全 文 :拟南芥角果衰老过程中膜脂的变化∗
禹晓梅1ꎬ2ꎬ4ꎬ 王 荣1ꎬ 李唯奇1ꎬ3∗∗
(1 中国科学院昆明植物研究所 中国西南野生生物种质资源库ꎬ 云南 昆明 650201ꎻ 2 中国科学院大学ꎬ 北京 100049ꎻ
3 红河学院生物系ꎬ 云南 蒙自 661100ꎻ 4 玉溪中烟种子有限责任公司ꎬ 云南 玉溪 653100)
摘要: 角果发育对某些物种的生殖发育具有重要的作用ꎮ 拟南芥种子附着在角果里ꎬ 角果在早期发育时进
行光合作用ꎬ 角果成熟后开裂散落种子之前ꎬ 其细胞会经历一个衰老的过程ꎮ 一般植物细胞在衰老过程中
要经历膜脂降解的过程ꎬ 但是角果细胞衰老过程仍未知ꎮ 通过比较角果衰老过程中拟南芥野生型 (WS)
及与膜脂代谢密切相关的磷脂酶 Dδ缺失突变体 (PLDδ ̄KO) 中膜脂分子的组成情况、 膜脂含量、 相对含
量及双键指数值ꎬ 结果发现ꎬ 在拟南芥角果衰老过程中: ( i) 质体膜脂和质体外膜脂显著下降ꎻ ( ii) 不
同膜脂降解速率不一样ꎬ 质体膜脂的降解比质体外膜脂的降解快ꎻ (iii) 总的双键指数 DBI下降ꎻ ( iv) 磷
脂酶 Dδ缺失突变体 (PLDδ ̄KO) 的角果膜脂组成的基本水平和变化样式与野生型 (WS) 非常相似ꎮ 结
果说明ꎬ 角果在衰老过程中发生了膜脂的激烈降解ꎮ 据此推测: (i) 膜脂水解产物可能转移到种子中用于
储藏脂三酰甘油的合成ꎻ ( ii) 质体膜脂相对含量下降和质体外膜脂相对含量上升导致了总的 DBI 下降ꎻ
(iii) PLDδ参与了角果衰老中的膜脂代谢ꎮ
关键词: 拟南芥ꎻ 角果衰老ꎻ 膜脂ꎻ 脂类组学
中图分类号: Q 945 文献标识码: A 文章编号: 2095-0845(2014)02-177-10
Changes in Membrane Lipids during Silique Senescence in Arabidopsis
YU Xiao ̄Mei1ꎬ2ꎬ4ꎬ Wang Rong1ꎬ LI Wei ̄Qi1ꎬ3∗∗
(1 Germplasm Bank of Wild Species in Southwest Chinaꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ Kunming
650201ꎬ Chinaꎻ 2 University of Chinese Academy of Sciencesꎬ Beijing 100049ꎬ Chinaꎻ 3 Department of Biologyꎬ
Honghe Universityꎬ Mengzi 661100ꎬ Chinaꎻ 4 Yuxi Zhongyan Tobacco Seed Co.ꎬ Ltdꎬ Yuxi 653100ꎬ China)
Abstract: Silique development plays an important role in the reproductive development of many species. In Arabi ̄
dopsisꎬ the seeds are contained within a siliqueꎬ which is to photosynthesize in the early stages of development and
the cell undergoes a programmed of senescence prior to dehiscence after silique riping. In generalꎬ degradation of
membrane lipids is an essential process during plant cell senescenceꎬ howeverꎬ the senescence of silique has not
been reported. In the present studyꎬ the changes of molecular species in membrane lipidsꎬ the contents of membrane
lipidsꎬ relative levels (%)ꎬ and the double ̄bond index (DBI) during the senescence of siliques were examined in
wild ̄type Arabidopsis ( ecotype Wassilewskijaꎻ WS) and an Arabidopsis mutant deficient in phospholipase Dδ
(PLDδ ̄KO). PLDδ is correlated closely with lipid metabolism in Arabidopsis. The present study revealed that during
the senescence of siliques of Arabidopsis: (i) levels of both extraplastidic and plastidic lipids decreased significant ̄
lyꎻ (ii) the degradation of lipids did not occur at the same rate for different lipid speciesꎬ the rate of decline in lev ̄
els of plastidic lipids was more rapid than that of extraplastidic lipidsꎻ ( iii) the DBI of total membrane lipids de ̄
creasedꎻ and (iv) in siliques of the PLDδ mutant plantsꎬ the levels and variations in the levels of membrane lipids
were similar to those observed in siliques of WS. These results suggest that severe degradation of lipid molecular spe ̄
植 物 分 类 与 资 源 学 报 2014ꎬ 36 (2): 177~186
Plant Diversity and Resources DOI: 10.7677 / ynzwyj201413107
∗
∗∗
Funding: The National Natural Science Foundation of China (NSFC 30670474ꎬ 30870571ꎬ and 31070262)
Author for correspondenceꎻ E ̄mail: weiqili@mail kib ac cn
Received date: 2013-05-05ꎬ Accepted date: 2013-07-10
作者简介: 禹晓梅 (1984-) 女ꎬ 博士ꎬ 主要从事种子生物学研究ꎮ
cies occurred during Arabidopsis silique senescence. Our findings suggest that (i) the products of hydrolysis of mem ̄
brane lipids may be transferred to seeds for the synthesis of triacylglycerols for lipid storageꎻ (ii) the decline of DBI
of total membrane lipids might be caused by the dramatic degradation of plastidic lipids and the relative increase of
extraplastidic lipidsꎻ and (iii) PLDδ is involved in the metabolism of membrane lipids during silique senescence.
