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Indian J. Plont Physio/., Vol. XXVII, No.2 pp. 153-158 (April 1984)
OSMOTIC AND IONIC EFFECTS IN SALT SENSITIVE AND
RESISTANT WHEAT VARIETIES
S.K. SHARMA, Y.C. JOSHI AND A.R. BAL
Division of Genetics and Plant Physiology, Central Soil Salinity Research Institute,
Karnal-132 001 (India)
(Revise. : July 7, 1984)
SUMMARY
25 days old seedlings of wheat varieties known for their sensitivity
(HD·4S02) and resistance (Kharchia-65) to saline conditions were exposed
to isosmotic levels of NaCl aDd polyethylene glycol (PEG. 6(00) induced
stress in a hydroponic experiment. NaC1 Proved more inhibitory to growth
of HD-4502 whereas PEG was more deterimental to Kbarchia-6S. The
poor performance of the salt sensitive variety under NaCl was traced to
excessive accumulation of Na and Cl iODs. The better performance of the
salt resistant Kharchia was because of its success in osmotic adjustment
without exposing itself to excess of ions.
INTRODUCTION
Salinity is one of the important factors limiting crop production and most
crops respond to salts as typical glycophytes. Fortunately agricultural crops in
general show marked differences in their ability to grow under saline conditions
and a great variability exists at varietal as wen as species level (Epstein, 1972;
Joshi. 1916; Maas and Hoffman, 1911). However. the reasons for such differen­
ces continue to evade the scientists and are poorly understood. High salts may
reduce plan~ growth by adverse effects on water relations (Bernstein and Hay­
ward, 1958) or by disturbing mineral nutrition of plants and by toxic effects of
ions i.e. specific ion effects (Strogonov, 1964; Levitt, 1972) and these components
might have varying effects in plants differing in salt resistance. An understand­
ing of these causes might expedite breeding programmes by providing rapid
screening methods. The present investigation was undertaken. by subjecting, two
wheat varieties known for their salt resistance and sensitivity, to isosmotic levels
of stress with NaCl and polydhylene glycol (PEG, molecular weight-6,OOO), so
as to know the physiological mechanisms governing their response to salinity.
MATERIALS AND METHODS
Two varieties of wheat viz. HD-4502 (T. durum-salt-sensitive) and Khar­
154
S,K, SHARMA, Y.C, JOSm AND A.R. HAL
chia-65 (T. aestivum-salt resistant) known for differences in salt resistance (Joshi,
1976) were chosen. 25 days old seedlings, grown in sand culture, were transfer­
red to isosmotic solutions of PEG and NaCI in nutrient solution. Plants grown
in nutrient solution only served as control. Leaves and roots were analysed for
Na, K and Cl at 7 and 12 days intervals and growth and osmotic potential were
monitored upto 12 days of the imposition of stress treatments. Na and K were
estima~d by flame photometry, and Cl by AgNOs titration. Osmolarity of the
exprd$sed sap was determined by Wescor 5100C Vapor Pressure Osmometer.
All \!stimations were made in tripJicate.
RESULTS AND DISCUSSION
Stress treatments inhibited growth and the degree of inhibition increased
with duration of stress (Table 0, NaCI was more inhibitory to salt-sensitive HD
4502 whereas PEG proved more deterimental to salt-resistant Kbarchia-65.
Maximum growth inhibition was witnessed in HD-4502 under NaCI treatment
and the differences between varieties widened with time. This growth inhibition
is accompanied by accumulation of Na and Cl ions (Table 2-data for 7 days
stage only are presented since there were no significant changes afterwards), The
two varieties differed in their responses to stress and the mechanisms of injury
also appeared to have different components. Sensitive crops like beans and maize
are known to suffer more in NaCl than isosmotic solution of PEG due to excess
ion accumulation (Lagerwerff, 1969; Gollek, 1973). However, Delane et al.
(1982) and Munns et al. (1982) attributed growth reduction in tolerant barley
variety tQ.water deficits in the growing leaf tissues. Greenway and Munns (1980)
suggested that salt resistant varieties may be more susceptible to water deficits
whereas ionic effects may dominate in the sensitive varieties.
Table 1 : Effect of isosmotic levels of PEG and NaCl (-6 bars) on total dry
matter
Growtb (% control)
12 days
7 days
PEG
NaCI
PEG
NaCl
HD - 4502
88
75
7S
47
Kharcbia - 65
76
86
67
81
Both varieties initially suffered osmotic stress and tended to cope with it
by increasing the osmolarity of roots and leaves through absorption of solutes
(Fig. 1). Excepting Kharchia-65 under PEG, an others would seem to achieve
it successfully. Kbarchia plants growing under PEG, had visual symptoms of
OSMATIC AND IONIC EFFECT ON WHEAT
Leaves
~
-'
155
.. --------.
