The Effect of Salinity, Photoinhibition and Interaction of Both on Photosynthesis in Barley
The effect of salinity, photoinhibition and interaction of the two on various photosynthetic parameters was investigated in leaves and isolated chloroplasts of barley. Plants were grown in a controlled environment and irrigated with different concentrations (0–200 mM) of NaCl + CaCl2 salts. Photoinhibition treatment was given at 1600 UE/M2/S for four hour at 5 C and 20 C. The light saturated rate of CO2 uptake and maximum quantum yield decreased with increasing salt concentrations. Photoinhibition also decreased the CO2 assimilation rate and apparent quantum yield. Stomatal conductance was more sensitive to salt stress than photoinhibition. Salt stress and photoinhibition both modified the amplitude of leaf variable fluorescence (Fm) at 20 C in the presence of DCMU. Electron transport activity measured in isolated chloroplasts from plants grown at low salinity levels showed a slight increase in photosystem II (PS II) and photosystem I (PS I) activity in comparison with control; higher salt concentrations did not affect the electron transport activity. In control plants photoinhibition significantly decreased the PS II activity but no changes were observed in PS I activity. Interaction of photoinhibition and salt stress increases the inhibition of PS II activity in comparison with control photoinhibited plants.
KeywordsSalt Stress Stomatal Conductance Photosynthetic Photon Flux Density Methyl Viologen Electron Transport Activity
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