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Australian
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Aust. J. Bot., 2002, 50, 163–169

Effects of sodium, magnesium and calcium salts
on seed germination and radicle survival of a halophyte,
Kalidium caspicum (Chenopodiaceae)
Kazuo TobeAD, Xiaoming LiB and Kenji OmasaC
A

Laboratory of Intellectual Fundamentals for Environmental Studies, National Institute for Environmental Studies,
16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
B
Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, 40 South Beijing Rd,
Urumqi, Xinjiang 830011, People’s Republic of China.
C
Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo,
Tokyo 113-8657, Japan.
D
Corresponding author; email: tobe@nies.go.jp

BT01065
eKE.tfoaTeblct.es,oXf.diLfaenrdKt.saOlmtsoasnradiclesurvial

Abstract. Kalidium caspicum (L.) Ung.-Sternb. is a common species of highly saline habitats of north-western
China, which in previous germination research has been shown to be rather sensitive to NaCl toxicity. To investigate
the effects of different salts on the seed germination and radicle survival of this halophytic shrub, seeds wereincubated in various salt (NaCl, Na2SO4, MgCl2, or MgSO4 with or without CaCl2) or polyethylene glycol-6000
solutions. The germination percentage and the percentage of emerging radicles surviving to a length of at least
4 mm were examined. The survival of K. caspicum radicles depended mainly on the cation composition of themedia: both Na+ and Mg2+ had toxic effects on the radicles, while Ca2+ alleviated the toxicity of these cations. Mg2+
was more toxic than Na+ and a higher concentration of Ca2+ was needed to alleviate its toxicity. It was suggested
that the establishment of seedlings of K. caspicum in the field is facilitated by the marked alleviation of salt toxicity
by Ca2+ and that the proportion of soluble Na, Mg and Ca ions in the soil determines the distribution of K. caspicumin the field.

Introduction
Kalidium caspicum (L.) Ung.-Sternb. (Chenopodiaceae) is astem-succulent halophytic shrub distributed in highly saline
locations in the desert regions of north-western China(Lanzhou Institute of Desert Research 1985). In a previous
study (Tobe et al. 2000a), we reported that the radicles of
K. caspicum were very sensitive to NaCl toxicity and thatmost of them were killed in media with NaCl concentrations
at which the radicles of many halophytic and non-halophytic
species survive. This unexpected result encouraged us to
examine more closely the effects of salinity on K. caspicum
radicles.
Saline soils contain multiple salt constituents that may
have different physiological effects on plant tissues. The
main salt components in saline soils are Na+, Mg2+ and Ca2+
cations and Cl– and SO42– anions (Shainberg 1975).
However, many studies examining the effects of salinity on
plants have been carried out with only Na salts or dilutionsof sea water and only a few (e.g. Younis and Hatata 1971;
Redmann 1974; Janzen and Chang 1987; Hardegree andEmmerich 1990; Pujol et al. 2000) have compared the effects© CSIRO 2002of Na, Mg and other salts on the germination or growth ofplants. Since the effects of salinity on the radicles of
K. caspicum are mainly salt-specific (Tobe et al. 2000a),different salt components in saline soils may have different
effects on radicle survival. Therefore, to understand theestablishment of this species in saline areas, we need toinvestigate the responses of its radicles to each of these salt
components.
It is well known that Ca2+ alleviates the adverse effects of
NaCl on many plant species (Jennings 1976; Greenway andMunns 1980; Rengel 1992; Marschner 1995). Adding Ca2+
to root media with NaCl favours plant growth in both
halophytic (Colmer et al. 1996) and non-halophytic species(LaHaye and Epstein 1969; Cramer et al. 1986; Kurth et al.
1986; Suhayda et al. 1992; Kinraide 1999). However, little is
known about the interaction of Ca2+ with Mg salts, which areoften abundant in saline soils. Furthermore, the implicationsof the effects of Ca2+ on the establishment of species in saline
areas are not clear. It is possible that the establishment of
K. caspicum in saline areas is facilitated by the alleviation ofsalt toxicity to its radicles by the Ca2+ present in saline soils.
10.1071/BT01065

