The Effects of Phospholipase Dδ Suppression on the Responsesof ROS and Hormones to Artificial Leaf Senescence in Arabidopsis thanliana

2012·2.4 MB·

by  Gu Yan-Xia-

植 物 分 类 与 资 源 学 报 ,35 ( ):
摇 2013 2 149~157
Plant Diversity and Resources :
摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 摇 DOI 10.7677/ynzwyj201312102
磷脂酶 D啄 对拟南芥叶片衰老过程中内源 ROS
和激素含量的影响
*
贾艳霞1,2, 陶发清1, 李唯奇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 云南昆明
(1 , 摇 650201;
中国科学院大学 北京
2 , 摇 100039)
摘要: 活性氧 和植物激素是植物衰老过程中重要的内在或者外在的调控因子 我们发现 相对于
(ROS) 。 ,
离体诱导的衰老过程 在脱落酸 和乙烯 促进的衰老过程中有较多的活性氧积累 在
, (ABA) (ethylene) ;
对拟南芥磷脂酶 缺失型突变体的研究中发现 与野生型相比 突变体在衰老过程中产生较少
D啄 (PLD啄) , ,
的活性氧 我们比较了上述两种基因型的离体叶片在离体 和 三种衰老处理下内源的
。 、 ABA ethylene ABA、
茉莉酸甲酯 玉米素核苷 和吲哚乙酸 的含量变化 发现每一种激
(MeJA)、 (ZeatinRiboside,ZR) (IAA) ,
素对上述三种衰老处理的响应模式都很相似 在离体诱导的衰老中 两种基因型拟南芥的内源激素含量没
。 ,
有差异 而在 促进的衰老过程中 缺失型突变体叶片中的 的含量较低 和 含量较
; ABA , PLD啄 MeJA , ZR IAA
高 在乙烯促进的衰老过程中 突变体中的 和 的含量较低 和 含量较高 上述内源激
; , ABA MeJA , ZR IAA 。
素的这种变化可能有助于延缓突变体的衰老
。
关键词: 磷脂酶 乙烯 脱落酸 衰老
D啄; ROS; ; ;
中图分类号: 文献标识码: 文章编号:
Q945摇 摇 摇 摇 摇 摇 A摇 摇 摇 摇 摇 摇 摇 2095-0845(2013)02-149-09
The Effects of Phospholipase D啄 Suppression on the Responses
of ROS and Hormones to Artificial Leaf Senescence
in Arabidopsis thanliana
1,2 1 1**
JIA Yan鄄Xia , TAO Fa鄄Qing , LI Wei鄄Qi
TheGermplasmBankofWildSpecies KunmingInstituteofBotany ChineseAcademyofSciences
(1 , , ,Kunming650201,China;
UniversityofChineseAcademyofSciences
2 ,Beijing100039,China)
Abstract
: The reactive oxygen species (ROS) and hormones can act as an important internal or external factor in鄄
fluencing plantsenescence. Inthepresentstudy,wefoundthatsuppressionofphospholipaseD啄(PLD啄) attenuated
ROS production during abscisic acid (ABA)鄄 and ethylene鄄promoted leaf senescence. We also comparatively ana鄄
lyzed thecontentofendogenoushormones,ABA,methyljasmonate(MeJA),indole鄄3鄄aceticacid(IAA),andtotal
zeatin in detachment induced鄄senescence leaves, exogenous ABA and ethylene鄄 promoted senescence in wild type
Arabidopsis
and PLD啄鄄knockout (PLD啄鄄KO) leaves. We found that the response patterns of the four endogenous
hormones to the three senescence treatments were identical. In comparison with wild type,PLD啄鄄KO plants showed
higher ZR and IAA levels and lower MeJA content under ABA and higher ZR and IAA levels and lower ABA and
MeJA content underethylene. TheresultssuggestedthatthesehormonesmightcontributetoretardingABA鄄andeth鄄
Arabidopsis
ylene鄄promoted senescence in PLD啄鄄knockout .
