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

CO2-exchange and transpiration responses to different degrees of rapid ly induced salt (NaCl) and drought (polyethylene-glycol) stress (osmol ality levels: 0, 50, 100, 200, 300 and 400 mOsm (kg water)(-1)) by a m aize cultivar and a drought tolerant line of sorghum were investigated in parallel with monitoring differences in leaf water potential and s hoot and root osmolalities. Maize proved to be more susceptible than s orghum to both stresses. Its leaf water potential was markedly decreas ed at low external osmolalities but showed no further decline at highe r ones. In sorghum, leaf water potential declined along with the incre asing external osmolalities in a linear fashion. Leaf water content de clined more in maize than in sorghum to reach low values of leaf water potentials. In maize, transpiration and net photosynthesis were stron gly reduced in culture solutions of low osmolalities, whereas in sorgh um these parameters declined more gradually with increasing external o smolality. Differences between the two species' responses to imposed s tresses were most markedly manifested in stomatal behaviour, largely i nfluencing the sensitivity of CO2-uptake to increases in external osmo lalities imposed either by PEG or NaCl.