全 文 :不同居群紫花针茅响应干旱胁迫的生理和分子差异分析∗
李 雄1ꎬ2ꎬ3ꎬ 杨时海3ꎬ4ꎬ 杨云强1ꎬ2ꎬ 尹 欣1ꎬ2ꎬ3ꎬ 孙旭东1ꎬ2ꎬ 杨永平1ꎬ2∗∗
(1 中国科学院昆明植物研究所东亚植物多样性与生物地理学重点实验室ꎬ 昆明 650201ꎻ 2 中国科学院中国西南野生
生物种质资源库ꎬ 昆明 650201ꎻ 3 中国科学院大学ꎬ 北京 100049ꎻ 4 中国科学院青藏高原研究所ꎬ 北京 100101)
摘要: 紫花针茅 (Stipa purpurea) 在青藏高原沿广阔的降水梯度分布ꎮ 长期的适应过程中ꎬ 不同地域的紫
花针茅可能对干旱具有不同的响应方式ꎮ 本研究以两个居群的紫花针茅为材料ꎬ 对干旱胁迫 14 天和随后
的复水过程中各自的生理和分子水平的变化差异进行研究ꎮ 结果发现两个居群的紫花针茅在植株死亡率、
叶片相对含水量、 叶绿素荧光、 活性氧积累、 脯氨酸含量、 抗氧化酶活性和抗旱相关基因表达量的变化等
方面都有明显差异ꎻ 且复水后各项指标的恢复水平也不相同ꎮ 分析表明来自降水较少的普兰地区的紫花针
茅的后代与来自降水较多的措勤地区的相比表现出更强的耐旱性ꎬ 说明不同居群的紫花针茅对干旱的响应
差异可能是遗传性ꎮ 本研究有助于认识紫花针茅在环境中的适应和进化ꎬ 以及对气候变化的响应ꎮ
关键词: 紫花针茅ꎻ 青藏高原ꎻ 干旱ꎻ 适应和进化ꎻ 气候变化
中图分类号: Q 945 文献标志码: A 文章编号: 2095-0845(2015)04-439-14
Comparative Physiological and Molecular Analyses of Intraspecific
Differences of Stipa purpurea (Poaceae) Response to Drought∗
LI Xiong1ꎬ2ꎬ3ꎬ YANG Shi ̄hai3ꎬ4ꎬ YANG Yun ̄qiang1ꎬ2ꎬ YIN Xin1ꎬ2ꎬ3ꎬ
SUN Xu ̄dong1ꎬ2ꎬ YANG Yong ̄ping1ꎬ2∗∗
(1 Key Laboratory for Plant Diversity and Biogeography of East Asiaꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ
Kunming 650201ꎬ Chinaꎻ 2 Germplasm Bank of Wild Species in Southwest Chinaꎬ Kunming Institute of Botanyꎬ Chinese
Academy of Sciencesꎬ Kunming 650201ꎬ Chinaꎻ 3 University of Chinese Academy of Sciencesꎬ Beijing 100049ꎬ Chinaꎻ
4 Institute of Tibetan Plateau Researchꎬ Chinese Academy of Sciencesꎬ Beijing 100101ꎬ China)
Abstract: Stipa purpurea Grisebꎬ the dominant species of alpine steppeꎬ is widely distributed across the large pre ̄
cipitation gradient on the Tibetan Plateau. It is possible that because of local adaptationꎬ S purpurea populations
from different habitats along this precipitation gradient respond differently to droughtꎬ which may affect their respon ̄
ses to climate change. To explore the problemꎬ in the present studyꎬ we investigated the physiological and molecular
response of S purpurea seedlings from two different populations (Pulan & Cuoqin) to 14 ̄d drought stress and subse ̄
quent recovery. The results showed that the relative water contentꎬ chlorophyll fluorescenceꎬ content of osmoticant
proline and malondialdehyde ( indicator of oxidative stress)ꎬ accumulation of reactive oxygen speciesꎬ antioxidant
enzyme activities and the expression of drought ̄related genes all changed under drought treatment and went back to
the control levels in the subsequent recovery in plants from Pulan. Howeverꎬ these patterns were quite different in
plants from Cuoqinꎬ in which these traits changed by inconsistent degrees and did not return to pretreatment levels
after rewatering. The results demonstrated that the plants from Pulan had greater resistance to drought stress com ̄
pared with those from Cuoqinꎬ which had a larger mortality rate ultimately. Combating the differences of offspring in
植 物 分 类 与 资 源 学 报 2015ꎬ 37 (4): 439~452
Plant Diversity and Resources DOI: 10.7677 / ynzwyj201514126
∗
∗∗
Funding: The National Natural Sciences Foundation of China (41271058) and the Major State Basic Research Development Program (2010CB951700)
Author for correspondenceꎻ E ̄mail: yangyp@mail kib ac cn
Received date: 2014-09-12ꎬ Accepted date: 2014-11-27
作者简介: 李雄 (1987-) 男ꎬ 博士研究生ꎬ 主要从事植物生理生态学和分子生物学研究ꎮ E ̄mail: lixiong@mail kib ac cn
response to drought and the habitat distribution of parentsꎬ we considered that genetic basis has been obtained in re ̄
sponse to precipitation difference among S purpurea populations. The results help to understand the adaptation and e ̄
volution of S purpurea to the special environment and the effect of climate change to this botanical system.
