Effects of Osmotic Water Stress on Metabolic Rates of Cotton Plants with Open Stomata

Abstract

Photo-synthesis, respiration, and the resistance to CO2 diffusion to leaf meso-phyll cells were studied in cotton plants subjected to a range of NaCl concentrations for 3-4 weeks. The resistance to diffusion of CO2 did not increase at high solute concentrations, indicating that stomata were open. Changes in the water potential of the leaf tissue followed changes in the potential of the root medium. Changes in the osmotic potential of the leaf tissue exceeded those of the root medium by a factor of 1.2-1.5. Turgor was approximately doubled at the highest NaCl concentration compared with that of tissue grown in nutrient solution. Photosynthesis and respiration were reduced whenever NaCl was present in the medium. In plants grown at NaCl levels which corresponded to -8.5 bars, photosynthesis and respiration were reduced 25% or more when measurements were expressed on the basis of leaf area, fresh weight of leaves, dry weight of leaves, or chlorophyll content.