0067-1924/02/02163

164

The objectives of this study were to investigate (1) how
different salts act on K. caspicum radicles and (2) whether
Ca2+ ameliorates the responses of K. caspicum radicles to Na
and Mg salts. We compared the effects of NaCl, Na2SO4,
MgCl2, MgSO4 and CaCl2 on seed germination and radicle
survival and examined the effects of low concentrations of
CaCl2 on the response of the radicles to a Na or Mg salt. To
evaluate the osmotic effects of the medium on seeds andradicles, we also examined seed and radicle responses tosolutions of polyethylene glycol (PEG)-6000, which cannot
permeate plant cell walls (Carpita et al. 1979) and acts solely
as an osmoticum on seeds and radicles (Sharma 1973;
Redmann 1974; Hardegree and Emmerich 1990). The
laboratory results were related to the composition of soluble
salts at 90 saline locations in China to understand how salt
composition in the soil might affect the establishment of
K. caspicum in saline areas.
Materials and methods
Materials
Seeds of K. caspicum [seed weight: 171 ± 45 µg (mean ± s.d.; n = 20)]
were collected in November 1996 from plants growing on saline soil in
Fukang, China (44°18′N, 87°55′E). The annual precipitation andannual mean temperature in Fukang are 172 mm and 6.1°C (meansfrom 1958 to 1980). Seeds were initially stored at about 5°C in the dark
until being transported to Japan in March 1997. In Japan, the seeds werestored at c. –18°C in the dark. During this storage period, seedgerminability was assayed at times by incubating the seeds with
deionised water at 20°C in dark and we found neither an indication ofseed dormancy nor a reduction of seed germinability. The germination
experiments were carried out during the period from September 2000 to
February 2001.

K. Tobe et al.

concentration in the dish constant. The seeds were considered to havegerminated when the radicles emerged. After 15 days of incubation, we
determined the final germination percentage (GF) and the final
percentage of seeds with radicles longer than 4 mm (SF); the survival
percentage of radicles was evaluated as (SF/GF) × 100. Each treatment
was replicated four times.
To statistically test the difference between two means, the Student’s
t-test was used. For comparison of multiple means, one-way ANOVA
and Tukey’s tests were used. Percentage values were arcsine
transformed before statistical analysis. All statistical tests wereconducted at P = 0.05.

Results
Effects of individual salts and PEG on germination andradicle survival
When K. caspicum seeds were moistened with deionised
water, or a solution of a salt (NaCl, Na2SO4, MgCl2, MgSO4,
or CaCl2) or PEG, the percentages of both germinated seeds
and seeds with emerging radicles longer than 4 mm reachedmaximum levels after 15 days (Fig. 1).
For all salt treatments, GF was higher than 50% at a totalion (cation + anion) concentration (TIC) <540 mmol kg–1,
but varied between 4% (NaCl) and 61% (MgSO4) at a TIC of
720 mmol kg–1 (Fig. 2). In contrast, SF decreased markedly
at a relatively low TIC for both Na and Mg salts but was highat a wide range of TICs for CaCl2 treatments. When seeds
were treated with a Na salt of TIC >120 mmol kg–1 or with a
Mg salt of TIC >12 mmol kg–1, some or most of theemerging radicles died before their lengths exceeded 4 mm.
In these solutions, most radicles, including those elongatedMethods

100

75

Percentage

Twenty-five seeds were sown on three layers of filter paper (Toyo,
no. 1) in a 90-mm plastic Petri dish. The filter paper was moistenedwith about 10 mL of deionised water, a salt solution (NaCl, Na2SO4,
MgCl2 or MgSO4 with or without CaCl2, or CaCl2 alone) or a PEG6000 solution of known water potential. The concentrations of the salt
solutions and the water potentials of the PEG solutions used were
determined from the results of preliminary experiments so as to makethe results clearly indicate the dependence of seed germination andradicle survival on salt concentrations. About half the volume of eachseed was immersed in the solution. Each salt solution was prepared bydissolving a commercial reagent-grade salt in deionised water and the
PEG solution of known water potential was prepared according to acalibration curve that was determined from isopiestic psychrometer(Boyer and Knipling 1965) measurements at 20°C. The Petri dishes
were covered with lids and the seeds were incubated for 15 days.
Because seeds of K. caspicum germinate most favourably in the dark
and at 20°C (Tobe et al. 2000a), all the experiments were carried out
under these conditions.
The seeds were observed daily in dim light through a magnifying
glass with a scale; the numbers of both germinated seeds and seeds withradicles longer than 4 mm were counted and seeds with radicles longer
than 4 mm were discarded. About two-thirds of the volume of thesolution in each Petri dish was replaced daily with the treatment
solution to avoid a change in the solute concentration of the solution;
because no decrease in the volume of solution in each dish caused byevaporation or seed water uptake was detectable, the daily solution
replacement would have sufficed for maintaining the solute

