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Viewing Leaf Shape and Size Variation in Tobacco Plants under Different Temperatures from a Hydraulic Perspective

从水力结构的角度解释生长温度对烟草叶片形状和大小的影响



全 文 :从水力结构的角度解释生长温度对烟草叶片形状和大小的影响∗
胡  静1ꎬ2ꎬ 胡  虹1∗∗
(1 中国科学院昆明植物研究所资源植物与生物技术所级重点实验室ꎬ 昆明  650201ꎻ
2 中国科学院研究生院ꎬ 北京  100049)
摘要: 叶片形状和大小在不同的生长温度下变化非常大ꎬ 但少有从水力结构的角度解释其变化原因的研
究ꎮ 本研究测定了生长于两个不同温度下 (24 ℃ / 18 ℃昼 /夜ꎻ 32 ℃ / 26 ℃昼 /夜) 的烟草叶片的解剖结构ꎬ
导水率ꎬ 叶片长宽比和叶面积ꎮ 生长在 24 ℃ / 18 ℃下的烟草叶片与生长在 32 ℃ / 18 ℃的叶片相比ꎬ 更狭
窄ꎬ 并有更小的叶柄导管直径ꎬ 更低的叶脉密度和导水率ꎮ 然而ꎬ 在不同的生长温度下ꎬ 烟草叶面积并没
有显著差异ꎮ 叶片导水率与叶脉密度呈正相关ꎬ 但与叶片长宽比呈负相关ꎮ 结果表明在不同的生长温度下
叶片解剖结构和叶片导水率可能对于改变叶宽比起着重要作用ꎮ
关键词: 温度ꎻ 叶片解剖ꎻ 叶片导水率ꎻ 叶片形状ꎻ 叶片大小ꎻ 烟草
中图分类号: Q 948􀆰 112ꎬ Q 944        文献标志码: A        文章编号: 2095-0845(2015)02-168-09
Viewing Leaf Shape and Size Variation in Tobacco Plants under
Different Temperatures from a Hydraulic Perspective
HU Jing1ꎬ2ꎬ HU Hong1∗∗
(1Key Laboratory of Economic Plants and Biotechnologyꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ
Kunming 650201ꎬ Chinaꎻ 2 University of Chinese Academy of Sciencesꎬ Beijing 100049ꎬ China)
Abstract: Although leaf shape and size are highly variable across different temperaturesꎬ few studies have investiga ̄
ted the reasons for their variations from the hydraulic perspective. We hypothesized that temperature will induce the
modification of leaf water ̄related anatomy and leaf hydraulic conductanceꎬ which may play an important role in affec ̄
ting leaf shape and size. Narrow and small leaf might be an adaptation to low water transport capacity under low tem ̄
peratureꎬ making the whole leaf obtain water more uniformly. To test the above hypothesisꎬ we investigated leaf anato ̄
myꎬ leaf hydraulic conductanceꎬ leaf shape and size of tobacco under two growth temperatures (24 ℃ / 18 ℃ day /
nightꎻ 32 ℃ / 26 ℃ day / night) and analyzed the associations between leaf hydraulic architecture and leaf length ̄to ̄
width ratio. We found that the tobacco leaves at 24℃ were significantly narrowerꎬ and had smaller petiole vessel diam ̄
eterꎬ lower minor vein density and hydraulic conductance compared with those at 32℃. Howeverꎬ there was no signifi ̄
cant difference in leaf size between two temperatures. Leaf hydraulic conductance was positively correlated with minor
vein densityꎬ but negatively with leaf length ̄to ̄width ratio. Our results suggested that the modification of leaf anatomy
and leaf hydraulic conductance might play an important role in affecting leaf shape under different temperatures.
Key words: Leaf anatomyꎻ Leaf hydraulic conductanceꎻ Leaf shapeꎻ Leaf sizeꎻ Nicotiana tabacumꎻ Temperature
  Plants can alter their anatomicalꎬ physiological
and morphological traits in response to environmental
changes (Givnishꎬ 1978ꎻ Abrams et al.ꎬ 1992ꎻ Xu
et al.ꎬ 2009). Leaf shape and size are highly varia ̄
植 物 分 类 与 资 源 学 报  2015ꎬ 37 (2): 168~176
Plant Diversity and Resources                                    DOI: 10.7677 / ynzwyj201514089

∗∗
Funding: The Yunnan Tobacco Academy of Agriculture [Grantnumbers 110201101003 (TS ̄03)ꎬ 2011YN02ꎬ and 2011YN03]
Author for correspondenceꎻ E ̄mail: huhong@mail􀆰 kib􀆰 ac􀆰 cn
Received date: 2014-06-16ꎬ Accepted date: 2014-10-27
作者简介: 胡静 (1989-) 女ꎬ 硕士研究生ꎬ 主要从事植物生理生态研究ꎮ E ̄mail: hujingb@mail􀆰 kib􀆰 ac􀆰 cn
ble across environmentsꎬ with narrower and smaller
leaves more frequent in dry and sunny habitats
(Givnishꎬ 1979ꎻ Roth ̄Nebelsick et al.ꎬ 2001ꎻ Guer ̄
in et al.ꎬ 2012). Previous studies reported that the
leaves grown in shade sites often tend to be wider
and larger compared to sun leaves (Ashton and Ber ̄
lynꎬ 1994ꎻ Yano and Terashimaꎬ 2004ꎻ March and
Clarkꎬ 2011). In dryer sites narrower and smaller
leaves are more frequent ( Givnishꎬ 1978ꎬ 1979ꎻ
Niinements and Kullꎬ 1994). The reasons for the
variations of leaf shape in different light environ ̄
ments and water availabilities have relatively strong
empirical supports. There are many physiological
factors involved for narrower or more lobed leaves in
dry and high light conditions. One advantage for
smallerꎬ narrower leaves in dry and high light sites
is to decrease their thinner boundary layer and im ̄
prove convective heat exchange with the environmentꎬ
enabling more rapid convective cooling ( Parkhurst
and Loucksꎬ 1972ꎻ Givnishꎬ 1978ꎬ 1979). Another
important physiological factor may be hydraulics.