Key words: Stipa purpureaꎻ Tibetan Plateauꎻ Droughtꎻ Adaptation and evolutionꎻ Climate change
Stress constantly challenges the survival and de ̄
velopment of plantsꎬ and plants have in turn evolved
many adaptations to different environments. Among
the different stressesꎬ drought stress draws much at ̄
tention because it is a major factor that decreases
plant growth and productivity (Yordanov et al.ꎬ 2000ꎻ
Aranjuelo et al.ꎬ 2011). Plants endure drought stress
mainly by avoiding tissue dehydrationꎬ while main ̄
taining as high tissue water potential as possibleꎬ or
by tolerating low tissue water potential. In factꎬ
plants initiate an integrative mechanism during this
processꎬ involving phenotypic plasticityꎬ alterations
in biochemical enzyme activity or proteomic dynam ̄
icsꎬ and stress ̄responsive changes in gene expres ̄
sion (Nicotra and Davidsonꎬ 2010). Under drought
stressꎬ water loss in plants can be minimized by roll ̄
ing leaves ( Turgut and Kadiogluꎬ 1998ꎻ Terzi et
al.ꎬ 2013)ꎬ thick leaves (Hu et al.ꎬ 2012)ꎬ devel ̄
oped trichomes ( Fu et al.ꎬ 2013)ꎬ or more rigid
cell walls (Moore et al.ꎬ 2008) etc. In additionꎬ the
plant can increase the root investmentꎬ such as in ̄
creasing the root depth (Moore et al.ꎬ 2008). Con ̄
sistent with phenotypic plasticityꎬ physiological and
biochemical adjustments are involved in the toler ̄
ance to a low tissue water potential (Chaves et al.ꎬ
2003). Plants close their stomata to reduce water tran ̄
spiration and photosynthesis when exposed to drought
(Chaves et al.ꎬ 2003). The osmotic compoundsꎬ
like prolineꎬ also regulate osmotic adjustment in plant
adaptation to drought (Morganꎬ 1984). A series of
scavenging mechanismsꎬ including antioxidant en ̄
zymesꎬ can restrict the over ̄accumulation of reactive
oxygen species ( ROS )ꎬ which can damage cell
membranes and other cellular components during
drought stress (Scandaliosꎬ 1993). Correlated with
both morphological and physiological divergenceꎬ
water shortage is reported to trigger drought ̄respon ̄
sive gene expressionꎬ which is characterized by the
induction of signal transduction ( Yamaguchi ̄Shi ̄
nozaki and Shinozakiꎬ 2004ꎬ Huang et al.ꎬ 2012)ꎬ
channel protein genes (Johanson et al.ꎬ 2001ꎻ Luu
et al.ꎬ 2007ꎻ Danielson and Johansonꎬ 2008)ꎬ tran ̄
scription factors (Nelson et al.ꎬ 2007ꎻ Qiu and Yu
2009ꎻ Tripathi et al. 2014 )ꎬ and other defense
genes (Hare et al.ꎬ 1999ꎻ Catala et al.ꎬ 2007ꎻ Sun
et al.ꎬ 2013)ꎬ to subsequently maintain homeostasis
(Fordyceꎬ 2006). Howeverꎬ plant drought stress re ̄
sponses are complex biological processes that are
controlled by multiple trait lociꎬ and most studies to
date have focused on model and crop plantsꎬ neglec ̄
ting alpine plants which survive under harsh environ ̄
mental stress and are possibly highly valuable for
their potential resistance genetic resources. Clearlyꎬ
many challenges remain for the comprehensive un ̄
derstanding of the mechanism of plant tolerance to
drought stress.
Climate warming has caused substantial changes
in temporal and spatial precipitation patterns in man ̄
y regions of the world (Zhuang et al.ꎬ 2010). The
Tibetan Plateauꎬ famous as “ The third pole” and
“Roof of the world”ꎬ is closely connected with glob ̄
al climate change ( Carlyle et al.ꎬ 2014ꎻ Wang et
al.ꎬ 2014). Although there are plentiful freshwater
resources in the Tibetan Plateauꎬ and this region
serves as the headwater for many of Asia’ s rivers
(Wang et al.ꎬ 2009)ꎬ the distribution of the water
resources is predominantly dependent on its topo ̄
graphic configuration and atmospheric circulation
pattern. The present atmospheric circulation in Asia
is dominated by a westerly and monsoon wind sys ̄
temꎬ which results in an approximate rainfall gradi ̄
ent from east to west on the Tibetan Plateau (Klein
et al.ꎬ 2004ꎻ Shen et al.ꎬ 2008)ꎬ with accompanying
changes in ecosystem types from alpine meadowꎬ
044 植 物 分 类 与 资 源 学 报 第 37卷
steppe to desert (Niꎬ 2000). Meanwhileꎬ global cli ̄
mate change and human activities are potential rea ̄
sons for the accelerating drought trend on the Tibet ̄
an Plateau. Tree ̄line data indicates that extreme
drought conditions have progressed into the north ̄
western Tibetan Plateau during the past 300 years
(Gou et al.ꎬ 2006ꎬ 2007). Thereforeꎬ rainfall is
one of the most important factors determining the
structure and function of plant populationsꎬ commu ̄
nities and alpine ecosystems on the Tibetan Plateauꎬ
indicating that relevant studies should be very help ̄
ful for ecosystem managementꎬ conservationꎬ and
development. Howeverꎬ most previous studies have
focused on macroecological effects ( Bothe et al.ꎬ
2010ꎬ 2011ꎻ Zhu et al.ꎬ 2011ꎻ Yang et al.ꎬ 2012ꎻ
Sun and Liuꎬ 2013ꎻ Wu et al.ꎬ 2013ꎻ Yang et al.ꎬ
2013ꎻ Wang et al.ꎬ 2013ꎻ Fang et al.ꎬ 2014)ꎬ
whereas very little is known with regard to the effects
of rainfall on the evolution and adaptation of the par ̄
ticular species or populations on the Tibetan Plateau
at the physiological and molecular levels.
