
performance in the Xishuangbanna Tropical Botanical
Garden (XTBG) (21°54′Nꎬ 101°46′E) that is loca ̄
ted in the northern boundary of the tropical zone. Be ̄
cause these two evergreen species do not drop their
leaves in winterꎬ we used them to study the effect of
natural winter low temperature on CEF and PSI activ ̄
ity. Three years older seedlings of these two species
were used in this study. During the experimentꎬ none
of the plants experienced any water or nutrient stres ̄
ses. At least five mature sun leaves that had flushed
in May 2010 were chosen for measuring in situ photo ̄
synthetic parameters in both summer and winter.
We mainly conducted photosynthetic measure ̄
ments in July 2010 ( summer) and January 2011
(winter) . In winterꎬ the outdoor air temperatures at
night and noon are ≈12 ℃ and ≈25 ℃ꎬ respective ̄
ly. In summerꎬ the outdoor air temperatures at night
and noon are ≈22 ℃ and ≈35 ℃ꎬ respectively. The
highest photosynthetic photon flux density (PPFD) at
midday is up to 1 850 μmol photons m-2 s-1 in sum ̄
mer and 1 350 μmol photons m-2 s-1 in winter.
1􀆰 2  Leaf pigment composition measurements
The contents for carotenoids and chlorophylls a
and b for leaves of E􀆰 guineense and D􀆰 odorifera in
summer and winter were determined according to the
method of Lichtenthaler and Wellburn (1983).
1􀆰 3  Photoinhibitory treatment
To examine the role of CEF in photoprotection
for PSII in leaves of E􀆰 guineense and D􀆰 odorifera
grown in an open fieldꎬ detached leaves were vacu ̄
um incubated with H2O or antimycin A ( AAꎬ 10
μMꎬ to specifically inhibit PGR5 ̄dependent CEF)
in darkness and then treated with 25 ℃ and 1 000
μmol photons m-2 s-1 for 2 hours on water. These
photoinhibitory treatments were conducted in 6 Sep ̄
213                                  植 物 分 类 与 资 源 学 报                            第 36卷
tember in 2012.
1􀆰 4   Chlorophyll fluorescence and P700 meas ̄
urements
To analyze the changes in distribution of light
energy in PSII and P700 redox state after full accli ̄
mation to winterꎬ in winter and summerꎬ we conduc ̄
ted measurements for the light responses of chloro ̄
phyll fluorescence and P700 redox state synchro ̄
nously in detached leaves at a controlled temperature
of 25 ℃ with the Dual PAM ̄100 (Heinz Walzꎬ Ef ̄
feltrichꎬ Germany) connected to a computer with
control software. Six to eight mature leaves were
light ̄adapted ( 450 μmol photons m-2 s-1 ) for 20
min at 25 ℃ before the measurement of light re ̄
sponse curvesꎬ and light ̄adapted fluorescence pa ̄
rameters were recorded after 2 min exposure to each
light intensity.
Chlorophyll fluorescence measurements were used
to calculate the following parameters: Fv / Fm =(Fm-
Fo) / Fmꎬ Fo′ = Fo / (Fv / Fm +Fo / Fm′) (Oxborough
and Bakerꎬ 1997)ꎬ Fv′ / Fm′= (Fm′-Fo′) / Fm′ꎻ qL
=(Fm′-Fs) / (Fm′-Fo′) ×Fo′ / Fs (Kramer et al.ꎬ
2004)ꎬ Y ( II) = (Fm′ - Fs ) / Fm′ ( Genty et al.ꎬ
1989)ꎬ Y(NO)= Fs / Fmꎬ Y(NPQ) = Fs / Fm′-Fs /
Fmꎬ ( Hendrickson et al.ꎬ 2004ꎻ Kramer et al.ꎬ
2004). Fo and Fo′ are the minimum fluorescence
values in the dark ̄adapted state and light ̄adapted
stateꎬ respectively. Fm and Fm′ are the dark ̄adapted
and light ̄adapted maximum fluorescence upon illu ̄
mination with a pulse (300 ms) of saturating light
(10 000 μmol photons m-2 s-1 )ꎬ respectively. Fo
and Fm were determined after an overnight dark ad ̄
aptation. Fs is steady ̄state fluorescence in light. The
ratio Fv / Fmꎬ where Fv = (Fm -Fo ) is the variable
fluorescenceꎬ reflects denotes the maximum quantum
yield of PSII ( see e􀆰 g.ꎬ Govindjeeꎬ 2004)ꎻ was
measured after an overnight dark adaptation. Fv′ /
Fm′ is the maximum quantum yield of PSII after light
adaptation. qL is the fraction of open PSII centers. Y
(II) is the effective quantum yield of PSII. Y(NO)
is the quantum yield of non ̄regulated energy dissipa ̄
tion of PSII. Y(NPQ) is the quantum yield of regu ̄
lated energy dissipation of PSIIꎬ mainly through the
xanthophyll cycle.
