INTERACTION OF SALT STRESS AND PHOTOINHIBITION ON PHOTOSYNTHESIS IN BARLEY AND SORGHUM

The effect of salinity (short term), high light and interaction of the two was investigated in leaves and isolated chloroplasts from these leaves of barley (C3) and sorghum (C4) plants. The light saturated rate of CO2 uptake and maximum quantum yield decreased with increasing salt concentrations. Stomatal conductance was more sensitive to salt stress than photoinhibition. Photoinhibition treatment of salt stressed plants resulted in a further decrease of the CO2 assimilation rate and quantum efficiency of photosynthesis. The recovery of the CO2 assimilation rate was considerably lower in salt and high light stressed plants compared to plants which were given a photoinhibition treatment only (no salt). It is concluded that salt stress itself does not exert adverse effects on the primary photosynthesis process since the F(v)/F(m) ratio and electron transport activity did not decrease with higher salt concentrations. However, salinity stress enhanced substantially the susceptibility to photoinhibition; this may be due to the predisposing of the photosynthetic apparatus to damage under salt stress, resulting in lower light saturated rates of photosynthesis a decreased ability to recover from photodamage.