Key words: Arabidopsisꎻ Silique senescenceꎻ Membrane lipidsꎻ Lipidomics
Abbreviations: ESI ̄MS / MSꎬ electrospray ionisation tandem mass spectrometryꎻ DAFꎬ days after floweringꎻ DBIꎬ
double ̄bond indexꎻ DGDGꎬ digalactosyldiacylglycerolꎻ MGDGꎬ monogalactosyldiacylglycerolꎻ PAꎬ phosphatidic
acidꎻ PCꎬ phosphatidylcholineꎻ PEꎬ phosphatidylethanolamineꎻ PGꎬ phosphatidylglycerolꎻ PIꎬ phosphatidylinosi ̄
tolꎻ PSꎬ phosphatidylserineꎻ WSꎬ Wassilewskijaꎻ PLDꎬ phospholipase Dꎻ PLDδ ̄KOꎬ phospholipase Dδ knock outꎻ
WSꎬ Wassilewskijaꎻ TAGꎬ triacylglycerolꎻ DAFꎬ days after flowering
The last phase of flower development is fertil ̄
isation of the ovules and the formation of fruit
(Folter et al.ꎬ 2004). Arabidopsis is a model system
to study the ripening and senescence of fruit (Gio ̄
vannoniꎬ 2004ꎻ Kou et al.ꎬ 2012). Arabidopsis fruitsꎬ
which are called siliquesꎬ are both biologically and
economically important because they produce seeds
and their dehiscence enables seed dispersal (Kou et
al.ꎬ 2012). Senescence is a highly organized process
regulating tissue ageing and death to enable nutrient
recycling to occur. Silique senescence is a complex
process that manifests at the levels of morphology
(e g.ꎬ greening and yellowing of siliques)ꎬ physiolo ̄
gy (e g.ꎬ photosynthesis)ꎬ cell composition (e g.ꎬ
regulated changes in the levels of sucroseꎬ chloro ̄
phyll)ꎬ biochemistry (e g.ꎬ changes in the concen ̄
trations of and sensitivities to hormones)ꎬ and mo ̄
lecular geneticsꎬ with all of these processes affecting
cell growth and differentiation (Folter et al.ꎬ 2004ꎻ
Louvet et al.ꎬ 2006ꎻ Fallahi et al.ꎬ 2008ꎻ Louvet et
al.ꎬ 2011ꎻ Walton et al.ꎬ 2012). Howeverꎬ there
has been only limited research on cell membrane lip ̄
ids during silique senescence.
Cellular lipids play pivotal roles in the struc ̄
tures and metabolic regulation of cell membranes
(Devaiah et al.ꎬ 2006). In plantsꎬ increasing evi ̄
dence has also demonstrated roles for lipids in cell
senescence. Loss of membrane phospholipids was ob ̄
served during natural and ethylene ̄induced senes ̄
cence of cut carnation flowers ( Thompson et al.ꎬ
1982ꎻ Brown et al.ꎬ 1987). Changes in the metabol ̄
ic relationships among phospholipidsꎬ and between
galactolipids and phospholipidsꎬ occur during senes ̄
cence ̄associated lipid breakdown. Both the natural
senescence of rose petals and dark ̄induced senes ̄
cence of cabbage leaves are associated with an over ̄
all decrease in the levels of membrane phospholipids
(Borochov et al.ꎬ 1982ꎻ Buchananꎬ 1997). In ad ̄
ditionꎬ levels of both extraplastidic and plastidic li ̄
pids decrease during the natural senescence of to ̄
bacco leaves (Koiwai et al.ꎬ 1981). Howeverꎬ many
questions related to the lipid metabolism of Arabidop ̄
sis during silique senescing remain unanswered. For
exampleꎬ how does the profile of membrane lipids
change during this process? Do changes in lipid me ̄
tabolism during the senescence of siliques resemble
those during the senescence of leavesꎬ and what are
the mechanisms involved?
In plantsꎬ the activities of several lipolytic en ̄
zymes have been describedꎬ including phospholipase
D (PLD)ꎬ PLAꎬ PLCꎬ nonspecific acyl hydrolaseꎬ
and galactolipases (Wangꎬ 2004ꎻ Li et al.ꎬ 2008).