.."....,
//
/
......,
L
f
'600
pr---b.-- -. __
'-/. ~.,.
,,"/'
II
,"
I
I
I
ca
~
D---~~~
I
II
- ---b.
H0 - 4502 PEG
---. HD-4502 NaCI
"
~
Kharchia-65 PEG
- . Kharchia-65 NaCI
--0
'0 200
E
E
~
...
:!:
o
"0
E
400
fI)
.----.
o
•
'.~
__-"
Roots
/ ."..-­
300
.&.
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....... --­
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/.
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200
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O~--~----~----~--~----~--~
Days after stress imposition (-6bars)
156
S.K. SHARMA, V.C. JOSHI AND A.R. BAL
wilting indicating their inability to absorb water. Low values of osmolarity in
roots as well as leaves would seem to support it (Fig. 1). This was due to the
absence of inorganic ions in the medium which otherwise could. have been used
for this purpose and is also indicated by low content of Na, K and Cl. Osmotic
adjustment and turgor potentia] maintenance are known to be accomplished by
the uptake of ions, chiefly K+, Na+ and Cl-. and by synthesizing water soluble
substances such as organic acids, amino acids, sugars and po]yols (Hellebust,
1976; Wyn Jones and Gorham, 1981; and others). Under NaC} both varieties
could absorb water initially but HD.4502 suffered later whereas Kharchia-65
could still perform better.
Poor growth of HD-4502 could be due to its inability to regulate osmotic
adjustment which subsequently caused excess ion accumulation as a result of
high Na and CI contents (Table 2). Gradually symptoms of ion injury become
evident on the leaves of such plants. High ion concentrations have been suggested
to be responsible for injury in species of glycine, vines and cotton (Wi1son et 01.,
1970, Ehlig; 1960 and Richards; 1954). On the other hand, Kharchia-65 restric­
ted ion entry firstly by absorbing less Na and Cl and then further retaining most
of Na and some of the C] also in its roots besides maintaining K content. This
facilitated water absorption in addition to preventing build up of ions. Thus,
the two varieties showed marked differences in uptake of ions by the roots, and
also in the proportion of the absorbed Na being translocated to the leaves. This
could also be due to the differences in the maintenance of root membrane
permeability in these varieties, wherein Kharchia allowed minimal change in
membrane permeability (Dwivedi et. 01., 1980. However, Lauchliand Wieneke
(1979) found no differences in ion concentration in soybean varieties differing in
salt resistance, although they differed in the proportion of absorbed C]- being
translocated. It remains to be seen whether Kharchia, uses some organic com­
pounds for osmotic adjustment although our earlier work has shown that it
JrIaintains higher content of organic acida as compared to HD-4502 (Sharma et.
01., 1981).
These results suggest that NaC] caused growth inhibition in the salt-sensi­
tive variety, is due to excessive ion uptake whereas in case of Kharchia SUbjected
to PEG stress, is due to osmotic stress. This strengthens the views of Green­
way and Munns (1980) that the mechanism of salt injury differs in salt-sensitive
and resistant varieties. Their performance depend upon success in achieving
osmotic adjustment without being exposed to ion excess.
ACKNOWLEGEMENT
The authors are thankful to Dr. J.S.P. Yadav, the former Director, and
at present Chairman, A.S.R.B., New Delhi, and Dr. R.K. Bhattacharyya,
0.25
0.78
0.21
0.80
0.08
0.88
1.33
0.13
0.15
0.68
PEG
NaCl
CD (P...O.OS) 0.05
0.10
0.21
0.29
1.78
Cl
0.18
K
Normal
Na
Shoot
Na
0.30
0.33
1.53
0.07
Cl
0.33
0.28
1.07
0.07
K
0.83
0.63
0.50
0.04
Root
0.11
0.66
0.83
1.88
Shoot
K
0.04
1.24
0.30
0.32
Cl
0.09
0.50
0.20
0.38
Na
HD·4502
0.12
0.73
0.45
1.13
K
Root
Table 2: Na and Cl content (% dry wt.) of Kh-65 and HD-4502 under isosmotic levels of stress (-6 bars)
0.07
0.90
0.48
0.45
Cl
\I>
0
~
-
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~
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~
~
~
n
~
Z
n
1:1
0
Z
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n
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-'"'
--
s::
;:aiI
]58
S.K. SHARMA, Y.C. JOHSI AND A.R. BAL Head of the Division for providing necessary facilities and encouragement. REFERENCES Bernstein, L. and Hayward, H.E. (1958). Physiology of Salt tolerance. Ann. Review PI. PhY4
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