There may be a direct hydraulic benefit of small
leaves because small leaf area (LA) may results in
the redundancy of major veins and increased minor
vein density (MVD) which protects leaf hydraulic
conductance ( K leaf ) from declining ( Sack and
Froleꎬ 2006ꎻ Brodribb et al.ꎬ 2007)ꎬ and thus con ̄
tributes to drought tolerance. Apart from thisꎬ smal ̄
ler LA reduces the transpiration rate and transpira ̄
tion demandꎬ which can reduce the water loss with
maintaining optimal carbon assimilation. Small and
narrow leaves present a more efficient control of wa ̄
ter losses when water is deficient (Mendes et al.ꎬ
2001).
Temperature would influence the variation of
leaf shape and size through affecting the gas ex ̄
change between leaf and atmosphere. Apart from
thisꎬ temperature can also influence leaf shape and
size indirectly through affecting leaf hydraulics.
Nicotra et al. ( 2011) concluded that several non ̄
mutually exclusive theories have been proposed to
explain leaf shape and size diversity across different
environmentsꎬ including thermoregulation of leaves
especially in arid and hot environmentsꎬ hydraulic
constraintsꎬ patterns of leaf expansion in deciduous
speciesꎬ biomechanical constraintsꎬ and adaptations
to optimize light interception. Despite a lot of func ̄
tional rolesꎬ Nicotra et al. (2011) thought that leaf
water relations may play an important role in affect ̄
ing leaf shape. Now the most discussed view may be
thermoregulationꎬ howeverꎬ little studies have viewed
the variation of leaf shape and size from the hydrau ̄
lic perspective.
The associations between leaf length to width
ratio and leaf hydraulic conductance (K leaf ) across
different temperatures are likely to be of great impor ̄
tance (Nicotra et al.ꎬ 2011). The K leaf represents
the capacity of the transport system to deliver waterꎬ
allowing stomata to remain open for photosynthesis
( Scoffoni et al.ꎬ 2011). Significant progress has
been made recently towards understanding the linka ̄
ges between anatomy and water transport efficiency
in leaves (Aasamaa et al.ꎬ 2005ꎻ Brodribb et al.ꎬ
2010)ꎬ and the hydraulic resistance of mesophyll
cells and veins. Structural traits and water ̄related
leaf anatomyꎬ e􀆰 g.ꎬ minor vein density ( MVD)ꎬ
are closely associated with leaf hydraulic efficiency
( Roth ̄Nebelsick et al.ꎬ 2001ꎻ Sack and Froleꎬ
2006ꎻ Brodribb et al.ꎬ 2007). For exampleꎬ under
a warmer regimeꎬ Poa foliosa plants have largerꎬ
denser vessels that allow for greater water transport
(Medek et al.ꎬ 2011). Higher vein density can cor ̄
respond to a greater capacity for water supply be ̄
cause it can expand the surface area available for ex ̄
changing xylem water with surrounding mesophyll
cells while also reducing the distance through which
water must travel outside of the xylem ( Sack and
Holbrookꎬ 2006). In additionꎬ major veins have
greater hydraulic conductance than higher order
veins and mesophyll cells (Zwieniecki et al.ꎬ 2002ꎻ
Sack et al.ꎬ 2004). These discoveries provide a no ̄
vel hydraulic perspective to view the variation of leaf
shape and leaf size. Plants grown at warmer tempera ̄
tures with a high vapor pressure deficit (VPD) often
9612期      HU and HU: Viewing Leaf Shape and Size Variation in Tobacco Plants under Different Temperatures 􀆺     
have larger vessel diameters and greater MVD which
can contribute to greater water transport capacity
(Medek et al.ꎬ 2011)ꎬ helping plants supply more
water to leaves to meet high transpiration demands.
