Abstract Studies to determine the role of proline, K/Na ratio and chlorophyll contents in salt tolerance of wheat genotypes were conducted in lysimeters using hydroponics technique. Seeds were allowed to germinate under normal condition (1.5 dS m -1 ) and salinity treatment of 12 dS m -1 was imposed after one week of germination. Crop was irrigated at the interval of two weeks or whenever required with 1/4 th Hoagland nutrient solution of respective concentrations. Results clearly indicated that wheat genotypes with higher proline, K/Na ratio and chlorophyll contents had higher grain yield. On the basis of yield reduction, three genotypes viz. Lu-26s, Sarsabz and KTDH were found tolerant. These genotypes also maintained the higher concentration of proline, K/Na ratio and chlorophyll contents under saline conditions

A Shereen

E Islam

M A Khan

M U Shirazi

M Yasin Ashraf

Muhammad Ali Khan

R U Ansari

S M Mujtaba

S Mumtaz

CiteSeerX

Pak. J. Bot., 41(2): 633-638, 2009. 
ROLE OF PROLINE, K/NA RATIO AND CHLOROPHYLL 
CONTENT IN SALT TOLERANCE OF WHEAT  
(TRITICUM AESTIVUM L.) 
 
M.A. KHAN, M.U. SHIRAZI, MUHAMMAD ALI KHAN, S.M. MUJTABA,  
E. ISLAM, S. MUMTAZ, A. SHEREEN, R.U. ANSARI AND M. YASIN ASHRAF* 
 
Plant Physiology Division, Nuclear Institute of Agriculture, Tandojam, Pakistan. 
Plant Stress Physiology Lab, Nuclear Institute for Agriculture & Biology (NIAB),  
Jhang Road, Faisalabad, Pakistan. 
 
Abstract 
 
Studies to determine the role of proline, K/Na ratio and chlorophyll contents in salt tolerance 
of wheat genotypes were conducted in lysimeters using hydroponics technique. Seeds were allowed 
to germinate under normal condition (1.5 dS m-1) and salinity treatment of 12 dS m-1 was imposed 
after one week of germination. Crop was irrigated at the interval of two weeks or whenever 
required with 1/4th Hoagland nutrient solution of respective concentrations. Results clearly 
indicated that wheat genotypes with higher proline, K/Na ratio and chlorophyll contents had higher 
grain yield. On the basis of yield reduction, three genotypes viz. Lu-26s, Sarsabz and KTDH were 
found tolerant. These genotypes also maintained the higher concentration of proline, K/Na ratio and 
chlorophyll contents under saline conditions.   
 
Introduction 
 
High soil salinity is one of the important environmental factors that limit distribution 
and productivity of major crops (Ashraf et al., 2005; Chandan et al., 2006). Agricultural 
productivity in arid and semiarid regions of the world is very low due to accumulation of 
salts in soils (Ashraf et al., 2002; Munns, 2002). Saline medium causes many adverse 
effects on plant growth, which is due to low osmotic potential of soil solution (osmotic 
stress) specific ion effects (salt stress), nutritional imbalance or a combination of these 
factors (Marschner, 1995, Ashraf, 2004). All these factors cause adverse effects on plant 
growth and development at physiological and biochemical activities (Ashraf & Sarwar, 
2002; Munns & James, 2003). 
Wheat is the major cereal crop of Pakistan, which is grown all over the country. It is 
grown to meet the food demand of over growing population of Pakistan, but per hectare 
yield of wheat is far below than its yield potential, which may be due to different reason 
i.e., lack of proper water and nutrient managements, unavailability of fertile soils, salinity, 
water logging and drought. In Pakistan, salinity is a serious threat for wheat production. 
The most of underground water utilized for wheat cropping is brackish, however, some 
areas are irrigated with canal water but having lack of drainage system both the irrigation 
systems are increasing the soil salinity problem in the country due to which heavy losses 
in crop yields are reported (Khan et al., 2006). The wheat crop is a moderately salt 
tolerant (Khan et al., 2004) and for screening or developing salt tolerant wheat varieties, 
physiological and biochemical studies are necessary to identify the physiological and 
biochemical markers. By using these markers available wheat germplasm can be screened 
for salt tolerance or by incorporating them new high yielding salt tolerant wheat varieties 
can be developed. This is essential to fulfill the wheat grain yield demands of ever-
growing population of Pakistan.   
*E-mail: niabmyashraf@hotmail.com 
M.A. KHAN ET AL., 
 
634
Plants differ genetically in their response to salt stress (Ahmed et al., 2005). 
Different mechanisms of salt tolerance by plants have been suggested by different 
workers (Flowers & Hajibagheri, 2001; Gorham, 1994; Schachtman & Munns, 1992). 
Keeping in view the importance of wheat and salinity, present study has been planned to 
examine the role of proline, K/Na ratio and chlorophyll content in salt tolerance of wheat 
(Triticum aestivum L.).  
 