PLD hydrolyses phospholipids to generate phospha ̄
tidic acid (PA)ꎬ which is the most active phospho ̄
lipase in plants. Recentlyꎬ studies have shown that
PLDα1 and PLDδꎬ the two most abundant types of
the 12 ̄member Arabidopsis PLD familyꎬ play impor ̄
tant roles in plant growth and resistance to stress
(Zien et al.ꎬ 2001ꎻ Wangꎬ 2002ꎬ 2004ꎻ Uraji et
al.ꎬ 2012). Phospholipase Dδ knock out ( PLDδ ̄
KO) plants are more sensitive to H2O2 ̄induced cell
death and less tolerant of freezing injuries than their
wild ̄type counterparts. PLDα1 contributes signifi ̄
cantly to PA levels in rootsꎬ seedsꎬ flowersꎬ and
871 植 物 分 类 与 资 源 学 报 第 36卷
flower stalksꎬ but little to the very low PA levels
found in siliques and leaves (Devaiah et al.ꎬ 2006).
Howeverꎬ it is unknown whether knock out of the
gene that encodes PLDδ affects the composition of
basal membrane lipids in Arabidopsis during silique
senescence.
Membranesꎬ particularly plasma and chloroplast
membranesꎬ are very important during plant growth.
Cell membranes can adjust the level of unsaturation
of their lipidsꎬ as well as their lipid composition and
structureꎬ in response to stress (Navari ̄Izzo et al.ꎬ
1993). The degree of unsaturation of membrane
glycerolipids (measured as the double ̄bond indexꎬ
DBI) is the major factor that determines membrane
fluidity. A high DBI indicates the presence of more
unsaturated membrane lipids and higher fluidity than
those of membranes with lower DBI values. When
membranes exhibit a decrease of membrane fluidityꎬ
this leads to leakiness and loss of selective permea ̄
bilityꎬ which are early and ubiquitous features of leaf
senescence (Fan et al.ꎬ 1997ꎻ Lim and Namꎬ 2005ꎻ
Espinoza et al.ꎬ 2007ꎻ Martinez et al.ꎬ 2008). How ̄
everꎬ the changes in the degree of unsaturation of
membrane lipids during silique senescence have not
been investigated.
To deepen our understanding of the metabolism
and functions of lipids in cellsꎬ increasing attention
has focused on the development of comprehensive
strategies for the analysis of these factors in recent
years (Brugger et al.ꎬ 1997ꎻ Han and Grossꎬ 2005ꎻ
Wenkꎬ 2005). This has promoted the emergence of
lipidomicsꎬ which is becoming an integral part of
functional genomics. Plant lipidomics is based on
electrospray ionisation tandem mass spectrometry
(ESI ̄MS / MS) analysisꎬ which makes it possible to
measure hundreds of lipid molecules in vivo with
small samples and in a short timeꎻ and this enables
accurate calculation of the DBI of all measured mem ̄
brane glycerolipids (Welti et al.ꎬ 2002). Several
studies have employed lipidomics to profile changes
in molecular species and DBI at low temperaturesꎬ
and to characterise the function of genes that encode
lipolytic enzymesꎬ in combination with genetic ap ̄
proaches (Devaiah et al.ꎬ 2007ꎻ Hong et al.ꎬ 2009ꎻ
Zhang et al.ꎬ 2009ꎻ Scherer et al.ꎬ 2011).
This study involved the use of lipidomics to:
(i) determine how membrane glycerolipid species
and DBI change during Arabidopsis silique senes ̄
cenceꎻ and (ii) compare changes in the glycerolipid
profiles during silique senescence between Wassil ̄
ewskija (WS) and PLDδ ̄KO plants in order to de ̄
termine the effect of PLDδ on changes in the lipid
compositions of siliques.
1 Methods and materials
1 1 Plant materials
PLDδ ̄KO plants were generated by T ̄DNA in ̄
sertion (PLDδ ̄KO) into the ecotype WSꎬ there were
no differences phenotype between WS and PLDδ ̄KO
plants during normal growth (Zhang et al.ꎬ 2003).
The loss of PLDδ was confirmed by the absence of its
transcriptꎬ proteinꎬ and activity (Zhang et al.ꎬ 2003ꎻ
Li et al.ꎬ 2008).
1 2 Plant growth and sampling
Both of the Arabidopsis genotypes studied were
grown in Scott’s Metro ̄Mix soil. Pots containing the
seeds were kept at 4 ℃ for two days and then moved
to a greenhouse with natural lighting during spring ̄
time. Individual flowers were tagged at the day of
floweringꎬ and developing and senescence siliques
were sampled 15ꎬ 20ꎬ 25ꎬ and 30 days after flower ̄
ing (DAF). In order to follow embryo development
of the seedsꎬ intact silique has been used (Folter et
al.ꎬ 2004ꎻ Louvet et al.ꎬ 2006ꎻ Wagstaff et al.ꎬ
2009). Siliques were harvested for lipid analysis at
each time point.