Under lower temperatureꎬ K leaf often tends to be
smaller (Way et al.ꎬ 2012). Because water is sup ̄
plied to the leaf through the petioleꎬ but lost to the
atmosphere across its entire surfaceꎬ the parameters
that determine the rate of water supply throughout
the lamina may constrain the shape and size of leaf
blade ( Zwieniecki et al.ꎬ 2004a ). Additionallyꎬ
major veins have greater hydraulic conductance than
higher order veins and mesophyll cells ( Zwieniecki
et al.ꎬ 2002ꎻ Sack et al.ꎬ 2004)ꎬ the lower hydrau ̄
lic conductance under a relative low temperature
may consequently impose great effects on the varia ̄
tion of leaf shape and size to be narrower and smal ̄
lerꎬ for removing hydraulic constraints on leaf mar ̄
gins. Sisóet al. ( 2001) investigated that a deeper
leaf lobation was associated with a lower leaf hydrau ̄
lic resistance in broadleaf Quercus species.
Thusꎬ we hypothesized that lower temperature
might induce lower minor vein density of tobacco
plants and lower leaf hydraulic conductance conse ̄
quently which might be negatively correlated with
the leaf length to width ratio of tobacco plants. To
test the hypothesisꎬ hereꎬ we grew tobacco seedlings
at two different temperatures (24 ℃ / 18 ℃ day / nightꎻ
32 ℃ / 26 ℃ day / night)ꎬ and quantified changes in
water ̄related leaf anatomyꎬ K leafꎬ LAꎬ and leaf
length to leaf width (L / W) ratio of tobacco plants.
We then investigated the potential impact of meas ̄
ured changes in anatomic traits on hydraulic con ̄
ductance and the changes in hydraulic conductance
on leaf shape. The first aim of our study is to investi ̄
gate whether water ̄related leaf anatomy and K leaf
would underlie variations of leaf shape for tobacco
plants under different growth temperatures. And our
second aim is to explain the functional significance
of leaf shape and size variation under a relative low
temperature from the hydraulic perspective for tobac ̄
co plants.
1  Materials and methods
1􀆰 1  Plant material and growth conditions
Seeds of a tobacco cultivar (Nicotiana tabacum
‘K326’ ) were obtained from the Seed Center of
Yunnan Academy of Tobacco (Yunnanꎬ China). The
normal growth temperature range of N􀆰 tabacum is al ̄
most between 24 ℃-32 ℃ (day temperature) (Ha ̄
roon et al.ꎬ 1972). Seeds were sown and cultured
within a germination cabinet at ambient temperature
and CO2 concentration. At 30 days after plantingꎬ
the seedlings were transplanted to pots (50 cm di ̄
am. × 50 cm tall) filled with red soil and humus
(3∶1ꎬ v ∶ v). The pots were placed in two adjacent
glasshouse rooms (4􀆰 0 m long × 3􀆰 4 m wide × 3􀆰 5
m high). Within each of two treatment roomsꎬ there
were 30 pots of tobacco plants. Day / night tempera ̄
ture treatments were programmed for two different
temperatures (24 ℃ / 18 ℃ and 32 ℃ / 26 ℃)ꎬ with
the temperatures set to change at 8􀆰 00 am and 8􀆰 00
pm. The rooms received natural lightingꎬ with a
maximum photosynthetic photon flux density (PPFD)
of 1 600 μmol m-2 s-1 . Relative humidity in each
room was maintained at a constant (60 ± 3) % over
the growing seasonꎬ such that the VPD co ̄varied
with temperature. During the daytimeꎬ the VPD un ̄
der 24 ℃ / 18 ℃ and 32 ℃ / 26 ℃ averaged 1􀆰 19 kPa
and 1􀆰 90 kPaꎬ respectivelyꎬ based on the combined
calculation of air temperature and relative humidity
(http: / / autogrow􀆰com/ downloads / download ̄software ̄
and ̄drivers) . All plants were irrigated daily and pro ̄
vided with adequate fertilizers during the experimen ̄
tal period.
1􀆰 2  Leaf hydraulic conductance
Measurements were made after 40 days of glass ̄
house growth. Maximum hydraulic conductance was
evaluated on four seedlings per chamber using a
high ̄pressure flow meter ( HPFMꎻ Dynamax Inc.ꎬ
Houstonꎬ TXꎬ USA) 40 days after transplanted to
chambers. The whole plants for measurements were
moved from the glasshouse rooms to the laboratory
for measuring K leaf . The leaves measured were ninth
to tenth leaves from the stem base for every tobacco
071                                  植 物 分 类 与 资 源 学 报                            第 37卷
plant. The high ̄pressure flow meter measured resist ̄
ance (the inverse of conductance) as the force re ̄
quired to push water through a sample for a given
flow rate. Leaf hydraulic conductance was measured
by the ‘ transient’ method between 11􀆰 00 am and
2􀆰 00 pmꎬ and was calculated on a leaf ̄area basis
(Sack et al.ꎬ 2002ꎻ Tyree et al.ꎬ 2005). Brieflyꎬ the
petiole was re ̄cut under water and then connected to
the flow meter. Water flowed into the leaf and the
necessary applied pressure were recorded every 3 s
while pressure was rampedꎬ at a constant rate of 3 to
7 kPa s-1ꎬ from 0 to 550 kPa. Hereꎬ K leaf was com ̄
puted as the water flow rate per unit leaf area divid ̄
ed by the pressure drop (between 200 and 550 kPa
for most measurements) driving the flow. Leaf area
(LA) was determined with a LI ̄3100C leaf area me ̄
ter (Li ̄Corꎬ Inc.). During this measurement periodꎬ
the laboratory temperature was 20􀆰 5 ℃ to 23􀆰 5 ℃
and laboratory irradiance was 20 to 45 μmol m-2 s-1 .