Material and Methods 
 
The experiment was conducted in lysimeters (cemented tanks), filled with river sand. 
The growing media was irrigated by 1/4th strength Hoagland solution, salinized by 
commercial NaCl salt to attain salinity level of 1.5 dS/m (control) and 12.0 dS/m. Six 
wheat genotypes viz., Lu-26s, Sarsabz, KTDH-22, V-7012, Khirman and Bakhtawar 
were sown in a randomized manner with three replicates. Growth observations were 
recorded at the time of maturity. Plant samples (flag leaves) were analyzed for soluble 
salts (Na, K and K/Na ratio), after extraction with 0.1 M. Acetic acid as described by 
Ansari & Flowers, (1986). Fresh leaves samples at flowering stage were analyzed for 
Chlorophyll (Lichtenthaler, 1987) and proline contents (Bates et al., 1973). 
 
Results 
 
Leaf chemical analysis of different wheat genotypes indicated that sodium (Na) 
contents increased under saline condition (Table 1). The genotypes Lu-26s Sarsabz and 
KTDH had comparatively less sodium contents than V-7012, Khirman and Bakhtawar. 
Results also indicated that Check wheat genotype (Lu-26s) had minimum Na contents 
than that of Sarsabz and KTDH-22 while potassium (K) contents reduced due to increase 
in salinity in all the wheat genotypes (Table 1). However, genotypes Lu-26s, Sarsabz and 
Khirman maintained higher potassium contents than others under saline conditions. The 
increase in sodium contents resulted a decrease in K/Na ratio in all the wheat genotypes 
(Table 1). However, salt tolerant check genotype (Lu-26s) showed minimum reduction in 
K/Na ratio which was closely followed by Sarsabz and KTDH-22. 
Biochemical analysis of leaves of different wheat genotypes for proline 
accumulation and chlorophyll contents indicated that proline accumulation increased and 
chlorophyll contents decreased under saline condition (Table 2). Wheat genotypes 
Sarsabz, Lu-26s and KTDH showed higher accumulation of proline than others (Table 2).  
Similarly minimum reduction in chlorophyll content was noted  in Sarsabz, Lu-26s and 
KTDH. Maximum chlorophyll contents were maintained by Sarsabz and KTDH followed 
by Lu-26s. 
Grain yield of different wheat genotypes was significantly influenced by the salinity 
(Table 2). The genotype Lu-26s showed minimum reduction, when compared with 
control, whereas maximum reduction over control was recorded in Khirman. The 
genotypes Sarsabz and KTDH were successful in maintaining grain yield more than 60% 
under salinity stress (12 dS/m).  
 
 
 
SALT TOLERANCE OF WHEAT  
 
635
Table 1. Effects of salinity on sodium (Na), potassium (K) contents and K/Na ratio in 
different wheat genotypes. 
Control Saline 
Na K Na K S.No. Variety 
mg g-1 D.W. K/Na mg g-1 D.W. K/Na 
1. Lu-26s 0.18 2.19 12.20 1.36 1.43 1.05 
2. Sarsabz 0.18 2.41 13.17 1.57 1.56 0.83 
3. KTDH-22 0.16 2.67 16.74 1.72 1.44 0.69 
4. V-7012 0.20 2.20 12.03 2.74 1.20 0.43 
5. Khirman 0.16 2.15 12.49 2.50 1.30 0.56 
6. Bakhtawar 0.15 2.18 14.43 2.81 1.20 0.43 
Mean 0.17 2.30 12.20 2.12 1.36 0.67 
LSD (0.05) 0.0919 0.1404 1.084 0.0919 0.1404 1.084 
   