The P700 redox state was measured by Dual
PAM ̄100 with a dual wavelength (830 / 875 nm) u ̄
nit (Klughammer and Schreiberꎬ 1994)ꎬ which was
widely used in recent studies (Huang et al.ꎬ 2010bꎬ
2011ꎬ 2012aꎬ bꎬ 2013ꎻ Yamori et al.ꎬ 2011). Sa ̄
turation pulses ( 10 000 μmol photons m-2 s-1 )ꎬ
which were introduced primarily for PAM fluores ̄
cence measurementꎬ were applied for the assessment
of P700 parameters as well. The P700+ signals (P)
may vary between a minimal (P700 fully reduced)
and a maximal level (P700 fully oxidized). Pm was
determined after a saturation pulse was given after 10
seconds pre ̄illumination with far ̄red light. The value
of Pm is calculated from the difference between maxi ̄
mal and the baseline and by the software of Dual ̄
PAM ̄100. At a defined optical propertyꎬ the ampli ̄
tude of Pm depends on the maximum amount of pho ̄
to ̄oxidizable P700ꎬ which is a parameter for repre ̄
senting the quantity of efficient PSI complex (Zhang
and Schellerꎬ 2004ꎻ Huang et al.ꎬ 2010aꎬ b). Pm′
was also defined in analogy to the fluorescence pa ̄
rameter Fm′ as Pm′ꎻ it was determined similarly to
Pmꎬ but with background actinic light instead of far ̄
red illumination.
The photochemical quantum yield of PSIꎬ Y(I)ꎬ
is defined by the fraction of overall P700 that in a
given state is reduced and not limited by the accep ̄
tor side. It is calculated as Y(I)= (Pm′-P) / Pm . Y
(ND)ꎬ represents the fraction of overall P700 that is
oxidized in a given stateꎬ which is enhanced by a
trans ̄thylakoid proton gradient ( photosynthetic con ̄
trol at cytb / f complex as well as down ̄regulation of
PSII) and photodamage to PSII. Y(ND)= P / Pm . Y
(NA)ꎻ thusꎬ it represents the fraction of overall
P700 that cannot be oxidized by a saturation pulse in
a given state due to a lack of oxidized acceptors. Y
(NA)= (Pm-Pm′) / Pm. We note that Y (I)+Y (ND)
+Y (NA)= 1.
1􀆰 5  Statistical analysis
The results were displayed as mean values of
3133期      HUANG and CAO: Photosynthetic Acclimation of Erythrophleum guineense and Dalbergia odorifera to 􀆺     
five independent experiments. The data were subjec ̄
ted to analysis of variance (ANOVA) using the SPSS
16􀆰 0 statistical software. Tukey’s multiple compari ̄
son test was used at α = 0􀆰 05 significance level to
determine whether significant differences existed be ̄
tween different treatments.
2  Results
The maximum quantum yield of PSII (Fv / Fm)
and maximum photo ̄oxidizable P700 (Pm) did not
significantly change in Erythrophleum guineense and
Dalbergia odorifera after full acclimation to winter in
this northern tropical area ( Fig􀆰 1Aꎬ B). Because
Fv / Fm and Pm represents PSII activity and PSI activ ̄
ityꎬ respectivelyꎬ this result indicated that PSI and
PSII activities of E􀆰 guineense and D􀆰 odorifera was
protected during the acclimation to low temperature
in winter in a marginal tropical area. The chlorophyll
(Chl) a and b content and carotenoid content did
not differ significantly between summer and winter
for both species (Fig􀆰 1Cꎬ D)ꎬ indicating the stabil ̄
ity of photosynthetic apparatus of E􀆰 guineense and
D􀆰 odorifera in winter in the marginal tropical area.
Light response curves indicated that qL largely
decreased in winter compared with summerꎬ and
then led to the strong decrease in Y(II) in E􀆰 guin ̄
eense and D􀆰 odorifera (Fig􀆰 2Aꎬ B)ꎬ indicating the
ability of tropical trees to utilize the products of line ̄
ar electron flow ( LEF ) was severely inhibited.
