全 文 :植物科学学报 2015ꎬ 33(1): 53~60
Plant Science Journal
DOI:10 11913 / PSJ 2095-0837 2015 10053
根尖分生组织细胞核大小:
一个可能用于植物入侵性评估的新指标
郭水良1ꎬ 陈国奇2
(1. 上海师范大学生命与环境科学学院ꎬ 上海 200234ꎻ 2. 广东农业科学院植物保护研究所ꎬ 广州 510640)
摘 要: 植物的入侵性与 DNA C ̄值之间存在统计学上的负相关关系ꎮ 在这种关系中ꎬ 细胞和细胞核大小可能起
关键作用ꎬ 因此我们推测分生组织细胞核大小在评估植物或至少某些分类群的入侵性方面有潜在的应用价值ꎮ
本研究以豌豆属(Vicia)5种入侵能力不同的植物为材料ꎬ 观察了它们的分生组织染色体、 细胞核和细胞大小以
及有丝分裂速率ꎬ 同时测定了种子产量、 单位种子干重产生的幼苗生物量(近似于幼苗相对生长速率)和生活史
的长短ꎮ 结果显示根尖分生区细胞核较小的植物细胞较小ꎬ 细胞分裂速率快ꎬ 单位种子干重产生的幼苗生物量
高ꎬ 种子小而数量多ꎬ 生活史短ꎮ 这些结果表明 5种豌豆属植物中分生组织细胞核较小的倾向于具有较高的入
侵性ꎬ 其原因主要是: (1)能够产生小而多的种子ꎻ (2)具有较高的有丝分裂速率、 相对较快的幼苗生长速率和
短的生活史ꎮ 分生组织细胞核大小影响植物入侵性与 DNA C ̄值的作用是一致的ꎬ 在植物入侵性评估模型中ꎬ 分
生组织细胞核大小在评估植物入侵性方面可能具有潜在的应用价值ꎬ 而且其测定方便、 费用低廉ꎮ 但是ꎬ 这一
指标的应用范围和条件需要进一步筛选ꎮ
关键词: 分生组织ꎻ 细胞学指标ꎻ 入侵性ꎻ 种子产量ꎻ 世代时间
中图分类号: Q16 文献标识码: A 文章编号: 2095 ̄0837(2015)01 ̄0053 ̄08
收稿日期: 2014 ̄05 ̄31ꎬ 退修日期: 2014 ̄06 ̄20ꎮ
基金项目: 国家自然科学基金项目(31070479)ꎻ 上海市科委基础研究重点项目(10JC1412100)ꎮ
作者简介: 郭水良(1964-)ꎬ 男ꎬ 教授ꎬ 主要从事植物分类与生态学研究(E ̄mail: gsg@shnu edu cn)ꎮ
Root Meristematic Karyon Size: Possible New Index
in the Evaluation of Plant Invasiveness
GUO Shui ̄Liang1ꎬ CHEN Guo ̄Qi2
(1. College of Life and Environmental Sciencesꎬ Shanghai Normal Universityꎬ Shanghai 200234ꎬ Chinaꎻ
2. Institute of Plant Protectionꎬ Guangdong Academy of Agricultural Sciencesꎬ Guangzhou 510640ꎬ China)
Abstract: Many reports have found a statistically negative correlation between DNA C ̄value
and plant invasivenessꎬ with meristematic karyon size playing a key role in this correlation
according to previous research. We hypothesized that meristematic karyon size could be
applied as an evaluation index of plant invasiveness for at least some taxa. To test this
hypothesisꎬ we examined the sizes of karyonsꎬ cellsꎬ and mitosis rates of five Vicia species
with different invasiveness and DNA C ̄valuesꎬ and also investigated their seed productionꎬ
seedling weight / dry seed weight ( similar to relative seedling growth rate)ꎬ and their life
spans. Results showed that plants with smaller meristematic karyons were prone to have
smaller chromosomesꎬ karyonsꎬ cellsꎬ and seedsꎬ quicker mitosisꎬ higher relative seedling
growth rateꎬ shorter generation timeꎬ and produce more and smaller seeds. Furthermoreꎬ
among the five Vicia speciesꎬ plants with smaller meristematic karyons exhibited higher
invasivenessꎬ which may be explained by two aspects: (1) smaller seeds with much higher
seed productionꎻ and ( 2) higher rates of cell division and seedling growth with shorter
generation times. The effects of meristematic karyon size on plant invasiveness coincided with
that of the DNA C ̄value. Thereforeꎬ for plant invasiveness evaluation modelsꎬ meristematic
karyon size has potential value in invasiveness assessment due to its convenience and lower
expenseꎬ though more work is needed to determine its application scope and methodology.