1 3 Lipid extraction and ESI / MS ̄MS analysis
The processes of lipid extractionꎬ ESI ̄MS / MS
analysisꎬ and quantification were performed as de ̄
scribed previously with minor modification (Welti et
al.ꎬ 2002ꎻ Li et al.ꎬ 2008ꎻ Zheng et al.ꎬ 2011).
Each sample contained dry weight of 10 to 20 mg. To
inhibit lipolytic activityꎬ the siliques were transferred
immediately into 3 mL of isopropanol containing 0 01%
9712期 YU Xiao ̄Mei et al.: Changes in Membrane Lipids During Silique Senescence in Arabidopsis
butylated hydroxytoluene in a 75 ℃ water bath. The
tissue was extracted three times with chloroform /
methanol (2∶1) containing 0 01% butylated hydroxy ̄
tolueneꎬ with continuous agitation over for 7 days.
The remaining plant tissue was dried overnight at
105 ℃ and weighed to give the dry weight of the tis ̄
sue. Lipid samples were analysed on a triple quadru ̄
pole MS / MS equipped for ESI. Automated ESI ̄MS /
MS analysis was performed in the Analytical Loabo ̄
ratory of the Kansas Lipidomics Research Centreꎬ
Manhattanꎬ USA. ESI ̄MS / MS analysis and quantifi ̄
cation were performed as described previously (Kan ̄
sas Lipidomics Research Centreꎬ http: / / wwwk ̄state
edu / lipid / lipidomics). The lipids of each head ̄
group class were quantified by comparison with two
internal standards for the specific class.
1 4 Data analysis
Data processing was performed as previously
described ( Welti et al.ꎬ 2002ꎻ Devaiah et al.ꎬ
2006ꎻ Zheng et al.ꎬ 2012). DBI was calculated u ̄
sing the following formula: DBI = [∑(N × mol%
lipid)] / 100ꎬ where N is the total number of double
bonds in the two fatty acid chains of each glycerolip ̄
id molecule (Osmond et al.ꎬ 1982ꎻ Rawyler et al.ꎬ
1999ꎻ Bakht et al.ꎬ 2006ꎻ Zheng et al.ꎬ 2011).
Five replicates of each treatment were analysed. The
Q ̄test was performed on the total amount of lipid in
each classꎬ and data from discordant samples were
removed. The data were subjected to one ̄way analy ̄
sis of variance (ANOVA) using SPSS 13 0. Statisti ̄
cal significance was tested by Fisher’s least signifi ̄
cant difference (LSD) method.
2 Results and discussion
2 1 Profiling changes in the molecular species
of membrane lipids during silique senescence in
Arabidopsis
Lipidomic analysis was applied to each stage of
silique senescence ( Fig 1). Silique senescence in
Arabidopsis is developmentally regulated and is far
less responsive to environmentally induced variability
than leavesꎬ andꎬ unlike petalsꎬ neither organ un ̄
dergoes abscission in Arabidopsis (Wagstaff et al.ꎬ
2009). The Arabidopsis silique elongates and devel ̄
oped immediately after pollination and reaches its fi ̄
nal length approximately 15 DAFꎬ at which point the
silique is most greenꎬ thereafter the siliques became
a little yellow at 20 DAF is associated with the se ̄
nescenceꎬ but the yellowing of siliques that is very
evident at 25 DAF is associated with the senescence
and desiccation. By 30 DAFꎬ the silique is fully
yellow and becomes shattered. Using a lipidomic ap ̄
proach based on ESI ̄MS / MS (Welti et al.ꎬ 2002ꎻ
Li et al.ꎬ 2008)ꎬ we identified more than 140 mo ̄
lecular species of polar glycerolipids in Arabidopsis
siliques of different ages in the absence of environ ̄
mental stress (Tables 1-2 and Fig 2-3). These mo ̄
lecular species included phospholipids of six head ̄
group classes: phosphatidylcholine (PC)ꎬ phosphati ̄
dylethanolamine (PE)ꎬ phosphatidylinositol ( PI)ꎬ
phosphatidylserine ( PS)ꎬ PAꎬ and phosphatidylg ̄
lycerol (PG)ꎬ as well as galactolipids of two head ̄
group classes: monogalactosyldiacylglycerol ( MG ̄
DG) and digalactosyldiacylglycerol (DGDG) (Welti
et al.ꎬ 2002). Each molecular species was identified
in relation to the total number of acyl carbon atoms
and double bonds (Welti et al.ꎬ 2002). An over ̄
view of the findings (Tables 1-2 and Figs 2-3) re ̄
veals that the levels of most lipid species changed
dramatically during silique senescence.