*Foundationitems:GrantsfromtheNationalBasicResearchProgramofChina(31070262),FundofStateKeyLaboratoryofPhytochemistry
andPlantResourcesinWestChina(O97C0211Z1)
**Authorforcorrespondence;E鄄mail: [email protected]
Receiveddate: 2012-08-06, Accepteddate: 2012-10-09
作者简介 贾艳霞 女 博士 工程师 主要从事植物逆境分子生理学研究
: (1982-) , , , 。 E鄄mail: [email protected]
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Key words
: Phospholipase D啄; ROS; Ethylene; Abscisic acid; Leaf senescence
Abbreviations
: abscisic acid, ABA; trichloroacetic acid, TCA; ethephon, ETH; thiobarbituric acid, TBA; jas鄄
monic acid, JA; methyl jasmonate (MeJA); indole鄄3鄄acetic acid, IAA; phospholipase D, PLD; reactive oxygen
species, ROS; malonyldialdehyde, MDA; Enzyme鄄linked Immunosorbent Assays (ELISAs)
Arabidopsis tomato
摇 Leaf senescence is the final phase from matura鄄 studies in and , has been used to
et al
tion to attrition in the leaf life history (Wang ., manipulate post鄄harvest senescence in crops such as
broccoli lettuce
2000). The senescence process takes place in a and (Gan and Amasino, 1995; Mc鄄
et al SAG12
highly regulated manner and the cell constituents are Cabe ., 2001). Using the promoter
et al Agrobacterium ipt
dismantled in an ordered progression (Quirino ., fused to the gene as described a鄄
2000). Senescence is associated with an increased bove to increase the endogenous cytokinin content
production of ROSsuchashydrogenperoxide (H2O2), (Gan and Amasino, 1995), delayed yellowing has
lettuce
superoxide and its more toxic derivative hydroxyl been shown in both before and after harvest
et al et al et al
radical (del Rio ., 1998). Chlorophyll degra鄄 (Chen .,2001; McCabe .,2001). Mean鄄
dation and a marked decline in photosynthesis will while, changes in endogenous hormone levels of de鄄
result in excessive excitation energy in leaves and tachment鄄induced senescing leaves in some plant
then the production of ROS will increase (Khanna鄄 species also have been examined. For example,
Chopra,2012). After the ROS reach certain thresh鄄 changes in the levels of endogenous ABA are meas鄄
lettuce
old levels, it will in turn damage the photosynthetic ured during the senescence of detached leaves
tobacco
apparatus, oxidize proteins, lipids and DNA. These (Aharoni and Richmond, 1978), leaves
nasturtium
result in degradation of cellular structures and en鄄 (Even鄄Chen and Itai,1975), and leaves
zymes, lipid peroxidation and membrane leakiness (Chin and Beevers,1970), whereas changes in the
et al et al
(Thompson ., 1987; del Rio ., 1998). levels of endogenous auxin are measured in detached
tobacco et al rape
Leaf senescence can be induced by both develo鄄 leaves (Evenchen ., 1978), and
pumpkin bean
pmental signals and environmental stress, and plant leaves, and excised leaves (Sheldrake
hormone and related growth substance as internal and Nobthcote, 1968). However, the correlations
factor play important roles in regulating senescence between hormone levels and senescence appear to be
(Guo and Gan, 2005). Hormonal controls singly or differ among plant species (Sheldrake and Nobth鄄
in combination are essential for overall control of cote, 1968). These differences underscore the need
growth,development and senescence in plants (Gan, for deeper understanding of the response of endoge鄄
2010). The five major classes of hormones, namely nous hormone levels to detachment鄄induced leaf se鄄
Arabidopsis
auxins, cytokinins (CKs), gibberellins (GAs), nescence in . The correlation between
ABA and ethylene, and other plant growth regulators hormone levels and senescence remains undocument鄄
such as jasmonic acid (JA), have been implicated ed in relation to leaf senescence that is promoted by
in the regulation of leaf senescence (Chin and Beev鄄 ABA or ethylene.