Key words: Meristematic tissuesꎻ Cytological indicesꎻ Invasivenessꎻ Seed productionꎻ Gene ̄
ration time
Plant invasion poses serious challenges in
the world today. Though many different indicesꎬ
including secondary chemistry[1]ꎬ species traitsꎬ
DNA C ̄value and genome size[2ꎬ3] and gene ex ̄
pression[4]ꎬ have been suggested to evaluate
plant invasivenessꎬ we still have no general tool
to predict which plants are potential invaders.
Thereforeꎬ it is important to determine which indi ̄
ces are clearly and broadly correlated with plant
invasiveness.
Weed plants are mainly distributed in human ̄
disturbed environments and are not purposely
cultivated[5] . Weeds exhibit many traits that allow
them to invade into human ̄disturbed ecosystems
easily. Studies have shown that invasiveness is
similar to weediness[6ꎬ7] . For exampleꎬ invasive
North and South American species naturalized in
France (274 species) could be divided into agri ̄
cultural weeds and environmental weeds accor ̄
ding to their habitats in France[8] . Sutherland
(2004) studied plant invasiveness by observing
the trait differences between weeds and non ̄
weeds in North America [9] .
Generally speakingꎬ weed species have hig ̄
her invasiveness[5ꎬ8]ꎬ and the success of many
important weeds may be associated with several
traits correlated with a low DNA C ̄value (amount
of DNA in the unreplicated gametic nucleus ).
These traits include establishingꎬ developingꎬ and
reproducing quickly with many small seeds[10ꎬ11] .
There are many reports on the potential of DNA
C ̄values to evaluate plant invasiveness[10ꎬ12-14] .
DNA C ̄values and genome size both have signifi ̄
cant effects on plant invasivenessꎬ especially in
herbsꎬ dicotsꎬ monocotsꎬ perennialsꎬ non ̄pe ̄
rennialsꎬ diploidsꎬ polyploidsꎬ and the Composi ̄
tae and Poaceae familiesꎬ but not significant in
trees or the Fabaceae family [3]ꎬ though there are
some exceptions in some taxa[15] .
With lower DNA C ̄valuesꎬ plants generally
have smaller karyons and cells[16-20] . This tendency
makes plants more highly invasive due to: 1) smal ̄
ler seeds and higher seed productionꎻ and 2) shor ̄
ter new cell reproduction timeꎬ which may acce ̄
lerate growth rate and shorten life span[12ꎬ13ꎬ21] .
According to this hypothesisꎬ the relationship be ̄
tween DNA C ̄values and plant invasiveness is
linked to karyon and cell size. In other wordsꎬ
karyon and cell size play a key role in the mecha ̄
nism of how the DNA C ̄value affects plant inva ̄
siveness. This begs the question of why karyon
and cell size is not used to evaluate plant inva ̄
siveness in lieu ofꎬ or at least as a supplement
toꎬ DNA C ̄values.
Moreoverꎬ DNA C ̄values of plants are main ̄
ly determined by flow cytometry[12ꎬ22] . Howeverꎬ
the values gained from different measuring strate ̄
giesꎬ with different dyes and instrumentsꎬ can
vary[23ꎬ24] . In additionꎬ flow cytometers are ex ̄
pensive and the measuring process is time ̄con ̄
suming. Converselyꎬ the karyon size of meriste ̄
matic cells is relatively stable and much more
convenient to determine.
