Photosynthetic gas exchange, electron transport, fluorescence and electrolyte leakage of wheat (Triticum aestivum L.) and tef (Eragrostis tef Z.) exposed to environmental stress

Scope and method of study. Biochemical/physiological components of leaf photosynthesis are restricted by excessively high or low temperatures and water stress. Experiments were conducted to study the photochemical properties, leaf gas exchange, chlorophyll content and cellular membrane stability of the temperate {dollar}rm Csb3{dollar} cereal wheat (Triticum aestivum L.) and the subtropical {dollar}rm Csb4{dollar} cereal tef (Eragrostis tef Z.) subjected to chilling low {dollar}rm(2spcirc C, 7spcirc C,{dollar} and {dollar}12spcirc C){dollar} or high {dollar}rm(35spcirc C, 40spcirc C, and 45spcirc C){dollar} temperatures, or water deficit stress. Photochemical properties were evaluated by {dollar}rm Osb2{dollar} evolution of isolated thylakoids, in vivo chlorophyll fluorescence of dark-adapted leaves and chlorophyll content of leaves. Net photosynthesis (A) and membrane integrity were determined using an open gas exchange system and electrolyte leakage measurements, respectively.; Findings and conclusions. High temperature and water deficit stress significantly decreased A and the activities of photosystem II (PSII) and whole chain electron transport. The reduction in wheat, however, was much greater than in tef and it was initiated at lower temperature and shorter exposure time or higher leaf water potential. Exposure to chilling low temperatures reduced PSII and whole chain electron transport rates and A in tef whereas wheat was less affected. Photosystem I and chlorophyll contents were largely unaffected by the stresses. The greater sensitivity in wheat of electron transport and A to high temperature and water deficit stress and of tef to low temperature, was consistent with susceptibility rankings based on variable to maximum fluorescence (Fv/Fm). A, PSII and whole chain electron transport were closely correlated with Fv/Fm. Electrolyte leakage confirmed the greater sensitivity of wheat to high temperatures and tef to chilling low temperatures. Membrane leakage became substantial first at severe stress whereas inhibition of A develop much earlier. The results suggest that water stress reduced {dollar}rm COsb2{dollar} fixation of wheat first by stomatal closure and later by inhibition of the Calvin cycle. Both electron transport and the Calvin cycle were reduced following heat stress. Stress inhibition of A of tef appeared dominated by the photosynthetic enzymes alone.