Ethylene Production by Fe-deficient Roots and its Involvement in the Regulation of Fe-deficiency Stress Responses by Strategy I Plants

Abstract

Species that showed marked morphological and physiological responses by their roots to Fe-deficiency (Strategy I plants) were compared with others that do not exhibit these responses (Strategy II plants). Roots from Fe-deficient cucumber (Cucumis sati us L. ' Ashley '), tomato (Lycopersicon esculentum Mill. T3238FER) and pea (Pisum sati um L. ' Sparkle ') plants produced more ethylene than those of Fe-sufficient plants. The higher production of ethylene in Fe-deficient cucumber and pea plants occurred before Fe-deficient plants showed chlorosis symptoms and was parallel to the occurrence of Fe-deficiency stress responses. The addition of either the ethylene precursor ACC, 1-aminocyclopropane-1-carboxylic acid, or the ethylene releasing substance, Ethephon, to several Fe-sufficient Strategy I plants [cucumber, tomato, pea, sugar beet (Beta ulgaris L.), Arabidopsis (Arabidopsis thaliana (L.) Heynh ' Columbia '), plantago (Plantago lanceolata L.)] promoted some of their Fe-deficiency stress responses : enhanced root ferric-reducing capacity and swollen root tips. By contrast, Fe-deficient roots from several Strategy II plants [maize (Zea mays L. ' Funo '), wheat (Triticum aesti um L. ' Ye! cora '), barley (Hordeum ulgare L. ' Barbarrosa ')] did not produce more ethylene than the Fe-sufficient ones. Furthermore, ACC had no effect on the reducing capacity of these Strategy II plants and, except in barley, did not promote swelling of root tips. In conclusion, results suggest that ethylene is involved in the regulation of Fe-deficiency stress responses by Strategy I plants.