ers,1970; Bleecker and Patterson,1997). The ex鄄 The PLD family comprises 12 members, which
ogenous application of ABA, ethylene and MeJA are classified into six types, PLD琢 (3), 茁 (2), 酌
strongly promotes senescence in detached leaves (3), 啄, 着, and 灼 (2) (Qin and Wang, 2002),
(Smart, 1994; Gan and Amasino, 1996), whereas ABA鄄and ethylene鄄promoted senescence can be re鄄
exogenous application of the remainders inhibit the tarded by the suppression of phospholipase D琢1
et al
process. Knowledge of the endogenous hormonal reg鄄 (PLD琢1) (Fan ., 1997). We found that the
ulating senescence, gained from leaf senescence retardation of senescence in PLD琢1鄄AS plants was
期 et al
2 摇 摇 JIA Yan鄄Xia .: The Effects of Phospholipase D啄 Suppression on the Responses of ROS and Hormones …摇 1摇51
et al
associated with changes in ABA, MeJA, ZR and out (Li ., 2008), were used. The plants were
IAA levels (our unpublished date). Most plant grown in a controlled growth chamber at 23 益
PLDs have distinctive molecular and biochemical (day) and 19益 (night) and60% relative humidi鄄
properties that are associated with diverse cellular ty under a 12鄄hr photoperiod fluorescent lighting of
-2 -1
and physiological roles (Qin and Wang, 2002). As 120 滋mol·m ·s .
1 2摇 Hormone treatments
one of most abundant of members of the PLD family .
Arabidopsis
in , PLD啄 regulates plant responses to Ethephon and ABA as mixed isomer were pur鄄
abiotic stresses, such as drought, freezing, high sa鄄 chased form Sigma. Ethephon is water soluble and
linity, and UV stress, through influencing the sig鄄 releases ethylene in the cell, which has the same
nalling and/or structural roles of its product phos鄄 function as ethylene but more feasible to control.
phatidic (PA) (Bargmann and Munnik, 2006). The detached leaves for treatment with several senes鄄
Our previous results indicated that suppression of cence鄄affecting factors were obtained by cutting at
PLD啄 retarded ABA鄄 and ethylene鄄promoted leaf se鄄 the approximately middle part of the petioles of the
nescence through attenuating degradation of mem鄄 third of fourth foliar leaves with sharp scalpel to min鄄
brane lipids (our unpublished data). However, if imize wound effect. The detached leaves were floa鄄
and how endogenous hormones respond to senes鄄 ted on deionized water containing 50 滋M abscisic
cence retarded by suppression of PLD啄 is unknown. acid, ethephon in Petri dishes with the abaxial side
et al
To address these questions,we used histochemi鄄 up (Fan ., 1997). The leaves were incubated
cal staining to detect the ROS accumulation and at 23 益 under a 12鄄hr photoperiod and light of 120
-2 -1
used enzyme鄄linked immunosorbent assays (ELI鄄 滋mol·m ·sec .
1 3摇 Measurement of endogenous hormones
SAs) to measure the changes in the endogenous con鄄 .
tent of ABA, MeJA, ZR and auxin (indole鄄3鄄acetic Plant sample extraction and preparation were
et al
acid, IAA) during detachment鄄induced and ABA鄄 modified according to Lei .(2007). The de鄄
Arabi鄄
or ethylene鄄promoted senescence in wild鄄type tached leaves (0.5-1 g) at sampling time were ho鄄
dopsis
and PLD啄鄄knockout mutant. Our results sug鄄 mogenized in2mL of80% methanol with1滋m buty鄄
gested that higher ROS level in ABA鄄 and ethylene鄄 lated hydroxytoluene and this procedure was repeated
promoted senescence compared to detachment鄄in鄄 twice by rinsing the mortar. After extracted and cen鄄
duced senescence, and suppression of PLD啄 attenu鄄 trifuged, the extracts were dried under nitrogen gas.
ation of ROS accumulation. We also provided the re鄄 The endogenous hormones in leaves incubated in
lationship between endogenous phytohormones (Me鄄 ABA, ethephon and water were determined with En鄄
JA, ABA, ZR, IAA) and the major factor that in鄄 zyme鄄linked Immunosorbent Assays (ELISAs).