Thereforeꎬ testing and comparing the corre ̄
lation between DNA C ̄values and invasiveness is
importantꎬ and experiments on the relationship
between karyon size and plant invasiveness
using related species are needed. We found five
Vicia species to be ideal materials. Vicia sativa
L.ꎬ V. tetrasperma (L.) Schreberꎬ and V. hirsuta
45 植 物 科 学 学 报 第 33卷
(L.) S. F. Gray are three widely occurring weed
species in Chinaꎬ as well as in many other
countries[25ꎬ26]ꎬ and their DNA C ̄values (pg) are
1 90ꎬ 3 25ꎬ and 4 25ꎬ respectively[27] . Vicia
tenuifolia Roth. is not clearly invasive[25ꎬ26]ꎬ and
its DNA C ̄value is 8 0 pg[27] . Vicia faba L. is a
highly domesticated and globally cultivated crop
species[25ꎬ26]ꎬ and its DNA C ̄value is 11 90 pg[27] .
Their ranks of invasiveness (or weediness) are
reversed with their DNA C ̄values.
By examining meristematic karyon sizeꎬ cell
sizeꎬ seed productionꎬ relative seedling growthꎬ
and life spans of the five Vicia speciesꎬ then ana ̄
lyzing the relationship of their invasiveness with
these indicesꎬ we investigated the feasibility of
whether meristematic karyon sizeꎬ in lieu of DNA
C ̄valuesꎬ could be applied as an index in the as ̄
sessment of plant invasiveness.
1 Materials and Methods
1 1 Seed collection and seed weight
In April 2007ꎬ seeds of V. sativaꎬ V. tetras ̄
permaꎬ V. hirsutaꎬ and V. faba were collected
from a suburb of Jinhua Cityꎬ Zhejiangꎬ China
(29°07′06″Nꎬ 119°37′47″ Eꎬ alt. 459 m) and V.
tenuifolia seeds were collected in August 2006 in
Shiheziꎬ Xinjiangꎬ China(44°20′50″ Nꎬ 85°58′57″
Eꎬ alt. 400 m ) . All seeds were air ̄dried and
stored in paper bags at room temperature in the
laboratory at Zhejiang Normal University. One
hundred mature seeds with five replicates for
each species were selected to determine seed
weight. The values were changed into 1000 ̄seed
weights.
1 2 Projected areas of meristematic karyonꎬ
cellsꎬ and mitosis rate
Seeds were placed into a 9 cm Petri dish
with five pieces of filter paper and 9 mL of deioni ̄
zed water. The seeds were not submerged but
imbibed on moistened paper. The dish was
sealed with Parafilm and then placed in a growth
chamber with constant temperature until seeds
germinated to form roots. The incubating tempe ̄
rature was set to a constant 25℃ꎬ with a 12 h
light / 12 h dark regime.
Root tips (1 5-2 0 cm for V. faba and 0 8-
1 2 cm for the other species) were treated for
24 h at 4℃ and fixed in 3 ∶1 (absolute ethanol:
acetic acid) for 24 h. The samples were then
stained with Carbol fuchsin for 30 -40 min after
8 min of hydrolysis in 1 ∶ 1 (95% ethanol: 38%
HCl) . Temporary slides for determining chromo ̄
someꎬ karyon and cell sizes were prepared using
the conventional squashing method. The micro ̄
graphs were taken under a 100× oil lens using a
Motic digital microscope DMB1 ̄223 (Motic Ltd.
Corp.ꎬ Xiamenꎬ China) . Five hundred cells and
karyons in mitotic interphase for each species
were used to determine the projected areas of
cells and karyons.
The five Vicia species are annual or biennial
plantsꎬ and the temperature in their growth
periods mostly varies from 10℃ to 30℃. For com ̄
parison of the relative seedling growth rates
(seedling dry weight / dry weight of seed) of the
five species under different temperaturesꎬ their
seedlings were cultivated for three days at 10℃ꎬ
15℃ꎬ 20℃ꎬ 25℃ꎬ and 30℃ꎬ respectively. Chro ̄
mosome slides from these seedlings were then
prepared. For each treatmentꎬ 10 slides pre ̄
pared with clear and dispersive meristematic
cells were used to take micrographs under a 40×
lens. To determine the mitosis rate ( number of
cells under prophaseꎬ metaphaseꎬ and ana ̄
phase / total meristematic cells)ꎬ 10 successive
graphs were taken for each slide using a Motic
digital microscope DMB1-223.