50

25

0
0

5

10

15

Days after moistening
Fig. 1. Changes over time in the percentage of germinated seeds(closed symbols connected with solid lines) and seeds with emerging
radicles longer than 4 mm (open symbols connected with dottedlines) for the following treatments: deionised water (, ), 60 mmol
kg–1 NaCl (, ), 240 mmol kg–1 NaCl () and 360 mmol kg–1 NaCl(). The percentages of seeds with emerging radicles longer than
4 mm for 240 and 360 mmol kg–1 NaCl treatments were zerothroughout 15 days and the data were not indicated. Each point
represents the mean of four replications.

Effects of different salts on radicle survival

165

Fig. 2. Effect of total ion (cation + anion) concentration (TIC) of single salts and water potential of PEG on final germination
percentage (GF, ) and final percentage of seeds from which radicles longer than 4 mm emerged (SF, ). Calculated from van’t Hoff’slaw, the lowest water potential in the horizontal axis for PEG (–1.73 MPa) is isotonic to 720 mmol kg–1 TIC. Each point represents themean of four replications; bars indicating s.e. are shown only where s.e. is larger than point size.

beyond 4 mm, were dark brown and had an unhealthy
appearance. In contrast, with the CaCl2 treatment, more than
90% of the emerging radicles elongated beyond 4 mm at a
TIC < 360 mmol kg–1. Although some radicles remained
shorter than 4 mm at a TIC > 540 mmol kg–1, they appeared
healthy. PEG-treated seeds showed high survival percentages
at a water potential higher than –0.8 MPa; some or mostradicles remained shorter than 4 mm at water potentials

lower than –1.2 MPa but appeared healthy. The similarity inthe response of CaCl2-treated seeds to that of PEG-treatedseeds suggests that suppression of SF at higher CaCl2
concentrations resulted mainly from osmotic inhibition of
the medium and that the toxic effect of Ca2+ or Cl– on theradicles, if any, was rather small even at relatively highconcentrations. On the other hand, the unhealthy appearanceof radicles treated with a Na or Mg salt at high166

K. Tobe et al.

concentrations was clearly distinguishable from the healthy
appearance of radicles treated with CaCl2 or PEG. Thus, theadverse effects of a Na or Mg salt on radicles are most likely
attributed to salt-specific toxicity. These results also suggest
a close relationship between salt toxicity and cation.
To investigate the relationships between cation
concentration and radicle survival, the survival percentage of
emerging radicles [(SF/GF) × 100, %] was plotted against the
cation concentrations for Na and Mg salts at a range of
0–80 mmol kg–1 (Fig. 3). This plot indicates that Mg2+ had
toxic effects on the radicles at concentrations several times
lower than those for Na+. At given Mg2+ concentrations,
MgCl2 and MgSO4 had essentially the same suppressive
effect on the survival percentage. Because we expected thatCl– would have none or very little toxicity to the radicles, thetoxicity of Mg salts can be attributed mostly to the Mg2+. For
similar reasons, the toxicity of the Na salts would be
expected to originate largely from the presence of Na+.
However, the survival percentage of radicles was smallerwith Na2SO4 than with NaCl treatments, although the TIC at
a given Na+ concentration was c. 1.3 times higher in NaClthan in Na2SO4 solutions. This suggests that SO42– either had
toxic effects on radicles or intensified the toxic effects of Na+
on the radicles.
Interactive effects of CaCl2 and other salts on radicle
survival
To investigate whether Ca2+ alleviates the toxic effects of Na
and Mg salts, we examined the survival percentages ofradicles in various salt solutions with or without 1.0 mmol
kg–1 CaCl2 (Table 1). In this experiment, the salt concentrationin each solution was that at which the SF approached zero
without Ca2+ in the solution. Thus, the salt concentration in