2 2 Dramatic decreases in the levels of lipid
molecular species during the senescence of Arabi ̄
dopsis siliques
Hierarchal clustering of the lipid profiles was
used to obtain an overall appreciation of the changes
in identities and concentrations of lipids during the
senescence of siliques (Fig 2). The total amounts of
lipid and the average levels of molecular species in
each head ̄group class are shown in Table 1. Levels of
both extraplastidic and plastidic lipids decreased dur ̄
ing silique senescence of Arabidopsis. The amount of
total lipids had declined by 11 2% at 20 DAF (from
123 7 to 109 96 nmolmg-1)ꎬ which was significant ̄
ly less than the decreases of 51 74% (at 25 DAF)
081 植 物 分 类 与 资 源 学 报 第 36卷
and 64 91% (at 30 DAF) observed in WS. These da ̄
ta indicate that the largest decline occurred during si ̄
lique senescenceꎬ although lipid levels had started to
decline even before distinct yellowing became appa ̄
rent. The decreases in the levels of lipid molecular
species during the senescence of Arabidopsis siliques is
resemble to leaf senescence (Wagstaff et al.ꎬ 2009).
Fig 1 The senescence of siliques at 15ꎬ 20ꎬ 25ꎬ and 30
days after flowering in WS
Fig 2 Hierarchal clustering analysis of Arabidopsis lipid molecular
species during the senescence of siliques in WS and PLDδ ̄KO plants.
Each coloured bar within a column represents a lipid molecular species
in the indicated cultivars and treatments. The colour of each bar repre ̄
sents the level of corresponding lipid speciesꎬ with expression shown
as log2 of the lipid amount (nmol / mg dry weight) . A total of 140 lipid
species in the indicated lipid classes were organised according to their
class (as indicated)ꎬ total acyl carbons ( in ascending order within a
class)ꎬ and total double bonds ( in ascending order with class and to ̄
tal acyl carbons) . The dry weight is dry weight minus lipid ( i e. dry
weight after lipid extraction)
In this contextꎬ an interesting question arises:
why do the levels of lipids decrease substantially
during the silique senescence that occurs naturally as
part of the plant life cycle? It seems that the most
likely answer to this question is that terminal events
in the life cycle of a plant organ initially provide a
mechanism for the mobilisation of nutrients from the
ageing tissue to support the development of younger
tissues or seeds. This is followed by a cell ̄death
phase during which unwanted structures are discar ̄
ded (Wagstaff et al.ꎬ 2009).
Unlike leavesꎬ the seeds contained within si ̄
liques contain not only membrane phospholipidsꎬ but
also storage lipidsꎬ 90% or more of which are pres ̄
ent only in triacylglycerols ( TAGs). During seed
maturationꎬ TAGs are biosynthesised ( Ting et al.ꎬ
1997ꎻ Siloto et al.ꎬ 2006) and accumulate in dis ̄
crete subcellular organelles called oil bodies. TAGs
in the oil bodies are hydrolysed by lipases to provide
energy and carbon during germination. The process
of TAG synthesis for the storage of lipids shares simi ̄
lar pathways and common chemical intermediates
(such as PA) with that of membrane lipids. PA is a
secondary product of PLC activityꎬ and it is the pri ̄
mary product of PLD signalling. PLD hydrolyses
structural lipids such as PC to produce PA (Hartog
et al.ꎬ 2001ꎻ Munnikꎬ 2001). The synthesised PA
is dephosphorylated to DAG by a PA phosphatase.
DAG is further acylated to form TAGs by DAG acyl ̄
transferase ( Parthibane et al.ꎬ 2012). Moreoverꎬ
the senescence of the silique walls is very closely
linked to seed maturationꎬ the process is far less re ̄
sponsive to environmental stimuli than the senes ̄
cence of most organs (Wagstaff et al.ꎬ 2009). This
suggests that the products of the hydrolysis of silique
membrane lipids may be transferred to seeds. As in
seedsꎬ assimilates such as PA are transferred from
silique walls and redistributed to the developing
seeds for the synthesis of TAGs. Howeverꎬ there re ̄
mains a need to verify what happens to those polar
lipids and TAGs during silique senescence and seed
maturation and germination.
1812期 YU Xiao ̄Mei et al.: Changes in Membrane Lipids During Silique Senescence in Arabidopsis
2 3 Levels of different lipid species do not de ̄
crease at the same rate during silique senescence
We analysed the changes in the relative levels of
the various lipid species (mol %)ꎬ which can reflect
interconversion among lipids (Fig 3 and Table 2).
Whereas the relative levels of some lipids declinedꎬ
those of others increased. This suggests that different
lipids were degraded at different rates. Specificallyꎬ
Table 1 Changes in lipid classes during Arabidopsis silique senescence in WS and PLDδ ̄KO plants (nmolmg-1 DW)
Values are means±SE (n= 4 or 5) . Values in the same row with different letters are significantly different (P < 0 05) .
