Investigating physiological and biochemical

 
 
 
 
 
 
 
 

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CHAPTER 5 
 
SUMMARY 
Salinity is the big threat throughout the world that drastically reduced the crop 
productivity. Increase in salinity tolerance to fulfill the increasing the increasing 
demand of food production and maintain food security of mankind, are important 
challenges to the world agriculture as the world population is increasing very rapidly 
than the area of agricultural land to support it. In addition, urbanization and 
industrialization on arable lands, shortage of good quality irrigation water and ever 
increasing salt-affected soils are among the worst problems in developing countries like 
Pakistan and compels to utilize every part of land for the production of crops. There are 
many crops which possess more salt tolerance and low water requirements than the 
conventional crops. Thus utilizing salt-affected soils and growing multipurpose crops on 
marginal lands to get benefits in terms of oil, medicine or other by-products of 
economic importance is the need of time especially in developing world. Keeping in 
view the above scenario, the present research work was planned on linseed for 
achieving the following objectives: 
 To explore the genetic variations in linseed genotypes for salt tolerance and 
selection of tolerant and sensitive genotypes.
 To assess the effect of salt stress on germination and ion distribution in linseed 
 To define the various physiological and biochemical traits having functional 
significance in determining salt tolerance and plant growth of linseed. 
 To evaluate the effect of salt stress on yield and oil contents of linseed 
To achieve these objectives, solution culture and pot experiments were conducted at 
wire house of Saline Agriculture Research Centre (SARC), University of Agriculture, 
Faisalabad. Sixty linseed genotypes were grown for four weeks in hydroponics using 

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three levels of salinity (control, 100 mM NaCl and 200 mM NaCl) to screen out salt 
tolerant and salt sensitive linseed genotypes. On the basis of some growth and ionic 
parameters, genotypes were identified as salt tolerant and salt sensitive genotypes.
In 2
nd
study, seeds of four linseed genotypes 637-72 and NO-303 identified as salt 
tolerant and S-907 and C-99-3-115 recognized as salt sensitive genotypes were grown 
in petri dishes and solution culture with three salinity levels (control, 100 mM NaCl and 
200 mM NaCl). An increase in concentration of NaCl significantly affected seed 
germination of the four linseed genotypes under investigation. The genotype NO-303 
attained the highest final germination percentages at all the salinity levels but the 
reduction in germination due to increase in salt level was much lower than in the other 
genotypes. Seedling survival of all the genotypes was significantly affected by NaCl. 
The results revealed that the genotypes sensitive to salinity at germination stage may 
also show sensitivity at seedling stage. Na
+
contents increased with increasing salinity 
level and peaked at 200 mM NaCl. This means that Na
+
accumulation was harmful 
because the genotypes with low Na
+
contents like 637-72 and NO-303 possessed more 
vigorous seedling growth than the other genotypes. Both salt tolerant genotypes (637-72 
and NO-303) accumulated considerably less concentrations of Na
+
in their shoots and 
leaves and more in the roots as compared to the two salt sensitive genotypes (S-907 and 
C-99-3-115). 
In study 3, solution culture experiment was conducted to assess the effect of salt 
stress on physiological and biochemical processes of salt tolerance in linseed. Salt 
tolerant and salt sensitive genotypes were used in this study with the same levels of 
salinity as in study 2. This study was carried out in College of Agriculture and 
Biotechnology, Zhejiang University, China. It is obvious that salinity stress reduced 
plant growth by affecting plant physiological processes, relative water contents, 
electrolyte leakage, decreasing stomatal conductance, activity of CA and NR and 
reducing photosynthetic rate, altering accumulation of organic osmolytes and 
antioxidant activities of all the four linseed genotypes. Salt tolerant linseed genotypes 
637-72 and NO-303 performed better in salinity stress as compared to salt sensitive 
genotypes. Proline, GB, total soluble sugars and total proteins are accumulated more 

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148 
and hence provide a good source to decrease osmotic potential and protect cellular 
organelles from the adverse effects of increased salt concentration. Activity of 
antioxidant enzymes, especially SOD, POD and APX may help them from protecting 
oxidative damage. Membrane damage in terms of lipid peroxidation was more severe in 
salt sensitive genotypes S-907 and C-99-3-115 which may be another important 
biochemical trait for better salinity tolerance in linseed genotypes.
In order to evaluate the effect of salt stress on yield, yield attributes and oil contents 
of linseed, a pot experiment was conducted in wire house of SARC, UAF. Same linseed 
genotypes (salt sensitive S-907, C-99-3-115 and salt tolerant 637-72 and NO-303) were 
grown in pots with following treatments (1) control; (2) 100 mM NaCl; (3) 200 mM 
NaClsalinity. In pot culture, crops failed to reach maturity at highest level of salinity 
(200 mM NaCl) but at other treatment level, yield attributes and oil contents of linseed 
were measured and analysed. In this study, it was revealed that soil salinity affects 
significantly on linseed yield attributes like number of branches plant
-1
, number of pods 
plant
-1
, number of seed pod
-1
, seed yield plant
-1
and 1000 seed weight primarily by 
affecting the production of photosynthates and their distribution between sinks. Oil 
contents of linseed were also affected by the application of salt stress but salt tolerant 
genotypes produced more oil contents than salt sensitive genotypes. 
By summarizing all these results, it can be concluded that salinity stress caused 
significant reduction on plant growth by affecting plant physiological characteristics 
especially photosynthetic rate and electrolyte leakage while the other physiological 
traits like relative water contents, stomatal conductance and enzyme activites were 
indirectly affected. Salt tolerant genotypes of linseed accumulate more Na
+
in roots than 
shoots and leaves while germination stage is not much sensitive to salt stress. Hence 
restricted entry of toxic ions at root level, increased uptake of K
+
ion and reduction in 
lipid peroxidation due to enhanced activity of antioxidant enzymes seems to be the salt 
tolerance traits in linseed genotypes of Pakistan.