CO2-EXCHANGE AND WATER RELATION RESPONSES OF SORGHUM AND MAIZE DURING WATER AND SALT STRESS

CO2-exchange and transpiration responses to different degrees of rapidly induced salt (NaCl) and drought (polyethylene-glycol) stress (osmolality levels: 0, 50, 100, 200, 300 and 400 mOsm (kg water)(-1)) by a maize cultivar and a drought tolerant line of sorghum were investigated in parallel with monitoring differences in leaf water potential and shoot and root osmolalities. Maize proved to be more susceptible than sorghum to both stresses. Its leaf water potential was markedly decreased at low external osmolalities but showed no further decline at higher ones. In sorghum, leaf water potential declined along with the increasing external osmolalities in a linear fashion. Leaf water content declined more in maize than in sorghum to reach low values of leaf water potentials. In maize, transpiration and net photosynthesis were strongly reduced in culture solutions of low osmolalities, whereas in sorghum these parameters declined more gradually with increasing external osmolality. Differences between the two species' responses to imposed stresses were most markedly manifested in stomatal behaviour, largely influencing the sensitivity of CO2-uptake to increases in external osmolalities imposed either by PEG or NaCl.