Transpiration rate (E) was determined with an open
gas exchange system that incorporated infrared CO2
and water vapor analyzers (Li ̄6400ꎻ Li ̄Corꎬ Inc.ꎬ
Lincolnꎬ NEꎬ USA). While the transpiration rates
were being recordedꎬ the leaves were exposed to
their specified treatment temperatureꎬ an relative hu ̄
midity of approximately 70%ꎬ and a CO2 concentra ̄
tion of 380 μmol mol-1 .
1􀆰 3  Leaf anatomy
After K leaf was assessedꎬ we examined the ana ̄
tomical features of these leaves in the laboratory. On
each leafꎬ two locations were selected for measure ̄
ments of vein density: the middle sites at the both
sides of the midvein. Fully expanded leaves were
sampled into 3 × 3 cm sections. Leaf materials were
then boiled in NaOH (7%) for three minutes for re ̄
moving pigments from the leaf to see the entire fine
vein networkꎬ and then stained with safranin. Last ̄
lyꎬ the sections were photographed under a light mi ̄
croscope at × 4 magnification (Nikon Optiphotꎻ Ni ̄
konꎬ Tokyoꎬ Japan) to record MVD. Minor vein
density was expressed as the sum of the lengths of
third ̄and higher ̄ order veins per unit area (Zhu et
al.ꎬ 2012). Petiole transverse sections (8 μm thick ̄
ness) were obtained by using a Leica CM 3050 S
freezing microtome ( Leica Microsystemsꎻ Wetzlarꎬ
Germany) and stained with safranin (0􀆰 01%) and
photographed under a light microscope at ×20 mag ̄
nification (Nikon Optiphotꎻ Nikonꎬ Tokyoꎬ Japan).
Representative sections of two tissue samples per
plant from four independent plants of each treatment
were examined and photographedꎬ for imaging and
measurement of diameters and density of the petiole
vessels. Petiole vessel density was calculated as the
vessel number per area of vascular bundle in the pet ̄
iole (Coomes et al.ꎬ 2008). Petiole vessel diameter
was calculated as the average diameter of all petiole
vessels in a petiole cross section. The ImageJ Soft ̄
ware (US National Institutes of Healthꎬ Bethesdaꎬ
MDꎬ USA) was used to measure MVDꎬ petiole ves ̄
sel density and petiole vessel diameter. At least 40
fields of view were measured from each treatment.
1􀆰 4  Leaf morphology
Leaf morphology was recorded on fully expand ̄
ed leaves which were removed from each of four
plants per treatment ( ninth to tenth leaf from the
stem base). Because tobacco leaves had simpleꎬ lin ̄
ear leaves with generally entire marginsꎬ leaf shape
was calculated as the ratio of leaf length to leaf width
at the widest point. 40 days after transplanted to
glasshouse rooms. Leaf area was measured with a LI ̄
3100C leaf area meter (Li ̄Corꎬ Inc.ꎬ Lincolnꎬ NEꎬ
USA).
1􀆰 5  Data analysis
Differences in data for leaf anatomyꎬ hydraulic
conductance and morphology between two different
treatments were evaluated by one ̄way ANOVA. Means
and standard errors were estimated from four repli ̄
cates. Error bars indicated the standard error of the
mean across replicates. Relationships between varia ̄
bles were examined by Pearson’ s product ̄moment
correlations. The results were accepted as significant
at P< 0􀆰 05. All statistical analyses were conducted
with SPSS 16􀆰 0 (SPSS Inc.ꎬ USA).
1712期      HU and HU: Viewing Leaf Shape and Size Variation in Tobacco Plants under Different Temperatures 􀆺     
2  Results
2􀆰 1  Variation of leaf hydraulic architecture be ̄
tween different temperatures
Great differences in leaf anatomy and K leaf of to ̄
bacco plants were observed between 24 ℃ and 32 ℃ .
Petiole vessel density of tobacco plants under 24 ℃
and 32 ℃ was 1 118􀆰 77 and 839􀆰 91 mm-2ꎬ respec ̄
tively. Tobacco leaves grown under 24 ℃ were 33􀆰 4%
greater in petiole vessel density than leaves grown un ̄
der 32 ℃ (P<0􀆰 01ꎻ Fig􀆰 2A). Petiole vessel diame ̄
ter of tobacco plants growing at 24 ℃ (20􀆰 67 μm)
was significantly less than that of tobacco leaves at
32 ℃ (26􀆰 9 μm) (P<0􀆰 001ꎻ Fig􀆰 2B). As expec ̄
tedꎬ a relative low temperature also induced a signi ̄
ficant decrease in MVD (P<0􀆰 01ꎻ Fig􀆰 2C). Minor
vein density of tobacco plants under 24 ℃ and 32 ℃
was 6􀆰 25 and 7􀆰 80 mm-2ꎬ respectively. When PPFD
was 1 500 μmol m-2 s-1ꎬ transpiration rates were
8􀆰 07 mmol m-1 s-1 for HT plants and 4􀆰 50 mmol m-1
s-1 for MT plants (P<0􀆰 01ꎻ Fig􀆰 1). There was also
a significant decrease (34%) in K leaf from a mean of
5􀆰 63 × 10-5Kg s-1 MPa-1 m-2 under 32 ℃ to 2􀆰 41 ×
10-5Kg s-1 MPa-1 m-2 under 24 ℃ ( P < 0􀆰 001ꎻ
Fig􀆰 2D).