 Table 2. Effect of salinity on accumulation of proline, total chlorophyll and grain yield of  
different wheat genotypes. 
Control Saline 
S. No. Variety Proline 
µmol g-1 F.W 
Total 
chlorophyll 
mg g-1 
Yield kg ha-1 Proline µmol g-1 F.W
Total 
chlorophyll 
mg g-1 
Yield kg ha-1 
1. Lu-26s 5.02 2.96 3503 19.37 2.43 2728 
2. Sarsabz 4.93 3.08 3747 22.77 2.56 2458 
3. KTDH-22 5.17 3.07 3298 18.31 2.41 2017 
4. V-7012 5.07 2.75 2906 10.21 1.51 1458 
5. Khirman 5.15 2.79 3684 11.32 1.62 1358 
6. Bakhtawar 5.03 2.69 2345 10.60 1.62 1195 
Mean 5.06 2.89 3247 15.43 2.03 1869 
LSD (0.05) 0.993 0.2056 429.7 0.993 0.2056 429.7 
 
Discussion 
 
Sodium contents increased due to salinity in all wheat genotypes however genotypes 
Bakhtawar and Khirman maintained the highest leaf Na concentration which is closely 
followed by V-7012. Minimum Na content was recorded by Lu-26s followed by Sarsabz 
and KTDH (Table 1). The low sodium  accumulation in Lu-26s, Sarsabz and KTDH-22 
indicated that these varieties were more tolerant than those which translocated maximum 
Na in leaves. It is well established fact that Na is a toxic element whose higher 
concentration disturbs the different metabolic activities (Akram et al., 2007). The 
varieties which were successful in retaining the Na in the root were tolerant (Khan et al., 
1990; Akram et al., 2007). Based on these reports, it may be concluded that genotypes 
Lu-26s, Sarsabz and KTDH-22 maintained less amount of Na in their leaves and hence 
were tolerant to salinity.   
In studies where salinity is developed with NaCl, a focus has been the transport 
systems that are involved in the utilization of Na as an osmotic solute (Yasar et al., 2006). 
Literature indicated that intracellular Na homeostasis and salt tolerance are modulated by 
calcium and high Na concentrations negatively affect K acquisition (Munns et al., 2002). 
Sodium competes with K for uptake through common transport system and does this 
effectively since the Na concentration in saline environments is usually considerably 
greater than that of K. It is also reported that sensitivity of some crops to salinity is due to 
the inability to keep Na and Cl out of transpiration streams (Gorham et al., 1990). Plants 
limiting the uptake of toxic ions or maintaining normal nutrient ion contents could show 
greater tolerance which was the case with present study. Uptake mechanism that 
M.A. KHAN ET AL., 
 
636
discriminates similar ions such as Na and K could be useful selection criteria for salt 
tolerance in wheat and breeding for efficient nutrient uptake. A significant negative 
correlation was observed between grain yield and increase in sodium contents of the 
wheat genotypes grown under sodium chloride concentration. 
In the present study all wheat genotypes showed decreasing trend in K content due to 
salinity stress. The decrease in K was due to the presence of excessive Na in the growth 
medium because high external Na content is known to have an antagonistic effect on K 
uptake in plant (Sarwar & Ashraf, 2003). It is also reported that salt tolerance is 
associated with K contents (Ashraf & Sarwar, 2002), because of its involvement in 
osmotic regulation and competition with Na (Ashraf et al., 2005). Regulation of K uptake 
and prevention of Na entry, efflux of Na from cell are the strategies commonly used by 
plants to maintain desirable K/Na ratio in the cytosole. In the present study, the tolerant 
genotypes are expressing the same trend for K/Na ratios. Genotypes Lu-26s, KTDH are 
comparatively higher in accumulating more K than sensitive ones. K/Na ratio is the 
criteria which is established by the scientist and the genetically approved for salt 
tolerance. So the varieties maintaining higher K/Na ratio are the salt tolerant and showing 
positive correlation between grain yield and K/Na ratio. 
There are some reports where an increase in chlorophyll contents was observed in 6 
genotypes of rice (Alamgir & Ali, 1999). However, the reduction in chlorophyll contents 
is to be expected under stress; being membranous bound, its stability is dependent on 
membrane stability, which under saline condition seldom remains intact (Ashraf et al., 
2005). The decrease in chlorophyll contents under saline conditions is reported by Iqbal 
et al., (2006); Ashraf et al., (2005). Our results are in agreement with these workers 
where in all genotypes, chlorophyll contents are decreasing. The decrease is significant in 
sensitive genotypes in comparison to tolerant.  
Accumulation of solutes especially proline, glycine-betaine and sugars is a common 
observation under stress condition (Ashraf et al., 1994; Naqvi et al., 1994, Qasim et al., 
2003). It is reported by Ashraf et al., (1998) that proline is an important osmolyte to 
adjust the plant under drought/saline conditions. In the present study, the accumulation of 
proline was commonly observed in almost all genotypes however, the genotypes Sarsabz 
followed by Lu-26s and KTDH-22 had higher proline accumulation (Table 2). These 
genotypes are the best performing ones and had higher grain yield under salinity stress. 
Similar observations were recorded by other workers (Ashraf & Foolad, 2005) in 
different crops. There are however reasons to believe that proline accumulation may play 
a role in the salinity tolerance. Firstly it is an osmolyte accumulated under stress in 
almost all the plant species. Secondly a high proline concentration has been described in 
organs which naturally have low water contents such as seed and inflorescence. The 
results of present study showed that there is a positive relationship between proline 
accumulation and performance of wheat genotypes in terms of grain yield under salinity 
stress. 
It was concluded that on the basis of less than 40% reduction in yield, three 
genotypes viz. Lu-26s, Sarsabz and KTDH-22 were better. It was also observed that the 
tolerant genotypes have higher proline accumulation, high K/Na ratio and less 
chlorophyll degradation as compared to sensitive ones. 
 