The average mitosis rate of each species
from 10℃ to 30℃ was calculatedꎬ and its rela ̄
tionship with karyon size was also analyzed.
1 3 Seedling growth rate
Seedling growth rates of the five Vicia spe ̄
55 第 1期 郭水良等: 根尖分生组织细胞核大小: 一个可能用于植物入侵性评估的新指标 (英文)
cies were compared. To destroy the epidermis
and thus overcome dormancyꎬ their seeds were
soaked in vitriol oil for 18 min and rinsed with
deionized water before the experiment. All seeds
were soaked in deionized water for 4 h before
germination. After rinsingꎬ seeds were placed in
Petri dishes with moist filter paper. Each dish was
sealed with Parafilm and placed in a growth cham ̄
ber at 15℃ꎬ with a 12 h light / 12 h dark cycle.
Immediately after germinationꎬ 35 seedlings
per treatment per species were selected and
placed into new Petri dishes for continued growth
in a growth chamber. Each species had five
treatments with cultivating temperatures of 10℃ꎬ
15℃ꎬ 20℃ꎬ 25℃ꎬ and 30℃ꎬ respectively. Va ̄
porized water in each Petri dish was replenished
as needed. Two weeks laterꎬ the 30 largest seed ̄
lings for each treatment were dried to a constant
weight at 80℃ and then weighed.
1 4 Life span and seed production
Field plots were established in December
2007 in the suburb of Jinhuaꎬ Zhejiang Provinceꎬ
China (29°07′06″Nꎬ 119°37′47″ E) . Five 1 m2
plots were cleared of the surface 5 cm of soilꎬ
and replaced with water ̄washed sand to remove
soil vegetation as well as for better fertilization.
Each plot received an initial application of 50 g / m2
of Fushengs Special Fertilizer (15 ̄15 ̄15) ( Fu ̄
sheng Fertilizer Co.ꎬ Ltdꎬ Tianjingꎬ China) . On
December 16ꎬ 2007ꎬ 15 seedlings per species
germinated in the growth chamber were cultivated
20 cm apart. Thereafterꎬ all plants were watered
as needed and fertilized every 30 days. The lowest
and highest temperatures were recorded each day.
On March 16ꎬ 2008ꎬ five seedlings of each
species with the lowest biosize were removed.
For each plant individualꎬ the first dates of flowe ̄
ring and production of mature fruits were recor ̄
dedꎬ and shedding seeds were collected and
stored. In May 2008ꎬ plants for which about half
of the seeds had matured were uprooted and
washed. Seed production of each individual was
counted. All plant individuals were dried to a con ̄
stant weight at 80℃ and weighed.
1 5 Data analysis
Data were presented as means ± standard
errors ( SE ) . A one ̄way analysis of variance
(ANOVA) using SPSS 150 statistical software
was employed to test differences. Least signifi ̄
cant difference (LSD) was used when the varia ̄
nces were homogeneousꎻ otherwiseꎬ Dunnetts
T3 test was used. Regression analyses were per ̄
formed using SPSS 150 software.
2 Results
2 1 Projected areas of meristematic karyons and
cellsꎬ and seed weight
The meristematic karyons and cells in the
root tip and seeds of V. faba were significantly
largerꎬ followed by V. tenuifoliaꎬ V. sativaꎬ V. hir ̄
suta and V. tetrasperma (Table 1) .