Fig􀆰 1  Changes in transpiration rate (E) for tobacco leaves in re ̄
sponse to PPFD when plants were grown at 24 and 32 ℃ . Vertical
bars indicate standard errors of means for 4 measurements
Fig􀆰 2  Petiole vessel densityꎬ petiole vessel diameterꎬ minor vein density (MVD)ꎬ and leaf hydraulic conductance (Kleaf) of tobacco
plants grown at 24 ℃ and 32 ℃ . Data bars not sharing the same lowercase letters (a and b) are statistically
different at P < 0􀆰 05 by Tukey’s test. Values are means ± SEꎻ n= 4 per treatment
271                                  植 物 分 类 与 资 源 学 报                            第 37卷
2􀆰 2  Changes in leaf morphology between dif ̄
ferent temperatures
Leaf length ̄to ̄width ratio reduced significantly
from 24 ℃ to 32 ℃ (P<0􀆰 001ꎻ Fig􀆰 3Aꎬ Fig􀆰 4).
The L / W ratio of tobacco leaves growing under 24 ℃
was substantially greater than that under 32 ℃ꎬ with
2􀆰 70 under 24 ℃ and 2􀆰 00 under 32 ℃ꎬ respective ̄
ly. Howeverꎬ there was no significant difference be ̄
tween LA of tobacco plants growing under 24 ℃ and
32 ℃ (P>0􀆰 05ꎻ Fig􀆰 3B). The LA of tobacco plants
under 24 ℃ and 32 ℃ was 527􀆰 5 cm2 and 506􀆰 00
cm2ꎬ respectively.
Fig􀆰 3  The leaf length ̄to ̄widthratio (L / W) and the leaf area of to ̄
bacco plants grown at 24 ℃ and 32 ℃ . Data bars not sharing the same
lowercase letters (a and b) are statistically different at P<0􀆰 05
by Tukey’s test. Values are means ± SEꎻ n= 4 per treatment
2􀆰 3  Relationship between leaf hydraulic archi ̄
tecture and L / W ratio
A significantly positive correlation was observed
between MVD and K leaf of tobacco leaves under two
different temperatures (R2 = 0􀆰 91ꎻ Fig􀆰 5A)ꎬ but a
negative correlation between leaf hydraulic conductance
and L / W ratio was observed (R2 = 0􀆰 70ꎻ Fig􀆰 5B).
Fig􀆰 4  Photographs of leaf shape of tobacco plants
grown at 24 ℃ and 32 ℃
Fig􀆰 5  A. the relationship between minor vein density (MVD) and
leaf hydraulic conductance (Kleaf) of tobacco plants grown under two
different temperaturesꎻ B. the relationship between leaf hydraulic
conductance (Kleaf) and the leaf length ̄to ̄width (L / W) ratio
of tobacco plants grown under different temperatures.
∗∗ꎬ P<0􀆰 01ꎻ ∗∗∗ꎬ P<0􀆰 001
3712期      HU and HU: Viewing Leaf Shape and Size Variation in Tobacco Plants under Different Temperatures 􀆺     
3  Discussions
3􀆰 1  Changes in leaf hydraulic architecture in ̄
duced by temperatures
Significant reductions occurred in MVDꎬ petiole
vessel diameter due to the effects of lower tempera ̄
tureꎬ with a trade ̄off between petiole vessel diameter
and vessel density. The modification of leaf anatomy
under lower temperature can be attributed to two rea ̄
sons (Medek et al.ꎬ 2011ꎻ Way et al.ꎬ 2012). The
first might be that the lower temperature changed the
development of leaf anatomy (Medek et al.ꎬ 2011).
Another reason might be the lower VPD and evapo ̄
rative demand under lower temperatures. As the rela ̄
tive humidity in our study remained constantꎬ the
decrease in temperature led to a lower VPD and de ̄
creased transpiration rate (Way et al.ꎬ 2012). Thusꎬ
there is no need for tobacco plants producing dense
minor veins to provide more water to leaves under
lower temperature.
Decreased MVD and changes in petiole vessels
partly resulted in lower water transport capacity un ̄
der lower temperatureꎬ which can be indicated by
the positive correlation between MVD and K leaf . De ̄
creased MVD reduced the surface area available for
exchanging xylem water with surrounding mesophyll
cells and also reduced the distance through which
water must travel outside of the xylem ( Sack and
Holbrookꎬ 2006). Petiole vessel density and diame ̄
ter are also closely correlated with hydraulic con ̄
ductance (Medek et al.ꎬ 2011). As proven by the
Hagen ̄Poiseuille equation (Hellemans et al.ꎬ 1980)ꎬ
conductance through an ideal pipe is proportional to
the fourth power of conduit radius. Thusꎬ in our
studyꎬ a decrease in petiole vessel diameter leads to
a large decrease in vascular hydraulic conductance
although petiole vessel density increased from 32 ℃
to 24 ℃ .