Meanwhileꎬ the fraction of energy dissipated in form
of heat via the regulated non ̄photochemical quench ̄
ing mechanism [ Y ( NPQ)] strongly increased in
winter in the two species (Fig􀆰 2C). The fraction of
energy that is passively dissipated in form of heat
and fluorescence [Y(NO)] changed slightly in win ̄
ter compared with summer ( Fig􀆰 2D)ꎬ indicating
that excess light energy was harmlessly dissipated in
winter.
Because Y( II) is responsible for LEF and Y
(I) involves LEF and CEFꎬ if CEF is activatedꎬ the
value of Y(I) / Y(II) will increase (Yamori et al.ꎬ
2011ꎻ Huang et al.ꎬ 2012bꎻ 2013). As a resultꎬ the
increase in Y(I) / Y(II) ratio has been regarded as
an indicator of the activation of CEF (Yamori et al.ꎬ
2011ꎻ Huang et al.ꎬ 2013). In our present studyꎬ the
Y( I) / Y( II) ratio highly increased in winter com ̄
pared with summer (Fig􀆰 3). In summer the value of
Y(I) / Y(II) under a light of 834 μmol photons m-2
s-1 was 1􀆰 4 in E􀆰 guineense and 1􀆰 3 in D􀆰 odorifera.
In winterꎬ the value of Y(I) / Y(II) under a light of
Fig􀆰 1  The maximum quantum yield of PSII ( Fv / Fm )ꎬ maximum
photo ̄oxidizable P700 (Pm) and pigment concentration (g m-2) for
leaves of E􀆰 guineense and D􀆰 odorifera in summer (black bars) and
winter (grey bars) . The mean ± SE was calculated from
five independent plants
413                                  植 物 分 类 与 资 源 学 报                            第 36卷
834 μmol photons m-2 s-1 increased to 2􀆰 6 in E􀆰 gu ̄
ineense and 2􀆰 3 in D􀆰 odorifera. These results indica ̄
ted the stimulation of CEF in winter compared with
summer in the two tropical tree species.
Fig􀆰 2  Light response change in distribution of light energy in PSII
for leaves of E􀆰 guineense and D􀆰 odorifera in summer (closed symbols)
and winter (open symbols). The mean ± SE was calculated from six in ̄
dependent plants. qL-fraction of open PSII centersꎻ Y( II) -effective
quantum yield of photosystem IIꎻ Y(NPQ)-fraction of energy dissipa ̄
ted in form of heat via the regulated non ̄photochemical quenching
mechanismꎻ Y(NO)-fraction of energy that is passively dissipated
in form of heat and fluorescence. Asterisk (∗) represents
significant difference between summer and winter
    The quantum yield of PSI [Y( I)] under high
light significantly decreased in winter compared with
summer in both species ( Fig􀆰 4A). The fraction of
total P700 that is oxidized in a given state [ Y
(ND)] increased in winter compared with summer
in both species (Fig􀆰 4B). In winterꎬ the fraction of
total P700 that cannot be oxidized in a given state
[Y(NA)] was maintained lower than 0􀆰 1 (Fig􀆰 4C)ꎬ
suggesting the over ̄reduction of acceptor in PSI was
prevented in winter in both species. Since the activa ̄
tion of CEF is necessary for the high oxidation ratio
of P700 and low acceptor side limitation of PSIꎬ the
high Y(ND) and a low Y(NA) implied that CEF
was stimulated in winter.
Pooling the data of Y( I) / Y( II) ratio and Y
(NPQ) in the two species measured at summer and
winterꎬ the value of Y(NPQ) was significantly and
linearly correlated with the value of Y(I) / Y(II) ra ̄
tio (Fig􀆰 5)ꎬ indicating that the stimulation of NPQ
in both species in winter was significantly correlated
with the up ̄regulation of CEF.
To examine the role of CEF in protecting PSII
from photoinhibition under high lightꎬ leaves of
E􀆰 guineense and D􀆰 odorifera were vacuum infiltrated
with antimycin A (AAꎬ a specific inhibitor for PGR5 ̄
dependent CEF) solution and then illuminated under
high light of 1 000 μmol photons m-2 s-1 at 25 ℃ for
Fig. 3  Light response change in Y(I) / Y(II) for leaves of
E􀆰 guineense and D􀆰 odorifera in summer (closed symbols) and
winter (open symbols) . The mean ± SE was calculated from
six independent plants. Asterisk (∗) represents significant
difference between summer and winter
5133期      HUANG and CAO: Photosynthetic Acclimation of Erythrophleum guineense and Dalbergia odorifera to 􀆺     
2 hours. After the high light treatmentꎬ the maximum
quantum yield of PSII after dark ̄adaptation ( Fv /
Fm) in the AA ̄treated samples decreased to 0􀆰 41 in
E􀆰 guineense and 0􀆰 49 in D􀆰 odorifera ( Fig􀆰 6). In
the H2O ̄treated samplesꎬ Fv / Fm decreased to 0􀆰 61
in E􀆰 guineense and 0􀆰 65 in D􀆰 odorifera ( Fig􀆰 6).