An asterisk indicates that the value is significantly different from that of WS under the same conditions (P < 0 05)
Lipid class Plant species
Lipids / nmolmg-1 DW
15 d 20 d 25 d 30 d
PG WSPLDδ ̄KO
7 03 ± 1 04a
5 00 ± 0 54a∗
6 20 ± 0 97a
3 29 ± 0 46b∗
3 07 ± 0 46b
1 66 ± 0 10c∗
1 96 ± 0 25c
1 03 ± 0 13d∗
PI WSPLDδ ̄KO
7 20 ± 1 01a
4 84 ± 0 36a∗
7 13 ± 0 71a
4 23 ± 0 54ab∗
5 14 ± 0 56b
3 64 ± 0 49bc∗
4 16 ± 0 62b
3 24 ± 0 38c
PE WSPLDδ ̄KO
13 38 ± 1 73a
11 33 ± 1 12a
11 57 ± 1 36a
8 34 ± 1 21b∗
5 79 ± 0 72b
6 02 ± 0 81c
6 09 ± 0 52b
5 50 ± 0 55c
PC WSPLDδ ̄KO
29 20 ± 2 83a
23 21 ± 1 83a∗
25 35 ± 4 83a
19 02 ± 1 93b
13 03 ± 0 23b
13 06 ± 1 31c
12 42 ± 1 09b
11 38 ± 0 80c
PA WSPLDδ ̄KO
0 22 ± 0 04a
0 22 ± 0 05a
0 11 ± 0 03b
0 08 ± 0 04b
0 12 ± 0 03b
0 05 ± 0 02b∗
0 15 ± 0 04a
0 10 ± 0 03b
PS WSPLDδ ̄KO
0 62 ± 0 10ab
0 43 ± 0 03a∗
0 70 ± 0 11a
0 36 ± 0 07ab∗
0 46 ± 0 07bc
0 29 ± 0 07bc∗
0 32 ± 0 07c
0 21 ± 0 05c
MGDG WSPLDδ ̄KO
52 79 ± 6 97a
36 71 ± 4 39a∗
47 07 ± 6 51a
24 71 ± 3 41b∗
25 39 ± 4 07b
12 57 ± 1 25c∗
14 02 ± 1 31c
6 42 ± 1 01d∗
DGDG WSPLDδ ̄KO
13 01 ± 2 02a
9 22 ± 1 13a∗
11 61 ± 1 55a
6 56 ± 1 06b∗
6 60 ± 0 93b
3 49 ± 0 48c∗
3 99 ± 0 62c
1 91 ± 0 21d∗
Total lipids WSPLDδ ̄KO
123 70 ± 19 78a
91 21 ± 13 99a
109 96 ± 14 78a
66 77 ± 10 07b∗
59 70 ± 6 79b
40 95 ± 3 97c∗
43 41 ± 5 72c
29 97 ± 3 22d∗
Table 2 Mol% changes in lipid classes during Arabidopsis silique senescence in WS and PLDδ ̄KO plants
Values are means±SE (n= 4 or 5) . Values in the same row with different letters are significantly different (P < 0 05) .
An asterisk indicates that the value is significantly different from that of WS under the same conditions (P < 0 05)
Lipid class Plant species
Lipids / mol%
15 d 20 d 25 d 30 d
PG WSPLDδ ̄KO
5 67 ± 0 63a
5 50 ± 0 32a
5 62 ± 0 75a
4 95 ± 0 44a
5 27 ± 0 56a
4 07 ± 0 25b∗
4 48 ± 0 61a
3 43 ± 0 33c∗
PI WSPLDδ ̄KO
5 86 ± 0 61b
5 40 ± 0 73c
6 52 ± 0 56b
6 32 ± 0 65c
9 00 ± 1 32a
8 86 ± 0 50b
9 59 ± 0 81a
10 84 ± 0 16a∗
PE WSPLDδ ̄KO
10 88 ± 0 84b
12 48 ± 0 75c
10 46 ± 0 82b
12 57 ± 0 74c∗
8 97 ± 1 09b
14 66 ± 0 86b∗
14 14 ± 1 28a
18 38 ± 0 60a∗
PC WSPLDδ ̄KO
23 84 ± 2 42a
25 63 ± 1 93a∗
23 00 ± 2 09a
28 79 ± 2 16b∗
20 20 ± 2 50b
31 91 ± 1 32c∗
28 77 ± 1 61b
38 12 ± 2 10c∗
PA WSPLDδ ̄KO
0 18 ± 0 03b
0 25 ± 0 04a
0 10 ± 0 01c
0 12 ± 0 04b
0 20 ± 0 04b
0 13 ± 0 03b∗
0 43 ± 0 07a
0 32 ± 0 05a
PS WSPLDδ ̄KO
0 50 ± 0 03b
0 48 ± 0 07c
0 63 ± 0 08a
0 55 ± 0 06bc
0 76 ± 0 11a
0 71 ± 0 09a
0 75 ± 0 12a
0 68 ± 0 10ab
MGDG WSPLDδ ̄KO
42 36 ± 3 13a
39 91 ± 3 28a
42 88 ± 3 24a
36 69 ± 2 84a∗
44 15 ± 7 07a
30 74 ± 1 92b∗
32 17 ± 1 87b
21 29 ± 2 13c∗
DGDG WSPLDδ ̄KO
10 53 ± 0 89a
10 05 ± 0 67a
10 59 ± 0 86a
9 73 ± 0 58a
11 23 ± 1 62a
8 51 ± 0 55b∗
9 57 ± 0 55a
6 36 ± 0 66c∗
281 植 物 分 类 与 资 源 学 报 第 36卷
Fig 3 The changes of relative levels (mol%) of lipid molecular species during Arabidopsis silique senescence
in WS and PLDδ ̄KO plants. Values are means±SE (n= 4 or 5)
differences in the rates of degradation of extraplastid ̄
ic and plastidic lipids occurred in terms of their rela ̄
tive abundances during silique senescence in Arabi ̄
dopsis. During silique senescence in both WS and
PLDδ ̄KO plantsꎬ the relative levels of plastidic lipi ̄
ds (PGꎬ MGDGꎬ DGDG) decreasedꎬ whereas those
of extraplastidic lipids ( PIꎬ PEꎬ PC) increased.