1 4摇 Histochemical staining for ROS detection
duce senescence. The association of PLD啄 with .
these hormones in regulating endogenous hormones Production of ROS in detached leaves was
during the three senescence treatments was also in鄄 measured by staining plants with 2忆, 7忆鄄Dichloroflu鄄
vestigated. orescin diacetate (H2DCFDA) as described with mi鄄
nor modification (McInnis, 2006). Briefly, leaves
1摇 Material and Methods
-1
were stained for10min with10滋g·mL H2DCFDA
1.1摇 Plant materials and growth conditions
(sigma), fluorescence intensity of the dye was ob鄄
Arabidopsis thaliana
, ecotype Wassilewskija e鄄 served using the Olympus LSCM FV1000 (488 nm
cotype (wild鄄type, WS) and PLD啄鄄knockout mutant excitation, 520 nm emission). H2DCFDA fluores鄄
(PLD啄鄄KO) generated from Wassilewskija ecotype, cence increases as the dye is oxidized by ROS to di鄄
in which PLD啄 is constitutively attenuated by knock鄄 chlorofluorescein (DCF).
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1 5摇 Detection of lipid peroxidation
. difference in the MDA content between the two geno鄄
Arabidopsis
The extent of lipid peroxidation in leaves was types detached leaves incubated within
estimated by measuring the amount of malonyldialde鄄 water (Fig.1A, top). With ABA or ethylene treat鄄
hyde (MDA), a decomposition product of the oxida鄄 ment, the MDA content of mutant leaves was only
tion of polyunsatured fatty acids, as described (Ha鄄 70% and 61.7% compared to wild type on day 3,
et al
vaux ., 2003). Briefly, about 0. 5-1 g leaf respectively (Fig. 1A). Increased ROS level is a
segments were homogenized in 4 mL of chilled rea鄄 common factor in different stress responses as well as
gent 10% [W/V] trichloroacetic acid (TCA), and in senescence. The accumulation of ROS indicated
g
centrifuged at 12000 for10 min. After that,2 mL oxidative damage in the form of protein and lipid oxi鄄
0.6% [W/V] thiobarbituric acid (TBA) in 10% dative which we had examined. More ROS were de鄄
TCA was added to an aliquot of2mL from the super鄄 tected in the ABA and ethylene鄄promoted senescence
natant. The mixture was heated in boiling water for leaves, and suppression of PLD啄 attenuated ROS
30 min, and then quickly cooled in an ice bath. Af鄄 production (Fig. 1B). These results indicated that
g
ter centrifugation at 10000 for 10 min, the absor鄄 much higher ROS levels produced in ABA鄄 and eth鄄
bance of the supernatant at 450, 532 and 600 nm ylene鄄promoted senescence than that in detachment鄄
was determined. The MDA content was calculated induced senescence, and PLD啄 might be involved
et al
according to Hodges .(1999). in ROS accumulation in detached leaves during
1 6摇 Data analysis
. ABA鄄and ethylene鄄promoted senescence and sup鄄
For all quantitative measurements in present pression of PLD啄 protected the leaves from oxidative
study, five replicates from each sampling time were stress.