Regression analyses with a linear model (Ta ̄
Table 1 Projected areas of total chromosomesꎬ karyons and cellsꎬ and seed weights of the five Vicia species
Species Karyon projectedarea (μm2)
Cell projected
area (μm2)
Chromosome
projected area (μm2)
Seed weight
(g)
DNA 1C ̄value∗
(pg)
V. sativa 89.47 ± 1.67 c 338.29 ± 4.98 c 55.41 ± 3.90 c 13.48 ± 0.03 c 1.90
V. tetrasperma 48.87 ± 0.82 e 220.52 ± 2.90 e 67.50 ± 6.23 d 3.81 ± 0.06 e 3.25
V. hirsuta 70.98 ± 1.22 d 267.57 ± 3.37 d 104.44 ± 4.34 b 4.89 ± 0.03 d 4.25
V. tenuifolia 124.00 ± 1.86 b 500.94 ± 6.47 b 113.65 ± 4.22 b 22.83 ± 0.05 b 8.00
V. faba 225.59 ± 2.85 a 724.14 ± 11.93 a 184.12 ± 10.68 a 1269.12 ± 4.82 a 11.90
★Regression with
karyon project area
R 2 = 0.976
P = 0.002
R 2 = 0.8095
P = 0.038
R 2 = 0.852
P = 0.025
R 2 = 0.837
P = 0.029
Notes: Same letter within a column indicates no difference among species at P < 0.05 level. ∗: NA C ̄values cited from Bennett
and Leitch (1995) [27] . ★: Cell projected areaꎬ chromosome projected areaꎬ 1000 ̄seed weight and DNA 1C ̄value are
regressed with karyon project area using a linear modelꎬ respectively.
65 植 物 科 学 学 报 第 33卷
ble 1) showed that the meristematic karyon pro ̄
jected area was significantly correlated with meri ̄
stematic cell projected areaꎬ chromosome pro ̄
jected areaꎬ seed weightꎬ and DNA 1C ̄value.
Additionallyꎬ the correlation between DNA 1C ̄
value and meristematic cell projected area was
significantꎬ while that between DNA 1C ̄value and
seed weight was not significant.
2 2 Mitosis rate
The relationship of the average mitosis rate
with meristematic karyon size is shown in Fig 1.
With the increase in meristematic karyon sizeꎬ the
mitosis rate decreased linearly (P < 0 2) .
y x= 0.027 + 9.039-
r P= 0.6465, < 0.2
0
2
4
6
8
10
12
0 50 100 150 200 250M
ito
si
s
ra
te
(n
um
be
r o
f c
el
ls
un
de
r p
ro
ph
as
e,
m
et
ap
ha
se
,
an
d
an
ap
ha
se
/
to
ta
l c
el
ls
)
Meristematic karyon size (μm )2
Fig 1 Relationship between average mitosis rate and
meristematic karyon projected area of the five Vicia species
2 3 Seedling growth rate
After two weeks cultivationꎬ the ranks of
seedling dry weight of the five Vicia species (Ta ̄
ble 2) were similar to that of their seed weightsꎬ
especially for the treatments at temperatures
higher than 15℃. The absolute seedling growth
rate (namelyꎬ absolute seedling dry weight) of
V. fabaꎬ which had the largest 1000 ̄seed
weightꎬ was the highestꎬ while those of V. tet ̄
rasperma and V. hirsuta with smaller 1000 ̄seed
weights were lower.
Neverthelessꎬ the situation on seeding dry
weight / seed weight (similar to relative seedling
growth rate)ꎬ which reflects competitive ability of
a speciesꎬ was different from absolute seedling
growth rate. For exampleꎬ with the smallest 1000 ̄
seed weightꎬ V. tetrasperma grew quicker than
V. hirsuta under all temperatures except 20℃. We
further analyzed the relationship of relative seed ̄
ling weight with karyon size among the five spe ̄
cies. Interestinglyꎬ the relative seedling weight
was significantly negatively related with karyon
projected area (Fig. 2) .
2 4 Life span and seed production
By May 18ꎬ 2008ꎬ all cultivated plants were
uprooted except V. tenuifolia ( it maintained strong
vegetative growth but did not flower during the
experiments) . In the 154 days of cultivation ( from
December 16ꎬ 2007)ꎬ the mean temperature was
11 72℃ꎬ with a lowest temperature of -2℃ and
highest temperature of 34℃.
The dry weight of V. faba individuals was the
highestꎬ followed by V. sativaꎬ V. hirsutaꎬ and V.
tetrasperma (Table 3). The juvenile period (period
from emergence to flowering) of V. faba (about
96 d) was the shortest. Howeverꎬ its generation
time ( period from emergence to first matured
fruit) was the longest. With the increase in karyon
size ( x)ꎬ their generation time ( y) extendedꎬ
following: y = 0 088x + 127 7 ( r = 0 9731ꎬ P<
0 01) (Fig 3) . The seed number per V. faba in ̄
dividual was about 16ꎬ which was significantly
lower than those of V. sativaꎬ V. Tetraspermaꎬ
and V. hirsuta (Table 3) .