This suggested that plastidic lipidsꎬ including MG ̄
DGꎬ DGDG and PG are degraded more rapidly than
non ̄plastidic lipidsꎬ such as PEꎬ PCꎬ PIꎬ and PSꎬ
which are found primarily in the membranes of non ̄
photosynthetic organellesꎬ such as the endoplasmic
reticulum and mitochondria. Shortly after the onset of
silique senescenceꎬ the catabolism of plastidic lipids
began before that of lipids in the plasma membrane.
In this studyꎬ levels of PA decreased after the begin ̄
ning of silique senescence. Membrane lipids normal ̄
ly contain less than 1% PAꎻ howeverꎬ the content of
PA was shown to increase dramatically upon expo ̄
sure to biotic and abiotic stresses (Wangꎬ 2005ꎻ Li
et al.ꎬ 2008). This suggests that silique senescence
is natural eventꎬ which occurs as plants age.
2 4 The DBI of total lipids decreasedꎬ with no
change of the DBIs of different lipid classes
Maintaining the integrity and optimal fluidity of
membranes is very important for organisms. In this
studyꎬ DBI was employed to reflect the membrane
fluidity. We determined the mol% content of each
lipid molecule species based on the data of nmol / mg
dry weightꎬ and calculated the DBI of each lipid
species.
We found that the DBI of total membrane lipids
decreased significantly during silique senescenceꎬ
especially at 30 DAF (Table 3)ꎬ from 4 67 to 4 27.
Howeverꎬ no significant changes in DBI of each
membrane lipid class except of total DBI in WS
3812期 YU Xiao ̄Mei et al.: Changes in Membrane Lipids During Silique Senescence in Arabidopsis
plants during silique senescence. The decrease in the
DBI of total membrane lipids might have been
caused by the dramatic decrease in the levels of
plastidic lipids and an increase in the relative levels
of extraplastidic lipids. Given that the DBI was cal ̄
culated based on the mol% content of each lipid
molecule speciesꎬ it is conceivable that the dramatic
decrease in the levels of galactolipids might have
contributed to the decrease of the DBI of total mem ̄
brane lipids. This suggested that silique senescence
were associated with the decrease in DBI of total lip ̄
idsꎬ which may have influenced the fluidity and in ̄
tegrity of cellular membranes.
2 5 The variation in levels of polar lipids in
PLDδ ̄KO plants was difference to that observed
in WS plants
The effect of PLD on senescence of siliques
might be related to its structural role or the effects of
its productꎬ PA (Hong et al.ꎬ 2008). To assess the
role of PLDδ in the senescence of Arabidopsis si ̄
liquesꎬ we employed compared the lipid profilesꎬ es ̄
pecially the level of PA between the Arabidopsis
PLDδ ̄KO mutant and wild ̄type WS plants. Although
growth conditions can affect PA levelsꎬ but the PA
content was very low and decreased during silique
senescence in WS plants. We also found that the lev ̄
el and variation of PA and other membrane lipid
components were different between WS and PLDδ ̄
KO plants (Tables 1-3 and Fig 2-3). For exam ̄
pleꎬ table1 indicated that rates of decline in levels of
PE and PC were more rapid in WS than in PLDδ ̄
KOꎬ especially during the senescence of siliques
(from 20 d to 25 d). More importantlyꎬ less PA was
detected in senesced ̄siliques of PLDδ ̄KO than that
of WS. Table 2 also showed that relative levels of
both PE and PC were higher in PLDδ ̄KO than in
WS. Total lipids at each stage are significantly lower
in PLDδ ̄KO mutant than in WS. Lipid profiling data
indicate that PLDδ was involved in the metabolism of
membrane lipids during silique senescence.
