Please have a look at these useful links.

http://link.springer.com/article/10.1007/s11816-010-0163-y

https://www.researchgate.net/publication/225040559_Salt_Stress_Tolerance_of_Plants

Article Salt Stress Tolerance of Plants

I suggest you go through my research work on research gate. simply you screen plant on different concentrations of NaCl or a mixture of salts at seed germination stage, seedlings, and mature plants. Record growth performance of the two types of plants under stress.

Summarizing:

1) Use several concentration of NaCl to cover the whole range of effects from neutral to 90% growth inhibition

2) Use NaCl and other salts (NaSO4, NaCO3, KCl,  heavy metals to study synergism of them

3) use plants of different age to find the most susceptible stages

4) Use permanent salt stress and temporary effect to compare plant ability to recover

5) measure effects of salt on plant (root, stem, leaf area) growth, stages development, yield, biochemical composition, NaCl and other salts accumilation, photosynthesis changes.

6) study effect of plant hormones and similar compounds on salt tolerance.

7) study salt effect on plant resistance to pests and pathogens.

To add to Alex' detailed response, you also might want to analyze priming and inhibitory effects during the (easiest) germination stage. To prime you use water, salts, and hormone(s); do mind that some plants show vartiation if seeds are dried after priming vs. priming with direct germination.

If your objective is the quantification of tissue tolerance, you need to first define a physiological trait of your interest, for example, leaf photosynthesis, stomatal conductance or enyzme activity. Second, you need to quantify the ion content of the tissue. The slope between your traits (y-axis) and ion content (x-axis) is the sensitivity of the trait to ion concentration in the measured tissue and can be define as a measure of tissue tolerance.

If I might suggest you my work:

http://onlinelibrary.wiley.com/doi/10.1111/pce.12504/pdf

The parameter nx in Eqn 14 and in Table 1 is the tissue tolerance for the trait x. If nx is more negative, the trait x is more sensitive to ion content, or having less tissue tolerance. This can be used to compare traits of a species, or compre a certain trait between cultivars or species.

I think all the above answers are very clear and helpful. I add, it depends upon which issue (trait) of salt tolerance you want to compare between two plants. Your question should have included that.

Often this question is about the technical action that one should take in order tp select èlants that tolerate more salinity. This is a property of soil and in cultivated lands depends entirely on management. With prgress in time the salinity raises if the primary aim is moving towards more tolerant species. Probably the first issue is lowering salinity by a complex strategy of water requirement and drainage. Water use and water equivalents needed for a crop unit are the first character of a selection for salinity.

You can screen your material at difference concentrations by using yoshida culture solution one experiment as control and in other add salt  , impose stress by adding NaCl at your desired concentration and estimate the sodium content in the tissue desired like Root Na , Shoot Na content. For the best explanation you can go through the IRRI salinity screening manual.

Thank you very much for your help ! but how can i  compare   between two plants of tissue (trait) of salt tolerance?

Niu , you need to define the salt tolerance traits of plants . For example , accumulation of Na n plants but still biomass is not severely affected , accumulation of proline as marker of stress , accumulation of polyamines like arginine , putrescine  etc as marker of salt stress  , relative water content , salt injury index,  root distribution pattern , root cation exchange capacity , relation between root CEC and chloride accumulation in leaves, 50% reduction in growth ...like that large number of traits can be decided from the published literature , and you depending upon your objective can shortlist them,...

To asses tissue salt tolerance, I would suggest determination of K, Ca, Na and Cl as well as compatible solutes such as glycinebetaine and proline. Also, further features such as ATPase and Na+/H+ antiporter activity of plasma membrane and vacuole. I think the above traits are enough to evaluate the salt tolerance mechanism in different plants.  

challenging with elevated levels of NaCl, then determine the growth inhibitory level