title: Regulation of the gravitropic response and ethylene biosynthesis in gravistimulated snapdragon spikes by calcium chelators and ethylene inhibitors.
abstract: The possible involvement of Ca2+ as a second messenger in snapdragon (Antirrhinum majus L.) shoot gravitropism, as well as the role of ethylene in this bending response, were analyzed in terms of stem curvature and gravity-induced asymmetric ethylene production rates, ethylene-related metabolites, and invertase activity across the stem. Application of Ca2+ chelators (ethylenediaminetetraacetic acid, trans-1,2-cyclohexane dinitro-N,N,N',N'-tetraacetic acid, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N',-tetraacetic acid) or a Ca2+ antagonist (LaCl3) to the spikes caused a significant loss of their gravitropic response following horizontal placement. Conversely, the Ca2+ ionophore A23187 or the agonist Bay K-8644 increased gravibending. Longitudinally halved stem sections had significantly higher amounts of ethylene, 1-aminocyclopropane-1-carboxylic acid, and 1-(malonylamino) cyclopropane-1-carboxylic acid compared with vertical controls, with the extra production arising exclusively from the lower half of the stem. trans-1,2-cyclohexane dinitro-N,N,N',N'-tetraacetic acid pretreatment completely abolished the gravity-induced ethylene gradient across the stem, thereby leading to a significant reduction of the curvature. Similarly, reduction of the ethylene produced in the gravistimulated with CoCl2 or inhibition of its action by silver thiosulfate or 2,5-norbornadiene significantly inhibited the subsequent gravibending. Silver thiosulfate and CoCl2 also abolished the gravity-induced gradient of invertase activity across the stem, which is associated with the asymmetric stem elongation. These results suggest that cytosolic Ca2+ may regulate auxin action in snapdragon spikes, manifested as increased ethylene production, which is, in turn, intimately correlated with stem bending. Therefore, both hormones seem to play significant roles in induction and progress of the gravibending of snapdragon spikes.
authors.affiliation: Department of Postharvest Science of Fresh Produce, The Volcani Center, Bet Dagan, Israel. vtsoniap@volcani.agri.gov.il
authors.forename: S
authors.initials: S
authors.lastname: Philosoph-Hadas
authors.forename: S
authors.initials: S
authors.lastname: Meir
authors.forename: I
authors.initials: I
authors.lastname: Rosenberger
authors.forename: A H
authors.initials: AH
authors.lastname: Halevy
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000598:Amino Acids, Cyclic; D002118:Calcium / Q000037:antagonists & inhibitors / Q000502:physiology*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D003521:Cyclopropanes / Q000378:metabolism; D005030:Ethylenes / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D018522:Gravitropism / Q000187:drug effects / Q000502:physiology*; D007210:Indoleacetic Acids / Q000378:metabolism / Q000502:physiology*; D007811:Lanthanum / Q000494:pharmacology; D009636:Norbornanes / Q000494:pharmacology; D063245:Plant Development; D018547:Plant Stems / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D010944:Plants / Q000187:drug effects / Q000378:metabolism; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D043324:beta-Fructofuranosidase
chemical_list: D000596:Amino Acids; D000598:Amino Acids, Cyclic; D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D002614:Chelating Agents; D003521:Cyclopropanes; D005030:Ethylenes; D007210:Indoleacetic Acids; D009636:Norbornanes; C028521:lanthanum chloride; D003035:Cobalt; C023863:1-aminocyclopropane-1-carboxylic acid; D007811:Lanthanum; C033894:1-(malonylamino)cyclopropane-1-carboxylic cid; C036216:ethylene; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase; C018021:cobaltous chloride; D002118:Calcium; C048294:2,5-norbornadiene