In plantsꎬ the PLD family comprises 12 mem ̄
bersꎬ whereas only two PLDs have been identified in
animals ( Qin and Wangꎬ 2002). It has been hy ̄
pothesised that the basis for the differences between
Table 3 Changes in the double ̄bond index (DBI) of membrane lipids during Arabidopsis silique senescence in WS and PLDδ ̄KO plants
Values are means±SE (n= 4 or 5) . Values in the same row with different letters are significantly different (P < 0 05) .
An asterisk indicates that the value is significantly different from that of WS under the same conditions (P < 0 05)
Lipid class Plant species
Double ̄bond index (DBI)
15 d 20 d 25 d 30 d
PG WSPLDδ ̄KO
2 64 ± 0 05b
2 60 ± 0 04b
2 62 ± 0 05b
2 59 ± 0 2b
2 68 ± 0 05ab
2 67 ± 0 01a
2 74 ± 0 03a
2 60 ± 0 07ab
PI WSPLDδ ̄KO
2 72 ± 0 04ab
2 70 ± 0 02ab
2 75 ± 0 02a
2 74 ± 0 04a
2 73 ± 0 02a
2 68 ± 0 01b∗
2 68 ± 0 02b
2 63 ± 0 03c
PE WSPLDδ ̄KO
3 65 ± 0 09ab
3 60 ± 0 06a
3 72 ± 0 05a
3 66 ± 0 06a
3 63 ± 0 02b
3 50 ± 0 02b∗
3 52 ± 0 02c
3 40 ± 0 02c∗
PC WSPLDδ ̄KO
3 69 ± 0 05a
3 61 ± 0 02a∗
3 72 ± 0 01a
3 63 ± 0 07ab∗
3 70 ± 0 03a
3 55 ± 0 02b∗
3 68 ± 0 06a
3 53 ± 0 03b∗
PA WSPLDδ ̄KO
3 44 ± 0 12a
3 44 ± 0 11a
3 46 ± 0 16a
3 38 ± 0 20a
3 58 ± 0 13a
3 57 ± 0 14a
3 69 ± 0 14a
3 63 ± 0 14a
PS WSPLDδ ̄KO
2 92 ± 0 09a
2 86 ± 0 09a
2 98 ± 0 07a
2 96 ± 0 07a
2 95 ± 0 06a
2 91 ± 0 06a
2 91 ± 0 06a
2 88 ± 0 07a
MGDG WSPLDδ ̄KO
5 87 ± 0 02a
5 84 ± 0 02a
5 87 ± 0 02a
5 84 ± 0 01a
5 87 ± 0 01a
5 86 ± 0 01a
5 88 ± 0 01a
5 85 ± 0 01a
DGDG WSPLDδ ̄KO
5 41 ± 0 02b
5 36 ± 0 03b
5 45 ± 0 05ab
5 42 ± 0 02a
5 47 ± 0 03a
5 44 ± 0 02a
5 47 ± 0 02a
5 39 ± 0 04ab∗
Total lipids WSPLDδ ̄KO
4 67 ± 0 06a
4 56 ± 0 09a
4 69 ± 0 10a
4 50 ± 0 07a∗
4 60 ± 0 12a
4 29 ± 0 05b∗
4 27 ± 0 08b
3 97 ± 0 06c∗
481 植 物 分 类 与 资 源 学 报 第 36卷
plant and animal PLDs is that they might play a
more diverse and important role in plants than in
other organisms (Wangꎬ 2002). This makes it espe ̄
cially interesting to elucidate the unique and redun ̄
dant functions of plant PLDs. This paper shows that
PLDδ is involved in changes in the levels of PLDs
during silique senescence because other PLDs can
compensate for the loss of PLDδ function in PLDδ ̄
deficient plants.
3 Conclusion
The metabolism of organelle membranes plays a
crucial role during silique senescence. This paper
has revealed complex and considerable changes in
lipid molecular species during silique senescence.
The degradation of membrane lipids and the decrease
of the DBI of total membrane lipids in siliques were
similar to those found in leaf senescence. The results
of this study also suggest that PLDδ is involved in
the metabolism of membrane lipids during silique se ̄
nescence. The terminal events in the life cycle of a
plant organ initially provide a mechanism for the mo ̄
bilisation of nutrients from ageing tissue to support
the development of younger tissue or seeds. From the
obtained findingsꎬ we inferred that the products of
hydrolysis of membrane lipids may be transferred to
seeds for the synthesis of storage lipidsꎬ namelyꎬ
TAGsꎻ howeverꎬ further studies are needed to con ̄
firm this hypothesis.
Acknowledgments: The authors thank Mary Roth (Kansas
Lipidomics Research Center) for lipid analysis.
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