Regression analyses showed that with increa ̄
Table 2 Seedling dry weights of the five Vicia species after cultivation at different temperatures for 14 days (mg)
Species 10℃ 15℃ 20℃ 25℃ 30℃
V. sativa 2.20 ± 0.06 b 4.00 ± 0.06 b 4.66 ± 0.07 b 3.83 ± 0.06 b 2.46 ± 0.05 b
V. tetrasperma 1.26 ± 0.02 c 1.95 ± 0.04 e 2.09 ± 0.04 d 2.21 ± 0.05 d 1.99 ± 0.04 d
V. hirsuta 0.71 ± 0.03 e 1.72 ± 0.03 d 2.10 ± 0.03 d 1.90 ± 0.04 e 1.56 ± 0.04 e
V. tenuifolia 1.12 ± 0.02 d 2.20 ± 0.06 c 3.14 ± 0.05 c 3.21 ± 0.04 c 2.25 ± 0.03 c
V. faba 45.36 ± 0.61 a 69.02 ± 1.64 a 138.95 ± 1.88 a 112.71 ± 2.48 a 90.25 ± 2.57 a
Note: Same letter within a column indicates no difference at the 0.05 level of significance.
75 第 1期 郭水良等: 根尖分生组织细胞核大小: 一个可能用于植物入侵性评估的新指标 (英文)
00.1
0.2
0.3
0.4
0.5
0.6
0.7
40 60 80 100 120 140 160 180 200 220
10°C R P2 = 0.893, = 0.018
15 R2 = 0.954, = 0.004P°C
20 R2 0.= 912, = 0.011P°C
25 R2 = 0.971, = 0.002P°C
30 R2 = 0.943, = 0.006P°C
R
el
at
iv
e
se
ed
in
g
w
ei
gh
t /
s
ee
d
dr
y
w
ei
gh
t (
m
g/
m
g)
Meristematic karyon projected area (μm )2
Regressions are drawn using the Power modelꎬ and relative R 2
and P values are shown.
Fig 2 Relationship between relative seedling weight
(seedling dry weight / seed weight) and meristematic
karyon projected area of the five Vicia species
sing karyon projected area ( x)ꎬ seed number
per individual ( Y1) decreased following Y1 =
-1 8049x + 437 79 (R 2 = 0 8989ꎬ P = 0 05)ꎬ
and seed number per dry weight of an individual
(Y2) decreased following Y2 = 1044 6 ×e-0 0331x
(R 2 = 0 9973ꎬ P = 0 001) (Fig 4).
3 Discussion
Exploring effective assessment models to e ̄
valuate plant invasiveness deserves more atten ̄
tion. Because plant invaders have many similar at ̄
tributesꎬ a robust assessment model needs to in ̄
clude many essential and practical indices. Our
results imply thatꎬ in lieu of DNA C ̄valueꎬ meris ̄
tematic karyon size may be an effective index for
evaluating plant invasiveness.
The species with smaller DNA C ̄valuesꎬ such
as V. tetrasperma and V. sativaꎬ tended to have
small meristematic karyons and cells (Table 1)ꎬ
higher mitosis ( Fig 1 ) and relative seedling
growth rates ( Fig 2)ꎬ developed more quickly
with shorter life spans (Table 3ꎬ Fig 3) and pro ̄
duced more and smaller seeds (Fig 4) .
There is a maximum limit to the mass of DNA
for species that can complete development in a
given time. In any environment where a plant
must complete its life ̄cycle in a given time in or ̄
der to surviveꎬ all reproducing species are cer ̄
tain to have a very low DNA C ̄value[33] . There ̄
foreꎬ short life ̄cyclesꎬ which are related to
small meristematic karyonsꎬ are vital for inva ̄
sive species.