Stipa purpurea Griseb. is an endemic and domi ̄
nant perennial grass species in the alpine steppe and
meadow environments that are widely distributed in
the Tibetan Plateauꎬ Pamirs Plateau and high moun ̄
tains in Central Asia (Yue et al.ꎬ 2011). Because
of the wide distribution and strong resistance to
coldꎬ drought and high winds (Zhou et al.ꎬ 1987)ꎬ
it plays a vital role in safeguarding soil and water re ̄
sourcesꎬ acting as a windbreak and preventing ero ̄
sion (Yue et al.ꎬ 2011). With global climate changeꎬ
S purpurea is an available candidate to study alpine
plants response to drought stress and mine the resist ̄
ance genetic resources. As S purpurea has an ex ̄
tremely wide range of distributions on the Tibetan
Plateauꎬ it may be locally adapted to regional envi ̄
ronmental variation. In the present studyꎬ we investi ̄
gated the physiological and molecular divergence of
plants of S purpurea from two population response to
drought stress in the laboratory and analyzed how the
difference was correlated with their respective pheno ̄
type and acclimation to habitat environments. We
supposed that the S purpurea population living in the
more arid regions might have relatively stronger tol ̄
erance to the same degree of drought as a result of
heredity effect. The results should help us to better
understand how physiological and molecular diver ̄
gence contributes to drought adaptation across natu ̄
ral populations of S purpurea on the Tibetan Plateau.
1 Materials and methods
1 1 Seed collection and cultivation
The mature S purpurea seeds were collected in
August 2013 at the time of seed release from two
populations of western Pulan and eastern Cuoqin re ̄
spectively on the Tibetan Plateau ( Fig 1). After
brought back to laboratoryꎬ the seeds were dried un ̄
der a constant condition of 15 ℃ꎬ 15% air humidity
for one week.
The full seeds of two populations were picked
out randomly and the seed awns were removed. Then
the seeds were sown in flowerpots 〔diameter = 6 8-
9 4 cm ( from bottom to top)ꎬ height = 8 cm〕 with
equal weight of humus soilꎬ watering to keep the soil
sufficiently moist. Each pot contained thirty seeds.
The pots were placed in a greenhouse under 12 ̄h ̄
light / 12 ̄h ̄darkꎬ 28 / 20 ℃ and a relative humidity of
40%-60%. For each populationꎬ leaves of ten ̄pot
seedlings were collected and grinded for prolineꎬ
MDAꎬ antioxidant enzyme activity measurement and
RNA extraction. 3 one ̄pot seedlings were used to
analyze change of morphologyꎬ RWC in leaf and
chlorophyll fluorescence respectively. Three leaves in
one pot were selected randomly for H2O2 and O2
-
detection. Three independent replications were car ̄
ried out for all sample measurements.
1 2 Drought treatment
Before drought treatmentꎬ the seedlings grew
for another three weeks watered every day uniformly.
When the plants reached the 3 ̄leaf seedling stage
(Liu et al.ꎬ 2013)ꎬ the plants were withheld water
for two weeks until the plants of one population showed
apparent death. Then the plants were rewatered for
1444期 LI Xiong et al.: Comparative Physiological and Molecular Analyses of Intraspecific Differences of
Fig 1 Geographical information and location on the precipitation distribution map of the two seed collection sites
another two weeksꎻ after recoveryꎬ the plant mortali ̄
ty for each population was counted. The leaves of
plants under drought for 0 d and 14 d and rehydra ̄
tion for 14 d were sampled for the following measure ̄
ment and analysis.
1 3 Water content measurement
The relative water content (RWC) of the leaves
was determined as: RWC = 〔Fresh weight ( FW) -
Drought weight ( DW)〕 / ( Turgid weight ̄DW). To
measure turgid weightꎬ leaves were kept in distilled
water in darkness at 4 ℃ to minimize respiration los ̄
ses until they reached a constant weight (Rivero et
al.ꎬ 2007). DW of the plants was obtained after 48 h
at 70 ℃ in an air oven (Rivero et al.ꎬ 2007).