3􀆰 2  Modification of leaf shape offsetting lower Kleaf
The negative association between leaf length to
width ratio and K leaf supported our hypothesis that
leaf shape may have important functions in hydrau ̄
lics. Narrow leaves might be an adaptation to low
water transport capacity induced by lower tempera ̄
ture. This is concordant with previous reports of
Nicotra et al. (2011) and Zwieniecki et al. (2004aꎬ
b) that hydraulic limitations is an important physio ̄
logical factor influencing leaf length to width ratio
during the period of leaf expansionꎬ although lots of
intrinsic and extrinsic factors are involved in deter ̄
mining leaf shapeꎬ such as thermoregulationꎬ pat ̄
terns of leaf expansionꎬ biomechanical constraintsꎬ
adaptations to optimize light interception.
Hydraulics might affect the shape of tobacco
leaves under lower temperature for several reasons.
The first reason might be that the increased distances
from the midrib to leaf margins need a larger vein
network and greater water transport capacity to trans ̄
port water to cellsꎬ preventing leaf margins drooping
(Xu et al.ꎬ 2009). Howeverꎬ tobacco plants grow ̄
ing under lower temperature have lower water trans ̄
port capacity. Reducing the distance from the vein to
the leaf margin can help tobacco leaves remove the
hydraulic constraint on leaf width because mesophyll
cells have a very limited capacity to transport water
compared with major veins (Cochard et al.ꎬ 2004).
Narrow leaves could maintain a greater proportion of
leaf tissue closer to main veins. Because first ̄order
veins have high axial conductance and relatively
small radial permeabilityꎬ and higher ̄order veins
and mesophyll cells tend to be more hydraulically re ̄
sistant than major veinsꎬ thus allowing water to
reach distal areas of the leaf is easier than leaf mar ̄
gins. Zwieniecki et al. (2002) found that in Laurus
nobibis leavesꎬ the leaf margins had pressures almost
0􀆰 2 MPa lower than that of the middle of the leaf.
Thereforeꎬ leaf margins are more likely to be hydrau ̄
lically disadvantaged relative to the rest of the leaf.
Consequentlyꎬ the distance from the midrib to leaf
margin might influence the ability to supply and dis ̄
tribute water to the leaf marginꎬ and in turn affect
leaf shape.
Another reason might be that water transported
to expanding cells across the leaf lamina during
growth can determine the extent of local expansionꎬ
471                                  植 物 分 类 与 资 源 学 报                            第 37卷
thereby affecting the morphology of leaves ( Zwie ̄
niecki et al.ꎬ 2004bꎻ Nicotra et al.ꎬ 2011). Zwie ̄
niecki et al. (2004b) reported that leaf shape could
be determined by cell expansion. The expansion of a
leaf is limited by its water status because further leaf
expansion will lead to stomatal closure at leaf mar ̄
gins with low water availability. Leaf shape could
therefore be directly controlled by the water availabil ̄
ity of leaf margins during the period of leaf expansion.
Howeverꎬ in our studyꎬ this suggestion lack abundant
evidenceꎬ and needs to be further investigated.
3􀆰 3  Leaf shape and size—a trade ̄off between
acclimating to hydraulic limitations and optimi ̄
zing light capture
In this studyꎬ leaf shape changed greatly be ̄
tween two different temperaturesꎻ howeverꎬ there is
no significant change in LA of tobacco leaves. In
cold areasꎬ LA often tends to be small. To increase
light interception area for photosynthesis might be
one of the reasons that why tabacco plants under
lower temperature did not reduce LA (Ball et al.ꎬ
1988ꎻ Nicotra et al.ꎬ 2008). Apart from accommo ̄
dating to lower K leaf under a relative low tempera ̄
tureꎬ narrower leaves might also plays a crucial role
in increasing the whole plant light capture efficiency.
Takenaka (1994) who used a computer simulation
to study the possible effects of the length ̄to ̄width ra ̄
tio of a leaf blade on shoot light captureꎬ found that
higher length ̄to ̄width ratios increased light capture
per unit leaf area due to a reduced aggregation of
leaves around the stem. The combination of narrower
leaves without reducing LA under lower temperature
might be a strategy to acclimate to lower water trans ̄
port capacity for providing a relatively homogeneous
water supply across the leaf lamina and at the same
time not reduce light interception area for photosyn ̄
thesis (Ball et al.ꎬ 1988ꎻ Nicotra et al.ꎬ 2008).
4  Conclusions
The present study investigated the interplay be ̄
tween the leaf hydraulic architecture and the varia ̄
tion of leaf shape and size under different tempera ̄
tures. Our results suggest that the combination of
narrower leaves without reducing LA under lower
temperature for tobacco plants might be a result of
decreased MVD and lower K leaf . Howeverꎬ the rela ̄
tionships between leaf shape and other structural and
physiological traits under different temperatures re ̄
main unclearꎬ we need to learn about the impacts of
temperature on leaf shape and size variation during
leaf expansion from a hydraulic perspective.
