Do phytotropins inhibit auxin efflux by impairing vesicle traffic?
Phytotropins such as 1-N-naphthylphthalamic acid (NPA) strongly inhibit auxin efflux, but the mechanism of this inhibition remains unknown. Auxin efflux is also strongly decreased by the vesicle trafficking inhibitor brefeldin A (BFA). Using suspension-cultured interphase cells of the BY-2 tobacco (Nicotiana tabacum L. cv Bright-Yellow 2) cell line, we compared the effects of NPA and BFA on auxin accumulation and on the arrangement of the cytoskeleton and endoplasmic reticulum (ER). The inhibition of auxin efflux (stimulation of net accumulation) by both NPA and BFA occurred rapidly with no measurable lag. NPA had no observable effect on the arrangement of microtubules, actin filaments, or ER. Thus, its inhibitory effect on auxin efflux was not mediated by perturbation of the cytoskeletal system and ER. BFA, however, caused substantial alterations to the arrangement of actin filaments and ER, including a characteristic accumulation of actin in the perinuclear cytoplasm. Even at saturating concentrations, NPA inhibited net auxin efflux far more effectively than did BFA. Therefore, a proportion of the NPA-sensitive auxin efflux carriers may be protected from the action of BFA. Maximum inhibition of auxin efflux occurred at concentrations of NPA substantially below those previously reported to be necessary to perturb vesicle trafficking. We found no evidence to support recent suggestions that the action of auxin transport inhibitors is mediated by a general inhibition of vesicle-mediated protein traffic to the plasma membrane.
Petrásek
Jan
J
Institute of Experimental Botany, The Academy of Sciences of the Czech Republic, Rozvojová 135, CZ-16502 Prague 6, Czech Republic.
Cerná
Adriana
A
Schwarzerová
Katerina
K
Elckner
Miroslav
M
Morris
David A
DA
Zazímalová
Eva
E
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D020126:Brefeldin A / Q000494:pharmacology*; D002478:Cells, Cultured; D022162:Cytoplasmic Vesicles / Q000187:drug effects* / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D007210:Indoleacetic Acids / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D010797:Phthalimides / Q000494:pharmacology*; D010937:Plant Growth Regulators / Q000494:pharmacology*; D014026:Nicotiana / Q000166:cytology / Q000187:drug effects*
D007210:Indoleacetic Acids; D010797:Phthalimides; D010937:Plant Growth Regulators; D020126:Brefeldin A; C002687:alpha-naphthylphthalamic acid