2 2摇 Endogenous ABA levels increased at the
analysed. The data were subjected to one鄄way analy鄄 .
onset of senescence and dropped during the late
sis of variance (ANOVA) with SPSS 16.0. Statisti鄄
stage of senescence
cal significance was tested by Fisher爷s least signifi鄄
cant difference (LSD) method. We measured endogenous ABA levels to see
how ABA respond to leaf senescence and if PLD啄
2摇 Results
has effect on its levels. Detachment itself could in鄄
2.1摇 ROS and oxidative stress were attenuated
duce leaf to senesce in a reasonable rate accompa鄄
in PLD啄鄄KO leaves during the ABA鄄 and ethyl鄄 et
nied with many senescence symptoms (Weaver
ene鄄promoted senescence al
., 1998), and the ABA levels of detached leaves
Leaf senescence occurs in detached/harvested incubated in water constantly increased at all the
leaves. In our experiment, three senescence proces鄄 sampling time, and increased to 3鄄fold at 5 days.
ses were conducted. The first, detachment鄄induced The sudden increase in endogenous ABA after the
Arabi鄄
senescence was measured by floating detached exogenous application of ABA (Fig.2, middle pan鄄
dopsis
leaves on water. In the second and the third, el) may be caused by the diffusion and/or uptake of
detachment鄄induced senescence was accelerated by ABA from outside. Nonetheless, even though the
ABA and ethylene, respectively. ABA鄄and ethylene鄄 ABA level increased to its highest point within1 day
promoted senescence was retarded in PLD啄鄄KO after ABA treatment, it then began to drop (Fig.2,
plants as previous found (our unpublished data). middle panel). Within 3 days of treatment with eth鄄
Arabidopsis
The level of MDA, a product of lipid oxidation, ylene, ABA levels of the two genotypes
increased in the three senescence treatments, and leaves reached a maximum (3鄄fold and 2 fold com鄄
the leaves incubated with ABA and ethylene under鄄 pared to each initial level), and the levels in PLD啄鄄
went more severe oxidative stress. There was no KO mutant leaves were much lower than that of wild
期 et al
2 摇 摇 JIA Yan鄄Xia .: The Effects of Phospholipase D啄 Suppression on the Responses of ROS and Hormones …摇 1摇53
Arabidopsis
Fig.1摇 ComparisonofROSlevelsinWSandPLD啄鄄knockout,analysisoflipidoxidationinsenescingleavesoftwogenotypes
A. MDAcontentwascalculatedbasedontheabsorbanceat600nm,WSandPLD啄鄄knockoutmutant. FW,freshweight. Valuesare
SD n
mean 依 ( =5);B. DCFFluorescentprobesreportschangesinROSabundancewithinwater,ABA,ethylenetreatmentleaves
Arabidopsis
type WS, 62% and 55% at day 2 and 3, respec鄄 mutant (Fig.3, top panel). MeJA lev鄄
tively (Fig. 2, bottom panel). Given above evi鄄 els of detached WS leaves incubated in ABA and
dences, it was concluded that endogenous ABA rap鄄 ethylene increased sharply, which increased to 4.6鄄
idly increased to respond to ABA鄄and ethylene鄄pro鄄 fold and 1.7鄄fold compared to control at day 3, re鄄
moted senescence. Furthermore, suppression of spectively. However, MeJA levels in PLD啄鄄KO
PLD啄 attenuated endogenous ABA accumulation leaves were significantly lower than those in WS
which contributed to delaying in ethylene鄄promoted leaves (Fig.3, middle and bottom panels). These
senescence. results indicated that lower MeJA levels in PLD啄鄄KO
2 3摇 Suppression of PLD啄 attenuated MeJA ac鄄
. leaves might contribute to retardation of ABA鄄and
cumulation during ABA鄄 and ethylene鄄promoted
ethylene鄄promoted senescence, that is regulated by
senescence
suppression of PLD啄 activity.