Acknowledgements: We thank Drs. Wei Huang and Shijian
Yang for their helpful comments on the manuscript. We thank
the Biological technology open platformꎬ Kunming Institute of
Botanyꎬ Chinese Academy of Sciences for providing glass ̄
houses. We thank Miss. Ting Yang for her help on the man ̄
agement of glasshouse rooms.
References:
Aasamaa Kꎬ Niinemets Üꎬ Sober ANUꎬ 2005. Leaf hydraulic con ̄
ductance in relation to anatomical and functional traits during
Populus tremula leaf ontogeny [ J ] . Tree Physiologyꎬ 25:
1409—1418
Abrams MDꎬ Kloeppel BDꎬ Kubiske MEꎬ 1992. Ecophysiological and
morphological responses to shade and drought in two contrasting
ecotypes of Prunus serotina [ J] . Tree Physiologyꎬ 10: 343—
355
Ashton PMSꎬ Berlyn GPꎬ 1994. A comparison of leaf physiology and
anatomy of Quercus (Section Erythrobalanus ̄Fagaceae) species in
different light environments [ J] . American Journal of Botanyꎬ
81: 589—597
Ball MCꎬ Cowan IRꎬ Farquhar GDꎬ 1988. Maintenance of leaf tem ̄
perature and the optimization of carbon gain in relation to water
loss in a tropical mangrove forest [ J] . Australian Journal of
Plant Physiologyꎬ 15: 263—276
Brodribb TJꎬ Feild TSꎬ Jordan GJꎬ 2007. Leaf maximum photosyn ̄
thetic rate and venation are linked by hydraulics [ J] . Plant
Physiologyꎬ 144: 1890—1898
Brodribb TJꎬ Feild TSꎬ Sack Lꎬ 2010. Viewing leaf structure and evo ̄
lution from a hydraulic perspective [J] . Functional Plant Biolo ̄
gyꎬ 37: 488—498
Cochard Hꎬ Nardini Aꎬ Coll Lꎬ 2004. Hydraulic architecture of leaf
blades: where is the main resistance? [ J] . Plant Cell & Envi ̄
ronmentꎬ 27: 1257—1267
Coomes DAꎬ Heathcote Sꎬ Godfrey ER et al.ꎬ 2008. Scaling of xylem
vessels and veins within the leaves of oak species [ J] . Biology
Lettersꎬ 4: 302—306
Givnish TJꎬ 1978. Ecological aspects of plant morphology: leaf form
5712期      HU and HU: Viewing Leaf Shape and Size Variation in Tobacco Plants under Different Temperatures 􀆺     
in relation to environment [J] . Acta Biotheoreticaꎬ 27: 83—142
Givnish TJꎬ 1979. On the adaptive significance of leaf form [A]. / /
Solbrig OTꎬ Subodh Jꎬ Johnson GBꎬ Raven PH eds.ꎬ Topics in
Plant Population Biology [M]. New York: Columbia University
Pressꎬ 375—407
Guerin GRꎬ Wen HXꎬ Lowe AJꎬ 2012. Leaf morphology shift linked
to climate change [J] . Biology Letters. doi: 10􀆰1098 / rsbl􀆰2012􀆰
0458
Haroon Mꎬ Long RCꎬ Weybrew JAꎬ 1972. Effect of day / night temper ̄
ature on factors associated with growth of Nicotiana tabacum L. in
controlled environments [J] . Agronomy Journalꎬ 64: 509—515
Hellemans Jꎬ Forrez Pꎬ Wilde RDꎬ 1980. Experiment illustrating Ber ̄
noulli’ s equation and Hagen ̄Poiseuille ’ s law [ J] . American
Journal Physiologyꎬ 48: 254—255
March RHꎬ Clark LGꎬ 2011. Sun ̄shade variation in bamboo (Poace ̄
ae: Bambusoideae) leaves [J] . Telopeaꎬ 13: 93—104
Medek DEꎬ Evans JRꎬ Schortemeyer M et al.ꎬ 2011. Effects of growth
temperature on photosynthetic gas exchange characteristics and
hydraulic anatomy in leaves of two cold ̄climate Poa species
[J] . Functional Plant Biologyꎬ 38: 54—62
Mendes MMꎬ Gazarini LCꎬ Rodrigues MLꎬ 2001. Acclimation of Myr ̄
tus communis to contrasting Mediterranean light environments ̄
effects on structure and chemical composition of foliage and plant
water relations [ J] . Environmental and Experimental Botanyꎬ
45: 165—178
Nicotra ABꎬ Cosgrove MJꎬ Cowling A et al.ꎬ 2008. Leaf shape linked
to photosynthetic rates and temperature optima in South African
Pelargonium species [J] . Oecologiaꎬ 154: 625—635
Nicotra ABꎬ Leigh Aꎬ Boyce CK et al.ꎬ 2011. The evolution and
functional significance of leaf shape in the angiosperms [ J] .