SALT TOLERANCE OF WHEAT  
 
637
Acknowledgement 
 
The authors are highly thankful to Dr. Mehboob Sial Wheat Breeder of NIA, 
Tandojam for supplying the seeds of wheat genotypes and Mr. Saqib Ali Memon for 
composing the manuscript. 
 
References 
 
Ahmad, M., B.H. Niazi, B. Zaman and M. Athar. 2005. Varietal differences in agronomic 
performance of six wheat varieties grown under saline field environment. Int. J. Environ. Sci 
Tech, 2(1): 49-57. 
Akram, M., M.A. Malik, M.Y. Ashraf, M.F. Saleem and M. Hussain. 2007. Competitive seedling 
growth and K+/Na+ ratio in different maize (Zea mays L.) hybrids under salinity stress. 
Pakistan Journal of Botany, 39: 2553-2563.  
Alamgir, A.N.M. and M.Y. Ali. 1999. Effect of salinity on leaf pigments, sugar and protein 
concentrations and chloroplast ATPase activity of rice (Oryza sativa L.). Bangladesh Journal 
of Botany, 28: 145-149. 
Ansari, R. and T.J. Flowers. 1986. Leaf to leaf distribution of ions in some monocotyledonous 
plants grown under saline conditions. In: Prospects for Biosaline Research (Ed.): Ahmed and 
A. San Pietro. University of Karachi, pp. 167-181. 
Ashraf, M. 2004. Some important physiological selection criteria for salt tolerance in plants. Flora 
Review, 199: 361-376. 
Ashraf, M. and M.R. Foolad. 2005. Pre-sowing seed treatment-a shotgun approach to improve 
germination, plant growth, and crop yield under saline and non-salne conditions. Advances in 
Agronomy, 88: 223-271.  
Ashraf, M. Y., K. Akhtar, G. Sarwar and M. Ashraf. 2005. Role of rooting system in salt tolerance 
potential of different guar accessions. Agronomy for Sustainable Development, 25: 243-249. 
Ashraf, M.Y. and G. Sarwar. 2002. Salt tolerance potential in members of Brassicaceae. 
Physiological studies on water relations and mineral contents. In: Prospects for saline 
Agriculture. (Eds.): R. Ahmad and K.A. Malik. Kluwer Academic Publishers, Netherlands, pp. 
237-245. 
Ashraf, M.Y., A.R. Azmi, A.H. Khan and S.A. Ala. 1994. Effect of water stress on total phenol, 
peroxidase activity and chlorophyll contents in wheat (Triticum aestivum L.). Acta 
Physiologeae Plantarum, 16: 185-191. 
Ashraf, M.Y., K. Akhtar, G. Sarwar and M. Ashraf. 2002. Evaluation of arid and semi-arid 
ecotypes of guar (Cyamopsis tetragonoloba L.) for salinity (NaCl) tolerance. Journal of Arid 
Environment, 52: 437-482.  
Ashraf, M.Y., Y. Ali and T.M. Qureshi. 1998. Effect of salinity on photosynthetic efficiency and 
yield of rice genotypes. Pakistan Journal of Biological Sciences, 1: 72-74.  
Bates, L.S., R.P. Waldren and I.D. Tears. 1973. Rapid determination of free proline for water stress 
studies. Plant and Soil, 39: 205-207. 
Chandan, S., A. Singh, E. Blumwald and A. Grover. 2006. Beyond osmolytes and transporters: 
novel plant salt-stress tolerance-related genes from transcriptional profiling data. Physiologia 
Plantarum, 127: 1-9.  
Flowers, T.J. and M.A. Hajibagheri. 2001. Salinity tolerance in Hordeum vulgare: ion 
concentrations in root cells of cultivars differing in salt tolerance. Plant and Soil, 23: 1-9.  
Gorham J., R.G. Wyn Jones and A. Bristol. 1990. Partial characterization of the trait for enhanced 
K+ - Na+ discrimination in the D genome of wheat. Planta, 180: 590- 597. 
Gorham, J. 1994. Salt tolerance in the Triticeae: K/Na discrimination in some perennial wheat 
grasses and their amphiploids with wheat. Journal of Experimental Botany, 45: 441-447.  
Iqbal, N., M. Y. Ashraf, Farrukh Javed, Vicente Martinez and Kafeel Ahmad. 2006. Nitrate 
reduction and nutrient accumulation in wheat (Triticum aestivum L.) grown in soil salinization 
with four different salts. Journal Plant Nutrition, 29: 409-421. 
M.A. KHAN ET AL., 
 