Survival percentage

100

75

50

25

0
0

20

40

60

80
-1

Cation concentration (mmol kg )Fig. 3. Dependence of the survival percentage [(SF/GF) × 100, %] ofKalidium caspicum radicles treated with a Na or Mg salt on the cation
concentration in each solution. Each point represents the mean of four
replications; bars indicating s.e. are shown only where s.e. is larger
than point size. NaCl (), Na2SO4 (), MgCl2 (), MgSO4 ().

Table 1. Effect of 1.0 mmol kg–1 Ca2+ on the germination
percentage (GF) and survival percentage [(SF/GF) × 100, %] ofKalidium caspicum radicles treated with different salts
Data are the means of four replications, s.e. is indicated in parentheses.
TIC, total ion (cation + anion) concentration
Salt in the medium

0 mmol kg–1 Ca2+
1.0 mmol kg–1 Ca2+
GF (%) Survival (%) GF (%) Survival (%)

80 mmol kg–1 NaCl
95 (1.0)(TIC = 160 mmol kg–1)
40 mmol kg–1 Na2SO4 93 (3.0)(TIC = 120 mmol kg–1)
98 (1.2)
12 mmol kg–1 MgCl2(TIC = 36 mmol kg–1)
12 mmol kg–1 MgSO4 95 (2.5)(TIC = 24 mmol kg–1)
88 (2.8)80 mmol kg–1 KCl(TIC = 160 mmol kg–1)

6 (1.2)

97 (1.9) 100 (0)0 (0)94 (2.0)98 (1.2)

4 (3.0)92 (1.6)

97 (1.1)

6 (6.0)95 (1.9)99 (1.0)

17 (4.3)

89 (4.1)

99 (1.0)

each solution was relatively low and the GF was high in alltreatments. Also KCl was incorporated in this examination(Table 1) and we found that its toxicity was slightly less thanthat of NaCl [SF for KCl was significantly higher than that for
NaCl at P = 0.05 (Student’s t-test)]. Therefore, CaCl2
alleviated the toxic effects of salts on radicles for all tested
salts; while the survival percentage was less than 17% in theabsence of CaCl2, it exceeded 90% in all the solutions with
1.0 mmol kg–1 CaCl2. All of the radicles that emerged insolutions without CaCl2 had an unhealthy appearance, but
most radicles emerging in solutions containing 1.0 mmol kg–1
CaCl2 were healthy and continued to elongate beyond 4 mm.
Because the addition of a small amount of CaCl2 to, forexample, an 80 mmol kg–1 NaCl solution (causing a verysmall increase in the proportion of Cl– in the solution)markedly improved the survival percentage of radicles, weconsidered that the alleviatory effect of CaCl2 on salt toxicity
resulted from the action of Ca2+.
To examine whether Ca2+ alleviates the toxic effects of salts
at much higher concentrations and to investigate therelationship between the alleviatory effect of Ca2+ and the salt
composition in the solution, we examined the survival
percentage of radicles in solutions with higher concentrationsof NaCl or MgCl2 to which various concentrations of CaCl2
had been added (Tables 2, 3). The final germination
percentage (GF) was not dependent on Ca2+ concentrations ateither concentration of NaCl or MgCl2 (ANOVA, P = 0.05),
but the survival percentage depended on Ca2+ concentrations
for both concentrations of NaCl or MgCl2 (ANOVA,P = 0.05). For both NaCl and MgCl2 treatments, the survival
percentages were higher at higher concentrations of Ca2+. For
NaCl treatments, the survival percentages were high at Ca2+
concentrations higher than 1.0 mmol kg–1 (Table 2). At
120 mmol kg–1 NaCl, most radicles were healthy at Ca2+
concentrations higher than 1.0 mmol kg–1 (ratio Ca2+ : Na+ =0.0083); however, at 240 mmol kg–1 NaCl, most radicles were

