Salinity effects on the stomatal behaviour of grapevine

An investigation of the time-course of inhibition of photosynthesis in salt-stressed grapevine (Vitis vinifera L.) leaves revealed two types of stomatal behaviour. Up to tissue concentrations of 165 mM chloride the inhibition was due to a uniform decrease in stomatal conductance, as indicated from autoradiograms of ¹⁴ CO₂ fixation and no change in the relationship of assimilation to calculated intercellular partial pressure of CO₂ (A-C₁ ) compared with control plants. The occurrence of non-stomatal inhibition of photosynthesis at higher levels of leaf chloride, suggested by a decline in the slope of the calculated (A-C₁ ) relationship, was associated with non-uniform ¹⁴ CO₂ uptake over the leaf surface similar to that previously observed for ABA-treated and water-stressed grapevine leaves where non-stomatal inhibition of photosynthesis was shown to be an artifact arising from non-uniform stomatal behaviour. These observations also provide an explanation for the stimulation of photorespiration during salt stress.