638
Khan, A.H., M.Y. Ashraf and A.R. Azmi. 1990. Effect of NaCl on growth and nitrogen metabolism 
of sorghum. Acta Physiol. Plant., 12: 233-238.  
Khan, M.A., M.U. Shirazi, Mukhtiar Ali, S. Mumtaz, A. Shereen and M.Y. Ashraf. 2006. 
Comparative Performance of some wheat genotypes growing under saline water. Pak. J. Bot., 
38(5): 1633-1639. 
Khan, M.A., N. Hussain, M. Abid and T. Imran. 2004. Screening of wheat (Triticum aestivum L.) 
cultivars for saline conditions under irrigated arid environment. Journal of Research (Science), 
Bahauddin Zakariya University, Multan, 15(4): 471-477. 
Lichtenthaler, H.K. 1987. Chlorophyll and carotenoids pigments of photosynthetic biomembranes. 
Methods Enzymols; 148: 350-382. 
Marschner, H. 1995. Mineral nutrition of higher plants. Acad. Pr., London.  
Munns, R. 2002. Comparative physiology of salt and water stress. Plant Cell Environ., 25: 239-250.  
Munns, R. and R.A. James. 2003. Screening methods for salinity tolerance: a case study with 
tetraploid wheat. Plant Soil, 253: 201-218. 
Munns, R., J.B. Passioura, J. Guo, O. Chazen and G.R. Cramer. 2002. Water relations and leaf 
expansion: importance of time scale. J. Exp. Bot., 51: 1495-1504.  
Naqvi, S.S.M., S. Mumtaz, S.A. Ali, A. Shereen, A.H. Khan, M.Y. Ashraf and M.A. Khan, 1994. 
Proline accumulation under salinity stress. Is abscisic acid involved? Acta Physiol. Plant., 
16(2): 117-122. 
Qasim, M., M. Ashraf, M. Amir Jamil, M.Y. Ashraf and E.S.R. Shafiq-ur-Rehman. 2003. Water 
relations and leaf gas exchange properties in some elite canola (Brassica napus) lines under 
salt stress. Annals App. Biol., 142: 307-316.  
Sarwar, G. and M.Y. Ashraf. 2003. Genetic variability of some primitive bread wheat varieties to 
salt tolerance. Pak. J. Bot., 35: 771-777. 
Schachtman, D.P. and R. Munns. 1992. Sodium accumulation in leaves for Triticum species that 
differ in salt tolerance. Aust. J. Plant Physiol., 19: 331-340. 
Yasar, F., S. Ellialtioglu and S. Kusvuran. 2006. Ion and lipid peroxide content in sensitive and 
tolerant eggplant callus cultured under salt stress. Europ. J. Hort. Sci., 71(4): 169-172. 
 
(Received for publication 15 November 2008) 


Role of proline, K/Na ratio and chlorophyll content in salt tolerance of wheat (Triticum aestivum

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=9E77227C169FC8160556BD7935D50A0C?doi=10.1.1.1055.424&rep=rep1&type=pdf

Role of proline, K/Na ratio and chlorophyll content in salt tolerance of wheat (Triticum aestivum

Abstract

Similar works

Full text

Available Versions

CiteSeerX