Spinach (Spinacia oleracea) plants were subjected to salt stress by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar. Plants were harvested 3 weeks after starting NaCI treatment. Fresh and dry weight of both shoots and roots was decreased more than 50% compared to control plants but the salt-stressed plants appeared healthy and were still actively growing. The salt-stressed plants had much thicker leaves. The salt-treated plants osmotically adjusted to maintain leaf turgor. Leaf K' was decreased but Na' and C-were greatly increased.The potential photosynthetic capacity of the leaves was measured at C02-dependent 02 evolution was decreased by 20% in chloroplasts isolated from salt-stressed plants. The concentration of K' in the chloroplast decreased by 50% in the salt-stressed plants, Na' increased by 70%, and C1 increased by less than 20% despite large increases in leaf Na' and C1l.It is concluded that, for spinach, salt stress does not result in any major decrease in the photosynthetic potential of the leaf. Actual photosynthesis by the plant may be reduced by other factors such as decreased stomatal conductance and decreased leaf area. Effective compartmentation of ions within the cell may prevent the accumulation of inhibitory levels of Na' and Cl-in the chloroplast.The growth ofplants is ultimately reduced by salinity although species vary in the salt concentration they can tolerate before growth is impaired (7, 10,16

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