Inhibition of the gravitropic response of snapdragon spikes by the calcium-channel blocker lanthanum chloride.
The putative Ca(2+)-channel blocker LaCl3 prevented the gravitropic bending of cut snapdragon (Antirrhinum majus L.) spikes (S. Philosoph-Hadas, S. Meir, I. Rosenberger, A.H. Halevy [1996] Plant Physiol 110: 301-310) and inhibited stem curvature to a greater extent than vertical and horizontal stem elongation at the bending zone. This might indicate that LaCl3, which modulates cytosolic Ca2+, does not influence general stem-growth processes but may specifically affect other gravity-associated processes occurring at the stem-bending zone. Two such specific gravity-dependent events were found to occur in the bending zone of snapdragon spikes: sedimentation of starch-containing chloroplasts at the bottom of stem cortex cells, as seen in cross-sections, and establishment of an ethylene gradient across the stem. Our results show that the lateral sedimentation of chloroplasts associated with gravity sensing was prevented in cross-sections taken from the bending zone of LaCl3-treated and subsequently gravistimulated spikes and that LaCl3 completely prevented the gravity-induced, asymmetric ethylene production established across the stem-bending zone. These data indicate that LaCl3 inhibits stem curvature of snapdragon spikes by preventing several gravity-dependent processes. Therefore, we propose that the gravitropic response of shoots could be mediated through a Ca(2+)-dependent pathway involving modulation of cytosolic Ca2+ at various stages.
Friedman
H
H
Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Bet Dagan, Israel.
Meir
S
S
Rosenberger
I
I
Halevy
A H
AH
Kaufman
P B
PB
Philosoph-Hadas
S
S
D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002736:Chloroplasts / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D003600:Cytosol / Q000378:metabolism; D005030:Ethylenes / Q000378:metabolism; D006112:Gravitation; D018522:Gravitropism / Q000187:drug effects*; D007811:Lanthanum / Q000494:pharmacology*; D019684:Magnoliopsida / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism; D018521:Plant Physiological Phenomena; D018547:Plant Stems / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D018087:Plastids / Q000378:metabolism
D002121:Calcium Channel Blockers; D005030:Ethylenes; D010937:Plant Growth Regulators; C028521:lanthanum chloride; D007811:Lanthanum; C036216:ethylene; D002118:Calcium