1 4 Analysis of chlorophyll fluorescence
Chlorophyll fluorescence was analyzed as previ ̄
ously described (Bai et al.ꎬ 2011)ꎬ with a pulse ̄
amplitude modulation chlorophyll fluorometer (Heinz
Walz GmbHꎬ Effeltrichꎬ Germany). Brieflyꎬ at the
time of samplingꎬ S purpurea seedlings were dark ̄a ̄
dapted for 30 min to measure the maximum quantum
yield of photosystemⅡ(PSⅡꎻ Fv / Fm)ꎬ and Fv / Fm
was determined for each sample by analyzing a whole
pot plant. The maximum fluorescence (Fm) was re ̄
corded by a 0 8 s pulsed light at 4 000 μmol s-1
m-2ꎬ and minimal fluorescence (Fo) was recorded
during the weak measuring pulses.
1 5 Proline and malondialdehyde content meas ̄
urement
Proline content was measured as previously re ̄
ported (Bates et al.ꎬ 1973)ꎬ with some modifica ̄
tion. Approximately 0 2 g of fresh leaves was homog ̄
enized in 10 mL of 3% aqueous sulphosalicylic acidꎬ
and the homogenate was centrifuged at 2 000 × g for
10 min. Thenꎬ 2 mL of the extract were reacted with
2 mL of acidic ̄ninhydrine and 2 mL of glacial acetic
acid for 1 h in boiling waterꎻ after thisꎬ the reaction
terminated in an ice bath. The reaction mixture was
extracted with 4 mL tolueneꎬ mixed vigorously with a
test tube stirrer for 15 - 20 sec. The chromophore
containing toluene was aspirated from the aqueous
phaseꎬ warmed to room temperature and the absor ̄
bance read at 520 nm using toluene for a blank. The
proline concentration was determined from a stand ̄
ard curve and calculated as mg g-1 DW.
The malondialdehyde (MDA) content was de ̄
244 植 物 分 类 与 资 源 学 报 第 37卷
termined as described previously (Li et al.ꎬ 2014).
Approximately 0 5 g of fresh leaves were homoge ̄
nized in 10 mL of 10% trichloroacetic acid (TCA)
and centrifuged at 12 000 × g for 10 min. Thenꎬ 2 mL
of 0 6% thiobarbituric acid in 10% TCA were added
to an aliquot of 2 mL of the supernatant. The mixture
was heated in boiling water for 30 min and then
quickly cooled in an ice bath. After centrifugation at
10 000 × g for 10 minꎬ the absorbance of the superna ̄
tant at 450ꎬ 532ꎬ and 600 nm was determined. The
MDA concentration was expressed as nmol g-1 DW.
1 6 In situ H2O2 and O2
- detection
The in situ detection of H2O2 and O2
- were per ̄
formed using a previously reported method with some
modifications (Ableꎬ 2003). The amount of H2O2
and O2
- was detected with 1 mg mL-1 of diaminobenz ̄
idine (DAB) and 10-2 M nitro ̄blue tetrazolium (NBT)
respectively. Leaves were vacuum ̄infiltrated in 10
mL solution for 2 h and then cleared in boiling etha ̄
nol (95%) for 10 min. Thenꎬ samples were stored
and examined in 95% ethanol.
1 7 Antioxidant enzyme activity assays
The activities of superoxide dismutase ( SODꎻ
EC1 15 1 1)ꎬ catalase (CATꎻ EC1 11 1 6) and
ascorbate peroxidase ( APXꎻ EC1 11 1 11) were
determined as previously described ( Nakano and
Asadaꎬ 1981ꎻ Jiang and Zhangꎬ 2001). Approxi ̄
mately 1 g of leaves collected from treated S purpur ̄
ea seedlings were homogenized in 10 mL extraction
buffer (50 mmolL-1 sodium phosphate pH 7 0ꎬ 1
mmolL-1 EDTAꎬ 1 mmolL-1 DTTꎬ 1 mmolL-1
GSHꎬ 5 mmolL-1 MgCl26H2Oꎬ 1% PVP ̄40 and
20% glycerin). The homogenates were centrifuged at
12 000 × g for 10 min at 4 ℃ꎬ and total soluble pro ̄
tein content of the supernatants was measured by the
Bradford method (Barbosa et al.ꎬ 2009).
1 8 RNA extraction and RT ̄PCR analysis
Total RNA was extracted from the leaves of dif ̄
ferent samples using TRIzol reagent ( Invitrogen )
and treated with RNase ̄free DNAse (Takara). The
RNA concentration was determined using a Nanodrop
1 000 (Thermo Scientific productꎬ USA). MMLV re ̄
verse transcriptase (Promega) was used to synthesize
the cDNAs. The alternatively spliced fragments were
amplified from the cDNA using primers listed in Ta ̄
ble 1ꎬ which were designed based on the transcrip ̄
tomic sequencing results. The amplification was per ̄
formed under conditions as follows: 94 ℃ꎬ 4 minꎻ 94
℃ꎬ 30 sꎻ 52-58 ℃ꎬ 30 sꎻ 72 ℃ꎬ 30 sꎻ 28-35 cyclesꎻ
72 ℃ꎬ 10 min (Table 1). The amplification products
were separated by electrophoresis on 2% agarose gels.