The decrease in Fv / Fm in the AA ̄treated samples was
significantly larger than that in the H2O ̄treated leav ̄
es in both speciesꎬ indicating that PGR5 ̄dependent
CEF plays an important role in protecting PSII for
leaves of these two evergreen tropical tree species.
Fig􀆰 4  Light response change in Y(I)ꎬ Y(ND) and Y(NA) for leaves
of E􀆰 guineense and D􀆰 odorifera in summer (closed symbols) and winter
(open symbols). The mean ± SE was calculated from six independent
plants. Y(I)-effective quantum yield of photosystem Iꎻ Y(ND)-fraction
of overall P700 that is oxidized in a given stateꎻ Y (NA)-fraction of
overall P700 that cannot be oxidized in a given state. Asterisk (∗)
represents significant difference between summer and winter
Fig􀆰 5  Change in Y(NPQ) as a function of Y(I) / Y(II) ratio measured
at 25 ℃ and 834 μmol photons m-2 s-1 in summer (closed symbols) and
winter (open symbols) for leaves of E􀆰 guineense and D􀆰 odorifera
Fig􀆰 6  Effect of antimycin A (AA) on PSII photoinhibition in leaves
of E􀆰 guineense ( A) and D􀆰 odorifera ( B). After infiltration as de ̄
scribed in Materials and Methodsꎬ detached leaves were exposed to
light at 1 000 μmol photons m-2 s-1 at 25 ℃ for 2 hours. The maxi ̄
mum quantum yield of PSII (Fv / Fm) was measured after 30 min dark
adaptation. The mean ± SE was calculated from six independent exp ̄
eriments. Different letters (aꎬ bꎬ c) indicate a significant difference
between different treatments (One ̄Way ANOVAꎬ P<0􀆰 05) .
613                                  植 物 分 类 与 资 源 学 报                            第 36卷
3  Discussion
3􀆰 1  Stability of photosynthetic apparatus after
full winter acclimation
Although air temperature decreased by 10 ℃ in
winter compared with summer and to ~12 ℃ at night
and ~25 ℃ at noon at the study siteꎬ E􀆰 guineense
and D􀆰 odorifera maintained stable maximum quan ̄
tum yield of PSII (Fv / Fm)ꎬ maximum photo ̄oxidiz ̄
able P700 (Pm) and pigment concentrations in win ̄
ter compared to summer ( Fig􀆰 1)ꎬ indicating the
stability of photosynthetic apparatus after full winter
acclimation in the both species. Night chilling tem ̄
perature could inhibit the photosynthetic capacity
and induce photoinhibition of PSII in the daytime
(Flexas et al.ꎬ 1999ꎻ Allen et al.ꎬ 2000). Both
studied species showed largely decreases in qL and
Y(II) in winter (Fig􀆰 2Aꎬ B)ꎬ suggesting that night
low temperature in winter depressed the ability to u ̄
tilize light energy in the daytime in tropical tree spe ̄
cies. Both studied species showed sensitivity of PSII
activity to chilling temperature associated with light
stress (Huang et al.ꎬ 2010aꎬ b). The stability of
PSII activity in winter in both species ( Fig􀆰 1A)
suggested that these two species have effective mech ̄
anisms to protect PSII against night low temperature
in winter in the marginal tropical area. Previous
studies have indicated that PSI activity is sensitive to
chilling temperature in Arabidopsis thaliana and cu ̄
cumber (Sonoikeꎬ 1996ꎬ 2006ꎻ Zhang and Schellerꎬ
2004). Our previous study indicated that PSI was
sensitive to chilling temperature under moderate light
intensity in E􀆰 guineense ( Huang et al.ꎬ 2010a).
The stability of PSI activity in E􀆰 guineense in winter
(Fig􀆰 1B) suggested that protective mechanisms for
PSI were activated in E􀆰 guineense during acclima ̄
tion to winter low temperature.
