20 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



creased osmotic pressure and leaf aging have been 

 found to be accompanied by increased dry weight 

 and decreased cell wall extensibility (29), and 

 increased turgor pressure is found to follow as 

 cell wall extensibility is reduced (9). Cell expan- 

 sion is dependent upon both turgor and cell ex- 

 tensibility, and they are interdependent (18). 

 Extensibility, thus, is a function of turgor pres- 

 sure as well as other variables (35). Since cell 

 wall growth is such a finely balanced sequence of 

 events, and the specific molecular structure of the 

 wall is due to this highly programmed sequence 

 (41), any alteration of these events would be ex- 



10 20 30 

 TIME (days) 



Figure 4. — Dry weight of total plant as affected by addi- 

 tion of NaCl to the growth solution. Symbols same as 

 in figure 3. 



15 



> 10 



< 



2 



3 

 Z 



5 - 



• No Stress 



w + 4 bars NaCl 



t i i i •» 



10 



20 

 DAYS 



30 



Figure 5. — Leaf initiation in bean plants as affected by 

 addition of NaCl to the growth solution. Full circles 

 are control plants and half-filled circles are salt-treated 

 plants. Average of 8 plants for each point. Arrows have 

 same meaning as in figures 3 and 4. 



pected to affect the extensibility of the cell walls. 

 Taylor (58) indicated that increased salinity fre- 

 quently leads to thicker and heavier cell walls. 

 Ordin (49) found that changes in w and turgor 

 pressure in cells lead to alterations in tj T pes of 

 cell wall polysaccharides that are formed, and 

 this alteration of polysaccharide sjmthesis might 

 explain the reduced cell extension in plants sub- 

 jected to lowered water potentials (21). All of 

 this information is compatible with the hypothe- 

 sis that increased osmotic pressure in cells induces 

 accelerated aging of the cells (46). This could 

 be due to higher -k of the leaf cells per se or de- 

 creased hormone delivery to the leaves, resulting 

 from stress in the roots (25, 46) ■ 



Recovery From Salinity Stress 



When plants subjected to water stress in dr}dng 

 soil are rewatered, they often exhibit growth 

 rates that are higher than the control plants 

 (13, 16, 17), and this may even result in the final 

 size of the stressed plants being larger than the 

 nonstressed plants (22). Rate of leaf expansion 

 usually has been employed as the measurement of 

 growth in those studies, and the increased rate 

 of leaf expansion, upon rewatering, could be ex- 

 plained by the accumulation of sugars in cells 