1 9 Data analysis
Statistical analyses were performed using the
statistical Software Package for Social Science (SPSS)
version 18 0. One ̄way ANOVA for all variables was
used for testing the treatment differences. Differences
were considered to be significant at the P < 0 05.
2 Results
2 1 The phenotypic difference between plants
from two sites
After exposure to drought stress for 14 days under
the same conditionsꎬ the plants of Cuoqin showed ob ̄
vious wilting compared with those of Pulan (Fig 2A).
Some of the plants died after another 14 ̄d rehydra ̄
tion with significant divergence between plants of two
sites. Actuallyꎬ 16 2% of the seedlings from Pulan
were dead while mortality rate of Cuoqin reached to
78 2% (Fig 2B). The phenotypic results fully dem ̄
onstrated that there was difference between the plants
from two sites in response to drought stress.
2 2 The changes of physiological status of the
plants
The RWC of the plants from both Pulan and Cuo ̄
qin had high values (83 9% and 83 3% respectively)
before drought treatment and dropped to dissimilarly
low levels ( 32 0% and 13 6% respectively) after
drought stress for 14 dꎬ with obvious difference be ̄
tween two sites (Fig 2C). After rewateredꎬ the RWC
of plants from Pulan returned to a relatively high level
(69 1%) while that of Cuoqin still had a very low
value (35 1%) ( Fig 2C)ꎬ indicating that maybe
the water absorption system of plants from Cuoqin
was destroyed by the stress.
3444期 LI Xiong et al.: Comparative Physiological and Molecular Analyses of Intraspecific Differences of
Table 1 The information of genes related to drought stress used for RT ̄PCR
Gene name GenBankaccession number Primer F (5′
-3′) Primer R (5′-3′)
Tm
/ ℃
PCR cycles
Actin1 KM216249 GCTGGATTCTGGAGATGGTGTC TTACTCATTCACCACTACGGCTG 52 28 and 35
APX1 KM201379 CACGAGGAAGAATACACCC GCATAAAGCTCCACATAGC 50 30
APX2 KM201380 CCTTCGGCACCATGAAGTG GCCTCAGCATAGTCAGCAAA 54 30
CAT KM201378 CACGCCTTCAAGCCCAAC ACGAACCTGTCCTGCCTGTC 56 30
DREB1 KM201387 GGACGTTCCCAACTGCTC CGGTTCACCTTCTATCGG 52 32
DREB3 KM201388 GTTGGCTCGTACTAACTTCC ATCATCGGTTCACCTTCTAT 56 32
P5CS KM201383 TCATAACTGGCGTCATTC TTGTCCACTCCCTCGTAG 50 30
PIP1 KM201389 TCCGAGGACAAGGACTACAAGG GGACGAAGGTGCCGATGAT 56 30
PIP2 KM201390 CATTGACTTCGAGGAGCTGACC GGTGCTTGTACCCGATGACG 56 30
SOD1 KM201381 CTTATTTGAGCAAGAGGG CTGATGGCATTTCGTGTA 48 30
SOD2 KM201382 GAAGCACCACGCCACCTA GCTCCCAGACATCAATCCC 54 30
WRKY4 KM201385 AGCCTTCACTGAGCCTTGACC CCTTCTGCCCGTACTTCCG 58 30
WRKY11 KM201386 CCCTCCCGTTTCTTCTCCTCCT GGGCTTCTGTCCGTACTTGCG 58 30
WRKY17 KM201384 CAGAAGCACGTTAAGGGA GAGGCTCACGGTTAGGTT 52 30
Fig 2 Changes in plant phenotype and relative water content of leaves during the process of drought treatment and subsequent recovery
of Stipa purpurea from two sites. A: The change of plant phenotype of Stipa purpurea from two sitesꎻ B: The change of plant mortality
rate of Stipa purpurea from two sitesꎻ C: The change in relative water content of leaves in Stipa purpurea from two sites.
Error bars indicate SE. Means denoted by different letters were significantly different (P < 0 05) (B & C)
The chlorophyll fluorescence was diversely in ̄
fluenced in the course of drought stress and subse ̄
quent recovery. The Fv / Fm of plants from Pulan just
changed from 0 86 to 0 52 during the drought treat ̄
ment (Fig 3)ꎻ neverthelessꎬ the Fv / Fm reduced from
0 86 to 0 05 in the plants from Cuoqin (Fig 3). In
the recovery stageꎬ the Fv / Fm returned to an average
value of 0 81 and 0 20 respectively in the plants of
Pulan and Cuoqin (Fig 3)ꎬ suggesting the different
influence degree under drought stress.
444 植 物 分 类 与 资 源 学 报 第 37卷
Fig 3 Effects of drought stress and subsequent recovery on leaf photosynthesis in Stipa purpurea from two sites. A: Fv / Fm images.