Effects of different salts on radicle survival

167

Table 2. Dependence of the germination percentage (GF) and survival percentage [(SF/GF)
× 100, %] of Kalidium caspicum radicles treated with 120 or 240 mmol kg–1 NaCl on Ca2+
concentration in the medium
In each column, the values followed by the same letter are not significantly different from eachother at P = 0.05 (Tukey’s test). Data are the means of four replications, s.e. is indicated inparentheses
Ca2+ concentration(mmol kg–1)

120 mmol kg–1 NaCl
GF (%)
Survival (%)

240 mmol kg–1 NaCl
GF (%)
Survival (%)

0.2
1.0
5.0

89a (7.6)
90a (2.6)
85a (3.8)70a (2.6)
72a (4.9)
59a (4.4)70a (5.5)99b (1.1)
99b (1.2)

3a (1.7)80b (7.3)
97b (1.8)

Table 3. Dependence of the germination percentage (GF) and survival percentage [(SF/GF)
× 100, %] of Kalidium caspicum radicles treated with 60 or 120 mmol kg–1 MgCl2 on Ca2+
concentration in the medium
In each column, the values followed by the same letter are not significantly different from eachother at P = 0.05 (Tukey’s test). Data are the means of four replications, s.e. is indicated inparentheses
Ca2+ concentration(mmol kg–1)

60 mmol kg–1 MgCl2
GF (%)
Survival (%)

120 mmol kg–1 MgCl2
GF (%)
Survival (%)

1.0
5.0
25

93a (2.5)
92a (3.7)
87a (1.9)

88a (1.6)
87a (3.4)
85a (1.9)

Salt composition in the field and its implication for theestablishment of K. caspicum
To relate the results obtained above to field conditions, weinvestigated the composition of soluble salts near the soil

0a (0)
13b (2.7)76c (10.8)

surface at 90 different saline locations in arid regions ofChina, on the basis of data from Wang et al. (1993) that
presented the concentrations of Na + K, Mg and Ca in thesoil at each location. The ratios of Ca : (Na + K) and Ca : Mg
near the soil surface were calculated for each saline location(Fig. 4). The mean ratios of Ca : (Na + K) and Ca : Mg were0.033 and 0.32, respectively. The data showed that the100

Ca / (Na + K) (mol / mol)healthy only at 5.0 mmol kg–1 (Ca2+ : Na+ = 0.021), and, at 1.0mmol kg–1 (Ca2+ : Na+ = 0.0042), many radicles appeared
unhealthy even though their lengths exceeded 4 mm. The
adverse effect of Mg2+ on radicle survival was alleviated bya concentration of Ca2+ that was about 10 times higher thanthat for Na+ (Table 3). For the 60 mmol kg–1 MgCl2 treatment,
the survival percentage was high and most radicles were
healthy only at 25 mmol kg–1 Ca2+ (Ca2+ : Mg2+ = 0.42). At
120 mmol kg–1 MgCl2, 25 mmol kg–1 Ca2+ (Ca2+ : Mg2+
= 0.21) did not suffice to completely recover the high survival
percentage and some radicles appeared unhealthy. When thisresult is compared with the 12 mmol kg–1 MgCl2 treatment(Table 1), in which 1.0 mmol kg–1 Ca2+ (Ca2+ : Mg2+ = 0.083)
sufficed to alleviate the Mg2+ toxicity, it is seen that a higher
Ca2+ : Mg2+ ratio is needed to alleviate the toxicity of higher
concentrations of Mg2+.
The results indicate that a high proportion of Mg2+ and/or
a lower proportion of Ca2+ in the medium jeopardises thesurvival of K. caspicum radicles. We roughly estimated fromthe results (Tables 1–3) that the required ratios forK. caspicum radicles to elongate beyond 4 mm without anindication of unhealthy appearance are Ca2+ : Na+ > 0.01 andCa2+/Mg2+ > 0.1.