3􀆰 2  Stimulation of cyclic electron flow in winter
favors photoprotection for PSII
Our results indicated that CEF was significantly
stimulated in winter in the two tropical tree species
(Fig􀆰 3)ꎬ which was accompanied with high NPQ
(Fig􀆰 2C). Previous studies (Guo and Caoꎬ 2004ꎻ
Feng and Caoꎬ 2005ꎻ Elsheery et al.ꎬ 2007ꎻ Jiangꎬ
2008ꎻ Zhu et al.ꎬ 2009) and our present results in ̄
dicated that NPQ is significantly stimulated in tropi ̄
cal trees by low winter temperature in the marginal
tropical area. We found that the stimulation of CEF
was significantly and positively correlated with the
up ̄regulation of NPQ in winter in both species
(Fig􀆰 5). Because the activation of NPQ is depend ̄
ent on the formation of proton gradient across thyla ̄
koid membrane that is largely based on cyclic elec ̄
tron flow (Munekage et al.ꎬ 2002ꎬ 2004ꎻ Takahashi
et al.ꎬ 2009ꎻ Johnsonꎬ 2011)ꎬ these results indica ̄
ted that the strong up ̄regulation of NPQ during ac ̄
climation to winter low temperature is largely attrib ̄
utable to the stimulation of CEF.
In winterꎬ the decrease in air temperature in ̄
duced the depression in Y(II) . To maintain the sta ̄
bility of PSII activityꎬ plants would up ̄regulate NPQ
to harmlessly dissipate excess light energy and then
alleviate the production of ROS that inhibit the re ̄
pair of PSII activity. It is well documented that
PGR5 ̄dependent CEF is essential for activation of
NPQ in Arabidopsis thaliana ( Munakage et al.ꎬ
2002ꎬ 2004ꎻ Takahashi et al.ꎬ 2009). Antimycin A
specifically inhibits PGR5 ̄dependent CEF (Munek ̄
age et al.ꎬ 2002ꎻ Shikanaiꎬ 2007). After high light
treatmentꎬ the AA ̄treated samples displayed more
PSII photoinhibition than the H2O ̄treated samples in
the two studied tree species (Fig􀆰 6)ꎬ suggesting that
PGR5 ̄dependent CEF is essential for alleviating PSII
photoinhibition in tropical evergreen tree species.
3􀆰 3  Stimulation of cyclic electron flow in winter
favors photoprotection for PSI
In the chilling ̄sensitive herbaceous plant cu ̄
cumberꎬ the preferential damage to photosystem I
(PSI) was suggested to be caused by the oxidation
by hydroxyl radicals ( Sonoikeꎬ 1996ꎬ 2006). The
hydroxyl radicalsꎬ the most reactive species of active
oxygenꎬ which are generated by the reaction between
hydrogen peroxide and photoreduced iron ̄sulfur cen ̄
tersꎬ destroy PSI at the site of production of hydroxyl
radicals ( Sonoikeꎬ 2006ꎬ 2011). Our results indi ̄
7133期      HUANG and CAO: Photosynthetic Acclimation of Erythrophleum guineense and Dalbergia odorifera to 􀆺     
cated that the value of Y(ND) was much higher in
winter than in summer in both species ( Fig􀆰 4B).
P700+ can dissipate excess light energy harmlessly
as heat (Nuijs et al.ꎬ 1986). Furthermoreꎬ Y(NA)
was low under high light in winter after full winter
acclimation ( Fig􀆰 4C)ꎬ suggesting the over ̄reduc ̄
tion of PSI acceptor side was prevented. In Arabidop ̄
sis thalianaꎬ the stoichiometry of any Lhca ( light ̄
harvesting complex a) antenna proteins with respect
to PSI core complex did not change during acclima ̄
tion to low temperature ( Ballotarri et al.ꎬ 2007).
Howeverꎬ the underlying mechanism of how overwin ̄
tering plants prevent PSI photoinhibition during ac ̄
climation to winter low temperature is unclear. Our
present study indicated that the stability of PSI activ ̄
ity during acclimation to winter low temperature in
both tropical tree species involves the stimulation of
CEF. The stimulation of CEF in winter leads to a
high level of Y(ND) and a low level of Y(NA) in
both speciesꎬ suggesting that stimulation of CEF is
an important mechanism for the stability of PSI ac ̄
tivity during the acclimation of overwintering plants
to natural low temperature in winter.
Acknowledgements: Xishuangbanna Station for Tropical Rain
Forest Ecosystem Studies (XSTRE) provided climatic data.
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