The pseudocolor code depicted at the bottom of the image ranges from 0 (red) to 1 0 (purple) . The experiment was replicated
three times with similar results. One representative result was shownꎻ B: Average Fv / Fm values. Fv / Fm was determined for
whole plants. Error bars indicate SE. Means denoted by different letters were significantly different (P < 0 05) (B)
2 3 The changes of proline and MDA content
The proline content of plants from both Pulan
and Cuoqin kept at a relatively low level before
drought stress (1 51 and 1 52 mg g-1 DW respec ̄
tively) (Fig 4A). After treated by drought stress for
two weeksꎬ to our surpriseꎬ the proline content of
plants from Pulan was drastically induced up to
10 11 mg g-1 while it rose up to 6 07 mg g-1 in
plants from Cuoqinꎬ which were 5 7 and 3 0 fold
respectively more than the corresponding controls
(Fig 4A). In the subsequent recoveryꎬ the proline
content in both plants recovered by certain degreeꎬ
but they were still higher than the controls ( 1 96
and 2 68 mg g-1 respectively) (Fig 4A).
The MDA content was diversely influenced in
the course of drought stress and subsequent recovery.
It changed from 4 18 to 17 09 nmol g-1 DW during
the drought stress in the plants from Pulan (Fig 4B)ꎬ
neverthelessꎬ it increased from 4 07 to 22 83 nmol
g-1 DW in the plants from Cuoqin (Fig 4B). In the
recovery stageꎬ the MDA content returned to the
control level in the plants from Pulan (3 34 nmol g 1
DW)ꎬ but it remained at a higher level than the
control in the plants from Cuoqin (12 86 nmol g-1
DW) (Fig 4B).
2 4 The accumulation of H2O2 and O2
-
Both the H2O2 and O2
- in plants from two sites
were accumulated under exposure to drought stress
and dropped to a low level after rewateredꎬ but they
both showed different change degree between plants
of two sites (Fig 4C). Both H2O2 and O2
- were in ̄
duced to a much lower level and returned to be more
similar with the control in the plants from Pulan
compared with those from Cuoqin (Fig 4C). The re ̄
sults were consistent with the MDA contentꎬ which
reflected the oxidation degree of cell membrane by
the excessive ROS accumulation.
2 5 The dynamic of antioxidant enzyme activities
The SOD activityꎬ as well as APX activityꎬ
were induced significantly under drought stress and
returned to the control level roughly in the plants
from Pulan ( Fig 5A). Howeverꎬ both SOD and
APX activities did not increase but decreased slight ̄
ly after drought treatment in plants from Cuoqin
(Fig 5A)ꎻ when the plants werewatered againꎬ the
activities of both the two antioxidant enzymes contin ̄
5444期 LI Xiong et al.: Comparative Physiological and Molecular Analyses of Intraspecific Differences of
ued to reduce to a lower level compared with the
control (Fig 5A). The CAT activity also rose greatly
in plants from Pulan when the plants were treated by
drought stress and went back to the control level af ̄
ter rehydration treatmentꎬ while it just increased
slightly under drought stress and the value reduced
to the control below after rehydration in the plants
from Cuoqin ( Fig 5A). The results indicated that
the antioxidant enzyme system in plants from Cuoqin
was inefficient and might be partly destroyed in the
course of drought stress.
2 6 The expression changes of genes related to
drought stress
To investigate the expression patterns and func ̄
tions of genes in response to droughtꎬ RT ̄PCR was
performed for several drought ̄related genes. The re ̄
sults indicated that different genes showed various
expression changes pattern with two common points
(Fig 5B). On one handꎬ nearly all genes’ expressions
were induced by different degrees under drought
treatment in both sites of plants ( Fig 5B). On the
other handꎬ most genes had higher expressions in
plants from of Pulan compared with those from Cuo ̄
qin after exposure to drought stress (Fig 5B). More
specificallyꎬ two SOD genes ( SOD1ꎬ SOD2) and
one CAT gene were all induced obviously under
drought stress and returned to the control levels after
rewatering in plants from Pulanꎬ but they showed
Fig 4 Accumulation of prolineꎬ malondialdehyde (MDA) and reactive oxygen species (ROS) (H2O2 and O2 -) in Stipa purpurea from
two sites during the process of drought treatment and subsequent recovery. A: Proline content changes in Stipa purpurea from two sitesꎻ
B: MDA content changes in Stipa purpurea from two sitesꎻ C: In situ detection of changes in leaf H2O2 and O2 - levels of Stipa purpurea
from two sites. Error bars indicate SE. Means denoted by different letters were significantly different (P < 0 05) (A and B)
644 植 物 分 类 与 资 源 学 报 第 37卷
slight induction under drought stress and dropped
below the control levels after watering again in plants
from Cuoqin ( Fig 5B). Two APX genes ( APX1ꎬ
APX2) were also induced under drought stress and
went back to the control levels in plants from Pulanꎻ
on the contraryꎬ expression of the two genes did not
increase but decrease after drought treatment in
plants from Cuoqin (Fig 5B). The delta ̄1 ̄pyrroline ̄
5 ̄carboxylate synthase ̄like ( P5CS ) gene showed
obviously high expression in both plants from Pulan
and Cuoqin (Fig 5B). Three WRKY family genes
(WRKY4ꎬ WRKY11 and WRKY17) had similar ex ̄
pression changes in the plants from the same siteꎻ
neverthelessꎬ they showed better induction and re ̄
covery in plants from Pulan than those of Cuoqin
(Fig 5B ). Interestinglyꎬ the similar results were
found in two dehydration responsive element bin ̄
ding protein ( DREB) family genes ( DREB1 and
DREB3) ( Fig 5B). Two aquaporin genes ( PIP1
and PIP2)ꎬ which belong to the class of plasma
membrane intrinsic proteins ( PIPs)ꎬ also showed
higher expressions in plants from Pulan compared
with those from Cuoqin after exposure to drought
stress (Fig 5B).