3a (2.1)
79b (8.4)
96c (1.8)

10
1
0.1
0.01
0.001
0.00010.00001
0.01

0.1

1

10

100

Ca / Mg (mol / mol)Fig. 4. The ratios of Ca : (Na + K) and Ca : Mg near the soil surface
at 90 saline locations in arid regions of China [data from Wang et al.
(1993)]. Each point () corresponds to a location. For reference, thevalue for sea water is shown by the symbol ().

168

composition of cations in the soil varied greatly amonglocations. Because the toxicity of K is similar to that of Na(Table 1) and the concentration of K is usually much smaller
than that of Na, the value Ca : (Na + K) can be regarded as
Ca : Na as far as the toxicity to K. caspicum radicles isconcerned. Then, two-thirds of the locations fulfill the above
requirement (Ca : Na >0.01 and Ca : Mg >0.1) for survival of
K. caspicum radicles.
Discussion
Effects of different salts on the initial developmental stage ofplants
The toxicity of Na and Mg salts to K. caspicum radicles was
attributed mainly to the cations. The fact that the toxic effectsof Na+, Mg2+ and K+ on radicles were alleviated by Ca2+
suggests that the toxicity of different salts to radicles
originated from a common mechanism. The radicles treatedwith a Na or Mg salt of a relatively higher concentration in
the absence of Ca2+ showed an unhealthy appearance, which
was clearly different from that of the radicles inhibited
osmotically from elongating by PEG. Thus, the adverse
effects of a Na or Mg salt on radicle survival would not
originate mainly from the inhibition of cell extension.
According to some researchers (Cramer et al. 1985; Kent
and Läuchli 1985; Marschner 1995), the toxicity of salt toplant tissues is attributable to the displacement of Ca2+
bound to the external surface of the plasma membrane ofplant cells with metal cations and the subsequent impairmentof the integrity and permeability of plasma membrane, andCa2+ in the external medium restores the cation-displaced
Ca2+ on the membrane. This explanation seems to be
applicable to the interpretation of the interactive effects ofNa, Mg and Ca salts on K. caspicum radicles. The fact that
CaCl2 caused a much smaller adverse effect on the survivalof K. caspicum radicles than Na and Mg salts would be dueto the fact that CaCl2 treatment did not cause thedisplacement of membrane-bound Ca2+ with other cations.
Higher toxicity and a higher requirement of Ca2+ for toxicity
alleviation in Mg2+ than in Na+ or K+ would reflect the higher
displacement ability of Mg2+ compared with that of Na+ or
K+ with Ca2+ bound to the surface of plasma membrane. Thismay be because Mg2+, which has the same valence as Ca2+
and a hydrated ionic radius similar to that of Ca2+, is more
replicable to membrane-bound Ca2+ than is Na+ or K+.
The toxic effects of salt on seed germination have beenreported in many halophytic and non-halophytic species(Redmann 1974; Bal and Chattopadhyay 1985; Bliss et al.
1986; Hardegree and Emmerich 1990; Katembe et al. 1998;
Tobe et al. 1999, 2001). However, these reports are based on
germination experiments with single salt components(especially NaCl). It is possible that Ca2+, which exists moreor less in saline soils, can alleviate salt toxicity to the seedgermination of these species. Thus, germination experiments