2 4摇 ZR levels decreased during detachment鄄in鄄
MeJA, which occurs widely in plants, can pro鄄 .
duced and ABA鄄promoted senescence and were
mote chlorophyll loss and accelerated leaf senes鄄 ,
higher in PLD啄鄄KO leaves than that in WS leav鄄
cence (Ueda and Kato, 1980). In this study, Me鄄
es under ABA treatments
JA levels were measured in the three senescence
treatments. In water treatment, MeJA levels of the Cytokinins (CKs) regulate cell division and va鄄
detached leaves increased a little and began to drop rious metabolic and developmental processes, inclu鄄
et al
slowly and no difference between WS and PLD啄鄄KO ding senescence (Smart ., 1991; Gan and
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Amasino, 1995). We measured the ZR content dur鄄 crease of ZR levels in senescing leaves of the three
ing the three senescence processes defined above. In treatments indicated that senescence in detached
the water treatment, ZR levels dropped by 35. 5% leaves associated with decrease in ZR abundance.
as the leaves detached from the whole plant for just The significant difference of ZR levels between WS
one day and kept decreasing during the treatment and PLD啄鄄KO leaves suggested that ZR might con鄄
period, and at 5 days, it had decreased by 64.5% tribute to attenuation of PLD啄鄄KO during ABA鄄 and
(Fig.4). Although the ZR levels of WS leaves de鄄 ethylene鄄promoted senescence.
2 5摇 IAA levels decreased during senescence
creased to 32.3% and 22.6% at 1 day after ABA . ,
and IAA levels in PLD啄鄄KO leaves were higher
and ethylene treatment, respectively, for the remain鄄
than that in WS
der of experiment the values increased, and then de鄄
creased again (Fig.4). However, deficient of PLD啄 In order to make clear how the auxin responded
made the mutant leaves have higher ZR content than to the three senescence鄄accelerators and whether
that of WS in certain sampling time (after ABA PLD啄 played any role in these processes, we meas鄄
treatment for 1, 2, 3 and 5 days; after ethylene ured content of IAA (a kind of well known auxin)
treatment for5 days) (Fig.4). The significantly de鄄 content. During detachment鄄induced senescence,
Fig.2摇 VariationinlevelsofendogenousABAinleavesfromWSand Fig.3摇 VariationinlevelsofendogenousMeJAinleavesfromWSand
PLD啄鄄KO plants during three different treatments. Detached leaves PLD啄鄄KO plants during three different treatments. Detached leaves
weretreated with deionized water (top),50滋M ABA (centre), or weretreated with deionized water (top),50滋M ABA (centre), or
50滋Methephon (ETH; bottom) and sampled at the indicated time 50滋Methephon (ETH; bottom) and sampled at the indicated time
SD n SD n
points. FW,freshweight. Valuesaremean依 ( =5). Valueswith points. FW,freshweight. Valuesaremean依 ( =5). Valueswith
P P
differentlettersaresignificantlydifferent( <0.05). “*冶 indicates differentlettersaresignificantlydifferent( <0.05). “*冶 indicates
that the value is significantly different from that of the WS under the that the value is significantly different from that of the WS under the
P P
samecondition( <0.05) samecondition( <0.05)
期 et al
2 摇 摇 JIA Yan鄄Xia .: The Effects of Phospholipase D啄 Suppression on the Responses of ROS and Hormones …摇 1摇55
IAA levels did not change at the first two days but ciated with senescence and involved in the attenua鄄
dropped to 50% of their initial levels at day 3. We tion of ABA鄄 and ethylene鄄promoted senescence in
found no difference in IAA levels between leaves PLD啄鄄KO plants.
from WS and PLD啄鄄KO plants in the detachment鄄in鄄
3摇 Discussion
duced senescence. During ABA鄄accelerated senes鄄
cence, IAA levels kept decreasing in the incubation There have been a number of reports indicating
course and decreased to 60% of the initial levels at that ROS levels increase during senescence, and the
day5 (Fig.5, middle and bottom panels). IAA lev鄄 increase is likely to be associated with macromole鄄
els of WS leaves incubated in ethylene increased a cule degradation, in particular lipid degradation.
