Calcium ion dependency of ethylene production in segments of primary roots of Zea mays.
We investigated the effect of Ca2+ on ethylene production in 2-cm long apical segments from primary roots of corn (Zea mays L., B73 x Missouri 17) seedlings.  The seedlings were raised under different conditions of Ca2+ availability.  Low-Ca and high-Ca seedlings were raised by soaking the grains and watering the seedlings with distilled water or 10 mM CaCl2, respectively.  Segments from high-Ca roots produced more than twice as much ethylene as segments from low-Ca roots.  Indoleacetic acid (IAA; 1 micromole) enhanced ethylene production in segments from both low-Ca and high-Ca roots but auxin-induced promotion of ethylene production was consistently higher in  segments from high-Ca roots.  Addition of 1-aminocyclopropane-1-carboxylic acid (ACC) to root segments from low-Ca seedlings doubled total ethylene production and the rate of production remained fairly constant during a 24 h period of monitoring.  In segments from high-Ca seedlings ACC also increased total ethylene production but most of the ethylene was produced within the first 6 h.  The data suggest that Ca2+ enhances the conversion of ACC to ethylene.  The terminal 2 mm of the root tip were found to be especially important to ethylene biosynthesis by apical segments and, experiments using 45Ca2+ as tracer indicated that the apical 2 mm of the root is the region of strongest Ca2+ accumulation.  Other cations such as Mn2+, Mg2+, and K+ could largely substitute for  Ca2+.  The significance of these findings is discussed with respect to recent evidence for gravity-induced Ca2+ redistribution and its relationship to the establishment of asymmetric growth during gravitropic curvature.
Hasenstein
K H
KH
Dept of Botany, Ohio State Univ., Columbus 43210, USA.
Evans
M L
ML
D000596:Amino Acids / Q000494:pharmacology / Q000502:physiology; D000598:Amino Acids, Cyclic; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002412:Cations; D004533:Egtazic Acid / Q000494:pharmacology; D005030:Ethylenes / Q000096:biosynthesis*; D018522:Gravitropism / Q000502:physiology; D007210:Indoleacetic Acids / Q000378:metabolism / Q000494:pharmacology; D010937:Plant Growth Regulators / Q000494:pharmacology / Q000502:physiology*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D003313:Zea mays / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D000596:Amino Acids; D000598:Amino Acids, Cyclic; D002412:Cations; D005030:Ethylenes; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; C023863:1-aminocyclopropane-1-carboxylic acid; D004533:Egtazic Acid; C030737:indoleacetic acid; C036216:ethylene; D002118:Calcium