Physiological and cytological aspects of manganese toxicity in barley seedlings

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Abstract
Symptoms of Mn toxicity in barley leaves (Hordeum vulgare cv Morex) grown in full concentration Hoagland and Arnon #2 nutrient solution, one‐fifth concentration nutrient solution, or 0.5 mM CaSO4 solution plus 9.1, 91, or 910 GMM Mn were tip chlorosis, marginal necrosis, and isolated necrotic lesions. Leaf toxicity symptoms, which were related to leaf Mn content, were more severe in plants grown in solutions which contained a greater concentration of Mn or a lesser concentration of other nutrient ions. Microscopic examination of leaves with Mn toxicity symptoms revealed that necrotic lesions first appeared in the walls of cells directly adjacent to the sub‐stomatal cavity, and then enlarged with time to produce an area of localized tissue necrosis between the vascular bundle. The profile of Mn absorption by excised roots in response to increasing absorption solution Mn concentration resembled a saturable curve, suggesting that Mn transport is carrier‐mediated.’ Mn absorption by roots was markedly reduced when the absorption solution contained full or one‐fifth concentration nutrient solution.