K. Tobe et al.

with a single salt component may not always simulate theseed germination behaviour of species in the saline field.
Distribution of species in saline soils
Seedlings are the most vulnerable stage in the life cycle ofplants (Kigel 1995) and adaptation of plants to salinity at theearly developmental stage is crucial in facilitating the
distribution of species in saline areas (Ungar 1991, 1995). In
this study, we investigated the effects of salt composition in
the media on seed germination and radicle survival of a
halophyte K. caspicum and, as a result, suggest that Ca2+
plays a critical role in allowing the establishment of
K. caspicum in saline areas. Seeds treated with a Na or Mg
salt demonstrated a high germination percentage in a wide
range of salt concentrations, but, in the absence of Ca2+, all
the emerging radicles were killed except at very low salt
concentrations. This indicates that seed germination in Na or
Mg salts without Ca2+ results in the death of a very highproportion of radicles. The toxicity of Mg salts was muchhigher than that of Na salts and a higher concentration of
Ca2+ was needed to alleviate the toxicity of Mg salts
compared with that of Na salts. From this result, weconcluded that the proportion of soluble Na, Mg and Ca in
the soil determines whether or not K. caspicum can become
established in saline areas. As a criterion for the survival of
K. caspicum radicles, we tentatively proposed ratios of
Ca2+ : Na+ > 0.01 and Ca2+ : Mg2+ > 0.1. However, thiscriterion was based on only a very early stage ofdevelopment and a higher proportion of Ca2+ may be needed
for the successful establishment of this species in saline
areas.
The seedlings or radicles of some halophytic and nonhalophytic species have been shown to continue to grow in
up to 200–400 mmol kg–1 NaCl in the absence of Ca2+ (Khanand Ungar 1984; Khan and Rizvi 1994; Tobe et al. 1999,
2001). Furthermore, in two Haloxylon species distributed in
the same region as K. caspicum, the radicles continued toelongate without suffering from salt toxicity in a medium
with a NaCl concentration higher than 650 mmol kg–1 andwithout the addition of Ca2+ (Tobe et al. 2000b). In contrast,
K. caspicum radicles were very sensitive to Na and Mg salts
without Ca2+. For example, at 80 mmol kg–1 NaCl, only 6%of the radicles survived beyond 4 mm. Kalidium caspicum isdistinguished by its absolute requirement for Ca2+ for radicle
survival in saline media. We have also found that the toxic
effect of salt on seed germination of several non-halophytic
species is markedly alleviated by the addition of Ca2+
(K. Tobe, unpubl. data). Moreover, Bliss et al. (1986) foundthat Ca2+ alleviates NaCl toxicity in the germination(plumule emergence) of barley seeds. Thus, some species
require external Ca2+ to become established in saline soils,
while others do not. The reason for this interspecificdifference in a Ca2+ requirement is unknown, but theseresults suggest that the proportion of Ca2+ in the soil in a

Effects of different salts on radicle survival

169

saline location can be an important factor determining which
species dominate.
References
Bal AR, Chattopadhyay NC (1985) Effect of NaCl and PEG 6000 on
germination and seedling growth of rice (Oryza sativa L.). Biologia
Plantarum 27, 65–69.
Bliss RD, Platt-Aloia KA, Thomson WW (1986) The inhibitory effectof NaCl on barley germination. Plant, Cell and Environment 9,727–733.
Boyer JS, Knipling EB (1965) Isopiestic technique for measuring leaf
water potentials with a thermocouple psychrometer. Proceedings of
the National Academy of Science USA 54, 1044–1051.
Carpita N, Sabularse D, Montezinos D, Delmer DH (1979)
Determination of the pore size of cell walls of living plant cells.
Science 205, 1144–1147.
Colmer TD, Fan TW-M, Higashi RM, Läuchli A (1996) Interactive
effects of Ca2+ and NaCl salinity on the ionic relations and proline
accumulation in the primary root tip of Sorghum bicolor.
Physiologia Plantarum 97, 421–424.
Cramer GR, Läuchli A, Polito VS (1985) Displacement of Ca2+ by Na+from the plasmalemma of root cells. A primary response to salt
stress? Plant Physiology 79, 207–211.
Cramer GR, Läuchli A, Epstein E (1986) Effects of NaCl and CaCl2 on
ion activities in complex nutrient solutions and root growth ofcotton. Plant Physiology 81, 792–797.
Greenway H, Munns R (1980) Mechanisms of salt tolerance innonhalophytes. Annual Review of Plant Physiology 31, 149–190.
Hardegree SP, Emmerich WE (1990) Partitioning water potential andspecific salt effect on seed germination of four grasses. Annals of
Botany 66, 587–595.
Janzen HH, Chang C (1987) Cation nutrition of barley as influenced bysoil solution composition in a saline soil. Canadian Journal of Soil
Science 67, 619–629.
Jennings DH (1976) The effects of sodium chloride on higher plants.
Biological Review 51, 453–486.
Katembe WJ, Ungar IA, Mitchell JP (1998) Effect of salinity on
germination and seedling growth of two Atriplex species(Chenopodiaceae). Annals of Botany 82, 167–175.
Kent LM, Läuchli A (1985) Germination and seedling growth ofcotton: salinity–calcium interactions. Plant, Cell and Environment
8, 155–159.
Khan MA, Rizvi Y (1994) Effect of salinity, temperature, and growth
regulators on the germination and early seedling growth of Atriplex
griffithii var. stocksii. Canadian Journal of Botany 72, 475–479.
Khan MA, Ungar IA (1984) The effect of salinity and temperature on
the germination of polymorphic seeds and growth of Atriplex
triangularis Willd. American Journal of Botany 71, 481–489.
Kigel J (1995) Seed germination in arid and semiarid regions. In ‘Seeddevelopment and germination’. (Eds J Kigel, G Galili) pp. 645–699.
(Marcel Dekker: New York)Kinraide TB (1999) Interactions among Ca2+, Na+ and K+ in salinity
toxicity: quantitative resolution of multiple toxic and ameliorative
effects. Journal of Experimental Botany 50, 1495–1505.