Fig 5 Changes in antioxidant enzyme activities and drought ̄related genes expression in Stipa purpurea from two sites during the
process of drought treatment and subsequent recovery. A: The changes of antioxidant enzyme activities in Stipa purpurea from
two sitesꎻ B: The changes of drought ̄related genes expression in Stipa purpurea from two sites. Actin was included as a cDNA
loading control. The abbreviations Coꎬ Dr and Re at the bottom represent Controlꎬ Drought and Recovery respectively.
Error bars indicate SE. Means denoted by different letters were significantly different (P < 0 05) (A)
7444期 LI Xiong et al.: Comparative Physiological and Molecular Analyses of Intraspecific Differences of
3 Discussion
Intraspecific variation in drought response has
been observed from a lot of species under different
growth conditions (Walker and Millerꎬ 1986ꎻ Sand ̄
quist and Ehleringerꎬ 1997ꎬ 1998ꎻ Beikircher and
Mayrꎬ 2009ꎻ Lu et al.ꎬ 2009ꎻ Hamanishi et al.ꎬ
2010). These findings show the effects of environ ̄
mental heterogeneity on the modification and accli ̄
mation in plant characteristics. As S purpurea is dis ̄
tributed along a representative precipitation gradi ̄
entꎬ the characteristics of response to water shortage
or excess also may exhibit significant differences in
different populationsꎬ with a hypothesis that plants
from more arid area may possess greater drought tol ̄
erance. In the present studyꎬ the results of morpho ̄
logical and physiological status in the course of
drought treatment and subsequent recovery fully sug ̄
gested that the seedlings from Pulan had stronger re ̄
sistance to the same degree of drought stress than
those from Cuoqin. That was to sayꎬ S purpurea from
more arid area had stronger resistivity to drought
stressꎻ thereforeꎬ the results implied that the in ̄
traspecific difference of response to drought presen ̄
ted genetic effects.
Low leaf RWC after drought caused obvious
withering and chlorsis in plants from Cuoqin that suf ̄
fered from greater mortality as a resultꎬ indicating
that plants from Cuoqin had been exceeded physio ̄
logical drought limit. Water shortage can induce
stomatal closureꎬ which will influence photosynthesis
process directly. The photosynthetic apparatus asso ̄
ciated with PS II is very sensitive to drought and va ̄
rious other stresses ( Yordanov et al.ꎬ 1999ꎻ Mi ̄
hailova et al.ꎬ 2011)ꎬ which usually reduces chloro ̄
phyll fluorescence. In the present studyꎬ the chloro ̄
phyll fluorescence ( Fv / Fm ) of plants from Pulan
dropped less and recovered more than those from
Cuoqinꎬ indicating that plants from Cuoqin were
more susceptible to drought and more difficult to re ̄
cover from the stress. The decline of Fv / Fm often re ̄
sulted from a non ̄radiative process of thermally dis ̄
sipating absorbed lightꎬ which played a central role
in leaf photoprotection under drought ( Chaves et
al.ꎬ 2003). If excess energy from absorbed light was
not coped with by either photosynthesis or photore ̄
spiration and the thermal dissipationꎬ the production
of highly reactive moleculesꎬ generated within the
chloroplastꎬ could be exacerbated to cause oxidative
damage to the pthotosynthetic apparatus ( Smirnoffꎬ
1998ꎻ Niyogiꎬ 1999).
Oxidative stress is a state of damage caused by
ROSꎬ which consists of H2O2ꎬ O2
-ꎬ OH and 1O2
(Chaves et al.ꎬ 2003). Under normal conditionsꎬ
ROS are scavenged by antioxidant molecules and en ̄
zymes that are located in different cell compart ̄
mentsꎬ which maintain ROS homeostasis in plants
(Li et al.ꎬ 2014). In this workꎬ we tested the ROS
(H2O2 & O2
-) accumulation in conjunction with the
antioxidant enzyme activities ( SODꎬ CAT & APX)
and the expression of their corresponding regulatory
genes. Smaller amounts of H2O2 and O2
- were ob ̄
served both after drought treatment and subsequent
recovery in plants from Pulanꎬ the reason could be
explained by the higher activities of antioxidant en ̄
zymes. For the plants from Cuoqinꎬ because the low ̄
er antioxidant enzymes activities had poor efficiency
to remove the excessive ROSꎬ so the plants failed to
maintain the normal physiological state and even
died heavily due to the oxidative damage partly. In ̄
terestinglyꎬ the changes of antioxidant enzyme activi ̄
ties were very similar to the expression results of the
corresponding genesꎬ implying that the divergences
between plants from two sites were internal genetic
properties. When the ROS dynamic equilibrium is
brokenꎬ a series of oxidation products will be gener ̄
atedꎬ such as MDAꎬ a commonly used index that
reflected grades of cellular oxidation ( Li et al.ꎬ
2014). In the present studyꎬ less content of MDA in
the seedlings of S purpurea from Pulan also indirect ̄
ly illustrated their better capability to cope with
drought stress.
