Water Relations and Photosynthesis in Barley Plants Grown Under Conditions of Deficiency and Toxicity of Iron

Barley (Hordeum vulgare L. cv. Azad) plants were grown at two deficient—0.28 and 0.56 nag l⁻¹, one excess — 28.0 mg 1⁻¹ and an optimum — 5.6 mg l⁻¹, levels of iron supply in sand culture. Iron deficiency increased water potential and transpiration, and decreased water saturation deficit and diffusive resistance. Iron deficient plants stewed a marked decrease in net photosynthesis and concentrations of sugars and starch in the leaves. Decrease in Hill reaction activity due to iron deficiency was substantially less marked per unit chlorophyll, compared to that per unit fresh weight Decrease in photosynthesis in iron deficient plants—a non stomatal effect, was primarily attributable to decrease in leaf chlorophyll concentration. Iron deficiency caused significant decrease in water use efficiency of plants. Excess supply of iron decreased plant water status, transpiration and photosyn-thetic activity.