Kurth E, Cramer GR, Läuchli A, Epstein E (1986) Effects of NaCl and
CaCl2 on cell enlargement and cell production in cotton roots. Plant
Physiology 82, 1102–1106.
LaHaye PA, Epstein E (1969) Salt toleration by plants: enhancementwith calcium. Science 166, 395–396.
Lanzhou Institute of Desert Research (1985) ‘Desert flora of China,
vol. 1.’ (Science Press: Beijing)
Marschner H (1995) ‘Mineral nutrition of higher plants.’ 2nd Edn.
(Academic Press: London)
Pujol JA, Calvo JF, Ramírez-Díaz L (2000) Recovery of germinationfrom different osmotic conditions by four halophytes fromsoutheastern Spain. Annals of Botany 85, 279–286.
Redmann RE (1974) Osmotic and specific ion effects on thegermination of alfalfa. Canadian Journal of Botany 52, 803–808.
Rengel Z (1992) The role of calcium in salt toxicity. Plant, Cell andEnvironment 15, 625–632.
Shainberg I (1975) Salinity of soils—Effects of salinity on the physics
and chemistry of soils. In ‘Plants in saline environments’. (Ed.
J Gale) pp. 39–55. (Springer-Verlag: Berlin)
Sharma ML (1973) Simulation of drought and its effect on germinationof five pasture species. Agronomy Journal 65, 982–987.
Suhayda CG, Redmann RE, Harvey BL, Cipywnyk AL (1992)
Comparative response of cultivated and wild barley species tosalinity stress and calcium supply. Crop Science 32, 154–163.
Tobe K, Zhang L, Omasa K (1999) Effects of NaCl on seed germinationof five nonhalophytic species from a Chinese desert environment.
Seed Science and Technology 27, 851–863.
Tobe K, Li X, Omasa K (2000a) Seed germination and radicle growthof a halophyte, Kalidium caspicum (Chenopodiaceae). Annals of
Botany 85, 391–396.
Tobe K, Li X, Omasa K (2000b) Effects of sodium chloride on seedgermination and growth of two Chinese desert shrubs, Haloxylon
ammodendron and H. persicum (Chenopodiaceae). Australian
Journal of Botany 48, 455–460.
Tobe K, Zhang L, Qiu GY, Shimizu H, Omasa K (2001) Characteristics
of seed germination in five non-halophytic Chinese desert shrub
species. Journal of Arid Environments 47, 191–201.
Ungar IA (1991) ‘Ecophysiology of vascular halophytes.’ (CRC Press:
Boca Raton)
Ungar IA (1995) Seed germination and seed-bank ecology inhalophytes. In ‘Seed development and germination’. (Eds J Kigel,
G Galili) pp. 599–628. (Marcel Dekker: New York)Wang Z, Zhu S, Shu R, Li L, Dan G, You W, Zeng X, Zhang C, Zhang
L, Song R (1993) ‘Saline soils in China.’ (Science Press: Beijing)
Younis AF, Hatata MA (1971) Studies on the effects of certain salts ongermination, on growth of root, and on metabolism. I. Effects ofchlorides and sulfates of sodium, potassium and magnesium on
germination of wheat grains. Plant and Soil 34, 183–200.

Manuscript received 2 August 2001, accepted 3 December 2001

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