Most plant invaders are considered to be
largely opportunisticꎬ capable of exploiting chan ̄
ging environmental conditions and human or na ̄
tural disturbances[28ꎬ29] . Invasive plants first colo ̄
nize and then persist in their new environmentsꎬ
and later become abundant and dominant com ̄
ponents of the plant community[30] . Producing
many small seeds greatly contributes to the ability
of plant invaders to overcome the difficulties of
long ̄distance distribution and population estab ̄
lishment. Furthermoreꎬ the ability to quickly grow
and develop enables plant species to swiftly uti ̄
lize environmental resources and space.
Based on these attributesꎬ plants with small
meristematic karyons may out ̄grow and out ̄re ̄
produce native species in new habitatsꎬ particu ̄
larly for annuals and biennials. It can be conclu ̄
dedꎬ thereforeꎬ that similar to the effect of the
DNA C ̄valueꎬ lower meristematic karyon size
benefits plant invasiveness.
Table 3 Life spansꎬ seed productionꎬ and dry weights of the four Vicia species
Species DW ( g) PF (d) PM (d) Seed production(seed number / individual)
V. sativa 7.7 ± 0.8 b 106.7 ± 0.5 a 133.5 ± 0.9 b 347.0 ± 30.5 a
V. tetrasperma 1.5 ± 0.1 d 106.4 ± 0.6 a 133.9 ± 0.8 b 312.0 ± 28.9 a
V. hirsuta 2.5 ± 0.2 c 105.6 ± 0.5 a 133.9 ± 0.8 b 290.4 ± 38.9 a
V. faba 27.6 ± 2.9 a 94.4 ± 0.3 b 148.2 ± 0.2 a 16.8 ± 1.9 b
Notes: Same letter within a column indicates no difference among species at the 0.05 level. DW = dry weight of the plant individualꎻ
PF = period from emergence to floweringꎻ PM = period from emergence to generation of a mature legume. V. tenuifolia
maintained strong vegetative growthꎬ but did not flower during the experiments.
85 植 物 科 学 学 报 第 33卷
y x= 0.088 + 127.7
r P= 0.9731, < 0.01
130
135
140
145
150
0 50 100 150 200 250
G
en
er
at
io
n
tim
e
(d
)
Meristematic karyon projected area (μm )2
Regressions are drawn using the linear modelꎬ and relative r
and P values are shown.
Fig 3 Relationship between generation time and
meristematic karyon projected area of the five Vicia species
Y 2 = 1044.6e-0.0331x
R 2 = 0.9973
0
50
100
150
200
250
0 50 100 150 200 250
Meristematic karyon projected area (μm )2
Se
ed
n
um
be
r /
d
ry
in
di
vi
du
al
w
ei
gh
t (
m
g)
Fig 4 Relationship between seed number per dry
individual weight and meristematic karyon
projected area of the Vicia species
Applying the squashing method to prepare
temporary slides for observation of karyon and
cell sizes is a conventional practice. Although the
sizes of karyons or cells may be affected by the
squashing forceꎬ in the present study more than
500 cells were observed in each treatmentꎬ and
thus the cytological differences among different
species were believable.
No single index can be applied to predict all
invasion phenomena. In current plant invasion risk
assessment systemsꎬ such as the Australian
exotic plant risk assessment system[31] and the
Chinese alien plant invasive risk assessment sys ̄
tems[32]ꎬ many indices have been applied to
form an integrated risk value to evaluate the inva ̄
siveness of a focal plant. The objective of the
present work was to find new indices to improve
or enrich the risk assessment index systemꎬ not
to replace existing evaluation indices. This study
showed that plants with small DNA C ̄values sta ̄
tistically had smaller apical meristem karyons and
cellsꎬ high mitosis ratesꎬ smaller seeds with hig ̄
her relative seedling growth ratesꎬ had shorter life
cyclesꎬ and thus tended to be more highly inva ̄
sive. Compared with DNA C ̄valuesꎬ the root
meristem karyon size is relatively easily deter ̄
mined. Thereforeꎬ karyon size is suggested as a
new index in the assessment of plant invasive ̄
ness in lieu of DNA C ̄value.
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(责任编辑: 刘艳玲)
06 植 物 科 学 学 报 第 33卷