CHANGES IN WATER RELATION PARAMETERS UNDER OSMOTIC AND SALT STRESSES IN MAIZE AND SORGHUM

A relatively drought tolerant cultivar of maize (Zea mays L. cv. Pione er 3950) and a drought tolerant line of sorghum (Sorghum bicolor [L.] Moench cv. ICSV 112) were grown hydroponically for 11 days. Treatments for non-ionic osmotic and salt stresses were started at the 8th day b y addition of polyethylene glycol 6000 and NaCl, respectively, at 200 mOsm equivalent concentrations in the presence or absence of 0.1 muM a bscisic acid. Relative growth rate was depressed by both stress factor s, more severely for maize than sorghum. Abscisic acid increased the g rowth rate and reverted the negative effect of NaCl in maize, while so rghum was only slightly affected. In general, sorghum had higher level s of K+ and lower levels of Na+ and the K+/Na+ ratio was further incre ased by abscisic acid treatment. From the pressure-volume curves, osmo tic potential. the water potential at turgor loss point, bulk elastic modulus and the water saturation deficit at initial turgor loss were e stimated. Most significantly, sorghum had a higher elastic modulus tha n maize and it decreased under osmotic treatment, while in maize it in creased under NaCl stress. The results suggest that bulk tissue turgor was not limiting growth under these conditions and underscores the po ssible implications of changes in the elastic condition of the cell wa lls in stress responses.