The changes which occur in the water-soluble protein nitrogen, the water-soluble nonprotein nitrogen, the total protein nitrogen and the total nitrogen of the leaf-blade of crops had been traced at successive growth stages in relation to the variation in their salt tolerance with environment.
In the 'saline' crops grown under higher level of nitrogen supply, the dry matter productivity was higher than in lower level and the ability of crops to survive salinized environment was raised.
Of the nitrogen fractions determined, the total nitrogen and the total protein nitrogen were found to increase in concentration in the leaf-blade along with the development of salt tolerance but there were no relation to the development of saline injurious symptom. A close relationship between the content of the water-soluble nitrogen fractions in the leaf-blade and salt tolerance was characteristically observed. The water-soluble protein nitrogen was found to increase in concentration in leaf-blade along with the development of salt tolerance and to decrease with the disappearance of salt tolerance, the saline injury producing an increase and then the water-soluble nonprotein nitrogen increased remarkably.
The correlation observed between the change in water-soluble protein and salt tolerance suggests that the constituent bears some causal relationship to the mechainsm of salt tolerance.