Functional Plant Biologyꎬ 38: 535—552
Niinemets Üꎬ Kull Kꎬ 1994. Leaf weight per area and leaf size of 85
Estonian woody species in relation to shade tolerance and light a ̄
vailability [J] . Forest Ecology and Managementꎬ 70: 1—10
Parkhurst DFꎬ Loucks OLꎬ 1972. Optimal leaf size in relation to envi ̄
ronment [J] . Journal of Ecologyꎬ 60: 505—537
Roth  ̄Nebelsick Aꎬ Uhl Dꎬ Mosbrugger V et al.ꎬ 2001. Evolution and
function of leaf venation architecture: a review [ J] . Annals of
Botanyꎬ 87: 553—566
Royer DLꎬ Wilf Pꎬ Janesko DA et al.ꎬ 2005. Correlations of climate
and plant ecology to leaf size and shape: Potential proxies for the
fossil record [J] . American Journal of Botanyꎬ 92: 1141—1151
Royer DLꎬ 2012. Leaf shape responds to temperature but not CO2 in
Acer rubrum [ J] . PLoS ONEꎬ 7: e49559. doi: 10􀆰1371 / jour ̄
nal􀆰 pone􀆰0049559
Sack Lꎬ Melcher PJꎬ Zwieniecki MA et al.ꎬ 2002. The hydraulic con ̄
ductance of the angiosperm leaf lamina: a comparison of three
measurement methods [ J] . Journal of Experimental Botanyꎬ
53: 2177—2184
Sack Lꎬ Cowan PDꎬ Jaikumar N et al.ꎬ 2003. The ‘ hydrology’ of
leaves: coordination of structure and function in temperate woody
species [J] . Plant Cell & Environmentꎬ 26: 1343—1356
Sack Lꎬ Streeter CMꎬ Holbrook NMꎬ 2004. Hydraulic analysis of wa ̄
ter flow through leaves of sugar maple and red oak [ J] . Plant
Physiologyꎬ 134: 1824—1833
Sack Lꎬ Frole Kꎬ 2006. Leaf structural diversity is related to hydraulic
capacity in tropical rain forest trees [ J] . Ecologyꎬ 87: 483—
491
Sack Lꎬ Holbrook NMꎬ 2006. Leaf hydraulics [J] . Annual Review of
Plant Biologyꎬ 57: 361—381
Scoffoni Cꎬ Rawls Mꎬ McKown A et al.ꎬ 2011. Decline of leaf hy ̄
draulic conductance with dehydration: relationship to leaf size and
venation architecture [J] . Plant Physiologyꎬ 156: 832—843
Sisó Sꎬ Camarero JJꎬ Gil ̄Pelegrin Eꎬ 2001. Relationship between hy ̄
draulic resistance and leaf morphology in broadleaf Quercus spe ̄
cies: a new interpretation of leaf lobation [J] . Treesꎬ 15: 341—
345
Takenaka Aꎬ 1994. Effects of leaf blade narrowness and petiole length
on the light capture efficiency of a shoot [ J] . Ecological Re ̄
searchꎬ 9: 109—114
Tyree MTꎬ Nardini Aꎬ Salleo S et al.ꎬ 2005. The dependence of leaf
hydraulic conductance on irradiance during HPFM measurements:
any role for stomatal response? [J] . Journal of Experimental Bot ̄
anyꎬ 56: 737—744
Way DAꎬ Domec JCꎬ Jackson RBꎬ 2012. Elevated growth tempera ̄
tures alter hydraulic characteristics in trembling aspen (Populus
tremuloides) seedlings: implications for tree drought tolerance
[J] . Plant Cell & Environmentꎬ 36: 103—115
Xu Fꎬ Guo WHꎬ Xu WH et al.ꎬ 2009. Leaf morphology correlates
with water and light availability: what consequences for simple
and compound leaves? [ J] . Progress in Natural Scienceꎬ 19:
1789—1798
Yano Sꎬ Terashima Iꎬ 2004. Developmental process in sun and shade
leaves of Chenopodium album L. [J] . Plant Cell & Environmentꎬ
27: 781—793
Zhu YHꎬ Kang HZꎬ Xie Q et al.ꎬ 2012. Pattern of leaf vein density
and climate relationship of Quercus variabilis populations remains
unchanged with environmental changes [ J] . Treesꎬ 26: 597—
607
Zwieniecki MAꎬ Melcher PJꎬ Boyce CK et al.ꎬ 2002. Hydraulic ar ̄
chitecture of leaf venation in Laurus nobilis L. [J] . Plant Cell &
Environmentꎬ 25: 1445—1450
Zwieniecki MAꎬ Boyce CKꎬ Holbrook NMꎬ 2004a. Functional design
space of single ̄veined leaves: role of tissue hydraulic properties
in constraining leaf size and shape [ J] . Annals of Botanyꎬ 94:
507—513
Zwieniecki MAꎬ Boyce CKꎬ Holbrook NMꎬ 2004b. Hydraulic limita ̄
tions imposed by crown placement determine final size and shape
of Quercus rubra L. Leaves [J] . Plant Cell & Environmentꎬ 27:
357—365
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