litter at day 1 and then decreased constantly in the We detected less accumulation of ROS and MDA
following treatment days. Moreover, there was obvi鄄 levels during the ABA and ethylene鄄promoted senes鄄
ous difference about the IAA content detected when cence in PLD啄鄄KO plants leaves, in comparison
PLD啄 was absent after ABA treated for 1 and 3days with WS (Fig.1A, B). ROS have been implicated
and ethylene treated for 2 and 5 days (IAA content as a second messenger in several plant hormone re鄄
of mutant leaves was higher than that of WS leaves) sponses (Lam, 2004; Tamaoki, 2008). ABA and
(Fig.5). These results indicated that IAA was asso鄄 ethylene signaling have important roles in regulating
Fig.4摇 Variation in levels of endogenous ZR in leaves from WS and Fig.5摇 VariationinlevelsofendogenousIAAinleavesfromWS and
PLD啄鄄KO plants during three different treatments. Detached leaves PLD啄鄄KO plants during three different treatments. Detached leaves
weretreated with deionized water (top),50滋M ABA (centre), or weretreated with deionized water (top),50滋M ABA (centre), or
50滋Methephon (ETH; bottom) and sampled at the indicated time 50滋Methephon (ETH; bottom) and sampled at the indicated time
SD n SD n
points. FW, fresh weight. Values are mean 依 ( =5). Values points. FW, fresh weight. Values are mean 依 ( =5). Values
P P
withdifferentlettersaresignificantlydifferent( <0.05). “*冶 indi鄄 withdifferentlettersaresignificantlydifferent( <0.05). “*冶 indi鄄
catesthatthevalueissignificantlydifferentfromthatoftheWSunder catesthatthevalueissignificantlydifferentfromthatoftheWSunder
P P
thesamecondition( <0.05) thesamecondition( <0.05)
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et al Arabidopsis
ROS production (Kwak ., 2006). Transcrip鄄 and MeJA content in PLD啄鄄KO mutant
PLD啄
tional express of are higher in senescent than were not just the consequence but the regulator to
in young tissue and also increases in response to se鄄 ABA鄄 and ethylene鄄promoted senescence.
vere dehydration and high salt (Wang and Wang, The complexity of leaf senescence is mainly due
2001). ABA stimulation of PLD acts upstream in to the involvement of multiple components that ex鄄
the transduction pathway leading to RAB18 expres鄄 hibit overlapping effects. This is particularly true for
et al
sion (Hallouin ., 2002). All these evidences the action of ROS and hormones. Our results demon鄄
suggest that the PLD啄 has roles in retardation of strate the association of ROS and hormones ZR,
ABA鄄 and ethylene鄄promoted senescence through IAA, ABA, and MeJA in retardation of senescence
ROS accumulation. in PLD啄鄄KO plants, which also provides clues for
Senescence is a very important aspect of post鄄 further investigate the roles of PLD啄 in senescence.
harvest physiology. Enormous literatures concern the Given the availability of various microarrays and the
effects of hormone treatments on maintenance and complexity of the senescence process, a systems bi鄄
survival of plant materials in storage, especially for ology approach should be taken for deciphering the
fruits and flowers, for example, fruit ripening or molecular regulatory mechanisms of leaf senescence
flower opening. Hormones play critical roles in these by plant hormones and other external and internal
processes, although much remains to be learned a鄄 factors. Once senescence is fully understood, it
bout correlations between hormone levels and senes鄄 should allow us to devise ways to manipulate leaf se鄄
cence, particularly during hormone鄄promoted senes鄄 nescence for agriculture improvement.
cence. To the best of our knowledge, this is the first
Acknowledgements
report on the change patterns of endogenous hor鄄 : We thank Dr. Hongyin Chen for her
critical reading of the paper.
mones in PLD啄鄄KO plants during detachment in鄄
duced鄄, ABA鄄 and ethylene鄄promoted senescence.
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