Osmotic adjustment is considered a crucial process
in plant adaptation to drought because of its role in
sustaining tissue metabolic activity and enabling re ̄
844 植 物 分 类 与 资 源 学 报 第 37卷
growth upon rewetting ( Morganꎬ 1984). Prolineꎬ
the synthesis of which is mainly regulated by P5CS
gene (Hare et al.ꎬ 1999)ꎬ is one of the most studied
compatible solutes in osmotic adjustment. Proline
helps to stabilize macromoleculesꎬ protect enzymesꎬ
and store carbon and nitrogen for use during stress
regimes in plants (Ashraf and Fooladꎬ 2007). Our
results showed that the proline production could be
rapidly and substantially induced under drought
stress in S purpureaꎬ and the accumulation amount
was much more in plants from Pulanꎬ which had
better drought tolerance. Interestinglyꎬ the change
trend of proline content was consistent with the ex ̄
pression of P5CS gene in the process. This suggested
that extremely efficient start of regulatory genesꎬ in ̄
cluding P5CSꎬ and accumulation of proline had sig ̄
nificant roles in response and resistance to drought in
S purpurea.
Transcription factors (TFs) have been demon ̄
strated to play important roles at various levels in the
signaling web to enable plants to deal with water ̄
stress / drought (Tripathi et al.ꎬ 2014). WRKY TFsꎬ
both positive and negative regulators of gene expression
(Eulgem and Somssichꎬ 2007)ꎬ have been reported to
play pivotal roles in regulating many stress reactions
in plants (Chen et al.ꎬ 2012ꎻ Rushton et al.ꎬ 2012).
Speciallyꎬ overexpression of several WRKY TFs has
been proved to enhance drought and some other
stresses tolerance in different species (Zhou et al.ꎬ
2008ꎻ Qiu and Yuꎬ 2009ꎻ Wu et al.ꎬ 2009ꎻ Moon
et al.ꎬ 2014). In the studyꎬ three WRKY TFs were
all induced under drought stress and had higher ex ̄
pression in S purpurea from Pulan rather than Cuo ̄
qinꎬ implying their important functions in response
to drought stress in S purpurea and the role of grea ̄
ter expression in strengthening drought tolerance in
plants from Pulan. DREBsꎬ which control stress ̄in ̄
ducible gene expression in the abscisic acid (ABA) ̄
independent pathway (Yamaguchi ̄Shinozaki and Shin ̄
ozakiꎬ 2006)ꎬ are another class of TFs that have
been reported to play an important role in plant re ̄
sponse to water stress in many species (Liu et al.ꎬ
2013). The expression changes of two DREB TFs in
our study also indicated their significant functions in
response to drought stress and the role of greater ex ̄
pression in driving stronger drought tolerance in
S purpurea from Pulan.
The regulation of aquaporins is one important
response of plant cells to water stress ( Luu et al.ꎬ
2007)ꎬ which tightly control the transcellular water
movement by their amount and activity ( Chaumont
and Tyermanꎬ 2014). PIPs are one of the five sub ̄
groups of aquaporins (Johanson et al.ꎬ 2001ꎻ Daniel ̄
son and Johansonꎬ 2008)ꎬ which can be divided in ̄
to two major groups in plantsꎬ PIP1 and PIP2ꎬ
based on their sequences and water ̄channel activity
(Kelly et al.ꎬ 2014). Sufficient evidence has dem ̄
onstrated that overexpression of PIPs significantly
enhanced the rates of growthꎬ transpiration and pto ̄
tosynthesis in Arabidopsis and tomato plants (Aha ̄
ron et al.ꎬ 2003ꎻ Flexas et al.ꎬ 2006ꎻ Sade et al.ꎬ
2010)ꎬ and the antisense suppression usually had
the opposite effects (Siefriz et al.ꎬ 2002ꎻ Uehlein et
al.ꎬ 2003ꎻ Siefritz et al.ꎬ 2004). In additionꎬ a pu ̄
tative aquaporin gene VfPIP1ꎬ isolated from Vicia
faba leaf epidermisꎬ was found to be induced in ex ̄
pression by ABA and polyethylene glycol 6 000 and
its expression might improve drought resistance of
the transgenic plants (Cui et al.ꎬ 2008). Like the
previous studiesꎬ two PIPs genesꎬ PIP1 and PIP2ꎬ
were both induced in expression in S purpurea under
drought stressꎻ furthermoreꎬ their expression were
much higher in plants from Pulanꎬ which displayed
greater drought tolerance in the study. The results
once again indicated that PIPs could improve the
drought resistance of plants.
Above allꎬ our study indicated that different S pu ̄
rpurea populations had variant responses to drought
stress throughout long ̄term adaptation and evolution.
Rapid and efficient start of response and protection
mechanism at physiological and molecular levels
might be the foundation of stronger resistance to
drought stress for S purpurea. The results indicated
the differential responses to climate change among
9444期 LI Xiong et al.: Comparative Physiological and Molecular Analyses of Intraspecific Differences of
different S purpurea populations. The study helps us
to understand more about the adaptation and evolu ̄
tion of alpine plants in the natural habitat on the Ti ̄
betan Plateau under global climate change.
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